An angiogenic role for the human peptide antibiotic LL-37/hCAP-18

Neutrophil extracellular trap-associated molecules: a review on their immunophysiological and inflammatory roles

Neutrophil extracellular traps (NETs) are a defense mechanism against pathogens. They are composed of DNA and various proteins and have the ability to hinder microbial spreading and survival. However, NETs are not only related to infections but also participate in sterile inflammatory events. In addition to DNA, NETs contain histones, serine proteases, cytoskeletal proteins and antimicrobial peptides, all of which have immunomodulatory properties that can augment or decrease the inflammatory response. Extracellular localization of these molecules alerts the immune system of cellular damage, which is triggered by recognition of damage-associated molecular patterns (DAMPs) through specific pattern recognition receptors. However, not all of these molecules are DAMPs and may have other immunophysiological properties in the extracellular space. The release of NETs can lead to production of pro-inflammatory cytokines (due to TLR2/4/9 and inflammasome activation), the destruction of the extracellular matrix, activation of serine proteases and of matrix metallopeptidases (MMPs), modulation of cellular proliferation, induction of cellular migration and adhesion, promotion of thrombogenesis and angiogenesis and disruption of epithelial and endothelial permeability. Understanding the dynamics of NET-associated molecules, either individually or synergically, will help to unravel their role in inflammatory events and open novel perspectives for potential therapeutic targets. We here review molecules contained within NETS and their immunophysiological roles.

Identification of Novel Cryptic Multifunctional Antimicrobial Peptides from the Human Stomach Enabled by a Computational-Experimental Platform

Novel approaches are needed to combat antibiotic resistance. Here, we describe a computational-experimental framework for the discovery of novel cryptic antimicrobial peptides (AMPs). The computational platform, based on previously validated antimicrobial scoring functions, indicated the activation peptide of pepsin A, the main human stomach protease, and its N- and C-terminal halves as antimicrobial peptides. The three peptides from pepsinogen A3 isoform were prepared in a recombinant form using a fusion carrier specifically developed to express toxic peptides in Escherichia coli. Recombinant pepsinogen A3-derived peptides proved to be wide-spectrum antimicrobial agents with MIC values in the range 1.56-50 μM (1.56-12.5 μM for the whole activation peptide). Moreover, the activation peptide was bactericidal at pH 3.5 for relevant foodborne pathogens, suggesting that this new class of previously unexplored AMPs may contribute to microbial surveillance within the human stomach. The peptides showed no toxicity toward human cells and exhibited anti-infective activity in vivo, reducing by up to 4 orders of magnitude the bacterial load in a mouse skin infection model. These peptides thus represent a promising new class of antibiotics. We envision that computationally guided data mining approaches such as the one described here will lead to the discovery of antibiotics from previously unexplored sources.

Carbon Nanoparticles Inhibit the Antimicrobial Activities of the Human Cathelicidin LL-37 through Structural Alteration

Host defense peptides, also known as antimicrobial peptides, are key elements of innate host defense. One host defense peptide with well-characterized antimicrobial activity is the human cathelicidin, LL-37. LL-37 has been shown to be upregulated at sites of infection and inflammation and is regarded as one of the primary innate defense molecules against bacterial and viral infection. Human exposure to combustion-derived or engineered nanoparticles is of increasing concern, and the implications of nanomaterial exposure on the human immune response is poorly understood. However, it is widely acknowledged that nanoparticles can interact strongly with several immune proteins of biological significance, with these interactions resulting in structural and functional changes of the proteins involved. This study investigated whether the potent antibacterial and antiviral functions of LL-37 were inhibited by exposure to, and interaction with, carbon nanoparticles, together with characterizing the nature of the interaction. LL-37 was exposed to carbon black nanoparticles in vitro, and the antibacterial and antiviral functions of the peptide were subsequently assessed. We demonstrate a substantial loss of antimicrobial function when the peptide was exposed to low concentrations of nanomaterials, and we further show that the nanomaterial-peptide interaction resulted in a significant change in the structure of the peptide. The human health implications of these findings are significant, as, to our knowledge, this is the first evidence that nanoparticles can alter host defense peptide structure and function, indicating a new role for nanoparticle exposure in increased disease susceptibility.

Antimicrobial peptide LL-37 and gastrointestinal diseases

Host defense antimicrobial peptides are key components of the human innate immunity that plays an indispensable role in human health. Cathelicidins are a family of antimicrobial peptides in mammals. LL-37, the only cathelicidin described so far in humans, plays a critical role in host defense against pathogen invasion, as well as regulating the functions of anti-inflammation, anti-tumorigenesis and tissue repair. Emerging evidence suggests that LL-37 is related to several kinds of gastrointestinal diseases, and its application to the diagnosis and treatment of gastrointestinal diseases has become a growing concern. This review aims to elucidate the structure and biological activity of LL-37 and discuss the recent progress in understanding the relationship between LL-37 and gastrointestinal diseases.

Alarmin function of cathelicidin antimicrobial peptide LL37 through IL-36γ induction in human epidermal keratinocytes

Several dermatoses, including psoriasis, atopic dermatitis, and rosacea, alter the expression of the innate immune effector human cathelicidin antimicrobial peptide (CAMP). To elucidate the roles of aberrant CAMP in dermatoses, we performed cDNA array analysis in CAMP-stimulated human epidermal keratinocytes, the primary cells responding to innate immune stimuli and a major source of CAMP LL37 in skin. Among LL37-inducible genes, IL-1 cluster genes, particularly IL36G, are of interest because we observed coordinate increases in CAMP and IL-36γ in the lesional skin of psoriasis, whereas virtually no CAMP or IL-36γ was observed in nonlesional skin and normal skin. The production and release of IL-36γ were up to 20-30 ng/ml in differentiated keratinocytes cultured in high-calcium media. G-protein inhibitor pertussis toxin and p38 inhibitor suppressed IL-36γ induction by LL37. As an alarmin, LL37 induces chemokines, including CXCL1, CXCL8/IL8, CXCL10/IP-10, and CCL20/MIP3a, and IL-36 (10-100 ng/ml) augments the production of these chemokines by LL37. Pretreatment with small interfering RNA against IL36γ and IL-36R IL36R/IL1RL2 and IL1RAP suppressed LL37-dependent IL8, CXCL1, CXCL10/IP10, and CCL20 production in keratinocytes, suggesting that the alarmin function of LL37 was partially dependent on IL-36γ and its receptors. Counting on CAMP induction in innate stimuli, such as in infection and wounding, IL-36γ induction by cathelicidin would explain the mechanism of initiation of skin inflammation and occasional exacerbations of psoriasis and skin diseases by general infection.

