T cell help to B cells in germinal centers: putting the jigsaw together.

The germinal center (GC) reaction supports the processes of affinity maturation and class switching in B cells that result in long-lasting humoral immunity. CD4(+) T follicular helper cells (Tfh) participate in the GC reaction to help B cells. However, recent studies highlight the heterogeneity of CD4(+) T cells in GCs, which confounds the understanding of Tfh cells. Based on many recent studies, we have tried to form a working model on the niche of Tfh cells in GCs. We have also addressed whether Tfh cells are a distinct lineage and how they may be generated to help B cells.