Background: Complement activation is critically involved in multiple autoimmune diseases. Immune thrombocytopenia (ITP) is a hemorrhagic condition with enhanced platelet clearance caused by antiplatelet autoantibodies. However, the roles of complements C3a, C5a, and soluble C5b-9 (sC5b-9) in the hemorrhage of ITP remain unknown.
Methods: Plasma C3a, C5a, and sC5b-9 levels in ITP patients were measured by enzyme-linked immunosorbent assay (ELISA). Antiplatelet autoantibodies (anti-GPIIb/IIIa and anti-GPIbα) were evaluated by modified monoclonal antibody immobilization of platelet antigen (MAIPA) assay. The severity of bleeding was assessed using the validated bleeding score for each ITP patient at onset.
Results: Levels of C3a, C5a, and sC5b-9 were significantly increased in active ITP patients, compared with those in controls (p < 0.001). However, levels of C3a, C5a, and sC5b-9 were not changed by treatment of HD-DXM. In addition, the C3a levels were correlated with the increase in bleeding scores from the patients with ITP (p < 0.05, r = 0.256). In contrast, neither platelet counts nor antiplatelet autoantibodies (anti-GPIIb/IIIa and anti-GPIbα) showed any correlation with levels of C3a, C5a, and sC5b-9.
Conclusions: Levels of C3a, C5a, and sC5b-9 are increased in patients with ITP, suggesting a hyperactive complement system. Certain complement components, such as C3a, may contribute to hemorrhage of patients with ITP.