Dectin-1 is expressed in human lung and mediates the proinflammatory immune response to nontypeable Haemophilus influenzae

The C-type lectin receptor Dectin-1 is expressed mainly on myeloid cells mediating the immune response targeting respiratory pathogens such as Aspergillus fumigatus and Mycobacterium tuberculosis. The pulmonary epithelium serves as an important interface for interactions between these pathogens and the respiratory tract. Therefore, we analyzed the expression pattern of Dectin-1 in the human lung. Immunohistochemically stained human lung sections from 17 out of 19 individuals were positive for Dectin-1, which was expressed mainly apically on bronchial and alveolar epithelium. Our results showed no correlation with chronic obstructive pulmonary disease (COPD) or the smoking habits of the patients. Nontypeable Haemophilus influenzae (NTHI), an important bacterial pathogen of the respiratory tract with significant importance in COPD, has also been proposed to be recognized by Dectin-1, suggesting a possible impact on the NTHI-dependent immune response in human airways. Therefore, the involvement of Dectin-1 in NTHI-triggered cytokine responses was investigated in primary normal human bronchial epithelial (NHBE) cells and in the A549 cell line stably transfected with Dectin-1. The presence of Dectin-1 significantly increased cytokine release in response to NTHI in NHBE and A549 cells. In addition, phosphorylation of the Dectin-1 hem-immunoreceptor tyrosine-based activation motif (hemITAM) was essential for the Dectin-1-triggered response to NTHI in A549 cells. In conclusion, in human airways, epithelium-expressed Dectin-1 may play a significant role in generating an NTHI-mediated, proinflammatory immune response.

IMPORTANCE

In this study, we demonstrated, for the first time, the expression of Dectin-1 on human lung tissues and, in particular, pulmonary epithelium by making use of immunohistochemical staining. The epithelial lining of the human airways is an important interface for host-pathogen interactions. Therefore, our data suggest that epithelium-expressed Dectin-1 is of considerable importance for the interaction of the human airways with pathogens detected by this receptor, such as A. fumigatus and M. tuberculosis. Moreover, we further demonstrated that, in pulmonary epithelial cells, Dectin-1 enhances the proinflammatory immune response to NTHI. In COPD patients, NTHI is a major cause of respiratory tract infections and is associated with proinflammatory immune responses in the lower airways. Therefore, our data suggest that the functional interaction of Dectin-1 with NTHI in human airways may have an important impact on the pathogenesis of COPD.

Citrullination alters immunomodulatory function of LL-37 essential for prevention of endotoxin-induced sepsis

Cathelicidin LL-37 plays an essential role in innate immunity by killing invading microorganisms and regulating the inflammatory response. These activities depend on the cationic character of the peptide, which is conferred by arginine and lysine residues. At inflammatory foci in vivo, LL-37 is exposed to peptidyl arginine deiminase (PAD), an enzyme released by inflammatory cells. Therefore, we hypothesized that PAD-mediated citrullination of the arginine residues within LL-37 will abrogate its immunomodulatory functions. We found that, when citrullinated, LL-37 was at least 40 times less efficient at neutralizing the proinflammatory activity of LPS due to a marked decrease in its affinity for endotoxin. Also, the ability of citrullinated LL-37 to quench macrophage responses to lipoteichoic acid and poly(I:C) signaling via TLR2 and TLR3, respectively, was significantly reduced. Furthermore, in stark contrast to native LL-37, the modified peptide completely lost the ability to prevent morbidity and mortality in a mouse model of d-galactosamine-sensitized endotoxin shock. In fact, administration of citrullinated LL-37 plus endotoxin actually exacerbated sepsis due to the inability of LL-37 to neutralize LPS and the subsequent enhancement of systemic inflammation due to increased serum levels of IL-6. Importantly, serum from septic mice showed increased PAD activity, which strongly correlated with the level of citrullination, indicating that PAD-driven protein modification occurs in vivo. Because LL-37 is a potential treatment for sepsis, its administration should be preceded by a careful analysis to ensure that the citrullinated peptide is not generated in treated patients.

Little peptide, big effects: the role of LL-37 in inflammation and autoimmune disease

The innate immune system utilizes many approaches for defense against invading microorganisms, including complement-mediated lysis, engulfment, formation of neutrophil extracellular traps, and release of antimicrobial peptides. Although classically thought to be driven by adaptive immunity, the development of autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus is increasingly associated with dysregulated innate immune pathways. An emerging theme within this literature is the contribution of antimicrobial peptides to the development of autoimmune disorders. This is best exemplified in atopic dermatitis and psoriasis where the defensins and the single human cathelicidin, LL-37, may contribute to disease. Furthermore, in the past few years, a role for LL-37 has emerged in the pathogenesis of systemic lupus erythematosus, rheumatoid arthritis, atherosclerosis, and possibly other diseases. In this review, we discuss the role of LL-37 and its murine ortholog, mCRAMP, in the modulation of immune and inflammatory pathways and their effects on autoimmune and inflammatory diseases.

β-Defensins activate human mast cells via Mas-related gene X2

Human β-defensins (hBDs) stimulate degranulation in rat peritoneal mast cells in vitro and cause increased vascular permeability in rats in vivo. In this study, we sought to determine whether hBDs activate murine and human mast cells and to delineate the mechanisms of their regulation. hBD2 and hBD3 did not induce degranulation in murine peritoneal or bone marrow-derived mast cells (BMMC) in vitro and had no effect on vascular permeability in vivo. By contrast, these peptides induced sustained Ca(2+) mobilization and substantial degranulation in human mast cells, with hBD3 being more potent. Pertussis toxin (PTx) had no effect on hBD-induced Ca(2+) mobilization, but La(3+) and 2-aminoethoxydiphenyl borate (a dual inhibitor of inositol 1,4,5-triphosphate receptor and transient receptor potential channels) caused substantial inhibition of this response. Interestingly, degranulation induced by hBDs was substantially inhibited by PTx, La(3+), or 2-aminoethoxydiphenyl borate. Whereas human mast cells endogenously express G protein-coupled receptor, Mas-related gene X2 (MrgX2), rat basophilic leukemia, RBL-2H3 cells, and murine BMMCs do not. Silencing the expression of MrgX2 in human mast cells inhibited hBD-induced degranulation, but had no effect on anaphylatoxin C3a-induced response. Furthermore, ectopic expression of MrgX2 in RBL-2H3 and murine BMMCs rendered these cells responsive to hBDs for degranulation. This study demonstrates that hBDs activate human mast cells via MrgX2, which couples to both PTx-sensitive and insensitive signaling pathways most likely involving Gαq and Gαi to induce degranulation. Furthermore, murine mast cells are resistant to hBDs for degranulation, and this reflects the absence of MrgX2 in these cells.

