TFH cells express CD40L and produce IL-21 and it was shown in vitro that, following stimulation with IL-21 and CD40, the B cells of ITP patients become plasma cells producing anti-GPIIb/IIIa antibodies and this indicates an important role of TFH cells in the pathogenesis of ITP [80]. The gene discussed is IL21; the disease is autoimmune thrombocytopenic purpura.