Lymphoid reservoirs of antigen-specific memory T helper cells.

How vaccines control the development of antigen-specific effector and memory T helper cells is central to protective immunity but remains poorly understood. Here we found that protein vaccination selected high-affinity, CXCR5+ICOS(hi) follicular B-helper T cells (T(FH) cells) that developed in draining lymphoid tissue to regulate B cell responses. In the memory phase, reservoirs of antigen-specific CXCR5+ICOS(lo) T(FH) cells persisted with less effector activity but accelerated antigen-recall ability.