Cathelicidin a potential therapeutic peptide for gastrointestinal inflammation and cancer

Cathelicidins, are host defense peptides synthesized and stored in circulating leukocytes and numerous types of epithelial tissues in particular the gastrointestinal (GI) tract and skin. They have been known for their antimicrobial activities against a variety of microbes. Recently it was discovered that they have other significant biological functions and produce appealing pharmacological actions against inflammation and cancer in the GI tract through defined mechanisms. Experimental evidence shows that these actions could be tissue and disease specific and concentration dependent. This article reviews some of the physiological functions of cathelicidins and also their therapeutic potential in the treatment of inflammation and cancer and also the delivery system for this peptide as targeted therapy for various disorders in the GI tract both in animals and humans.

Antibacterial activity of the human host defence peptide LL-37 and selected synthetic cationic lipids against bacteria associated with oral and upper respiratory tract infections

OBJECTIVES

We aim to develop antibacterial peptide mimics resistant to protease degradation, with broad-spectrum activity at sites of infection.

METHODS

The bactericidal activities of LL-37, ceragenins CSA-13, CSA-90 and CSA-92 and the spermine-conjugated dexamethasone derivative D2S were evaluated using MIC and MBC measurements. Gingival fibroblast counting, interleukin-8 (IL-8) and lactate dehydrogenase (LDH) release from keratinocytes (HaCat) were used to determine effects on cell growth, pro-inflammatory response and toxicity.

RESULTS

All tested cationic lipids showed stronger bactericidal activity than LL-37. Incubation of Staphylococcus aureus with half the MIC of LL-37 led to the appearance of bacteria resistant to its bactericidal effects, but identical incubations with CSA-13 or D2S did not produce resistant bacteria. Cathelicidin LL-37 significantly increased the total number of gingival fibroblasts, but ceragenins and D2S did not alter gingival fibroblast growth. Cationic lipids showed no toxicity to HaCat cells at concentrations resulting in bacterial killing.

CONCLUSIONS

These data suggest that cationic lipids such as ceragenins warrant further testing as potential novel antibacterial agents.

The human lactoferrin-derived peptide hLF1-11 exerts immunomodulatory effects by specific inhibition of myeloperoxidase activity

Because of their ability to eliminate pathogens and to modulate various host immune responses, antimicrobial peptides are considered as candidate agents to fight infections by (antibiotic-resistant) pathogens. We recently reported that hLF1-11 (GRRRRSVQWCA), an antimicrobial peptide derived from the N terminus of human lactoferrin, displays diverse modulatory activities on monocytes, thereby enhancing their actions in innate immune responses. The aim of this study was to identify the cellular target of hLF1-11 that mediates these effects. Results revealed that hLF1-11 binds and subsequently penetrates human monocytes, after which it inhibits the enzymatic activities of myeloperoxidase (MPO). Moreover, a chemical inhibitor of MPO (aminobenzoic acid hydrazide) mimicked the effects of hLF1-11 on the inflammatory response by monocytes and on monocyte-macrophage differentiation. Computer-assisted molecular modeling predicted that hLF1-11 can bind to the edge of and within the crevice of the active site of MPO. Experiments with a set of hLF1-11 peptides with amino acid substitutions identified the stretch of arginines and the cysteine at position 10 as pivotal in these immunomodulatory properties of hLF1-11. We conclude that hLF1-11 may exert its modulatory effects on human monocytes by specific inhibition of MPO activity.

Molecular regulators of resolution of inflammation: potential therapeutic targets in the reproductive system

Inflammatory processes are central to reproductive events including ovulation, menstruation, implantation and labour, while inflammatory dysregulation is a feature of numerous reproductive pathologies. In recent years, there has been much research into the endogenous mechanisms by which inflammatory reactions are terminated and tissue homoeostasis is restored, a process termed resolution. The identification and characterisation of naturally occurring pro-resolution mediators including lipoxins and annexin A1 has prompted a shift in the field of anti-inflammation whereby resolution is now observed as an active process, triggered as part of a normal inflammatory response. This review will address the process of resolution, discuss available evidence for expression of pro-resolution factors in the reproductive tract and explore possible roles for resolution in physiological reproductive processes and associated pathologies.

Flagellin stimulates protective lung mucosal immunity: role of cathelicidin-related antimicrobial peptide

TLRs are required for generation of protective lung mucosal immune responses against microbial pathogens. In this study, we evaluated the effect of the TLR5 ligand flagellin on stimulation of antibacterial mucosal immunity in a lethal murine Pseudomonas aeruginosa pneumonia model. The intranasal pretreatment of mice with purified P. aeruginosa flagellin induced strong protection against intratracheal P. aeruginosa-induced lethality, which was attributable to markedly improved bacterial clearance, reduced dissemination, and decreased alveolar permeability. The protective effects of flagellin on survival required TLR5 and were observed even in the absence of neutrophils. Flagellin induced strong induction of innate genes, most notably the antimicrobial peptide cathelicidin-related antimicrobial peptide. Finally, flagellin-induced protection was partially abrogated in cathelicidin-related antimicrobial peptide-deficient mice. Our findings illustrate the profound stimulatory effect of flagellin on lung mucosal innate immunity, a response that might be exploited therapeutically to prevent the development of gram-negative bacterial infection of the respiratory tract.

Synthetic cationic peptide IDR-1002 provides protection against bacterial infections through chemokine induction and enhanced leukocyte recruitment

With the rapid rise in the incidence of multidrug resistant infections, there is substantial interest in host defense peptides as templates for production of new antimicrobial therapeutics. Natural peptides are multifunctional mediators of the innate immune response, with some direct antimicrobial activity and diverse immunomodulatory properties. We have previously developed an innate defense regulator (IDR) 1, with protective activity against bacterial infection mediated entirely through its effects on the immunity of the host, as a novel approach to anti-infective therapy. In this study, an immunomodulatory peptide IDR-1002 was selected from a library of bactenecin derivatives based on its substantially more potent ability to induce chemokines in human PBMCs. The enhanced chemokine induction activity of the peptide in vitro correlated with stronger protective activity in vivo in the Staphylococcus aureus-invasive infection model, with a >5-fold reduction in the protective dose in direct comparison with IDR-1. IDR-1002 also afforded protection against the Gram-negative bacterial pathogen Escherichia coli. Chemokine induction by IDR-1002 was found to be mediated through a Gi-coupled receptor and the PI3K, NF-kappaB, and MAPK signaling pathways. The protective activity of the peptide was associated with in vivo augmentation of chemokine production and recruitment of neutrophils and monocytes to the site of infection. These results highlight the importance of the chemokine induction activity of host defense peptides and demonstrate that the optimization of the ex vivo chemokine-induction properties of peptides is a promising method for the rational development of immunomodulatory IDR peptides with enhanced anti-infective activity.

