Increased efficiency of binding of nascent C3b to the erythrocytes of chronic cold agglutinin disease

Abstract

The pathogenesis of chronic cold agglutinin disease (CCAD) has been enigmatic. To determine if abnormal erythrocyte membrane constitutents might improve the stimulus for antibody production, we compared the electrophoretic pattern of radiolabeled membrane glycoproteins of four patients with CCAD to that of normal control erythrocytes. For the CCAD erythrocytes, fluorographs revealed the appearance of an abnormal band whose molecular weight was estimated at 126,000 D. Using two-dimensional gel analysis and immunoblotting techniques, it was determined that the 126,000 D glycoprotein consisted predominantly of polymeric glycophorin-α. Previous investigations had suggested that abnormalities in glycophorin-α influence the functional activity of the complement system. When purified complement (C)3 was activated in the fluid-phase by cobra venom factor complexes, CCAD erythrocytes bound nascent C3b 7-27 times more efficiently than normal erythrocytes. Normal erythrocytes could be induced to manifest the appearance of the 126,000 D band, and the increased efficiency of binding of nascent C3b by incubation with CCAD serum or with the purified cold agglutinin antibody plus autologous serum, but not with purified antibody alone or the purified antibody plus EDTA-chelated autologous serum. These studies demonstrate that the interactions of IgM cold-reacting antibody and complement with glycophorin induce changes in the biophysical properties of the erythrocyte membrane which modify subsequent interactions with complement.