T follicular helper cells in space-time.

T follicular helper (TFH) cells play a crucial part in the development of humoral immunity by controlling the formation of, and the cellular reactions that occur in, germinal centres. Within these organized lymphoid tissue microstructures, B cells proliferate and somatically mutate to produce long-lived, high-affinity plasma cells and memory B cells. TFH cells exhibit unique molecular, cellular and tissue-dynamic features that are integral to their development and function but that are not necessarily compatible with the classical paradigm of effector CD4(+) T cell differentiation. Here, I discuss recent advances in TFH cell biology and their implications for our understanding of T cell differentiation and memory in humoral immunity from spatiotemporal and functional perspectives.