The host defense peptide cathelicidin is required for NK cell-mediated suppression of tumor growth

Tumor surveillance requires the interaction of multiple molecules and cells that participate in innate and the adaptive immunity. Cathelicidin was initially identified as an antimicrobial peptide, although it is now clear that it fulfills a variety of immune functions beyond microbial killing. Recent data have suggested contrasting roles for cathelicidin in tumor development. Because its role in tumor surveillance is not well understood, we investigated the requirement of cathelicidin in controlling transplantable tumors in mice. Cathelicidin was observed to be abundant in tumor-infiltrating NK1.1(+) cells in mice. The importance of this finding was demonstrated by the fact that cathelicidin knockout mice (Camp(-/-)) permitted faster tumor growth than wild type controls in two different xenograft tumor mouse models (B16.F10 and RMA-S). Functional in vitro analyses found that NK cells derived from Camp(-/-) versus wild type mice showed impaired cytotoxic activity toward tumor targets. These findings could not be solely attributed to an observed perforin deficiency in freshly isolated Camp(-/-) NK cells, because this deficiency could be partially restored by IL-2 treatment, whereas cytotoxic activity was still defective in IL-2-activated Camp(-/-) NK cells. Thus, we demonstrate a previously unrecognized role of cathelicidin in NK cell antitumor function.

Intracellular receptor for human host defense peptide LL-37 in monocytes

The human cationic host defense peptide LL-37 has a broad range of immunomodulatory, anti-infective functions. A synthetic innate defense regulator peptide, innate defense regulator 1 (IDR-1), based conceptually on LL-37, was recently shown to selectively modulate innate immunity to protect against a wide range of bacterial infections. Using advanced proteomic techniques, ELISA, and Western blotting procedures, GAPDH was identified as a direct binding partner for LL-37 in monocytes. Enzyme kinetics and mobility shift studies also indicated LL-37 and IDR-1 binding to GAPDH. The functional relevance of GAPDH in peptide-induced responses was demonstrated by using gene silencing of GAPDH with small interfering RNA (siRNA). Previous studies have established that the induction of chemokines and the anti-inflammatory cytokine IL-10 are critical immunomodulatory functions in the anti-infective properties of LL-37 and IDR-1, and these functions are modulated by the MAPK p38 pathway. Consistent with that, this study demonstrated the importance of the GAPDH interactions with these peptides since gene silencing of GAPDH resulted in impaired p38 MAPK signaling, downstream chemokine and cytokine transcriptional responses induced by LL-37 and IDR-1, and LL-37-induced cytokine production. Bioinformatic analysis, using InnateDB, of the major interacting partners of GAPDH indicated the likelihood that this protein can impact on innate immune pathways including p38 MAPK. Thus, this study has demonstrated a novel function for GAPDH as a mononuclear cell receptor for human cathelicidin LL-37 and immunomodulatory IDR-1 and conclusively demonstrated its relevance in the functioning of cationic host defense peptides.

International Union of Basic and Clinical Pharmacology. LXXIII. Nomenclature for the formyl peptide receptor (FPR) family

Formyl peptide receptors (FPRs) are a small group of seven-transmembrane domain, G protein-coupled receptors that are expressed mainly by mammalian phagocytic leukocytes and are known to be important in host defense and inflammation. The three human FPRs (FPR1, FPR2/ALX, and FPR3) share significant sequence homology and are encoded by clustered genes. Collectively, these receptors bind an extraordinarily numerous and structurally diverse group of agonistic ligands, including N-formyl and nonformyl peptides of different composition, that chemoattract and activate phagocytes. N-formyl peptides, which are encoded in nature only by bacterial and mitochondrial genes and result from obligatory initiation of bacterial and mitochondrial protein synthesis with N-formylmethionine, is the only ligand class common to all three human receptors. Surprisingly, the endogenous anti-inflammatory peptide annexin 1 and its N-terminal fragments also bind human FPR1 and FPR2/ALX, and the anti-inflammatory eicosanoid lipoxin A4 is an agonist at FPR2/ALX. In comparison, fewer agonists have been identified for FPR3, the third member in this receptor family. Structural and functional studies of the FPRs have produced important information for understanding the general pharmacological principles governing all leukocyte chemoattractant receptors. This article aims to provide an overview of the discovery and pharmacological characterization of FPRs, to introduce an International Union of Basic and Clinical Pharmacology (IUPHAR)-recommended nomenclature, and to discuss unmet challenges, including the mechanisms used by these receptors to bind diverse ligands and mediate different biological functions.

Alarmins and antimicrobial immunity

Alarmins are endogenous mediators capable of enhancing innate and adaptive immune response through induction of concomitant recruitment and activation of antigen-presenting cells. Here we provide a brief overview of various alarmins, highlight their critical roles in innate and adaptive antimicrobial immunity, and speculate on potential usage of alarmins in combating aspergillosis.

IL-17A enhances vitamin D3-induced expression of cathelicidin antimicrobial peptide in human keratinocytes

Cathelicidin is strongly expressed in lesional skin in psoriasis and may play an important role as both an antimicrobial peptide and as an autoinflammatory mediator in this chronic skin disease. The mechanism of increased cathelicidin in psoriatic keratinocytes is not known, but recent observations have found that psoriasis has abundant Th17 cells that produce IL-17A and IL-22. We found that human keratinocytes stimulated with supernatants from T cells isolated from lesional psoriatic skin increased expression of cathelicidin when stimulated in the presence of 1,25-dihydroxyvitamin D(3) (1,25D(3)). This increase was signaled through the IL-17RA. In vitro, IL-17A, but not IL-22, enhanced cathelicidin mRNA and peptide expression in keratinocytes dependent on the presence of 1,25D(3). At the same time, coincubation with 1,25D(3) blocked induction of human beta-defensin 2 (HBD2), IL-6, and IL-8, which are other target genes of IL-17A. Act1, an adaptor associated with IL-17RA and essential for IL-17A signaling, mediated cathelicidin induction, as its suppression by small interfering RNA inhibited HBD2 and cathelicidin. Both, 1,25D(3) and IL-17A signaled cathelicidin induction through MEK-ERK. These results suggest that increased IL-17A in psoriatic skin increases cathelicidin through a vitamin D(3)-, Act1-, and MEK-ERK-dependent mechanism. Therapy targeting this cathelicidin-regulating system might be beneficial in patients suffering from psoriasis.

