Complement Activation in Patients With Immune Thrombocytopenic Purpura According to Phases of Disease Course

Immune Thrombocytopenic Purpura (ITP) is an autoimmune thrombocytopenia with a shortened platelet survival and relative bone marrow failure. The pathogenesis involves antibody production, cytokine release, T-cell impairment, complement activation, and clearance of platelets. We measured plasma levels of C3, C4, C1q, and sC5b-9 in 80 ITP patients in acute phase, 50 ITP patients in complete (CR) or partial (PR) remission, and 50 age- and sex-matched healthy volunteers. Statistical analyses showed that acute ITP patients had higher plasma levels of sC5b-9 and C1q than CR or PR patients (median of sC5b-9: 200 vs 98 mg/dL, p-value<0.001) (median of C1q: 2.11 vs 1.00 mg/dL, p-value<0.001). CR and PR ITP patients had sC5b-9 and C1q plasma levels comparable to those observed in healthy volunteers. There was a significant correlation between sC5b-9 and C1q plasma levels (Spearman's rho correlation index on 130 ITP patients equal to 0.58, p-value<0.001). We also found that sC5b-9 plasma level is inversely correlated with the number of platelets. Furthermore, we divided acute ITP patients into subjects with detectable (24 of 80, 30%) or undetectable (56 of 80, 70%) antiplatelet antibodies; patients with detectable antiplatelet antibodies have significantly higher plasma levels of C1q and sC5b-9. This research will potentially offer novel therapeutic strategies in light of new drugs affecting the complement activation for monitoring therapy response.