Receptor for Native C3 on Human Lymphoblastoid Cell Lines

Abstract

Abstract When Burkitt lymphoma (RaJi) cells are incubated in fresh human serum in the presence of 0.01 M EDTA, C3 can be detected on the surface of all cells with fluoresceinated anti-C3 antiserum. Only 5 to 10% of cells of line 8866 and none of line Wil2, two human lymphoblastoid cell lines, showed C3 uptake under the same experimental conditions. When RaJi cells were treated with aged human serum containing only the fragments C3c and C3d, no uptake was observed. Serum was not required for the binding of C3 since isolated C3 and C3b could bind to RaJi cells. Binding of C3 and C3b by RaJi cells occurs at 4°C, however, is greatly enhanced at 37°C. Agglutination of C3 and C3b bearing RaJi cells with anti-C3 indicates a high binding affinity of the receptor toward C3 and C3b. Uptake experiments with radiolabeled C3 and C3b revealed a greater affinity of the receptor toward C3 than C3b.