LL-37 regulates the overexpression of vascular endothelial growth factor (VEGF) and c-IAP-2 in human keratinocytes

BACKGROUND

The antimicrobial peptide PR39 is a porcine cathelicidin with angiogenic and antiapoptotic activities, as it can regulate the expression of vascular endothelial growth factor (VEGF) and inhibitor apoptosis protein-2 (c-IAP-2) in endothelial cells. The human homolog LL-37 has been found to be highly expressed in human keratinocytes from psoriatic patients, but it is not known whether LL-37 can modulate the expression of VEGF and c-IAP-2 in keratinocytes, as both molecules are involved in the overgrowth of psoriatic skin. Therefore, in this work, we studied the possible role of CAP18/LL-37 in the modulation of VEGF and c-IAP-2 expression in human keratinocytes.

METHODS

The CAP18/LL-37 gene was cloned into a plasmid that contained green fluorescent protein (GFP). This plasmid was called pGFP-CAP18/LL-37. The expression of LL-37, VEGF, and c-IAP-2 was determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting in HaCaT cells transfected with pGFP-CAP18/LL-37. Specific DNAzymes were used to break the CAP18/LL-37 mRNA (DNAz-CAP18/LL-37).

RESULTS

HaCaT cells transfected with pGFP-CAP18/LL-37 showed the upregulation of VEGF and c-IAP-2 mRNAs. Hypoxia-inducible factor-1alpha (HIF-1alpha) mRNA expression did not change during the assays; however, its protein was increased, as well as the VEGF protein. HaCaT cells cotransfected with pGFP-CAP18/LL-37 and DNAz-CAP18/LL-37 showed depleted expression of LL-37, VEGF, and c-IAP-2 mRNAs.

CONCLUSIONS

These results suggest that LL-37 may modulate the expression of VEGF and c-IAP-2 via HIF-1alpha in human keratinocytes.

Salivary mucins inhibit antibacterial activity of the cathelicidin-derived LL-37 peptide but not the cationic steroid CSA-13

OBJECTIVES

Cationic antimicrobial peptides (CAPs) are the effector molecules of innate immunity, similar in potency to classic antibiotics that function in the first-line of defence against infectious agents. The purpose of this study was to investigate the effects of negatively charged mucins on the antibacterial activity of the positively charged cathelicidin LL-37 peptide, its synthetic analogue WLBU2 and the antimicrobial cationic steroid CSA-13.

METHODS

Mucin, DNA, F-actin and hCAP-18/LL-37 in saliva samples were evaluated by microscopy or immunoblotting. Bacterial killing assays and determination of MICs were used to determine bactericidal activity. Binding of rhodamine-B-labelled LL-37 peptide to mucin was fluorimetrically assessed.

RESULTS

Microscopic evaluation of saliva after addition of rhodamine-B-labelled LL-37 showed localization similar to that observed after the addition of a specific mucin-binding lectin. Immunoblotting confirmed the presence of hCAP-18/LL-37 in saliva samples and LL-37 peptide bound to isolated submaxillary gland mucin-coated plates. Mucin/LL-37 binding was partially prevented by treatment of mucin with neuraminidase, indicating involvement of sialic acid moieties. Decreased LL-37 and WLBU2 antibacterial activity was observed in the presence of mucin or dialysed human saliva, whereas CSA-13 antibacterial activity was significantly resistant to inhibition by mucins.

CONCLUSIONS

This study shows that the antibacterial LL-37 peptide and its synthetic analogue WLBU2 are inhibited by salivary mucin and that the cationic steroid CSA-13 retains most of its function in the presence of an equal amount of mucin or saliva.

Immune regulation by microvascular endothelial cells: directing innate and adaptive immunity, coagulation, and inflammation

An effective immune response depends not only on the proper activation, regulation, and function of immune cells, but also on their distribution and retention in diverse tissue microenvironments where they encounter a number of stimuli and other cell types. These activities are mediated by endothelial cells, which form specialized microcirculatory networks used by immune cells under both physiological and pathological circumstances. Endothelial cells represent a highly heterogeneous population of cells with the ability to interact with and modulate the function of immune cells. This review is focused on the role of microvascular endothelial cells in innate and adaptive immunity, inflammation, coagulation, angiogenesis, and the therapeutic implications of targeting endothelial cells in selected autoimmune and chronic inflammatory disorders.

Under-expression of VHL and over-expression of HDAC-1, HIF-1?, LL-37, and IAP-2 in affected skin biopsies of patients with psoriasis

BACKGROUND

A feature of psoriasis is the rapid proliferation of keratinocytes, during which apoptosis is blocked and angiogenesis starts. It is known that tumor hypoxic cells produce histone deacetylase-1 (HDAC-1), which up-regulates hypoxia-inducible factor-1alpha (HIF-1alpha) and down-regulates von Hippel-Lindau (VHL) protein by up-regulating vascular endothelial growth factor (VEGF) expression. It has been reported recently that the porcine peptide PR39 (homologous to human LL-37) has angiogenic and antiapoptotic activity. Thus, LL-37, induced by insulin-like growth factor-1 (IGF-1), could help in the production of VEGF. PR39 also induces the expression of inhibitor of apoptosis protein-2 (IAP-2), which blocks apoptosis. The purpose of this work was to analyze whether these genes and their proteins are expressed in psoriatic biopsies.

METHODS

Using semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) messenger RNA (mRNA) expression and immunohistochemical staining, we studied VHL, IAP-2, and related genes in skin biopsies from psoriatic patients and healthy subjects.

RESULTS

An over-expression of the mRNA for HDAC-1, HIF-1alpha, LL-37, and IGF-1 in psoriatic skin, in comparison with skin from healthy subjects, was found. The antiangiogenic VHL mRNA and protein were under-expressed in psoriatic skin and highly expressed in healthy skin. The antiapoptotic IAP-2 was over-expressed in dermal endothelial cells from psoriatic skin. The pro-apoptotic Bax, Fas, and FasL mRNAs were expressed.

CONCLUSIONS

These findings suggest that there could be an association of HDAC-1, HIF-1alpha, LL-37, VHL, and IAP-2 with angiogenic and apoptotic mechanisms in psoriasis.

