The Function And Mechanisms Of Interleukin-33 In Staphylococcus Aureus Cutaneous Infection

Interleukin-33, also named IL-1F11, is a new member of IL-1 family cytokines, and induces signal transduction by binding to the heterodimeric receptor complex consisting of ST2 and IL-1 receptor accessory protein (IL-1RAcP). Although IL-33 has been reported to protect hosts from parasites infection, the function of IL-33 in bacterial cutaneous infection remains to be determined. Here we determine the function of IL-33 in Staphylococcus aureus skin infection and dissect the mechanisms by which IL-33 increases host antibacterial defenses.We first evaluated the expression of IL-33 in skin from S.aureus-infected human patients. Compared to normal controls, IL-33 was abundantly increased in skin of S.aureus-infected patients. We next developed a S.aureus cutaneous infection mouse model and found that IL-33 was significantly increased in keratinocytes and dermal macrophages of infected mouse skin. We thereby focused on macrophages and keratinocytes to explore the functions and mechanisms of IL-33 in Staphylococcus aureus skin infection.On one hand, we found IL-33 increased antibacterial defense by activation of inducible nitric oxide synthase in macrophages. The expression of IL-33 by macrophages was induced by staphylococcal peptidoglycan (PGN) and lipoteichoic acid (LTA) via activation of toll-like receptor 2(TLR2)-mitogen-activated protein kinase(MAPK)-AKT-signal transducer and activator of transcription 3(STAT3) signaling pathway as PGN, and LTA failed to induce IL-33 in Tlr2-deficient peritoneal macrophages, and MAPK, AKT, STAT3 inhibitors significantly decreased PGN-or LTA-induced IL-33. IL-33, in turn, acted on macrophages to induce microbicidal nitric oxygen (NO) release. This induction was dependent on inducible nitric oxide synthase (iNOS) activation, as treatment of macrophages with an inhibitor of iNOS, aminoguanidine, significantly decreased IL-33-induced NO release. Moreover, aminoguanidine significantly blocked the capacity of IL-33 to inhibit the growth of S.aureus, and IL-33 silencing in macrophages significantly increased the survival of S.aureus in macrophages. Furthermore, the administration of IL-33-neutralizing antibody into mouse skin decreased iNOS production but increased the survival of S.aureus in skin. These findings reveal that IL-33 can promote antimicrobial capacity of dermal macrophages, thus enhancing antimicrobial defense against skin bacterial infections.On the other hand, we found IL-33 increased antibacterial defense by regulating REG3A expression in keratinocytes, as S.aureus did not induce REG3A expression after IL-33 was neutralized. The expression of IL-33 by keratinocytes was induced by S.aureus via activation of toll-like receptor 2(TLR2)-p38 mitogen-activated protein kinase (MAPK) signaling pathway as S.aureus failed to induce IL-33 in Tlr2-deficient mice, and p38MAPK inhibitor significantly decreased S.aureus-induced IL-33 expression in keratinocytes. And then IL-33 acted on keratinocytes to induce antimicrobial peptide REG3A expression, thus inhibiting S.aureus survival in vivo and in vitro.In conclusion, our results show that IL-33 induces and activates inducible nitric oxide synthase in macrophages as well as increases REG3A expression in keratinocytes to enhance host antibacterial defense. These findings provide new insights into pathways contributing to antimicrobial defense, which may ultimately lead to the development of novel treatment regimens for skin bacterial infection.