Tài liệu Báo cáo khoa học: Multifunctional host defense peptides: Antimicrobial peptides, the small yet big players in innate and adaptive immunity docx

MINIREVIEW
Multifunctional host defense peptides: Antimicrobial
peptides, the small yet big players in innate and adaptive
immunity
Constance Auvynet
1,2,
* and Yvonne Rosenstein
1
1 Instituto de Biotecnologia, Universidad Nacional Auto
´
noma de Me
´
xico, Cuernavaca, Mor. Mexico
2 FRE 2852, Peptidome de la peau des amphibiens, CNRS ⁄ Universite
´
Pierre et Marie Curie, Paris, France
Introduction
Antimicrobial peptides constitute a heterogeneous
group of peptides with respect to their primary and
secondary structures, their antimicrobial potentials,
their effects on host cells, and the regulation of their
expression. Most antimicrobial peptides are small (12–
50 amino acids), have a positive charge provided by
Arg and Lys residues, and an amphipathic structure
that enables them to interact with bacterial
membranes. Cationic peptides are divided into several
subfamilies, of which the most extensively studied are
the mammalian gene families of antimicrobial peptides,
the cathelicidins and defensins [1–3]. A comprehensive
view of the field can be obtained through recent
reviews that have covered this subject extensively [4–7].

Keywords
antimicrobial peptides; cathelicidins;
defensins; gene expression; immunity
Correspondence
Y. Rosenstein, Instituto de Biotecnologia,
Universidad Nacional Auto
´
noma de Me
´
xico,
Av. Universidad 2001, Col. Chamilpa,
Cuernavaca, Mor. 62210, Mexico
Fax: +52 777 317 2388
Tel: +52 777 329 1606
E-mail:
*Present address
INSERM UMR-S 945 Immunite
´
et
Infection ⁄ Universite
´
Pierre et Marie Curie,
Paris, France
(Received 31 May 2009, revised 3
September 2009, accepted 4 September
2009)
doi:10.1111/j.1742-4658.2009.07360.x
The term ‘antimicrobial peptides’ refers to a large number of peptides first
characterized on the basis of their antibiotic and antifungal activities. In
addition to their role as endogenous antibiotics, antimicrobial peptides, also

called host defense peptides, participate in multiple aspects of immunity
(inflammation, wound repair, and regulation of the adaptive immune sys-
tem) as well as in maintaining homeostasis. The possibility of utilizing these
multifunctional molecules to effectively combat the ever-growing group of
antibiotic-resistant pathogens has intensified research aimed at improving
their antibiotic activity and therapeutic potential, without the burden of an
exacerbated inflammatory response, but conserving their immunomodula-
tory potential. In this minireview, we focus on the contribution of small
cationic antimicrobial peptides – particularly human cathelicidins and defen-
sins – to the immune response and disease, highlighting recent advances
in our understanding of the roles of these multifunctional molecules.
Abbreviations
CRAMP, murine cathelin-related antimicrobial peptide; EGFR, epidermal growth factor receptor; ET, extracellular trap; GM-CSF, granulocyte–
macrophage colony-stimulating factor; HD, human defensin; hBD, human b-defensin; HNP, human neutrophil peptide (a-defensins); IFN-c,
interferon-c; IL, interleukin; LPS, lipopolysaccharide; NFjB, nuclear factor kappaB; NK, natural killer; SCCE, stratum corneum chymotryptic
enzyme; SCTE, stratum corneum tryptic enzyme; TCF-4, transcription factor-4; TLR, Toll-like receptor; TNF-a, tumor necrosis factor-a; VDR,
vitamin D receptor.
FEBS Journal 276 (2009) 6497–6508 ª 2009 The Authors Journal compilation ª 2009 FEBS 6497
Herein, we have centered our attention on the most
recent findings regarding the transcriptional regulation
of cathelicidins and defensins, and the mechanisms
through which they modulate different facets of immu-
nity and disease.
Defensins are cationic peptides containing six Cys
residues forming three intramolecular disulfide bonds.
On the basis of the position of the six conserved Cys
residues and on sequence identity, members of this
family of peptides have been classified into a-defensins,
b-defensins, and h-defensins. Defensins are widely
expressed [8], and in mammalian species more than

100 have been identified. Depending on the cell, they
will exert their function either in the intracellular or
extracellular compartment. They exhibit bactericidal,
fungicidal and antiviral activity [9–11]. Defensins are
either stored in granules of neutrophils or Paneth cells
or secreted by monocytes, macrophages, mast cells,
natural killer (NK) cells, keratinocytes, and epithelial
cells. When released into the extracellular milieu, they
exert their antimicrobial activity directly by attacking
the microbe membrane, and in the intracellular com-
partment, they contribute to the oxygen-independent
killing of phagocytosed microorganisms. Furthermore,
defensins are mediators in the crosstalk between the
innate and adaptive immune systems [4].
In addition to a highly conserved cathelin domain,
cathelicidins have an N-terminal signal peptide and a
structurally variable antimicrobial peptide at the C-ter-
minus. Humans and mice have only one cathelicidin
gene, whereas other mammals, such as pigs and cattle,
have several genes [12]. In humans, the cathelicidin
antimicrobial peptide gene encodes an inactive precur-
sor protein (hCAP18) that is processed to release a 37
amino acid peptide (LL-37) from the C-terminus of
the precursor protein. Several cell types produce cath-
elicidins: keratinocytes, macrophages, mast cells,
neutrophils, and eccrine glands [13]. Cathelicidins kill
Gram-positive and Gram-negative bacteria and
Trypanosoma cruzi. Similar to defensins, cathelicidins
participate actively in linking innate and adaptive
immunity and in modulating the amplitude of immune

responses [14].
Expression pattern and gene regulation
In general, mature, biologically active peptides require
proteolytic cleavage from a precursor peptide [15]. The
expression pattern of antimicrobial peptides is not uni-
form across species, and within a species it is regulated
by the cellular lineage, the differentiation ⁄ activation
state of the cell, and the tissue type [16]. Some antimi-
crobial peptides are synthesized in the absence of infec-
tion or inflammation, whereas others are upregulated
in response to endogenous or infectious ‘alarm’ signals,
suggesting different functions for these peptides under
different physiological settings. Moreover, differential
proteolytic processing can modulate their activity and,
by extension, their ability to modulate immunity [17].
Consequently, the combination of defense peptides
produced by different cell types in a given tissue can
positively or negatively modify cell functions, ulti-
mately promoting bacterial clearance, albeit not neces-
sarily through direct killing, but through the
establishment of immune cell circuits.
Defensins
Genes for antimicrobial peptides tend to cluster within
a chromosomal region. In the human genome, the
genes encoding most human defensins are grouped
within the same chromosomal region (8p21–23) [18],
suggesting evolution from a single precursor gene as
well as the existence of a master switch to orchestrate
the synthesis of these molecules. However, the genes
encoding the defensin family secreted in epididymis,

testis, pancreas, kidney and skeletal muscle are located
in chromosome 20. These peptides seem to be unique
in the sense that they are only synthesized in those
locations, and not in the skin or airways, the common
sites for b-defensins, indicative of an as yet undiscov-
ered biological function [19]. Interestingly, the number
of defensin genes on chromosome 8 appears to fluc-
tuate among individuals, partially explaining genetic
susceptibility to infection [20].
Human a-defensins [human neutrophil peptides
(HNPs) 1–4] are produced by leukocytes, Paneth cells
of the small intestine, and epithelial cells of the female
urogenital tract [1]. On stimulation through Toll-like
receptor (TLR)-2, TLR-3, and TLR-5, neutrophils,
NK cells and Paneth cells will release stored a-defen-
sins to the extracellular milieu, where they will exert
their antimicrobial activity. Interestingly, in addition
to its antimicrobial capacity, a-defensin HNP1 has
antiviral activity, as it inhibits HIV and influenza virus
replication, following viral entry into target cells. It
diminishes HIV replication by, on the one hand, block-
ing steps subsequent to reverse transcription and inte-
gration, and on the other by hindering a cellular
protein kinase C-dependent mechanism that partici-
pates in viral infection [21,22]. Similarly, it can inacti-
vate herpes simplex virus, cytomegalovirus, vesicular
stomatitis virus, and adenovirus [23]. Whether the
molecular mechanisms that mediate these antiviral
effects are common or virus-specific remains an open
question.

