Contextual control of skin immunity and inflammation by <i>Corynebacterium</i>

Abstract

How defined microbes influence the skin immune system remains poorly understood. Here we demonstrate that <i>Corynebacteria</i>, dominant members of the skin microbiota, promote a dramatic increase in the number and activation of a defined subset of γδ T cells. This effect is long-lasting, occurs independently of other microbes, and is, in part, mediated by interleukin (IL)-23. Under steady-state conditions, the impact of <i>Corynebacterium</i> is discrete and noninflammatory. However, when applied to the skin of a host fed a high-fat diet, <i>Corynebacterium accolens</i> alone promotes inflammation in an IL-23-dependent manner. Such effect is highly conserved among species of <i>Corynebacterium</i> and dependent on the expression of a dominant component of the cell envelope, mycolic acid. Our data uncover a mode of communication between the immune system and a dominant genus of the skin microbiota and reveal that the functional impact of canonical skin microbial determinants is contextually controlled by the inflammatory and metabolic state of the host.