Staphylococcus aureus is a human commensal that colonizes the skin. While it is normally innocuous, it has strong associations with atopic dermatitis pathogenesis and has become the leading cause of skin and soft tissue infections in the United States. The factors that dictate the role of S. aureus in disease are still being determined. In this work, we utilized primary keratinocyte culture and an epidermal murine colonization model to investigate the role of S. aureus phenol-soluble modulins (PSMs) in proinflammatory cytokine release and inflammation induction. We demonstrated that many species of Staphylococcus are capable of causing release of interleukin 18 (IL-18) from keratinocytes and that S. aureus PSMs are necessary and sufficient to stimulate IL-18 release from keratinocytes independently of caspase 1. Further, after 7 days of epicutaneous exposure to wild-type S. aureus, but not S. aureus ⌬psm, we saw dramatic changes in gross pathology, as well as systemic release of proinflammatory cytokines. This work demonstrates the importance of PSM peptides in S. aureus-mediated inflammatory cytokine release from keratinocytes in vitro and in vivo and further implicates PSMs as important contributors to pathogenesis. Staphylococcus aureus is a human commensal that lives in the nose, skin, and throat in approximately 30% of the human population (1, 2). While S. aureus is usually harmless, it is an opportunistic pathogen that has become a leading cause of nosocomial infections in the United States (3) and can manifest as skin and soft tissue infections, infective endocarditis, osteomyelitis, and sepsis (1). Further, it has a role in exacerbation of atopic dermatitis (AD), a chronic inflammatory disease of the skin that affects up to 20% of children and up to 3% of adults (4, 5). Chronic cutaneous inflammation during AD results in increased production of extracellular matrix components that permit attachment of S. aureus (6). Subsequently, S. aureus promotes AD by stimulating a strong proinflammatory response (7). S. aureus proteins, such as hemolysin ␣ (HLA), staphylococcal protein A (SPA), and lipoteichoic acids (LTA), promote proinflammatory cytokine production from keratinocytes (7-11). However, this stimulation requires the concurrent presence of a surfactant, such as SDS (11).Keratinocytes serve as the first line of defense against cutaneous pathogens and are able to stimulate an immune response by releasing cytokines, defensins, and antimicrobial cationic peptides, such as LL-37, to fight off pathogens (12). One cytokine that is produced by keratinocytes and has a role in promoting AD is interleukin 18 (IL-18) (13,14). IL-18 is a proinflammatory cytokine that is cleaved and activated primarily by caspase 1 (15). Caspase 1 activation occurs following exposure to danger-associated molecular patterns (DAMPs) or pathogen-associated molecular patterns (PAMPs), which stimulate the activation of the inflammasome (16). Caspase 1 activation can also result in the activation of the proinflammatory cytokine IL-1␤ (17)...

Systemic lupus erythematosus is clinically characterized by episodes of flare and remission. In patients, cutaneous exposure to ultraviolet light has been proposed as a flare trigger. However, induction of flare secondary to cutaneous exposure has been difficult to emulate in many murine lupus models. Here, we describe a system in which epidermal injury is able to trigger the development of a lupus nephritis flare in New Zealand Mixed (NZM) 2328 mice. 20-week old NZM2328 female mice underwent removal of the stratum corneum via duct tape, which resulted in rapid onset of proteinuria and death when compared to sham-stripped littermate control NZM2328 mice. This was coupled with a drop in serum C3 concentrations and dsDNA antibody levels and enhanced immune complex deposition in the glomeruli. Recruitment of CD11b+CD11c+F4/80high macrophages and CD11b+CD11c+F4/80low dendritic cells was noted prior to the onset of proteinuria in injured mice. Transcriptional changes within the kidney suggest a burst of type I IFN-mediated and inflammatory signaling which is followed by upregulation of CXCL13 following epidermal injury. Thus, we propose that tape stripping of lupus-prone NZM2328 mice is a novel model of lupus flare induction that will allow for the study of the role of cutaneous inflammation in lupus development and how crosstalk between dermal and systemic immune systems can lead to lupus flare.

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Objective Caspase-1 is required for nephritis and robust autoantibody development in the pristane model of murine lupus. The objective of this study was to evaluate the immune response and to study the splenic B and T cell populations in wild-type (WT) and caspase-1 −/− mice following pristane injection in order to develop an understanding of why absence of caspase-1 is protective in pristane-induced lupus. Methods Immunization responses to NP-Ficoll and NP-Ovalbumin were assessed in WT and caspase-1 −/− mice. In vitro IgM and IgG responses to R848 was measured by ELISA. Serum IgM anti-double stranded DNA and IL-1β was measured by ELISA. B and T cell populations 2 weeks and 6 months following pristane injection were measured by flow cytometry in WT and caspase-1 −/− mice. Results Caspase-1 −/− mice generate equivalent IgG responses to NP-Ficoll and NP-Ova antigens when compared to wild-type mice. Additionally, they secrete IgM and IgG in response to TLR7 activation. Pristane injected WT and caspase-1 −/− mice generate robust IgM anti-dsDNA responses. Caspase-1 −/− mice have a significant reduction in marginal zone B cell populations compared to WT 6 months after pristane exposure whereas T cell responses are intact in these mice. Conclusions Caspase-1 −/− mice have intact immune responses but do not develop an expanded marginal zone B cell population in response to pristane-induced lupus. This may be one explanation for reduced IgG autoantibody production in these mice.