T cells in ITP: Focus on T follicular helper cells and cytotoxic T cells

Immune thrombocytopenia (ITP) is an autoimmune disease where premature destruction of platelets as well as inhibition of platelet production leads to thrombocytopenia and associated bleeding. It has long been considered a disease primarily caused by B cells, but the role of T lymphocytes in its pathogenesis is now better understood and deserves elucidation. Two types of T cells will be discussed: (1) splenic T follicular helper cells (TFH) that participate in differentiation of B cells within germinal centres (GC) and stimulate the production of antiplatelet antibodies, thus supporting the humoral autoimmune response; and (2) antibody-independent mechanisms of action of cytotoxic T lymphocytes (CTL) that may directly participate in platelet destruction as well as inhibit their production by targeting megakaryocytes. To date, most novel therapies target antibody-mediated disease, but targeting either TFH or CTL may provide new therapeutic opportunities.