AMPs, the small yet big players of immunity C. Auvynet and Y. Rosenstein
6498 FEBS Journal 276 (2009) 6497–6508 ª 2009 The Authors Journal compilation ª 2009 FEBS
Human b-defensins (hBDs) 1–4 show unique as
well as overlapping expression patterns. The hBD-1
b-defensin is constitutively synthesized by epithelia that
are in direct contact with the environment or microbial
flora, such as lung, salivary gland, mammary gland,
prostate, gut, as well as by leukocytes; it is upregulated
by lipopolysaccharide (LPS) and peptidoglycan [24].
Although the expression pattern of hBD2 overlaps
with that of hBD1, it is also present in skin, pancreas,
leukocytes, and bone marrow. In addition to epithelia,
hBD3 has been detected in nonepithelial cells, in the
heart, liver, and placenta [4], and hBD4 mRNA has
been detected in the testis, epididymis, lung tumor tis-
sue [25], and gastric epithelial cells [26]. hBD1 and
hBD2 have predominant antibacterial activity against
Gram-negative bacteria and some fungi, whereas
hBD3 has a broader spectrum and kills many patho-
genic Gram-positive and Gram-negative bacteria and
opportunistic yeasts such as Candida albicans [27].
b-Defensin expression is modulated in response to
bacterial-derived molecules and ⁄ or to cytokines and
chemokines produced by the immune system or dam-
aged cells [16]. In keratinocytes stimulated by bacteria,
interferon-c (IFN-c), tumor necrosis factor-a (TNF-a),
interleukin (IL)-b, IL-17, or IL-22, hBD2 and hBD4
gene expression is upregulated, like that of hBD1 and
hBD3 in airway, intestinal or uterine epithelial cells
[28,29], whereas it is inhibited by retinoic acid [30] and

heat shock [31]. In immune cells, their production is
also upregulated following exposure to bacteria, LPS,
IFN-c, or IL-b [29].
Cathelicidins
The human cathelicidin gene is located on chromo-
some 3 (3p21.3), in close proximity to the genes encod-
ing TLR-9 and Myd88 (3p22). Cathelicidins are
constitutively synthesized in thymus, spleen, bone mar-
row, liver, skin, stomach, intestine, and testis. Besides
epithelial cells, they are produced by neutrophils,
monocytes, T-lymphocytes, B-lymphocytes, and NK
cells. Upon epidermal injury, the concentration of
human cathelicidin LL-37 is augmented significantly in
keratinocytes and epidermal mast cells [32], and it has
been detected in wound and blister fluid as well
[33,34]. In keratinocytes, synthesis of LL-37 is induced
in response to insulin-like growth factor 1, TNF-a [35],
IL-1a, and IL-6 [36], and upon contact with Staphylo-
coccus aureus [37]. Cathelicidin peptides have potent,
direct antimicrobial activity against Gram-positive and
Gram-negative bacteria and, importantly, against some
antibiotic-resistant bacteria [38]. Conversely, virulence
proteins of pathogenic microorganisms can negatively
modulate the transcription of antimicrobial peptides,
notably hBD-1 and LL-37 in intestinal epithelial cells
[39], through a signaling pathway dependent on
cAMP, protein kinase A, extracellular signal-related
kinase, and Cox2 [40], counterbalancing the positive
signals of alarmins.
LL-37 was assumed to be the only active form of

cathelicidin in the skin. However, LL-37 is susceptible
to proteolytic processing, generating multiple cathelici-
din-derived peptides that are present in normal human
skin. LL-37 actually represents < 20% of the cathelic-
idin-derived peptides, smaller forms of the peptide
being more abundant. These smaller peptides result
from proteolytic processing by two serine proteases
belonging to the tissue kallicrein family: stratum corne-
um tryptic enzyme (SCTE) (kallicrein-5) and stratum
corneum chymotryptic enzyme (SCCE) (kallicrein-7).
Based on its specificity, each enzyme generates a differ-
ent set of peptides. SCTE generates three main pep-
tides (KS30, KS22, and LL29), whereas the cleavage
of LL-37 by SCCE yields two peptides (RK31 and
KR20). SCTE is considered to be the generator of the
cathelicidin-derived antimicrobial activity (KS30, KS22
and LL29 are very potent antimicrobial compounds,
but lack chemotactic activity), and SCCE may be
considered as the inactivator of LL-37, rather than a
generator of antimicrobial peptides [17]. Ultimately,
the relative proportions of these peptides may set the
balance between antimicrobial activity and immuno-
modulatory function.
Expression of defensin-coding and
cathelicidin-coding genes
The final combination of peptides at a specific location
reflects the signaling of pattern ⁄ pathogen-associated
receptors as well as that of other molecules that sense
the environmental conditions. A proof of this was pro-
vided by experiments showing that frogs do not syn-

thesize and produce the same combinations and
relative proportions of antimicrobial peptides in a ster-
ile environment as they do in their natural one. More-
over, once they are pharmacologically depleted of
antimicrobial peptides, frogs will not reaccumulate
skin antimicrobial peptides until they are re-exposed to
bacteria [41]. In agreement with the different environ-
mental cues that promote antimicrobial peptide syn-
thesis, multiple signaling pathways are involved.
Upregulation of cathelicidin and defensin gene expres-
sion in response to bacterial products and proinflam-
matory molecules depends on the activation of the
nuclear factor kappaB (NFjB), AP-1, JAK2 and
STAT3 signaling pathways [16].
C. Auvynet and Y. Rosenstein AMPs, the small yet big players of immunity
FEBS Journal 276 (2009) 6497–6508 ª 2009 The Authors Journal compilation ª 2009 FEBS 6499
Transcription of the human defensin (HD)5 and
HD6 genes in Paneth cells is under the control of tran-
scription factor-4 (TCF-4) (also named TCF7L2), a
Wnt signaling pathway transcription factor, also
involved in Paneth cell differentiation [42]. Reduced
amounts of HD5 and HD6 peptides have been associ-
ated with the development of Crohn’s disease [43,44].
Consistent with this, heterozygous TCF-4 knockout
mice show decreased production of Paneth cell a-de-
fensins and diminished bacterial killing capacity. The
promoter region of neutrophil-derived defensins con-
tains recognition sequences for transcription factors
such as the hematopoietic-specific Ets family transcrip-
tion factor PU.1 and C ⁄ EBP-a [16]), as well as an

NFAT binding site overlapping the Pu.1 site. Interest-
ingly, NFAT was found to be associated with the pro-
moter in response to hepatitis C infection, thus
suggesting a correlation between a-defensin expression
and liver fibrosis [45]. In human skin, during wound
healing, the synthesis of antimicrobial peptides by
incoming neutrophils, and notably that of hBD-3, is
induced through an LL-37-mediated mechanism of
transactivation of the epidermal growth factor receptor
[46].
The promoter regions of cathelicidin genes have
consensus binding sites for NFjB, IL-6, acute phase
response factor and IFN-c response element as well
[16]. In mice, murine cathelin-related antimicrobial
peptide (CRAMP) is dependent on hypoxia-inducible
factor-1a, a factor now understood to play a key role
in the bactericidal capacity of phagocytic cells such as
macrophages and neutrophils [47]. In different human
cell types (keratinocytes, monocytes, neutrophils, and
bone marrow-derived macrophages), cathelicidin gene
expression is under the control of vitamin D-respon-
sive elements [48]. In turn, upregulation of the vita-
min D receptor (VDR) and Cyp27B1, the enzyme
that catalyzes the conversion of 25-hydroxyvitamin
D
3
to the active 1,25-hydroxyvitamin D
3
, is depen-
dent on TLR-mediated signals. Moreover, 1,25-hy-

