The 1-1-1 fallacy.

T-cell help to B cells is a fundamental aspect of adaptive immunity and the generation of B-cell memory (memory B cells and plasma cells). Follicular helper CD4(+) T (Tfh) cells are the specialized providers of B-cell help, and Tfh cells depend on Bcl6 for their differentiation. This review discusses Tfh cell functions, transcription factors, and induction signals, with particular focus on the richness of the underlying biology and assessing the simplicity or complexity of each of these processes.