Functional diversity of human vaginal APC subsets in directing T cell responses

Human vaginal mucosa is the major entry site of sexually transmitted pathogens and thus has long been attractive as a site for mounting mucosal immunity. It is also known as a tolerogenic microenvironment. Here, we demonstrate that immune responses in the vagina are orchestrated by the functional diversity of four major antigen-presenting cell (APC) subsets. Langerhans cells (LCs) and CD14(−) lamina propria (LP)-DCs polarize CD4(+) and CD8(+) T cells toward Th2, whereas CD14(+) LP-DCs and macrophages polarize CD4(+) T cells toward Th1. Both LCs and CD14(−) LP-DCs are potent inducers of Th22. Due to their functional specialties and the different expression levels of pattern-recognition receptors on the APC subsets, microbial products do not bias them to elicit common types of immune responses (Th1 or Th2). To evoke desired types of adaptive immune responses in the human vagina, antigens may need to be targeted to proper APC subsets with right adjuvants.