droxyvitamin D
3
increases CD14 and TLR-2
synthesis. All together, these data reveal a direct link
between 1,25-hydroxyvitamin D
3
, TLR activation, the
VDR and downstream targets such as cathelicidin,
ultimately regulating the antibacterial response [49].
Interestingly, many autoimmune patients are deficient
in vitamin D, and providing greater quantities of it
reduces the symptoms [50]. Likewise, VDR-deficient
mice or vitamin D-deficient mice show increased sen-
sitivity to autoimmune diseases such as inflammatory
bowel disease and type I diabetes [51]. Whether there
is a direct connection between low levels of 1,25-di-
hydroxyvitamin D
3
, low levels of cathelicidin produc-
tion, poor clearance of bacterial pathogens and
autoimmunity is certainly a challenging concept that
needs to be further investigated.
A recent computational analysis of the promoter
region of 61 genes belonging to 29 families of mouse,
rat and human antimicrobial peptide-encoding genes
identified factors that regulate the transcription of anti-
microbial peptides. In addition to predicting most of
the transcription factors already described individually
for antimicrobial peptides, this study suggests that the
influence of the VDR and new nuclear hormone recep-

tors (glucocorticoid receptor, retinoic receptor, etc.) is
not restricted to cathelicidins, and that it extends to
other antimicrobial peptides, in particular a-defensins.
Furthermore, this in silico study identified a core set of
transcription factors regulating the transcription of the
majority of antimicrobial peptides considered. The
transcription factors were grouped in tissue specific-
categories, of which the liver-specific, neuron-specific
and nuclear hormone-specific factors occupied the first
positions, underscoring new functions for antimicrobial
peptides in energy metabolism and neuroendocrine
regulation [52], in addition to their role in immunity.
Immunomodulatory properties of
antimicrobial peptides
By disrupting bacterial membranes, antimicrobial pep-
tides participate as direct effectors of innate immunity.
Multiple antimicrobial peptides are simultaneously
present at the same site, and they are thought to
work in concert, to effectively fight infection. It has
frequently been argued that the minimal inhibitory con-
centration of antimicrobial peptides needed to effec-
tively combat microbial infection is rarely found in
in vivo conditions, despite the fact that antimicrobial
peptide gene expression is mostly under the control of
innate immunity-related transcription factors. However,
in addition to the concentration of these natural antibi-
otics, the resistance of the microbial membrane (i.e. the
target of the antimicrobial peptides) in a given ionic
environment is the counterpart to effectiveness of anti-
microbial activity. In support of this, it has recently

been shown that S. aureus and Escherichia coli grown
in carbonate-containing solutions are more susceptible
to physiological concentrations of antimicrobial pep-
tides, as a result of changes in bacterial gene expression
that translate into changes in cell wall thickness and the
expression of several genes related to virulence [53].
Thus, the balance in the host’s ionic condition is an
important element to consider when evaluating the
antimicrobial activity of a given peptide. Also, it should
be considered that the microbicidal activity of most
AMPs, the small yet big players of immunity C. Auvynet and Y. Rosenstein
6500 FEBS Journal 276 (2009) 6497–6508 ª 2009 The Authors Journal compilation ª 2009 FEBS
antimicrobial peptides is very potent in the intracellular
compartment, in phagocytic vacuoles, and on the exter-
nal surface of skin and mucosa, three low-salt compart-
ments. Updating the molecular mechanisms involved in
this microbicidal effect is beyond the scope of this
minireview, but it is a field of extensive research.
Innate immunity cells such as neutrophils, mast cells
and eosinophils can form extracellular traps (ETs) that
consist of a chromatin–DNA backbone, to which anti-
microbial peptides and enzymes are attached, ultimately
forming a net in which microbes are entrapped and
killed [54]. An NAPDH oxidase-dependent mechanism
initiates a signaling cascade that leads to the disintegra-
tion of the nuclear and cellular membrane [55], leading
to cell death and the formation of ETs. Besides
augmenting the local concentration of antimicrobial
peptides and effectively killing the microbes, it is possi-
ble to think that ETs limit the diffusion of microbe-

derived alarmins, minimizing tissue damage.
Data from experiments with knockout and trans-
genic mice highlight the direct antimicrobial effect of
antimicrobial peptides [7,16]. However, given the cen-
tral role that antimicrobial peptides seem to play in
the outcome of an infection ⁄ injury, it is surprising to
see that all knockout mice lacking antimicrobial pep-
tides are quite healthy, with only modest alterations in
susceptibility to specific infectious agents. For example,
mice lacking b-defensin-1 are inefficient at clearing
Haemophilus influenzae from their lungs [56], and
CRAMP-deficient mice are impaired in their ability to
clear skin infections caused by group A Streptococcus
[57]. These results underline the fact that antimicrobial
peptides work in concert, and that their ranges of
activity frequently overlap.
Apart from efficient antimicrobial activity, antimi-
crobial peptides modulate immunity. They seem to
participate in every facet of it, by boosting the immune
response to prevent infection, and also by suppressing
other proinflammatory responses to avoid uncontrolled
inflammation. Furthermore, some antimicrobial pep-
tides synergize with cytokines and modify their immuno-
modulatory activity.
Chemotactic activity
In addition to their direct microbicidal activity, antimi-
crobial peptides are chemotactic for leukocytes and
other nonimmune cells at nanomolar concentrations.
Despite a certain overlap, antimicrobial peptides work
in concert, as they complement each other to direct

effector cells to the site of inflammation, organizing the
order of appearance of the different players in different
scenarios, and modulating the local immune response.
Phagocytic cells, neutrophils and monocytes that are
recruited through a-defensins, HNP1–3 and b-defen-
sins hBD3 and hBD4, and mast cells that are attracted
through LL-37, HNP1–3 and hBD2 contribute to
increase the local density of neutrophils [58]. In addi-
tion, hBD1 and hBD3 are chemotactic for immature
dendritic cells and memory T-cells, whereas human
a-defensins selectively induce the migration of human
naı
¨
ve CD4
+
CD45
+
and CD8
+
cells [7]. The combina-
tion of these peptides and cytokines present at the site
of injury will contribute to the maturation of these
immature dendritic cells, enabling them to process
antigen and to migrate to proximal lymph nodes to
present antigens to naı
¨
ve cells, thus setting in motion
the adaptive immune response machinery, and shaping
the outcome of the response. Besides their intrinsic
chemoattractant properties, which directly promote the

locomotion and arrival of different cohorts of cells to
the site of injury, antimicrobial peptides indirectly
favor chemotaxis by inducing or increasing the secre-
tion of chemokines. For example, LL-37 has been
shown to induce IL-8 release by lung epithelial cell
lines [59,60], and human defensins HNP1–3 also favor
the recruitment of neutrophils by inducing the activa-
tion and degranulation of mast cells, augmenting neu-
trophil influx and further stimulating the transcription
and production of IL-8 by bronchial epithelial cells
[61–64].
Antimicrobial peptide-induced chemotaxis is pre-
sumably mediated through G-protein-coupled recep-
tors, as pretreatment of the cells with pertussis toxin
or phospholipase C, phosphoinositide-3-kinase and
Rho kinase inhibitors abolishes cell migration [65].
According to the peptide and the cell, several receptors
have been identified. LL-37, like the frog peptides tem-
porin A and probably Drs S9, attracts cells through
formyl peptide receptor-like-1, whereas defensins
hBD2 and hBD3 use CC-chemokine receptor-6, pres-
ent on memory T-cells, immature dendritic cells, and
human colonic epithelial cells [66–69]. CC-chemokine
receptor-6 is also the receptor for macrophage inflam-
matory protein-3a, a chemokine involved in homeo-
static lymphocyte homing as well as in epithelial cell
migration, further suggesting a function for hBD2
in healing and protection of the intestinal epithelial
barrier [70].
Proinflammatory and anti-inflammatory signals

of antimicrobial peptides
Antimicrobial peptides have a dual identity: they pro-
tect the host against potentially harmful pathogens
through their antimicrobial activity and by stimulating
C. Auvynet and Y. Rosenstein AMPs, the small yet big players of immunity
FEBS Journal 276 (2009) 6497–6508 ª 2009 The Authors Journal compilation ª 2009 FEBS 6501
innate immune functions, yet, at the same time, they
protect the organism from the detrimental effects of an
excessive inflammatory response.
In addition to their direct antimicrobial capacity, the
in vivo contribution of antimicrobial peptides to anti-
microbial defense depends on their capacity to induce
the production of proinflammatory cytokines, to pro-
mote the recruitment of dendritic cells and monocytes
to the site of injury, and to enhance phagocytosis and
the maturation of dendritic cells. All of these effects
will augment the uptake, processing and presentation
of antigen, and stimulate the clonal expansion of
T-lymphoctes and B-lymphocytes. B-lymphocytes will
produce antibodies that are highly specific for patho-
gen antigens, contributing to the clearance of microbes
through phagocytosis [16].
Some of the molecular mechanisms that control this
positive feedback loop have been described recently.
Human a-defensins and b-defensins induce the release
of histamine and prostaglandin D
2
in a G-protein–
phospholipase C-dependent manner [62] [71]; HPN1–3
bind C1q and activate the classic complement pathway

