Follicular helper T cells as cognate regulators of B cell immunity.

Follicular helper T (T(FH)) cells are a class of helper T cells specialized in the cognate control of antigen-specific B cell immunity. Upon first contact with antigen-primed B cells, pregerminal center effector T(FH) cells promote B cell clonal expansion, antibody isotype switch, plasma cell differentiation, and the induction of germinal centers. By contrast, within germinal centers, T(FH) cells regulate the fate of antigen-specific GC B cells expressing high-affinity variant B cell receptors to promote memory B cell and long-lived plasma cell development. Recent studies unravel multiple signals controlling T(FH) development and functional subtypes of antigen-specific T(FH) cells, including memory T(FH) cells that accelerate memory B cell responses to antigen rechallenge in vivo.