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Background: Interleukin (IL)-37, a new member of the IL-1 family, is characterized as a fundamental inhibitor of innate immunity: it dampens the production of proinflammatory cytokines, protects against inflammatory and autoimmune diseases, and plays a potent immunosuppressive role in the pathogenesis of psoriasis. IL-37 is highly expressed in psoriatic skin, in which human β-defensins (hBDs) have been detected. Although hBDs enhance the production of cytokines, including IL-1 cytokines, whether they stimulate the production of IL-37 remains unclear., Objectives: To assess the ability of hBDs to stimulate IL-37 expression/production by human keratinocytes and to determine the mechanism involved., Methods: Real-time PCR and Western blotting were used to evaluate IL-37 expression. Caspase activities were assessed using colorimetric assay kits. A CCR6 antibody, siRNA, and caspase, Smad3, MAPK and NF-κB inhibitors were used to investigate the signaling mechanism of hBDs., Results: Among the four hBDs used, only hBD-3 up-regulated the mRNA and protein expression of IL-37. The combination of TNF-α, EGF and poly (I:C) with hBD-3 synergistically enhanced the mRNA but not the protein expression of IL-37. Furthermore, hBD-3 increased the release of IL-37 into the culture supernatants. Evaluation of the signaling mechanism of hBD-3 suggested that caspases 1 and 4, Smad3, CCR6, MAPKs and NF-κB were required for hBD-3-mediated IL-37 expression., Conclusions: The finding that hBD-3 stimulates IL-37 expression, a novel target for the pathogenesis and therapy of cutaneous inflammatory diseases, provides evidence that hBDs contribute to the suppression of inflammatory and innate immune responses through the regulation of IL-37 expression., (Copyright © 2014. Published by Elsevier Ireland Ltd.)

Human β-defensins (hBDs) are host defense peptides that not only exhibit microbicidal properties but also stimulate various cellular activities, including keratinocyte proliferation, migration, and wound healing. hBDs are overexpressed in the skin in cases of psoriasis but are downregulated in atopic dermatitis skin, although both diseases are associated with stratum corneum barrier defects. Because the tight-junction (TJ) barrier is also dysfunctional in both atopic dermatitis and psoriasis patients, we hypothesized that hBDs may regulate the TJ barrier function in keratinocytes. We observed that, among the hBDs tested, only hBD-3 increased the expression of several claudins and their localization along the cell-cell borders. In addition, hBD-3 elevated the transepithelial electrical resistance and reduced the paracellular permeability of keratinocyte layers, and this effect was reversed by the claudin inhibitor ochratoxin A, CCR6 antibody, and CCR6 small interfering RNA. Moreover, hBD-3 enhanced the activation of Rac1, atypical protein kinase C, glycogen synthase kinase-3, and phosphatidylinositol 3 kinase, which are required for the hBD-3-mediated regulation of the TJ barrier function, as evidenced by the effects of their respective inhibitors. Collectively, our findings provide evidence regarding the contribution of host defense peptides to the innate immunity of skin by regulating TJ barrier function, in addition to their antimicrobial and other immunomodulatory activities.

In addition to their microbiocidal properties, human beta-defensins (hBDs) and cathelicidin LL-37 stimulate a number of mammalian cell activities, including migration, proliferation, and cytokine/chemokine production. Because hBDs and LL-37 cause mast cells to release pruritogens such as histamine and PGs, we hypothesized that these peptides would stimulate the secretion of a novel pruritogenic mediator IL-31, predominantly produced by T cells. hBDs and LL-37 enhanced IL-31 gene expression and IL-31 protein production and release in the human mast cell line LAD2, as well as in peripheral blood-derived cultured mast cells, suggesting that mast cells are another source of IL-31. Moreover, the expression of IL-31 was elevated in psoriatic skin mast cells, and hBD-2-4 and LL-37, but not hBD-1, enhanced its expression in vivo in rat skin mast cells. hBDs and LL-37 also induced the release of other pruritogenic mediators, including IL-2, IL-4, IL-6, GM-CSF, nerve growth factor, PGE(2), and leukotriene C(4), and increased mRNA expression of substance P. hBD- and LL-37-mediated IL-31 production/release was markedly reduced by pertussis toxin and wortmannin, inhibitors of G-protein and PI3K, respectively. As evidenced by the inhibitory effects of MAPK-specific inhibitors, hBD-2-4 and LL-37 activated the phosphorylation of MAPKs p38, ERK, and JNK that were required for IL-31 production and release. The ability of hBDs and LL-37 to stimulate the production and release of IL-31 by human mast cells provides a novel mechanism by which skin-derived antimicrobial peptides/proteins may contribute to inflammatory reactions and suggests a central role of these peptides in the pathogenesis of skin disorders.