[72], increase the production of TNF-a and IL-1b, and
decrease the production of IL-10 by monocytes
[61,62,73]. Furthermore, as an endogenous ligand for
TLR-4, b-defensin-2 activates immature dendritic cells
through TLR-4-dependent mechanisms, triggering a
robust Th1 response [74]. Consistent with their role in
wounding, b-defensin-mediated signals positively regu-
late the expression of matrix metalloproteinase genes
and negatively regulate that of tissue inhibitor of
matrix metalloproteinase genes, thus modulating tissue
repair [75,76]. LL-37 induces the release of IL-1b, IL-
8, TNF-a, IL-6 and granulocyte–macrophage colony-
stimulating factor (GM-CSF) by keratinocytes, and of
TNF-a and IL-6 by immature dendritic cells [58,77].
Moreover, LL-37 and GM-CSF synergize, as the pres-
ence of GM-CSF augments LL-37-mediated mitogen-
activated protein kinase activation and reduces the
amount of LL-37 required for this activation and for
cytokine production [78,79].
Cathelicidins function as anti-inflammatory mole-
cules as well. In in vivo models, administration of
LL-37 protects mice and rats from LPS-mediated
lethality [60,80]. Indeed, LL-37 binds and neutralizes
LPS, possibly by dissociation of LPS aggregates, limit-
ing the extent of inflammation [60,81–84]. Addition-
ally, cathelicidin abrogates the expression of
proinflammatory molecules such as TNF-a and IL-6
and the nuclear translocation of NFjB p50 ⁄ p65
induced by TLR-2 and TLR-4 in response to lipoteic
acid and LPS, respectively, through a partially defined

mechanism involving mitogen-activated protein kinase
p38 inactivation [85]. This immunomodulatory effect
of the TLR response is mediated through the binding
of the mid-region of LL-37, comprising amino acids
13–31, to TLR ligands through an LPS-binding mech-
anism [86]. Moreover, LL-37 was found to selectively
permeabilize the membranes of apoptotic human
leukocytes through a mechanism similar to the direct
microbicidal effect, independently of known surface
receptors or cell signaling, leaving viable cells un-
affected. This causes the cells to empty the cytoplasm
as well as intragranular molecules to the extracellular
compartment, shifting the balance between proinflam-
matory and anti-inflammatory signals [87]. Further-
more, the fact that, as mentioned, LL-37 is shortened
by a serine protease-dependent mechanism, generating
novel antimicrobial peptides with enhanced antimicro-
bial action, but reduced proinflammatory activity, con-
tributes to controlling the inflammatory response [88].
In addition, these data point to the role of hydropho-
bicity in the immunomodulatory capacity of LL-37
[86] and potentially in new synthetic peptides designed
to downmodulate inflammatory responses. Accord-
ingly, IDR-1, a synthetic peptide derived from LL-37,
although devoid of direct antimicrobial activity, is
effective in limiting a broad range of Gram-positive
and Gram-negative pathogens, through signaling path-
ways that increase the level of monocyte cytokines
while diminishing proinflammatory responses [89].
Such peptides, capable of suppressing the host’s harm-

ful proinflammatory responses without losing the
beneficial infection-fighting components of host innate
defenses, are desirable tools for antisepsis therapies.
Defensins play the same dual role as cathelicidins.
The activation of TLR-4, mediated through murine
b-defensin-2, leads to atypical death of dendritic cells,
through upregulation of membrane-bound TNF-a and
tumor necrosis factor receptor 2. This suggests that
b-defensins participate in the triggering of an immune
response and in the natural process of elimination of
activated antigen-presenting cells and termination of
the immune response [90].
Healing
Infection and injury provoke tissue damage. Immedi-
ately after injury, innate immune cells, mostly neu-
trophils and macrophages, together with antimicrobial
peptides, produced by immune cells or secreted by
local cells, will take care of microbe clearance and
removal of debris. Other cells, such as T-lymphocytes,
secrete cytokines and chemokines that will further
activate macrophages and induce inflammation and
vasodilatation, and enhance vessel permeability. Tissue
AMPs, the small yet big players of immunity C. Auvynet and Y. Rosenstein
6502 FEBS Journal 276 (2009) 6497–6508 ª 2009 The Authors Journal compilation ª 2009 FEBS
regeneration requires multiple events. Following
removal of bacteria and debris, the release of growth
factors will promote the migration and proliferation of
fibroblasts, which will deposit the extracellular matrix
over which epithelial cells will crawl and cover the
wound bed [91].

A recent report showed the secretion of hBD3 and
other antimicrobial peptides by human keratinocytes,
after the disappearance of neutrophils and before the
re-establishment of the physical barrier, in sterile
wounds as well as in microbe-induced wounds [35,46].
The expression of antimicrobial peptides at that time is
probably protective against subsequent infections.
However, the fact that growth factors such as IGF-1,
transforming growth factor-a, and epidermal growth
factor, in combination with IL-1, induce the secretion
of LL-37, hBD3 and other antimicrobial peptides by
human keratinocytes [35,59] suggests that antimicro-
bial peptides participate in additional tasks. LL-37 is
mostly present in the inflammatory infiltrate as well as
in the epithelium migrating over the wound, but not at
the wound edge. Interestingly, its highest level in the
skin wounds is reached 48 h postinjury, whereas the
normal level is achieved only upon wound closure,
after infection resolution, suggesting direct participa-
tion of LL-37 in wounding [92]. Indeed, through trans-
activation of epidermal growth factor receptor, LL-37
induces keratinocyte migration [93], and through for-
myl peptide receptor-like-1, it induces angiogenesis
[94]. Consistent with this role in wound healing, and in
addition to increased bacterial colonization, mice lack-
ing the cathelicidin gene have longer periods of wound
healing than their wild-type counterparts [57,95]. Simi-
larly, hBD-2 was recently described as also being a
potent promoter of human endothelial cell migration,
proliferation and, in the presence of angiogenic factors,

tube formation [96], accelerating wound closure. LL-37
may also have antifibrotic activity during the wound
repair process, as it inhibits baseline and transforming
growth factor-b-induced collagen expression at nanom-
olar concentrations, through an extracellular signal-
related kinase-dependent and G-protein-dependent
pathway [97].
These data regarding the role of antimicrobial pep-
tides in wounding provide evidence for their dual role;
they serve as sentinels and they actively participate in
tissue regeneration. Whether noninducible antimicro-
bial peptides function in a similar way during infec-
tion, under normal conditions or during development
is an attractive possibility. In conclusion, the multiple,
yet sometimes opposite, functions of antimicrobial
peptides are complementary, and they control homeo-
stasis through complex regulatory loops that involve
different cells responding to multiple signaling path-
ways.
Antimicrobial peptides and disease
Dysregulated production of antimicrobial peptides is
associated with disease. As we recognize that these
molecules are multifunctional and that they modulate
multiple events, the list of diseases in which anti-
microbial peptides participate is growing. Throughout
previous sections of this minireview, we have pointed
to the participation of antimicrobial peptides in several
diseases. In this section, we will highlight recent data
on psoriasis, rosacea, atopic dermatitis and Crohn’s
disease.

