T Follicular Helper Cells in Transplantation.

The recently described T follicular helper (Tfh) cell is required for the production of high affinity antibody. After contact with follicular dendritic cells, Tfh cells move into the germinal centre and provide help to B cells both by direct B cell-T cell interaction and production of IL-21. This drives proliferation, differentiation, and affinity maturation of the B cells to produce plasma cells capable of secreting high-affinity antibody. Circulating Tfh cells are produced by movement of Tfh cells from lymph nodes after dendritic cell contact. A reduction of Tfh cell-associated molecules is linked with increased expression of other chemokine receptors to form Th1-, Th2-, and Th17-like Tfh cells. These circulating Tfh cells are able to help B cells in vitro and to move into target tissues to support antibody production. Alloantibody production is dependent on T-cell help via the indirect pathway. Antibody-mediated rejection is therefore dependent on Tfh cells. Animal data suggest that Tfh cells and B cells migrate to the allograft and are involved in alloantibody production within a tertiary lymphoid organ. There is some data supporting the same process within human allografts. The requirement for T-cell help provides a potential therapeutic target in the treatment of antibody-mediated rejection.