Besides their microbicidal functions, human beta-defensins (hBD) and LL-37 activate different immune and inflammatory cells, and their expression is enhanced in inflamed skin and cutaneous wound sites. To protect against pathogens, the skin produces antimicrobial peptides including hBDs and LL-37. Therefore, the aim of our study was to investigate whether hBDs participate in cutaneous inflammation and wound healing by inducing keratinocyte migration, proliferation, and production of proinflammatory cytokines/chemokines. We found that hBD-2, -3, and -4 but not hBD-1 stimulated human keratinocytes to increase their gene expression and protein production of IL-6, IL-10, IP-10, monocyte chemoattractant protein-1, macrophage inflammatory protein-3alpha, and RANTES. This stimulatory effect was markedly suppressed by pertussis toxin and U-73122, inhibitors for G protein and phospholipase C, respectively. We also demonstrated that hBDs elicited intracellular Ca2+ mobilization, and increased keratinocyte migration, and proliferation. In addition, these peptides induced phosphorylation of EGFR, signal transducer and activator of transcription (STAT)1, and STAT3, which are intracellular signaling molecules involved in keratinocyte migration and proliferation. In our study, inhibition of these molecules significantly reduced hBD-mediated keratinocyte migration and proliferation. In conclusion, this study provides evidence that human antimicrobial peptides may be involved in skin immunity through stimulating cytokine/chemokine production, and participate in wound healing by promoting keratinocyte migration and proliferation.

Antimicrobial peptides human beta-defensins (hBD) are mainly produced by epithelia of several organs including skin, and participate in innate immunity by killing invading pathogens. Besides their microbicidal activities, hBD activate several inflammatory and immune cells. Since hBD are generated by tissues where mast cells are present, we hypothesized that these peptides could activate mast cells. In this study, we demonstrated that both hBD-3 and hBD-4 induced mast cell degranulation, prostaglandin D2 production, intracellular Ca2+ mobilization and chemotaxis. Furthermore, hBD-3- and hBD-4-induced activation of mast cells was suppressed by pertussis toxin and U-73122, inhibitors for G protein and phospholipase C, respectively. We further revealed that hBD-3 and hBD-4 increased vascular permeability in the skin, which was dependent on the presence of mast cells, because hBD-3 and hBD-4 failed to enhance vascular permeability in mast cell-deficient Ws/Ws rats. We also demonstrated that hBD-3 and hBD-4 induced phosphorylation of MAPK p38 and ERK1/2, which were further required for hBD-mediated mast cell activation, as evidenced by the inhibitory effects of p38 and ERK1/2 inhibitors on mast cell degranulation. Together, these findings suggest the key role of hBD in inflammatory responses by recruiting and activating mast cells, and increasing vascular permeability.

Background: The antimicrobial properties of the skin are attributed to several agents including human beta-defensins (hBDs), cathelicidin LL-37 and skin lysozyme. Although these antibacterial agents reside in the skin to protect it against infection, it is not well known whether the total analysis of all combinations of these agents may result in synergistic effect to enhance their antibacterial activities against invading microorganisms., Objective: To elucidate the interactions between keratinocyte-derived antibacterial agents in the extracellular milieu, we investigated the individual and synergistic activities of hBDs, LL-37 and lysozyme against Staphylococcus aureus and Escherichia coli in neutral and acidic milieus., Methods: The colorimetric method using alamarBlue was employed to assess the antibacterial activities of hBD-1, -2, -3, LL-37 and lysozyme and the viability of bacteria was read spectrophotometrically., Results: In both neutral and acidic pH milieus, hBD-1, -2, -3, LL-37 and lysozyme exhibited antibacterial activity against S. aureus and E. coli in a dose-dependent manner. Interestingly, the antibacterial activity of hBD-1, -2, -3 and lysozyme but not LL-37 was significantly enhanced in acidic milieu (pH 4.6). Furthermore, various combinations of above agents resulted in a synergistic or additive antibacterial effect against S. aureus and E. coli in neutral milieu. The synergistic effect of hBDs, LL-37 and lysozyme against S. aureus was further significantly enhanced in acidic milieu. In contrast, above antibacterial agents exhibited mainly additive rather than synergistic effect on antibacterial activity against E. coli in acidic milieu., Conclusion: Taken together, these results provide a novel evidence of antimicrobial mechanism of natural human skin-derived antibacterial agents against bacterial infection, and their involvement in innate immunity.

In addition to its physical barrier against invading microorganisms, the skin produces antimicrobial peptides, human beta-defensins (hBDs) and cathelicidin LL-37, that participate in the innate host defense. Because IL-18 is produced by keratinocytes and involved in skin diseases in which hBDs and LL-37 are highly expressed, we hypothesized that these peptides would activate keratinocytes to secrete IL-18. We found that hBD-2, -3, and -4 and LL-37, but not hBD-1, activated normal human keratinocytes to secrete IL-18; this secretion reached peak strength at 3 h. In addition, the combination of peptides resulted in a synergistic effect on IL-18 secretion. We also revealed that hBD-2, -3, and -4 and LL-37 increased IL-18 mRNA expression, and that IL-18 secretion was more enhanced in keratinocytes differentiated in vitro with high Ca2+-containing medium. Furthermore, because IL-18 secretion induced by hBDs and LL-37 could not be suppressed by caspase-1 or caspase family inhibitors, and because these peptides failed to increase caspase-1 activity, we suggest that hBD- and LL-37-induced IL-18 secretion is probably via a caspase-1-independent pathway. To determine the molecular mechanism involved, we demonstrated that IL-18 secretion was through p38 and ERK1/2 MAPK pathways, because the inhibitors of p38 and ERK1/2, but not JNK, almost completely nullified IL-18 secretion. Moreover, hBD-2, -3, and -4 and LL-37 could induce the phosphorylation of p38 and ERK1/2, but not JNK. Thus, the ability of hBDs and LL-37 to induce IL-18 secretion by keratinocytes provides a new mechanism for these peptides in innate immunity and an understanding of their role in the pathogenesis of skin disorders.