It was long considered that skin passively obstructed
the entrance of pathogens, thus constituting a natural
barrier against potential microbial pathogens and other
assaults from the external environment. It is now clear
that, through the antimicrobial activity and inmuno-
modulatory functions of antimicrobial peptides, the
skin plays a major and active role in the onset and
development of an immune response to injury and
microbial insult. Recent publications have narrowed
the role of cathelicidins and defensins in psoriasis, ros-
acea and atopic dermatitis, providing evidence that the
concentration, processing and signaling of antimicro-
bial peptides are critical parameters for maintaining
the delicate equilibrium between effective protection
and autoimmunity.
As mentioned, cathelicidin and hBD1–4 are present
in low amounts in healthy skin keratinocytes, but in
response to injury or infection, their synthesis is signifi-
cantly enhanced [98]. In atopic dermatitis, the continu-
ous bacterial and viral infections produce chronic
inflammation. It was recently shown that the cytokine
milieu (IL-4 and IL-13) of this Th2-type inflammatory
skin disease downregulates the gene expression of LL-
37, and thus contributes to a partially uncontrolled
cutaneous innate immune response in those patients
[99]. A recent report showed that Bcl-3, a protein with
close homology to IjB proteins and that interacts with
p50 NFjB homodimers, is overexpressed in skin
lesions of patients with atopic dermatitis, and that its
silencing reverses the inhibitory effect of IL-4 on hBD3

gene expression. Moreover, Bcl-3 silencing upregulates
the 1,25-dihydroxyvitamin D
3
-dependent production of
cathelicidin in keratinocytes, and 1,25-dihydroxyvita-
min D
3
suppresses Bcl-3 expression [100]. In addition,
Bcl-3 synthesis is upregulated in the presence of IL-4
[101], thus generating a negative feedback loop that
will reduce the cathelicidin concentration, favoring
skin infections and chronic inflammation.
C. Auvynet and Y. Rosenstein AMPs, the small yet big players of immunity
FEBS Journal 276 (2009) 6497–6508 ª 2009 The Authors Journal compilation ª 2009 FEBS 6503
Unlike atopic dermatitis, psoriasis, a common auto-
immune disease of the skin, results partially cathelici-
din overproduction. By binding to damaged or
apoptotic skin cells self-DNA, cathelicidin converts it
into aggregated and condensed structures. That will be
delivered to plasmocytoid dendritic cells. These, in
turn, will infiltrate the psoriatic skin, triggering en-
dosomal TLR-9 and subsequent IFN-c production,
thus driving autoimmune skin inflammation [102].
Patients with rosacea have abnormal inflammation
and vascular reactivity in facial skin. These individuals
have high levels of cathelicidin and higher levels of the
enzyme that processes the propeptide into the LL-37
biologically active peptide and of other unusual iso-
forms of the peptide. The current thinking is that, at
least partially, the chronic inflammation results from

the increased chemotactic and angiogenic activity of
the LL-37-derived peptides [103].
Crohn’s disease is an inflammatory disease of the
small intestine and ⁄ or the colon. As mentioned
already, in the small intestine, the pathogenesis is asso-
ciated with a reduced expression of the Wnt signaling
pathway TCF-4, involved in Paneth cell differentiation
and in a-defensin gene expression [42]. Consequently,
a-defensin-2 and a-defensin-3 genes are deficiently
expressed, regardless of the inflammation. Moreover,
single-nucleotide polymorphisms in TCF-4 are directly
related to ileal Crohn’s disease incidence, providing
evidence that low levels of HD5 and HD6 are directly
associated with the disease [43]. In contrast, in the
colon, Crohn’s disease is associated with impaired
expression of the genes encoding hBD5 and hBD6.
Patients affected with this form of disease tend to have
fewer gene copy numbers in the locus of b-defensin in
chromosome 8. As a result of this deficiency in a-de-
fensins and b-defensins, luminal microbes invade the
mucosa and trigger inflammation [104].
Concluding remarks
Initially described as molecules with bactericidal capac-
ity, antimicrobial peptides are now considered to be
multifunctional molecules. They stimulate the produc-
tion and release of proinflammatory and anti-inflam-
matory molecules, they recruit inflammatory cells to
the site of injury, they function as antimicrobial mole-
cules directly and by promoting ingestion of microbes
by phagocytic cells, and they participate in damage

repair. These pleiotropic effects reflect the diversity of
effector molecules and their targets, as well as the
sometimes overlapping, yet very specific, functions.
Through elaborate feedback mechanisms, they control
immune cells as well as nonimmune cells, link innate
immunity to adaptive immunity, and maintain homeo-
stasis. Alterations in their physiological concentrations
correlate with disease. Their antimicrobial activity,
immunomodulatory functions, adjuvant properties and
low toxicity make antimicrobial peptides the object of
intense investigation in order to develop new therapeu-
tic agents with specific activities. A deeper understand-
ing of the signaling pathways underlining these effects
and of the physiological processes that are controlled
by antimicrobial peptides will help in the better exploi-
tation of the potential use of these peptides.
Acknowledgements
We thank Drs L. Perez, G. Pedraza, Claire Lacombe
and G. Corzo for their helpful discussions and com-
ments, and S. Ainsworth for her librarian support.
Work in the Y. Rosenstein laboratory is supported by
CONACyT and DGAPA ⁄ UNAM, Mexico.
References
1 Selsted ME & Ouellette AJ (2005) Mammalian defen-
sins in the antimicrobial immune response. Nat Immu-
nol 6, 551–557.
2 Zasloff M (2002) Antimicrobial peptides of multicellu-
lar organisms. Nature 415, 389–395.
3 Hancock RE (2001) Cationic peptides: effectors in
innate immunity and novel antimicrobials. Lancet

Infect Dis 1, 156–164.
4 Pazgier M, Hoover DM, Yang D, Lu W & Lubkowski
J (2006) Human beta-defensins. Cell Mol Life Sci 63,
1294–1313.
5 Yeaman MR & Yount NY (2007) Unifying themes in
host defence effector polypeptides. Nat Rev Microbiol
5, 727–740.
6 Holzl MA, Hofer J, Steinberger P, Pfistershammer K
& Zlabinger GJ (2008) Host antimicrobial proteins as
endogenous immunomodulators. Immunol Lett 119,
4–11.
7 Lai Y & Gallo RL (2009) AMPed up immunity: how
antimicrobial peptides have multiple roles in immune
defense. Trends Immunol 30, 131–141.
8 Ganz T (2003) Defensins: antimicrobial peptides of
innate immunity. Nat Rev Immunol 3, 710–720.
9 Selsted ME, Szklarek D & Lehrer RI (1984) Purifica-
tion and antibacterial activity of antimicrobial peptides
of rabbit granulocytes. Infect Immun 45, 150–154.
10 Ganz T, Selsted ME, Szklarek D, Harwig SS, Daher
K, Bainton DF & Lehrer RI (1985) Defensins. Natural
peptide antibiotics of human neutrophils. J Clin Invest
76, 1427–1435.
11 Lehrer RI, Daher K, Ganz T & Selsted ME (1985)
Direct inactivation of viruses by MCP-1 and MCP-2,
AMPs, the small yet big players of immunity C. Auvynet and Y. Rosenstein
6504 FEBS Journal 276 (2009) 6497–6508 ª 2009 The Authors Journal compilation ª 2009 FEBS
natural peptide antibiotics from rabbit leukocytes.
J Virol 54, 467–472.
12 Tomasinsig L & Zanetti M (2005) The cathelicidins –

structure, function and evolution. Curr Protein Pept
Sci 6, 23–34.
13 Zanetti M (2005) The role of cathelicidins in the innate
host defenses of mammals. Curr Issues Mol Biol 7,
179–196.
14 Zaiou M & Gallo RL (2002) Cathelicidins, essential
gene-encoded mammalian antibiotics. J Mol Med 80 ,
549–561.
15 Uzzell T, Stolzenberg ED, Shinnar AE & Zasloff M
(2003) Hagfish intestinal antimicrobial peptides are
ancient cathelicidins. Peptides 24, 1655–1667.
16 Yang D, Biragyn A, Hoover DM, Lubkowski J &
Oppenheim JJ (2004) Multiple roles of antimicrobial
defensins, cathelicidins, and eosinophil-derived neuro-
toxin in host defense. Annu Rev Immunol 22, 181–215.
17 Yamasaki K, Schauber J, Coda A, Lin H, Dorschner
RA, Schechter NM, Bonnart C, Descargues P,
Hovnanian A & Gallo RL (2006) Kallikrein-mediated
proteolysis regulates the antimicrobial effects of
cathelicidins in skin. FASEB J 20, 2068–2080.
18 Schutte BC, Mitros JP, Bartlett JA, Walters JD, Jia
HP, Welsh MJ, Casavant TL & McCray PB Jr (2002)
Discovery of five conserved beta-defensin gene clusters
using a computational search strategy. Proc Natl Acad
Sci USA 99, 2129–2133.
19 Rodriguez-Jimenez FJ, Krause A, Schulz S, Forss-
mann WG, Conejo-Garcia JR, Schreeb R & Motzkus
D (2003) Distribution of new human beta-defensin
genes clustered on chromosome 20 in functionally dif-
ferent segments of epididymis. Genomics 81, 175–183.

