Cutaneous injury induces the release of cathelicidin anti-microbial peptides active against group A Streptococcus

Cathelicidin antimicrobial peptides are expressed in salivary glands and saliva

The expression of antimicrobial peptides at epithelial surfaces such as skin, lung, and intestine is thought to provide protection against infection. Cathelicidin antimicrobial peptides are essential for the protection of skin against invasive bacterial infection. To determine if cathelicidins are also present in the oral cavity, we examined the expression of both mRNA and protein in mice and human saliva. The murine cathelicidin (CRAMP) was detected in the adult by reverse-transcription/polymerase chain-reaction (RT-PCR), and in embryonic, newborn, and adult tissues by in situ hybridization and immunohistochemistry. CRAMP mRNA and protein were localized to the salivary glands, specifically in acinar cells of the submandibular gland and palatine minor glands, as well as in lingual epithelium and palatal mucosa. In man, the human cathelicidin LL-37 was detected in human saliva by Western blotting. These results indicate that cathelicidins are present in the salivary system, in some oral epithelia, and in saliva, contributing to broad-spectrum defense of the oral cavity.

Biology and clinical relevance of naturally occurring antimicrobial peptides

Within the last decade, several peptides have been discovered on the basis of their ability to inhibit the growth of potential microbial pathogens. These so-called antimicrobial peptides participate in the innate immune response by providing a rapid first-line defense against infection. Recent advances in this field have shown that peptides belonging to the cathelicidin and defensin gene families are of particular importance to the mammalian immune defense system. This review discusses the biology of these molecules, with emphasis on their structure, processing, expression and function. Current evidence has shown that both cathelicidins and defensins are multifunctional and that they act both as natural antibiotics and as signaling molecules that activate host cell processes involved in immune defense and repair. The abnormal expression of these peptides has also been associated with human disease. Current and future studies are likely to implicate the presence of antimicrobial peptides in several unexplained human inflammatory disorders and to provide novel therapeutic approaches to the treatment of disease.

Cathelicidin anti-microbial peptide expression in sweat, an innate defense system for the skin

The eccrine gland is one of the major cutaneous appendages and secretes sweat. Its principal function is thermoregulation during exposure to a hot environment or physical exercise. In addition to this function, we show that LL-37, a member of cathelicidin family of anti-microbial peptides, is expressed in sweat. LL-37 protein and mRNA was seen in the eccrine structures of normal human skin by immunohistochemistry and in situ hybridization. LL-37 was localized to both the eccrine gland and sweat ductal epithelial cells, whereas dermcidin, a previously described natural antibiotic in sweat, was expressed only in the gland itself. The anti-microbial activity of LL-37 and dermcidin against various bacteria in the sweat ionic environment was demonstrated by solution colony forming assay using synthetic peptides, and in sweat obtained from normal volunteers. These results indicate that cathelicidin is secreted in human sweat, has potent anti-microbial activity against both gram-positive and gram-negative bacteria, and can, after processing from the preproform, provide a barrier for protection against infection. Thus, sweat represents a unique mode of delivery for potent innate immune effector molecules in the absence of inflammation.

Endogenous antimicrobial peptides and skin infections in atopic dermatitis

BACKGROUND

The innate immune system of human skin contains antimicrobial peptides known as cathelicidins (LL-37) and beta-defensins. In normal skin these peptides are negligible, but they accumulate in skin affected by inflammatory diseases such as psoriasis. We compared the levels of expression of LL-37 and human beta-defensin 2 (HBD-2) in inflamed skin from patients with atopic dermatitis and from those with psoriasis.

METHODS

The expression of LL-37 and HBD-2 protein in skin-biopsy specimens from patients with psoriasis, patients with atopic dermatitis, and normal subjects was determined by immunohistochemical analysis. The amount of antimicrobial peptides in extracts of skin samples was also analyzed by immunodot blot analysis (for LL-37) and Western blot analysis (for HBD-2). Quantitative, real-time reverse-transcriptase-polymerase-chain-reaction (RT-PCR) assays were used to confirm the relative expression of HBD-2 and LL-37 messenger RNA (mRNA) in the skin-biopsy specimens. These peptides were also tested for antimicrobial activity against Staphylococcus aureus with the use of a colony-forming assay.

RESULTS

Immunohistochemical analysis confirmed the presence of abundant LL-37 and HBD-2 in the superficial epidermis of all patients with psoriasis. In comparison, immunostaining for these peptides was significantly decreased in acute and chronic lesions from patients with atopic dermatitis (P=0.006 and P=0.03, respectively). These results were confirmed by immunodot blot and Western blot analyses. Real-time RT-PCR showed significantly lower expression of HBD-2 mRNA and LL-37 mRNA in atopic lesions than in psoriatic lesions (P=0.009 and P=0.02, respectively). The combination of LL-37 and HBD-2 showed synergistic antimicrobial activity by effectively killing S. aureus.

CONCLUSIONS

A deficiency in the expression of antimicrobial peptides may account for the susceptibility of patients with atopic dermatitis to skin infection with S. aureus.

