Endogenous retrovirus control of homeostatic and inflammatory responses to the microbiota [RNA-seq]

The microbiota plays a fundamental role in regulating host immunity. However, the processes that initiate homeostatic immunity to the microbiota remain largely unknown. Here, we show that the skin microbiota promotes the discrete expression of defined endogenous retrovirus (ERVs). Keratinocyte-intrinsic responses to ERVs depended on cGAS/STING signaling and promoted the induction commensal specific T cells including CD8+, CD4+ and MAIT cells. Inhibition of reverse transcriptase significantly impacted these responses resulting in impaired homeostatic immunity to the microbiota and associated tissue repair function. Conversely, diets that caused an increase in dietary lipids primed the skin for aberrant ERV expression in response to commensal colonization, leading to tissue inflammation. Together, our results support the idea that the host may have coopted its endogenous virome as a means to communicate with the exogenous microbial microbiota, resulting in a multikingdom dialogue that controls both tissue homeostasis and inflammation.