Comparison of platelet immunity in patients with SLE and with ITP

Idiopathic thrombocytopenic purpura (ITP) is characterized by the developme nt of a specific anti-platelet autoantibody immune response mediating the d evelopment of thrombocytopenia. Systemic lupus erythematosus (SLE) is an au toimmune disease characterized by the production of a wide variety of autoa ntibodies. In 15-20% of SLE cases, patients develop thrombocytopenia which appears to be autoimmune in nature (SLE-TP). To better understand the patho genesis of the thrombocytopenia associated with SLE, we investigated the ov erlapping platelet and cellular immune features between SLE and ITP. Thirty -one patients with SLE, eight with SLE-TP, and 17 with ITP, were studied an d compared to 60 healthy controls. We evaluated platelet-associated IgG, pl atelet microparticles, reticulated platelets, platelet HLA-DR expression, i n vivo cytokine levels, lymphocyte proliferation, and the T lymphocyte anti -platelet immune response in these patients. Patients with SLE-TP and those with ITP had increased platelet-associated IgG, an increased percentage of platelet microparticles, a higher percentage of reticulated platelets and larger platelets, suggesting antibody-mediated platelet destruction and inc reased platelet production. More than 50% of patients with ITP had increase d HLA-DR on their platelet surface whereas subjects with SLE-TP did not. An alysis of serum cytokines demonstrated increased levels of IL-10, IL-15 and TNF-alpha in patients with SLE, but in those with ITP, only increased leve ls of IL-15 were seen, no increases in any of these cytokines were observed in patients with in SLE-TP. The ability of lymphocytes to proliferate in r esponse to phorbol myristate acetate (PMA) stimulation was increased in SLE -TP, but was normal in both SLE and ITP. Lymphocytes from subjects with ITP displayed an increased ability to proliferate on exposure to platelets, in contrast, those with SLE-TP did not. While the number of subjects evaluate d with SLE-TP was small, these data reveal a number of differences in the i mmunopathogenesis between SLE-TP and ITP. (C) 2000 Elsevier Science Ltd. Al l rights reserved.