In vivo binding of circulating immune complexes by C3b receptors (CR1) of transfused erythrocytes.

The effects of packed erythrocyte transfusion with high CR1 activity on circulating immune complex concentrations were studied in 14 transfusion experiments involving 12 patients with immune complex related diseases. Before erythrocyte transfusion circulating immune complex concentrations ranged from 8 to 128 micrograms/ml. After transfusion (2-3 units) immune complex concentrations decreased depending on the levels of CH50 titres in the recipients. In 11 experiments, in which the patients' CH50 titres ranged from 21 to 44, immune complex concentrations decreased by 75-100% within five days. The CH50 titres were also decreased after erythrocyte transfusion but subsequently increased to initial ranges within 6-35 days. In three patients with low CH50 titres (1.0-10.0) decreases in immune complexes were not observed. Direct Coombs' tests for IgG and C3 were performed before and after erythrocyte transfusion to determine potential in vivo binding of circulating immune complexes. Thus in eight of 14 experiments, in which erythrocytes carried no IgG before packed erythrocyte transfusion, seven became Coombs' positive for IgG after the transfusion. In seven of 14 experiments, in which erythrocytes were negative for complement before transfusion, five became positive afterwards. Moreover, in 12 instances slight increases of CR1 activity of patients' erythrocytes were observed within eight days, which improved further within 35 days after erythrocyte transfusion. These studies suggest that transfusion of erythrocytes with high CR1 activity results in the removal of circulating immune complexes and that this process is dependent on complement consumption. These experiments support the hypothesis that erythrocyte-CR1 has a functional role in the removal of circulating immune complexes and may thereby inhibit the deposition of immune complexes within body tissue constituents.