Multifunctional antimicrobial peptides: therapeutic targets in several human diseases

Antimicrobial peptides have emerged as promising agents against antibiotic-resistant pathogens. They represent essential components of the innate immunity and permit humans to resist infection by microbes. These gene-encoded peptides are found mainly in phagocytes and epithelial cells, showing a direct activity against a wide range of microorganisms. Their role has now broadened from that of simply endogenous antibiotics to multifunctional mediators, and their antimicrobial activity is probably not the only primary function. Although antimicrobial peptide deficiency, dysregulation, or overproduction is not known to be a direct cause of any single human disease, numerous studies have now provided compelling evidence for their involvement in the complex network of immune responses and inflammatory diseases, thereby influencing diverse processes including cytokine release, chemotaxis, angiogenesis, wound repair, and adaptive immune induction. The purpose of this review is to highlight recent literature, showing that antimicrobial peptides are associated with several human conditions including infectious and inflammatory diseases, and to discuss current clinical development of peptide-based therapeutics for future use.

The lipoxin receptor ALX: potent ligand-specific and stereoselective actions in vivo

Lipoxins (LXs) and aspirin-triggered LX (ATL) are trihydroxytetraene-containing eicosanoids generated from arachidonic acid that are distinct in structure, formation, and function from the many other proinflammatory lipid-derived mediators. These endogenous eicosanoids have now emerged as founding members of the first class of lipid/chemical mediators involved in the resolution of the inflammatory response. Lipoxin A(4) (LXA(4)), ATL, and their metabolic stable analogs elicit cellular responses and regulate leukocyte trafficking in vivo by activating the specific receptor, ALX. ALX was the first receptor cloned and identified as a G protein-coupled receptor (GPCR) for lipoxygenase-derived eicosanoids with demonstrated cell type-specific signaling pathways. ALX at the level of DNA has sequence homology to the N-formylpeptide receptor and as an orphan GPCR was initially referred to as the N-formylpeptide receptor-like 1. Although LXA(4) is the endogenous potent ligand for ALX activation, a number of peptides can also activate this receptor to stimulate calcium mobilization and chemotaxis in vitro. In contrast with LXA(4), the counterparts of many of these peptides in vivo remain to be established. The purpose of this review is to highlight the molecular characterization of the ALX receptor and provide an overview of the ALX-LXA(4) axis responsible for anti-inflammatory and proresolving signals in vivo. The information in this review provides further support for the initial nomenclature proposition for this GPCR as ALX.

Serum Amyloid A Binding to Formyl Peptide Receptor-Like 1 Induces Synovial Hyperplasia and Angiogenesis

Serum amyloid A (SAA) is a major acute-phase reactant, and has been demonstrated to mediate proinflammatory cellular responses. Although SAA has been used as an indicator for a variety of inflammatory diseases, the role of SAA in synovial hyperplasia and proliferation of endothelial cells, a pathological hallmark of rheumatoid arthritis (RA), has yet to be elucidated. In this study, we have demonstrated that SAA promotes the proliferation of human fibroblast-like synoviocytes (FLS). In addition, SAA protects RA FLS against the apoptotic death induced by serum starvation, anti-Fas IgM, and sodium nitroprusside. The activity of SAA appears to be mediated by the formyl peptide receptor-like 1 (FPRL1) receptor, as it was mimicked by the WKYMVm peptide, a specific ligand for FPRL1, but completely abrogated by down-regulating the FPRL1 transcripts with short interfering RNA. The effect of SAA on FLS hyperplasia was shown to be caused by an increase in the levels of intracellular calcium, as well as the activation of ERK and Akt, which resulted in an elevation in the expression of cyclin D1 and Bcl-2. Moreover, SAA stimulated the proliferation, migration, and tube formation of endothelial cells in vitro, and enhanced the sprouting activity of endothelial cells ex vivo and neovascularization in vivo. These observations indicate that the binding of SAA to FPRL1 may contribute to the destruction of bone and cartilage via the promotion of synoviocyte hyperplasia and angiogenesis, thus providing a potential target for the control of RA.

Antimicrobial peptide LL-37 internalized by immature human dendritic cells alters their phenotype

The human cathelicidin LL-37 has been shown to be involved in the barrier function of the innate immunity, being released from specific cells upon challenge and exerting immunomodulatory effects. We here demonstrate that LL-37 affects immature dendritic cells, derived from human peripheral blood monocytes (MDDC). LL-37 is internalized by MDDC with subsequent localization primarily in the cytoplasmic compartment. However, LL-37 could also be detected in the nuclei of MDDC, suggesting that LL-37 may be transported into the nucleus. The uptake of LL-37 is dose, time and energy dependent, indicating that the observed internalization process involves an endocytic pathway. Incubation of immature MDDC with LL-37 caused phenotypic changes, characterized by an increased expression of the antigen-presenting molecule HLA-DR, and the costimulatory molecule CD86. Taken together, these findings suggest that LL-37 released upon triggering of the innate immunity, may affect cellular adaptive immunity through an interaction with immature dendritic cells.

The cationic host defense peptide rCRAMP promotes gastric ulcer healing in rats

Cathelicidin, a cationic host defense peptide, has been shown to promote cutaneous wound repair and reaches high levels in the gastric mucosa during infection and inflammation. Therefore, we investigated whether this peptide contributes to gastric ulcer healing in rats. Ulcer induction increased the expression of rat cathelicidin rCRAMP in the gastric mucosa. Further increase in expression of rCRAMP by local injection of rCRAMP-encoding plasmid promoted ulcer healing by enhancing cell proliferation and angiogenesis. rCRAMP directly stimulated proliferation of cultured rat gastric epithelial cells (RGM-1), which was abolished by inhibitors of matrix metalloproteinase (MMP), epidermal growth factor receptors (EGFR) tyrosine kinase, or mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase. rCRAMP also increased EGFR and ERK1/2 phosphorylation via an MMP-dependent mechanism. Knockdown of transforming growth factor alpha (TGFalpha), which is a ligand of EGFR, by small interfering RNA completely nullified the mitogenic signals evoked by rCRAMP in RGM-1 cells. These findings suggest that rCRAMP exhibits prohealing activity in stomachs through TGFalpha-dependent transactivation of EGFR and its related signaling pathway to induce proliferation of gastric epithelial cells.