20 Linzmeier RM & Ganz T (2005) Human defensin gene
copy number polymorphisms: comprehensive analysis
of independent variation in alpha- and beta-defensin
regions at 8p22–p23. Genomics 86, 423–430.
21 Chang TL, Vargas J Jr, DelPortillo A & Klotman ME
(2005) Dual role of alpha-defensin-1 in anti-HIV-1
innate immunity. J Clin Invest 115, 765–773.
22 Salvatore M, Garcia-Sastre A, Ruchala P, Lehrer RI,
Chang T & Klotman ME (2007) alpha-Defensin inhib-
its influenza virus replication by cell-mediated
mechanism(s). J Infect Dis 196 , 835–843.
23 Daher KA, Selsted ME & Lehrer RI (1986) Direct
inactivation of viruses by human granulocyte
defensins. J Virol 60, 1068–1074.
24 Sorensen OE, Thapa DR, Rosenthal A, Liu L,
Roberts AA & Ganz T (2005) Differential regulation
of beta-defensin expression in human skin by microbial
stimuli. J Immunol 174, 4870–4879.
25 Shestakova T, Zhuravel E, Bolgova L, Alekseenko O,
Soldatkina M & Pogrebnoy P (2008) Expression of
human beta-defensins-1, 2 and 4 mRNA in human lung
tumor tissue: a pilot study. Exp Oncol 30, 153–156.
26 Otte JM, Neumann HM, Brand S, Schrader H,
Schmidt WE & Schmitz F (2009) Expression of beta-
defensin 4 is increased in human gastritis. Eur J Clin
Invest 39, 126–138.
27 De Smet K & Contreras R (2005) Human antimicro-
bial peptides: defensins, cathelicidins and histatins.
Biotechnol Lett 27, 1337–1347.
28 Duits LA, Ravensbergen B, Rademaker M, Hiemstra

PS & Nibbering PH (2002) Expression of beta-defensin
1 and 2 mRNA by human monocytes, macrophages
and dendritic cells. Immunology 106, 517–525.
29 Brown KL & Hancock RE (2006) Cationic host defense
(antimicrobial) peptides. Curr Opin Immunol
18, 24–30.
30 Harder J, Meyer-Hoffert U, Wehkamp K, Schwichten-
berg L & Schroder JM (2004) Differential gene induc-
tion of human beta-defensins (hBD-1, -2, -3, and -4) in
keratinocytes is inhibited by retinoic acid. J Invest
Dermatol 123, 522–529.
31 Bick RJ, Poindexter BJ, Bhat S, Gulati S, Buja M &
Milner SM (2004) Effects of cytokines and heat shock
on defensin levels of cultured keratinocytes. Burns 30,
329–333.
32 Braff MH & Gallo RL (2006) Antimicrobial peptides:
an essential component of the skin defensive barrier.
Curr Top Microbiol Immunol 306, 91–110.
33 Frohm M, Gunne H, Bergman AC, Agerberth B,
Bergman T, Boman A, Liden S, Jornvall H & Boman
HG (1996) Biochemical and antibacterial analysis of
human wound and blister fluid. Eur J Biochem 237,
86–92.
34 Dorschner RA, Pestonjamasp VK, Tamakuwala S,
Ohtake T, Rudisill J, Nizet V, Agerberth B,
Gudmundsson GH & Gallo RL (2001) Cutaneous
injury induces the release of cathelicidin anti-microbial
peptides active against group A Streptococcus.
J Invest Dermatol 117, 91–97.
35 Sorensen OE, Cowland JB, Theilgaard-Monch K, Liu

L, Ganz T & Borregaard N (2003) Wound healing and
expression of antimicrobial peptides ⁄ polypeptides in
human keratinocytes, a consequence of common
growth factors. J Immunol 170, 5583–5589.
36 Erdag G (2002) Interleukin-1alpha and interleukin-6
enhance the antibacterial properties of cultured com-
posite keratinocyte grafts. Ann Surg 235, 113–124.
37 Midorikawa K, Ouhara K, Komatsuzawa H, Kawai
T, Yamada S, Fujiwara T, Yamazaki K, Sayama K,
Taubman MA, Kurihara H et al. (2003) Staphylo-
coccus aureus susceptibility to innate antimicrobial
peptides, beta-defensins and CAP18, expressed by
human keratinocytes. Infect Immun 71 , 3730–3739.
38 Saiman L, Tabibi S, Starner TD, San Gabriel P,
Winokur PL, Jia HP, McCray PB Jr & Tack BF
(2001) Cathelicidin peptides inhibit multiply antibiotic-
resistant pathogens from patients with cystic fibrosis.
Antimicrob Agents Chemother 45, 2838–2844.
C. Auvynet and Y. Rosenstein AMPs, the small yet big players of immunity
FEBS Journal 276 (2009) 6497–6508 ª 2009 The Authors Journal compilation ª 2009 FEBS 6505
39 Islam D, Bandholtz L, Nilsson J, Wigzell H, Christens-
son B, Agerberth B & Gudmundsson G (2001) Down-
regulation of bactericidal peptides in enteric infections:
a novel immune escape mechanism with bacterial
DNA as a potential regulator. Nat Med 7, 180–185.
40 Chakraborty K, Ghosh S, Koley H, Mukhopadhyay
AK, Ramamurthy T, Saha DR, Mukhopadhyay D,
Roychowdhury S, Hamabata T, Takeda Y et al.
(2008) Bacterial exotoxins downregulate cathelicidin
(hCAP-18 ⁄ LL-37) and human beta-defensin 1

(HBD-1) expression in the intestinal epithelial cells.
Cell Microbiol 10, 2520–2537.
41 Mangoni ML, Miele R, Renda TG, Barra D &
Simmaco M (2001) The synthesis of antimicrobial
peptides in the skin of Rana esculenta is stimulated by
microorganisms. FASEB J 15, 1431–1432.
42 van Es JH, Jay P, Gregorieff A, van Gijn ME,
Jonkheer S, Hatzis P, Thiele A, van den Born M,
Begthel H, Brabletz T et al. (2005) Wnt signalling
induces maturation of Paneth cells in intestinal crypts.
Nat Cell Biol 7, 381–386.
43 Wehkamp J, Wang G, Kubler I, Nuding S, Gregorieff
A, Schnabel A, Kays RJ, Fellermann K, Burk O,
Schwab M et al. (2007) The Paneth cell alpha-defensin
deficiency of ileal Crohn’s disease is linked to
Wnt ⁄ Tcf-4. J Immunol 179, 3109–3118.
44 Koslowski MJ, Kubler I, Chamaillard M, Schaeffeler
E, Reinisch W, Wang G, Beisner J, Teml A, Peyrin-
Biroulet L, Winter S et al. (2009) Genetic variants of
Wnt transcription factor TCF-4 (TCF7L2) putative
promoter region are associated with small intestinal
Crohn’s disease. PLoS ONE 4, e4496.
45 Aceti A, Mangoni ML, Pasquazzi C, Fiocco D,
Marangi M, Miele R, Zechini B, Borro M, Versace I
& Simmaco M (2006) Alpha-defensin increase in
peripheral blood mononuclear cells from patients with
hepatitis C virus chronic infection. J Viral Hepatol 13,
821–827.
46 Sorensen OE, Thapa DR, Roupe KM, Valore EV,
Sjobring U, Roberts AA, Schmidtchen A & Ganz T

