Skin autonomous antibody production regulates host-microbiota interactions

Host symbiosis with its microbiota can represent a liability for the host. Indeed, while these communities of microbes broadly control host physiology, the microbiota can also promote inflammation and represent a source of local and systemic infection. The unique strategies employed by each tissue to maintain and control coexistence with commensal microbes remain largely unclear. Here we uncover that, within the skin, host protection from its microbiota depends on the remarkable ability of the skin to act as an autonomous lymphoid organ. Notably, an encounter with a new skin microbe is associated with two parallel responses both, under the control of Langerhans cells. On one hand, skin commensal promotes the development of classical germinal centers within secondary lymphoid organs leading to IgG1 and IgG3 responses. On the other hand, microbial colonization also leads to the development of tertiary lymphoid organs that can locally sustain and mature IgG2b and IgG2c responses. The ability of the skin to develop as a lymphoid compartment is at least in part mediated by the ability of the local Treg pool to convert into T follicular helper cells accumulating within organized tertiary lymphoid organs surrounding the hair follicles. Remarkably, skin autonomous production of antibodies is sufficient to control both microbial colonization within the skin as well as subsequent infection with the same commensal. Collectively these results reveal a profound compartmentalization of humoral responses between the lymph nodes and the skin. Further, this work uncovers a previously unappreciated function for the skin as a compartment able to develop, in the absence of inflammation, powerful and long-lived antibody responses independently of secondary lymphoid organs. Overall design: T cells were extracted for single cell RNA-seq from skin of mice treated with Stapholococcus epidermidies