Proteinases of common pathogenic bacteria degrade and inactivate the antibacterial peptide LL-37

Effectors of the innate immune system, the anti-bacterial peptides, have pivotal roles in preventing infection at epithelial surfaces. Here we show that proteinases of the significant human pathogens Pseudomonas aeruginosa, Enterococcus faecalis, Proteus mirabilis and Streptococcus pyogenes, degrade the antibacterial peptide LL-37. Analysis by mass spectrometry of fragments generated by P. aeruginosa elastase in vitro revealed that the initial cleavages occurred at Asn-Leu and Asp-Phe, followed by two breaks at Arg-Ile, thus inactivating the peptide. Proteinases of the other pathogens also degraded LL-37 as determined by SDS-PAGE. Ex vivo, P. aeruginosa elastase induced LL-37 degradation in human wound fluid, leading to enhanced bacterial survival. The degradation was blocked by the metalloproteinase inhibitors GM6001 and 1, 10-phenantroline (both of which inhibited P. aeruginosa elastase, P. mirabilis proteinase, and E. faecalis gelatinase), or the inhibitor E64 (which inhibited S. pyogenes cysteine proteinase). Additional experiments demonstrated that dermatan sulphate and disaccharides of the structure [DeltaUA(2S)-GalNAc(4,6S)], or sucroseoctasulphate, inhibited the degradation of LL-37. The results indicate that proteolytic degradation of LL-37 is a common virulence mechanism and that molecules which block this degradation could have therapeutic potential.

Cathelicidins: microbicidal activity, mechanisms of action, and roles in innate immunity

Antimicrobial peptides are important host-defense molecules of innate immunity. Cathelicidins are a diverse family of potent, rapidly acting and broadly effective antimicrobial peptides, which are produced by a variety of cells. This review examines the classification, antimicrobial spectrum, mechanism of action, and regulation of cathelicidins.

Cell differentiation is a key determinant of cathelicidin LL-37/human cationic antimicrobial protein 18 expression by human colon epithelium

Antimicrobial peptides are highly conserved evolutionarily and are thought to play an important role in innate immunity at intestinal mucosal surfaces. To better understand the role of the antimicrobial peptide human cathelicidin LL-37/human cationic antimicrobial protein 18 (hCAP18) in intestinal mucosal defense, we characterized the regulated expression and production of this peptide by human intestinal epithelium. LL-37/hCAP18 is shown to be expressed within epithelial cells located at the surface and upper crypts of normal human colon. Little or no expression was seen within the deeper colon crypts or within epithelial cells of the small intestine. Paralleling its expression in more differentiated epithelial cells in vivo, LL-37/hCAP18 mRNA and protein expression was upregulated in spontaneously differentiating Caco-2 human colon epithelial cells and in HCA-7 human colon epithelial cells treated with the cell differentiation-inducing agent sodium butyrate. LL-37/hCAP18 expression by colon epithelium does not require commensal bacteria, since LL-37/hCAP18 is produced with a similar expression pattern by epithelial cells in human colon xenografts that lack a luminal microflora. LL-37/hCAP18 mRNA was not upregulated in response to tumor necrosis factor alpha, interleukin 1alpha (IL-1alpha), gamma interferon, lipopolysaccharide, or IL-6, nor did the expression patterns and levels of LL-37/hCAP18 in the epithelium of the normal and inflamed colon differ. On the other hand, infection of HCA-7 cells with Salmonella enterica serovar Dublin or enteroinvasive Escherichia coli modestly upregulated LL-37/hCAP18 mRNA expression. We conclude that differentiated human colon epithelium expresses LL-37/hCAP18 as part of its repertoire of innate defense molecules and that the distribution and regulated expression of LL-37/hCAP18 in the colon differs markedly from that of other enteric antimicrobial peptides, such as defensins.

Cathelicidins: a family of endogenous antimicrobial peptides

The cytoplasmic granules of mammalian neutrophils contain several antimicrobial peptides. Some, like defensins, are fully processed before storage, whereas others are stored as precursors that require additional processing. Cathelicidins are bipartite molecules with an N-terminal cathelin domain and an antimicrobial C-terminal domain. Humans apparently have only one cathelicidin gene. Its product, hCAP-18, is present in the secondary (specific) granules of neutrophils, and its C-terminal antimicrobial peptide, LL-37, is liberated by proteinase 3 coincident with degranulation and secretion. Many nonmyeloid tissues also express hCAP-18, including epididymis, spermatids, keratinocytes, epithelial cells, and various lymphocytes. LL-37 stimulates chemotaxis, acting via the formyl peptide-like receptor-1. The structurally diverse cathelicidin-derived antimicrobial peptides of animals provide interesting models for pharmaceutical development. PR-39, a proline-rich porcine cathelicidin, has shown efficacy in limiting myocardial damage after experimental ischemia in rodent models. Porcine protegrins are in stage III clinical trials to prevent oral mucositis caused by radiation or chemo-therapy.

Innate antimicrobial peptide protects the skin from invasive bacterial infection

In mammals, several gene families encode peptides with antibacterial activity, such as the beta-defensins and cathelicidins. These peptides are expressed on epithelial surfaces and in neutrophils, and have been proposed to provide a first line of defence against infection by acting as 'natural antibiotics'. The protective effect of antimicrobial peptides is brought into question by observations that several of these peptides are easily inactivated and have diverse cellular effects that are distinct from antimicrobial activity demonstrated in vitro. To investigate the function of a specific antimicrobial peptide in a mouse model of cutaneous infection, we applied a combined mammalian and bacterial genetic approach to the cathelicidin antimicrobial gene family. The mature human (LL-37) and mouse (CRAMP) peptides are encoded by similar genes (CAMP and Cnlp, respectively), and have similar alpha-helical structures, spectra of antimicrobial activity and tissue distribution. Here we show that cathelicidins are an important native component of innate host defence in mice and provide protection against necrotic skin infection caused by Group A Streptococcus (GAS).