Modulation of the TLR-mediated inflammatory response by the endogenous human host defense peptide LL-37

The sole human cathelicidin peptide, LL-37, has been demonstrated to protect animals against endotoxemia/sepsis. Low, physiological concentrations of LL-37 (< or =1 microg/ml) were able to modulate inflammatory responses by inhibiting the release of the proinflammatory cytokine TNF-alpha in LPS-stimulated human monocytic cells. Microarray studies established a temporal transcriptional profile and identified differentially expressed genes in LPS-stimulated monocytes in the presence or absence of LL-37. LL-37 significantly inhibited the expression of specific proinflammatory genes up-regulated by NF-kappaB in the presence of LPS, including NFkappaB1 (p105/p50) and TNF-alpha-induced protein 2 (TNFAIP2). In contrast, LL-37 did not significantly inhibit LPS-induced genes that antagonize inflammation, such as TNF-alpha-induced protein 3 (TNFAIP3) and the NF-kappaB inhibitor, NFkappaBIA, or certain chemokine genes that are classically considered proinflammatory. Nuclear translocation, in LPS-treated cells, of the NF-kappaB subunits p50 and p65 was reduced > or =50% in the presence of LL-37, demonstrating that the peptide altered gene expression in part by acting directly on the TLR-to-NF-kappaB pathway. LL-37 almost completely prevented the release of TNF-alpha and other cytokines by human PBMC following stimulation with LPS and other TLR2/4 and TLR9 agonists, but not with cytokines TNF-alpha or IL-1beta. Biochemical and inhibitor studies were consistent with a model whereby LL-37 modulated the inflammatory response to LPS/endotoxin and other agonists of TLR by a complex mechanism involving multiple points of intervention. We propose that the natural human host defense peptide LL-37 plays roles in the delicate balancing of inflammatory responses in homeostasis as well as in combating sepsis induced by certain TLR agonists.

Induction of Keratinocyte Migration via Transactivation of the Epidermal Growth Factor Receptor by the Antimicrobial Peptide LL-37

The closure of skin wounds is essential for resistance against microbial pathogens, and keratinocyte migration is an important step in skin wound healing. Cathelicidin hCAP18/LL-37 is an innate antimicrobial peptide that is expressed in the skin and acts to eliminate microbial pathogens. Because hCAP18/LL-37 is up-regulated at skin wound sites, we hypothesized that LL-37 induces keratinocyte migration. In this study, we found that 1 microg/ml LL-37 induced the maximum level of keratinocyte migration in the Boyden chamber assay. In addition, LL-37 phosphorylated the epidermal growth factor receptor (EGFR) after 10 min, which suggests that LL-37-induced keratinocyte migration occurs via EGFR transactivation. To test this assumption, we used inhibitors that block the sequential steps of EGFR transactivation, such as OSU8-1, CRM197, anti-EGFR no. 225 Ab, and AG1478. All of these inhibitors completely blocked LL-37-induced keratinocyte migration, which indicates that migration occurs via HB-EGF-mediated EGFR transactivation. Furthermore, CRM197, anti-EGFR no. 225, and AG1478 blocked the LL-37-induced phosphorylation of STAT3, and transfection with a dominant-negative mutant of STAT3 abolished LL-37-induced keratinocyte migration, indicating the involvement of the STAT3 pathway downstream of EGFR transactivation. Finally, we tested whether the suppressor of cytokine signaling (SOCS)/cytokine-inducible Src homology 2-containing protein (CIS) family of negative regulators of STAT3 regulates LL-37-induced keratinocyte migration. Transfection with SOCS1/Jak2 binding protein or SOCS3/CIS3 almost completely abolished LL-37-induced keratinocyte migration. In conclusion, LL-37 induces keratinocyte migration via heparin-binding-EGF-mediated transactivation of EGFR, and SOCS1/Jak 2 binding and SOCS3/CIS3 negatively regulate this migration. The results of this study suggest that LL-37 closes skin wounds by the induction of keratinocyte migration.

Mouse cathelin-related antimicrobial peptide chemoattracts leukocytes using formyl peptide receptor-like 1/mouse formyl peptide receptor-like 2 as the receptor and acts as an immune adjuvant

Mammalian antimicrobial proteins, such as defensins and cathelicidin, have stimulating effects on host leukocytes. Cathelin-related antimicrobial peptide (CRAMP), the orthologue of human cathelicidin/LL-37, is the sole identified murine cathelicidin. CRAMP has been shown to have both antimicrobial and angiogenic activities. However, whether CRAMP, like human cathelicidin/LL-37, also exhibits a direct effect on the migration and function of leukocytes is not known. We have observed that CRAMP, like LL-37, was chemotactic for human monocytes, neutrophils, macrophages, and mouse peripheral blood leukocytes. CRAMP also induced calcium mobilization and the activation of MAPK in monocytes. CRAMP-induced calcium flux in monocytes was desensitized by MMK-1, an agonistic ligand specific for formyl peptide receptor-like-1 (FPRL1), and vice versa, suggesting the use of FPRL1 by CRAMP as a receptor. Furthermore, CRAMP induced the chemotaxis of human embryonic kidney 293 cells transfected with either FPRL1 or mouse formyl peptide receptor-2, the mouse homologue of FPRL1, but not by untransfected parental human embryonic kidney 293 cells, confirming the use of FPRL1/mouse formyl peptide receptor-2 by CRAMP. Injection of CRAMP into mouse air pouches resulted in the recruitment predominantly of neutrophils and monocytes, indicating that CRAMP acts as a chemotactic factor in vivo. Finally, simultaneous administration of OVA with CRAMP to mice promoted both humoral and cellular Ag-specific immune responses. Thus, CRAMP functions as both a chemoattractant for phagocytic leukocytes and an enhancer of adaptive immune response.

Defensins and cathelicidins: neutrophil peptides with roles in inflammation, hyperlipidemia and atherosclerosis

Atherosclerosis is a disease that begins in fetal life and represents a leading cause of morbidity and mortality associated with significant socioeconomic consequences. A central concept with regard to its pathogenesis is that of endothelial cell dysfunction, which is associated with the release of a large number of mediators secreted by leukocytes that are present in large numbers at the sites of atheroma formation. Neutrophil peptides defensins and cathelicidins are essential elements of the innate immunity and have been present in high concentrations in atherosclerotic plaques in humans. Recently, their role as potential mediators of vascular disease was investigated. Defensins are involved in the lipoprotein metabolism in the vessel wall, favoring LDL and lipoprotein (a) accumulation and modification in the endothelium and the extracellular matrix. They also interfere with the vascular smooth muscle cell function, exhibit prothrombotic activity, and play an inhibitory role in various phases of angiogenesis. Cathelicidins were recently found to enhance endothelial proliferation in cultures, induce functionally significant angiogenesis in animal models, and regulate endothelial cell apoptosis. Further study of these peptides could provide useful insight in the relationship between inflammation and atherosclerosis and is anticipated to have therapeutic and prognostic ramifications.

