Summary Staphylococcus aureus commonly colonizes the epidermis, but the mechanisms by which the host senses virulent but not commensal S. aureus to trigger inflammation remain unclear. Using a murine epicutaneous infection model, we found that S. aureus expressed phenol-soluble modulin (PSM)α, a group of secreted virulence peptides, is required to trigger cutaneous inflammation. PSMα induces the release of keratinocyte IL-1α and IL-36α, and signaling via IL-1R and IL-36R was required for induction of the pro-inflammatory cytokine IL-17. The levels of released IL-1α and IL-36α, as well as IL-17 production by γδ T cells and ILC3 and neutrophil infiltration to the site of infection were greatly reduced in mice with total or keratinocyte-specific deletion of the IL-1R and IL-36R signaling adaptor Myd88. Further, Il17a−/−f−/− mice showed blunted S. aureus-induced inflammation. Thus, keratinocyte Myd88 signaling in response to S. aureus PSMα drives an IL-17-mediated skin inflammatory response to epicutaneous S. aureus infection.

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. Introduction Kashiwara and Kawai [16] defined microhyperbolicity and proved that the microlocal Cauchy problem for microhyperbolic pseudodifferential operators is well-posed in the framework of microfunctions, which is a microlocalization of the results obtained by Bony and Schapira [3].In the microlocal studies of pseudo-differential operators, the concept of microhyperbolicity is very useful.From their results one can obtain results on propagation of analytic singularities (propagation of micro-analyticities) of solutions for microhyperbolic operators (see [28]). On the other hand, Bronshtein [5] proved that the hyperbolic Cauchy problem is well-posed in some Gevrey classes which are intermediate spaces between the space of real analytic functions and C°° (see, also, [14], [15]). So we can generalize the definition of microhyperbolicity in the framework of some Gevrey classes, to say the least of it. In doing so, we expect to get a clue to a generalization of microhyperbolicity and microlocal studies of microhyperbolic operators in the framework of C°°.In this paper we shall consider microhyperbolic operators in Gevrey classes and prove microlocal well-posedness of the microlocal Cauchy problem and theorems on propagation of singularities for microhyperbolic operators. Our aims are to show how one can obtain microlocal results (microlocal well-posedness and, therefore, a microlocal version of Holmgren's uniqueness theorem) from methods to prove well-posedness of the Cauchy problem and to show that theorems on propagation of singularities are immediate consequences of a microlocal version of Holmgren's uniqueness theorem, using

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