"Although T cell help to B cells was one of the very first defined functions of T cells (Crotty, 2015), the identification of the CD4+ T cell subset responsible for T cell-dependent humoral immune responses developed much later. The term T follicular helper (Tfh) cell was coined in a series of studies on human tonsillar germinal center (GC) CD4+ T cells and CXCR5+ CD4+ T cells in blood (Crotty, 2011). Early converts rightly point to those papers as seminal for establishing the field, but it was not until Bcl6 was determined to be a lineage-defining transcription factor (TF) of Tfh cells that Tfh cells were broadly accepted among immunologists as a distinct lineage of helper CD4+ T cells and required for GCs. That trifecta of papers was published 10 years ago (Johnston et al., 2009, Nurieva et al., 2009, Yu et al., 2009), including the demonstration that the TFs Blimp1 and Bcl6 are potent reciprocal antagonists (Johnston et al., 2009) …"