Lineage specification and heterogeneity of T follicular helper cells.

T follicular helper (Tfh) cells were originally described as a non-polarized CD4(+) T cell subset with follicular homing capacity and a potent ability to induce antibody production from B cells. However, a number of studies published in the past year have revealed a degree of heterogeneity within the germinal center CD4(+) T cell population, which suggests additional complexity. The overzealous activities of Tfh cells, or inappropriate expression of certain cytokines, represent new pathways for the development of autoimmune diseases. This review focuses on current progress in unraveling the biology of Tfh cells in health and disease, and understanding the relationship of Tfh cells to other CD4(+) T cell lineages.