New insights into the differentiation and function of T follicular helper cells.

The seminal studies characterizing T follicular helper (T(FH)) cells described a non-polarized CD4(+) T cell population with a unique ability to home to B cell follicles and to induce antibody production by B cells. In the past few years, the study of T(FH) cells has enjoyed a renaissance and there has been a surge of research activity aimed at understanding the function and differentiation of these important cells. This Review focuses on the current progress in T(FH) cell biology and the important questions that remain unanswered. Particular attention is paid to recent studies that support the idea that T(FH) cells are a separate T cell lineage and those that probe the relationship of T(FH) cells to other T helper cell subsets.