Demonstration of Immune Complexes in Thrombotic Thrombocytopenic Purpura and Effect of Exchange Transfusion

Abstract

A 30‐year‐old man with clinical and laboratory features of thrombotic thrombocytopenic purpura (ITP) underwent exchange transfusion with 9 units of whole blood over a 24‐h period. Then, the neurological, renal, and haematological manifestations resolved and the patient recovered completely. Serial plasma samples were obtained before and at 8 h intervals during the exchange transfusion. A convalescent plasma sample was obtained 14 and 80 d later. Immune complexes were demonstrated in the pre‐exchange transfusion plasma, by polyethylene glycol (PEG) gradient sedimentation, separated by electrophoresis and analysed immunochemically. There were shown to be light, medium and high molecular weight sedimentation zones in the PEG gradients. The medium zone consisted of immune complexes containing platelet membrane asrociated antigens and IgG antibody; the heavy and light zones only showed the presence of IgG. There was progressive clearance of these zones by the exchange transfusion with the convalescent specimens showing a marked decrease in all zones, especially those of the middle molecular weight (which on analysis represent true immune complexes). The clearance of these immune complexes from the circulation by exchange transfusion could explain the clinical response seen in the patient.