Stimulation of lymphocytes by platelet-antibody-complexes and their role in the pathogenesis of idiopathic thrombocytopenia.

The effect of washed human platelets, platelet lysates, and platelet antibody complexes on 14C-thymidine incorporation by human lymphocytes was studied. For sensitization of platelets, HLA-specific alloantibodies as well as platelet autoantibodies were used. Lymphocytes for in vitro cultures were collected from unsensitized individuals, healthy women with proven fetomaternal immunization against HLA antigens and patients with idiopathic thrombocytopenic purpura (ITP). Unsensitized platelets have a dose-dependent inhibitory effect on the in vitro proliferation of normal lymphocytes induced by mitogens (PHA, ConA, PWM). Platelet antibody complexes (allo- and autoantibodies; allogenic and autologous lymphocyte-platelet combinations) did not stimulate 14C-thymidine incorporation. Lymphocytes from ITP patients showed a significantly reduced stimulatory response toward PHA compared to normal persons. These findings are discussed in the light of our present knowledge regarding the role of cellular immune reactions in the pathogenesis of ITP.