Host-microbiota interaction is regulated by skin autonomous production of antibodies
The microbiota colonizes each barrier site and broadly controls host physiology. However, when uncontrolled, microbial colonists can also promote inflammation and induce systemic infection. The unique strategies employed at each barrier tissue to control the coexistence of the host with its microbiota remain largely elusive. Here we uncover that, within the skin, host-microbiota symbiosis depends on the remarkable ability of the skin to act as an autonomous lymphoid organ. Notably, an encounter with a new skin commensal promotes two parallel responses, both under the control of Langerhans cells. On one hand, skin commensals induce the formation of classical germinal centers within secondary lymphoid organs associated with IgG1 and IgG3 antibody responses. On the other hand, microbial colonization also leads to the development of tertiary lymphoid organs within the skin itself that can locally sustain and mature IgG2b and IgG2c responses. These phenomena are supported, at least in part, by the ability of the skin regulatory T cells to convert into T follicular helper cells that accumulate within organized tertiary lymphoid organs within the dermis. Skin autonomous production of antibodies is sufficient to control local commensal colonization as well as subsequent systemic infection with the same microbe. Collectively, these results reveal a striking compartmentalization of humoral responses to the microbiota. 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: WT CD4 T cells were sorted by FACS from the skin 7 days post topical association (TA) with S. epidermidies and 5' single cell RNA-seq was performed with HTO hashtags.  Single-cell RNA sequencing (scRNAseq) of FACS-sorted CD19+B220+ B cells from Lta-/- mice at 14 days post-TA