(2006) Injury-induced innate immune response in
human skin mediated by transactivation of the
epidermal growth factor receptor. J Clin Invest 116,
1878–1885.
47 Peyssonnaux C, Boutin AT, Zinkernagel AS, Datta V,
Nizet V & Johnson RS (2008) Critical role of
HIF-1alpha in keratinocyte defense against bacterial
infection. J Invest Dermatol 128, 1964–1968.
48 Wang TT, Nestel FP, Bourdeau V, Nagai Y, Wang Q,
Liao J, Tavera-Mendoza L, Lin R, Hanrahan JW,
Mader S et al. (2004) Cutting edge: 1,25-dihydroxy-
vitamin D3 is a direct inducer of antimicrobial peptide
gene expression. J Immunol 173, 2909–2912.
49 Liu PT, Stenger S, Li H, Wenzel L, Tan BH, Krutzik
SR, Ochoa MT, Schauber J, Wu K, Meinken C et al.
(2006) Toll-like receptor triggering of a vitamin D-
mediated human antimicrobial response. Science 311,
1770–1773.
50 Cantorna MT (2006) Vitamin D and its role in immu-
nology: multiple sclerosis, and inflammatory bowel dis-
ease. Prog Biophys Mol Biol 92, 60–64.
51 Bouillon R, Carmeliet G, Verlinden L, van Etten E,
Verstuyf A, Luderer HF, Lieben L, Mathieu C & Demay
M (2008) Vitamin D and human health: lessons from
vitamin D receptor null mice. Endocr Rev 29, 726–776.
52 Brahmachary M, Schonbach C, Yang L, Huang E,
Tan SL, Chowdhary R, Krishnan SP, Lin CY, Hume
DA, Kai C et al. (2006) Computational promoter anal-
ysis of mouse, rat and human antimicrobial peptide-
coding genes. BMC Bioinformatics 7(Suppl 5), S8.

53 Dorschner RA, Lopez-Garcia B, Peschel A, Kraus D,
Morikawa K, Nizet V & Gallo RL (2006) The mamma-
lian ionic environment dictates microbial susceptibility
to antimicrobial defense peptides. FASEB J 20, 35–42.
54 Wartha F, Beiter K, Normark S & Henriques-Normark
B (2007) Neutrophil extracellular traps: casting the
NET over pathogenesis. Curr Opin Microbiol 10, 52–56.
55 von Kockritz-Blickwede M & Nizet V (2009) Innate
immunity turned inside-out: antimicrobial defense by
phagocyte extracellular traps. J Mol Med 87, 775–783.
56 Moser C, Weiner DJ, Lysenko E, Bals R, Weiser JN
& Wilson JM (2002) beta-Defensin 1 contributes to
pulmonary innate immunity in mice. Infect Immun 70,
3068–3072.
57 Nizet V, Ohtake T, Lauth X, Trowbridge J, Rudisill J,
Dorschner RA, Pestonjamasp V, Piraino J, Huttner K
& Gallo RL (2001) Innate antimicrobial peptide pro-
tects the skin from invasive bacterial infection. Nature
414, 454–457.
58 Davidson DJ, Currie AJ, Reid GS, Bowdish DM,
MacDonald KL, Ma RC, Hancock RE & Speert DP
(2004) The cationic antimicrobial peptide LL-37 modu-
lates dendritic cell differentiation and dendritic cell-
induced T cell polarization. J Immunol 172, 1146–1156.
59 Tjabringa GS, Aarbiou J, Ninaber DK, Drijfhout JW,
Sorensen OE, Borregaard N, Rabe KF & Hiemstra PS
(2003) The antimicrobial peptide LL-37 activates
innate immunity at the airway epithelial surface by
transactivation of the epidermal growth factor recep-
tor. J Immunol 171, 6690–6696.

60 Scott MG, Davidson DJ, Gold MR, Bowdish D &
Hancock RE (2002) The human antimicrobial peptide
LL-37 is a multifunctional modulator of innate
immune responses. J Immunol 169, 3883–3891.
61 Befus AD, Mowat C, Gilchrist M, Hu J, Solomon S &
Bateman A (1999) Neutrophil defensins induce hista-
mine secretion from mast cells: mechanisms of action.
J Immunol 163, 947–953.
62 Niyonsaba F, Someya A, Hirata M, Ogawa H &
Nagaoka I (2001) Evaluation of the effects of peptide
AMPs, the small yet big players of immunity C. Auvynet and Y. Rosenstein
6506 FEBS Journal 276 (2009) 6497–6508 ª 2009 The Authors Journal compilation ª 2009 FEBS
antibiotics human beta-defensins-1 ⁄ -2 and LL-37 on
histamine release and prostaglandin D(2) production
from mast cells. Eur J Immunol 31, 1066–1075.
63 Malaviya R, Ikeda T, Ross E & Abraham SN (1996)
Mast cell modulation of neutrophil influx and bacterial
clearance at sites of infection through TNF-alpha.
Nature 381, 77–80.
64 Echtenacher B, Mannel DN & Hultner L (1996) Criti-
cal protective role of mast cells in a model of acute
septic peritonitis. Nature 381, 75–77.
65 Vongsa RA, Zimmerman NP & Dwinell MB (2009)
CCR6 regulation of the actin cytoskeleton orchestrates
human beta defensin-2- and CCL20-mediated restitu-
tion of colonic epithelial cells. J Biol Chem 284,
10034–10045.
66 Chertov O, Michiel DF, Xu L, Wang JM, Tani K,
Murphy WJ, Longo DL, Taub DD & Oppenheim JJ
(1996) Identification of defensin-1, defensin-2, and

CAP37 ⁄ azurocidin as T-cell chemoattractant proteins
released from interleukin-8-stimulated neutrophils.
J Biol Chem 271, 2935–2940.
67 Yang D, Chen Q, Chertov O & Oppenheim JJ (2000)
Human neutrophil defensins selectively chemoattract
naive T and immature dendritic cells. J Leukoc Biol
68, 9–14.
68 Chen T, Tang L & Shaw C (2003) Identification of
three novel Phyllomedusa sauvagei dermaseptins
(sVI–sVIII) by cloning from a skin secretion-derived
cDNA library. Regul Pept 116 , 139–146.
69 Auvynet C, El Amri C, Lacombe C, Bruston F,
Bourdais J, Nicolas P & Rosenstein Y (2008) Struc-
tural requirements for antimicrobial versus chemo-
attractant activities for dermaseptin S9. FEBS J 275,
4134–4151.
70 Otte JM, Werner I, Brand S, Chromik AM, Schmitz
F, Kleine M & Schmidt WE (2008) Human beta defen-
sin 2 promotes intestinal wound healing in vitro. J Cell
Biochem 104, 2286–2297.
71 Chen X, Niyonsaba F, Ushio H, Hara M, Yokoi H,
Matsumoto K, Saito H, Nagaoka I, Ikeda S, Okumura
K et al. (2007) Antimicrobial peptides human beta-
defensin (hBD)-3 and hBD-4 activate mast cells and
increase skin vascular permeability. Eur J Immunol 37,
434–444.
72 Prohaszka Z, Nemet K, Csermely P, Hudecz F, Mezo
G & Fust G (1997) Defensins purified from human
granulocytes bind C1q and activate the classical com-
plement pathway like the transmembrane glycoprotein

gp41 of HIV-1. Mol Immunol 34, 809–816.
73 Chaly YV, Paleolog EM, Kolesnikova TS, Tikhonov
II, Petratchenko EV & Voitenok NN (2000) Neutro-
phil alpha-defensin human neutrophil peptide modu-
lates cytokine production in human monocytes and
adhesion molecule expression in endothelial cells.
Eur Cytokine Netw 11, 257–266.
74 Biragyn A, Ruffini PA, Leifer CA, Klyushnenkova E,
Shakhov A, Chertov O, Shirakawa AK, Farber JM,
Segal DM, Oppenheim JJ et al. (2002) Toll-like
receptor 4-dependent activation of dendritic cells by
beta-defensin 2. Science 298, 1025–1029.
75 Varoga D, Pufe T, Harder J, Schroder JM, Mentlein
R, Meyer-Hoffert U, Goldring MB, Tillmann B,
Hassenpflug J & Paulsen F (2005) Human beta-
defensin 3 mediates tissue remodeling processes in
articular cartilage by increasing levels of metallo-
proteinases and reducing levels of their endogenous
inhibitors. Arthritis Rheum 52, 1736–1745.
76 Chan YR & Gallo RL (1998) PR-39, a syndecan-
inducing antimicrobial peptide, binds and affects
p130(Cas). J Biol Chem 273, 28978–28985.
77 Braff MH, Hawkins MA, Di Nardo A, Lopez-Garcia
B, Howell MD, Wong C, Lin K, Streib JE, Dorschner
R, Leung DY et al. (2005) Structure–function relation-
ships among human cathelicidin peptides: dissociation
of antimicrobial properties from host immunostimula-
tory activities. J Immunol 174
, 4271–4278.
78 Barreda DR, Hanington PC & Belosevic M (2004)

