Fixation of C3 to platelets in vitro by antiplatelet antibody from patients with immune thrombocytopenic purpura.

Chronic immune thrombocytopenic purpura (ITP) is due to platelet destruction by an IgG antiplatelet antibody. Recent studies by some investigators suggest in vivo fixation of C3 by the antiplatelet antibody in ITP patients; other groups have not confirmed these findings. In the present studies, purified IgG produced in vitro by splenic cells from two patients with ITP resulted in C3 fixation to target platelets. Since cell-bound C3 increases the efficiency of cell destruction in many experimental antibody systems, the ability of the IgG antibody in patients with ITP to fix C3 may influence the severity of their disease.