Signaling via the IL-20 receptor inhibits cutaneous production of IL-1ß and IL-17A to promote infection with methicillin-resistant Staphylococcus aureus.

Staphylococcus aureus causes most infections of human skin and soft tissue and is a major infectious cause of mortality. Host defense mechanisms against S. aureus are incompletely understood. Interleukin 19 (IL-19), IL-20 and IL-24 signal through type I and type II IL-20 receptors and are associated with inflammatory skin diseases such as psoriasis and atopic dermatitis. We found here that those cytokines promoted cutaneous infection with S. aureus in mice by downregulating IL-1ß- and IL-17A-dependent pathways. We noted similar effects of those cytokines in human keratinocytes after exposure to S. aureus, and antibody blockade of the IL-20 receptor improved outcomes in infected mice. Our findings identify an immunosuppressive role for IL-19, IL-20 and IL-24 during infection that could be therapeutically targeted to alter susceptibility to infection.

Prostaglandin E2 suppresses antifungal immunity by inhibiting interferon regulatory factor 4 function and interleukin-17 expression in T cells.

T helper 17 (Th17) cells play an important role in mucosal host defense through production of the signature cytokines IL-17 and IL-22. Prostaglandin E2 (PGE2) has been shown to enhance IL-17 production by mature Th17 cells. However, when present during Th17 cell differentiation, we found that PGE2 inhibited the transcription factor IRF4 and suppressed production of IL-17 but not IL-22. We show that IRF4 was required for IL-17 expression but inhibited IL-22 expression, highlighting the potential for discordant regulation of these two cytokines in Th17 cells. The pathogenic fungus Cryptococcus neoformans produces PGE2, and we found that it uses PGE2- and IRF4-dependent mechanisms to specifically inhibit induction of IL-17 during Th17 cell differentiation. Blockade of host PGE2 during infection led to increased IL-17 production from CD4(+) T cells and increased survival of mice. These findings suggest that host- or pathogen-derived PGE2 can act directly on Th17 cells during differentiation to inhibit IL-17-dependent antimicrobial responses.

Parental dietary fat intake alters offspring microbiome and immunity.

Mechanisms underlying modern increases in prevalence of human inflammatory diseases remain unclear. The hygiene hypothesis postulates that decreased microbial exposure has, in part, driven this immune dysregulation. However, dietary fatty acids also influence immunity, partially through modulation of responses to microbes. Prior reports have described the direct effects of high-fat diets on the gut microbiome and inflammation, and some have additionally shown metabolic consequences for offspring. Our study sought to expand on these previous observations to identify the effects of parental diet on offspring immunity using mouse models to provide insights into challenging aspects of human health. To test the hypothesis that parental dietary fat consumption during gestation and lactation influences offspring immunity, we compared pups of mice fed either a Western diet (WD) fatty acid profile or a standard low-fat diet. All pups were weaned onto the control diet to specifically test the effects of early developmental fat exposure on immune development. Pups from WD breeders were not obese or diabetic, but still had worse outcomes in models of infection, autoimmunity, and allergic sensitization. They had heightened colonic inflammatory responses, with increased circulating bacterial LPS and muted systemic LPS responsiveness. These deleterious impacts of the WD were associated with alterations of the offspring gut microbiome. These results indicate that parental fat consumption can leave a "lard legacy" impacting offspring immunity and suggest inheritable microbiota may contribute to the modern patterns of human health and disease.

Epidermal growth factor improves survival and prevents intestinal injury in a murine model of pseudomonas aeruginosa pneumonia.

Mortality from pneumonia is mediated, in part, through extrapulmonary causes. Epidermal growth factor (EGF) has broad cytoprotective effects, including potent restorative properties in the injured intestine. The purpose of this study was to determine the efficacy of EGF treatment following Pseudomonas aeruginosa pneumonia. FVB/N mice underwent intratracheal injection of either P. aeruginosa or saline and were then randomized to receive either systemic EGF or vehicle beginning immediately or 24 h after the onset of pneumonia. Systemic EGF decreased 7-day mortality from 65% to 10% when initiated immediately after the onset of pneumonia and to 27% when initiated 24 h after the onset of pneumonia. Even though injury in pneumonia is initiated in the lungs, the survival advantage conferred by EGF was not associated with improvements in pulmonary pathology. In contrast, EGF prevented intestinal injury by reversing pneumonia-induced increases in intestinal epithelial apoptosis and decreases in intestinal proliferation and villus length. Systemic cytokines and kidney and liver function were unaffected by EGF therapy, although EGF decreased pneumonia-induced splenocyte apoptosis. To determine whether the intestine was sufficient to account for extrapulmonary effects induced by EGF, a separate set of experiments was done using transgenic mice with enterocyte-specific overexpression of EGF (IFABP-EGF [intestinal fatty acid-binding protein linked to mouse EGF] mice), which were compared with wild-type mice subjected to pneumonia. IFABP-EGF mice had improved survival compared with wild-type mice following pneumonia (50% vs. 28%, respectively, P < 0.05) and were protected from pneumonia-induced intestinal injury. Thus, EGF may be a potential adjunctive therapy for pneumonia, mediated in part by its effects on the intestine.