Regulation of myeloid development and function by
colony stimulating factors. Dev Comp Immunol 28,
509–554.
79 Bowdish DM, Davidson DJ, Speert DP & Hancock
RE (2004) The human cationic peptide LL-37 induces
activation of the extracellular signal-regulated kinase
and p38 kinase pathways in primary human mono-
cytes. J Immunol 172, 3758–3765.
80 Cirioni O, Giacometti A, Ghiselli R, Bergnach C,
Orlando F, Silvestri C, Mocchegiani F, Licci A,
Skerlavaj B, Rocchi M et al. (2006) LL-37 protects
rats against lethal sepsis caused by gram-negative
bacteria. Antimicrob Agents Chemother 50, 1672–1679.
81 Scott MG, Vreugdenhil AC, Buurman WA, Hancock
RE & Gold MR (2000) Cutting edge: cationic antimicro-
bial peptides block the binding of lipopolysaccharide
(LPS) to LPS binding protein. J Immunol 164, 549–553.
82 Oppenheim JJ & Yang D (2005) Alarmins: chemo-
tactic activators of immune responses. Curr Opin
Immunol 17, 359–365.
83 Rosenfeld Y, Papo N & Shai Y (2006) Endotoxin
(lipopolysaccharide) neutralization by innate immunity
host-defense peptides. Peptide properties and plausible
modes of action. J Biol Chem 281, 1636–1643.
84 Bhunia A, Mohanram H & Bhattacharjya S (2009)
Lipopolysaccharide bound structures of the active
fragments of fowlicidin-1, a cathelicidin family of anti-
microbial and antiendotoxic peptide from chicken,
determined by transferred nuclear overhauser effect
spectroscopy. Biopolymers 92, 9–22.

85 Mookherjee N, Brown KL, Bowdish DM, Doria S,
Falsafi R, Hokamp K, Roche FM, Mu R, Doho
GH, Pistolic J et al. (2006) Modulation of the
C. Auvynet and Y. Rosenstein AMPs, the small yet big players of immunity
FEBS Journal 276 (2009) 6497–6508 ª 2009 The Authors Journal compilation ª 2009 FEBS 6507
TLR-mediated inflammatory response by the endo-
genous human host defense peptide LL-37. J Immunol
176, 2455–2464.
86 Molhoek EM, den Hertog AL, de Vries AM, Nazmi
K, Veerman EC, Hartgers FC, Yazdanbakhsh M,
Bikker FJ & van der Kleij D (2009) Structure–function
relationship of the human antimicrobial peptide LL-37
and LL-37 fragments in the modulation of TLR
responses. Biol Chem 390, 295–303.
87 Bjorstad A, Askarieh G, Brown KL, Christenson K,
Forsman H, Onnheim K, Li HN, Teneberg S,
Maier O, Hoekstra D et al. (2009) The host defense
peptide LL-37 selectively permeabilizes apoptotic
leukocytes. Antimicrob Agents Chemother 53,
1027–1038.
88 Murakami M, Lopez-Garcia B, Braff M, Dorschner
RA & Gallo RL (2004) Postsecretory processing
generates multiple cathelicidins for enhanced topical
antimicrobial defense. J Immunol 172, 3070–3077.
89 Scott MG, Dullaghan E, Mookherjee N, Glavas N,
Waldbrook M, Thompson A, Wang A, Lee K, Doria
S, Hamill P et al. (2007) An anti-infective peptide that
selectively modulates the innate immune response.
Nat Biotechnol 25, 465–472.
90 Biragyn A, Coscia M, Nagashima K, Sanford M,

Young HA & Olkhanud P (2008) Murine beta-
defensin 2 promotes TLR-4 ⁄ MyD88-mediated and
NF-kappaB-dependent atypical death of APCs via
activation of TNFR2. J Leukoc Biol 83, 998–1008.
91 Martin P & Leibovich SJ (2005) Inflammatory cells
during wound repair: the good, the bad and the ugly.
Trends Cell Biol 15, 599–607.
92 Heilborn JD, Nilsson MF, Kratz G, Weber G, Soren-
sen O, Borregaard N & Stahle-Backdahl M (2003) The
cathelicidin anti-microbial peptide LL-37 is involved in
re-epithelialization of human skin wounds and is lack-
ing in chronic ulcer epithelium. J Invest Dermatol 120,
379–389.
93 Tokumaru S, Sayama K, Shirakata Y, Komatsuzawa
H, Ouhara K, Hanakawa Y, Yahata Y, Dai X,
Tohyama M, Nagai H et al. (2005) Induction of
keratinocyte migration via transactivation of the
epidermal growth factor receptor by the antimicrobial
peptide LL-37. J Immunol 175, 4662–4668.
94 Koczulla R, von Degenfeld G, Kupatt C, Krotz F,
Zahler S, Gloe T, Issbrucker K, Unterberger P, Zaiou
M, Lebherz C et al. (2003) An angiogenic role for the
human peptide antibiotic LL-37 ⁄ hCAP-18. J Clin
Invest 111, 1665–1672.
95 Braff MH, Zaiou M, Fierer J, Nizet V & Gallo RL
(2005) Keratinocyte production of cathelicidin pro-
vides direct activity against bacterial skin pathogens.
Infect Immun 73 , 6771–6781.
96 Baroni A, Donnarumma G, Paoletti I, Longanesi-
Cattani I, Bifulco K, Tufano MA & Carriero MV

(2009) Antimicrobial human beta-defensin-2 stimulates
migration, proliferation and tube formation of human
umbilical vein endothelial cells. Peptides 30, 267–272.
97 Park HJ, Cho DH, Kim HJ, Lee JY, Cho BK, Bang
SI, Song SY, Yamasaki K, Di Nardo A & Gallo RL
(2009) Collagen synthesis is suppressed in dermal fi-
broblasts by the human antimicrobial peptide LL-37.
J Invest Dermatol 129, 843–850.
98 Gambichler T, Skrygan M, Tomi NS, Othlinghaus N,
Brockmeyer NH, Altmeyer P & Kreuter A (2008)
Differential mRNA expression of antimicrobial pep-
tides and proteins in atopic dermatitis as compared to
psoriasis vulgaris and healthy skin. Int Arch Allergy
Immunol 147, 17–24.
99 Howell MD, Gallo RL, Boguniewicz M, Jones JF,
Wong C, Streib JE & Leung DY (2006) Cytokine milieu
of atopic dermatitis skin subverts the innate immune
response to vaccinia virus. Immunity 24, 341–348.
100 Buchau AS, Macleod DT, Morizane S, Kotol PF,
Hata T & Gallo RL (2009) Bcl-3 acts as an innate
immune modulator by controlling antimicrobial
responses in keratinocytes. J Invest Dermatol 129,
2148–2155.
101 Richard M, Louahed J, Demoulin JB & Renauld JC
(1999) Interleukin-9 regulates NF-kappaB activity
through BCL3 gene induction. Blood 93, 4318–4327.
102 Lande R, Gregorio J, Facchinetti V, Chatterjee B,
Wang YH, Homey B, Cao W, Wang YH, Su B, Nestle
FO et al. (2007) Plasmacytoid dendritic cells sense self-
DNA coupled with antimicrobial peptide. Nature 449,

564–569.
103 Yamasaki K, Di Nardo A, Bardan A, Murakami M,
Ohtake T, Coda A, Dorschner RA, Bonnart C,
Descargues P, Hovnanian A et al. (2007) Increased
serine protease activity and cathelicidin promotes skin
inflammation in rosacea. Nat Med 13, 975–980.
104 Gersemann M, Wehkamp J, Fellermann K & Stange
EF (2008) Crohn’s disease – defect in innate defence.
World J Gastroenterol 14, 5499–5503.
AMPs, the small yet big players of immunity C. Auvynet and Y. Rosenstein
6508 FEBS Journal 276 (2009) 6497–6508 ª 2009 The Authors Journal compilation ª 2009 FEBS