Migrant memory B cells secrete luminal antibody in the vagina

Antibodies secreted into the mucosal barriers serve to protect the host from a variety of pathogens, and are the basis for successful vaccines(1). In type I mucosa such as the intestinal tract, dimeric IgA secreted by local plasma cells is transported through polymeric Ig receptors (pIgR)(2), and mediates robust protection against viruses in the vaccinees(3,4). However, due to the paucity of pIgR and plasma cells, how and whether antibodies are delivered to the type II mucosa represented by the lower female reproductive tract (FRT) lumen remains unclear. Here, using genital herpes infection in mice, we show that primary infection does not establish plasma cells in the lamina propria of FRT. Instead, upon secondary challenge with herpes simplex virus 2 (HSV-2), circulating memory B cells that enter the FRT serve as the source of rapid and robust antibody secretion into the FRT lumen. CD4 tissue-resident memory T cells (T(RM)) secrete interferon gamma (IFN-γ), which induces expression of chemokines including CXCL9 and CXCL10. Circulating memory B cells are recruited to the vaginal mucosa in CXCR3-dependent manner, and secrete virus-specific IgG2b, IgG2c and IgA into the FRT lumen. These results reveal circulating memory B cells as a rapidly inducible source of mucosal antibodies for the FRT.