Expression and Activity of β-Defensins and LL-37 in the Developing Human Lung

Immaturity of innate immunity contributes to the increased susceptibility of human neonates to infection. The lung is a major portal of entry for potential pathogens in the neonate, and human beta-defensins (HBDs) and LL-37 participate in pulmonary innate immunity. We hypothesized that these antimicrobial factors would be developmentally regulated, expressed by neonatal pulmonary tissues, and participate in neonatal innate immunity. We found HBD-2 to be the predominant beta-defensin in human neonatal lung. HBD-2 mRNA expression was developmentally regulated, induced by the proinflammatory factor IL-1beta, and decreased by dexamethasone. Additionally, HBD-2 abundance in neonatal tracheal aspirates increased as a function of gestational age. HBD-1 had a lower level of expression compared with HBD-2 and was induced by dexamethasone. HBD-3 and LL-37 messages were not detected in airway epithelial cultures. Additionally, each antimicrobial peptide exhibited a unique spectrum of antimicrobial activity and salt sensitivity against bacteria commonly causing sepsis in the neonate. Lower levels of HBD-2 may be one factor contributing to the increased susceptibility of premature infants to pulmonary infections.

Temporin A and related frog antimicrobial peptides use formyl peptide receptor-like 1 as a receptor to chemoattract phagocytes

Many mammalian antimicrobial peptides (AMPs) have multiple effects on antimicrobial immunity. We found that temporin A (TA), a representative frog-derived AMP, induced the migration of human monocytes, neutrophils, and macrophages with a bell-shaped response curve in a pertussis toxin-sensitive manner, activated p44/42 MAPK, and stimulated Ca(2+) flux in monocytes, suggesting that TA is capable of chemoattracting phagocytic leukocytes by the use of a G(ialpha) protein-coupled receptor. TA-induced Ca(2+) flux in monocytes was cross-desensitized by an agonistic ligand MMK-1 specific for formyl peptide receptor-like 1 (FPRL1) and vice versa, suggesting that TA uses FPRL1 as a receptor. This conclusion was confirmed by data showing that TA selectively stimulated chemotaxis of HEK 293 cells transfected with human FPRL1 or its mouse ortholog, murine formyl peptide receptor 2. In addition, TA elicited the infiltration of neutrophils and monocytes into the injection site of mice, indicating that TA is also functionally chemotactic in vivo. Examination of two additional temporins revealed that Rana-6 was also able to attract human phagocytes using FPRL1, but temporin 1P selectively induced the migration of neutrophils using a distinct receptor. Comparison of the chemotactic and antimicrobial activities of several synthetic analogues suggested that these activities are likely to rely on different structural characteristics. Overall, the results demonstrate that certain frog-derived temporins have the capacity to chemoattract phagocytes by the use of human FPRL1 (or its orthologs in other species), providing the first evidence suggesting the potential participation of certain amphibian antimicrobial peptides in host antimicrobial immunity.

The human cationic peptide LL-37 induces activation of the extracellular signal-regulated kinase and p38 kinase pathways in primary human monocytes

LL-37 is a cationic peptide that is found in the granules of neutrophils and is secreted by epithelial cells from a variety of tissues. Levels of LL-37 in vivo increase upon infection, and its production and secretion are increased upon stimulation with proinflammatory mediators. It has been postulated that LL-37 modulates the immune response by interacting with the effector cells of innate immunity; however, the mechanism of this interaction is unknown. LL-37 induced phosphorylation and activation of the mitogen-activated protein kinases, extracellular signal-regulated kinase 1/2 (ERK1/2) and p38, in human peripheral blood-derived monocytes and a human bronchial epithelial cell line, but not in B or T lymphocytes. Phosphorylation was not dependent on the G protein-coupled formyl peptide-like receptor 1, which was previously proposed to be the receptor for LL-37-induced chemotaxis on human monocytes and T cells. Activation of ERK1/2 and p38 was markedly increased by the presence of GM-CSF, but not M-CSF. Exposure to LL-37 also led to the activation of Elk-1, a transcription factor that is downstream of and activated by phosphorylated ERK1/2, the up-regulation of various Elk-1-controlled genes, and the transcription and secretion of IL-8. Inhibition of either p38 or ERK1/2 kinases led to a reduction in LL-37-induced IL-8 secretion and inhibition of the transcription of various chemokine genes. The ability of LL-37 to signal through these pathways has broad implications in immunity, monocyte activation, proliferation, and differentiation.

Postsecretory processing generates multiple cathelicidins for enhanced topical antimicrobial defense

The production of antimicrobial peptides and proteins is essential for defense against infection. Many of the known human antimicrobial peptides are multifunctional, with stimulatory activities such as chemotaxis while simultaneously acting as natural antibiotics. In humans, eccrine appendages express DCD and CAMP, genes encoding proteins processed into the antimicrobial peptides dermcidin and LL-37. In this study we show that after secretion onto the skin surface, the CAMP gene product is processed by a serine protease-dependent mechanism into multiple novel antimicrobial peptides distinct from the cathelicidin LL-37. These peptides show enhanced antimicrobial action, acquiring the ability to kill skin pathogens such as Staphylococcus aureus and Candida albicans. Furthermore, although LL-37 may influence the host inflammatory response by stimulating IL-8 release from keratinocytes, this activity is lost in subsequently processed peptides. Thus, a single gene product encoding an important defense molecule alters structure and function in the topical environment to shift the balance of activity toward direct inhibition of microbial colonization.

The antimicrobial peptide LL-37 activates innate immunity at the airway epithelial surface by transactivation of the epidermal growth factor receptor

Antimicrobial peptides produced by epithelial cells and neutrophils represent essential elements of innate immunity, and include the defensin and cathelicidin family of antimicrobial polypeptides. The human cathelicidin cationic antimicrobial protein-18 is an antimicrobial peptide precursor predominantly expressed in neutrophils, and its active peptide LL-37 is released from the precursor through the action of neutrophil serine proteinases. LL-37 has been shown to display antimicrobial activity against a broad spectrum of microorganisms, to neutralize LPS bioactivity, and to chemoattract neutrophils, monocytes, mast cells, and T cells. In this study we show that LL-37 activates airway epithelial cells as demonstrated by activation of the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) and increased release of IL-8. Epithelial cell activation was inhibited by the MAPK/ERK kinase (MEK) inhibitors PD98059 and U0126, by the epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor AG1478, by blocking anti-EGFR and anti-EGFR-ligand Abs, and by the metalloproteinase inhibitor GM6001. These data suggest that LL-37 transactivates the EGFR via metalloproteinase-mediated cleavage of membrane-anchored EGFR-ligands. LL-37 may thus constitute one of the mediators by which neutrophils regulate epithelial cell activity in the lung.