Quantification of C3dg/Epstein-Barr virus receptors on human B cells and B cell lines

The expression of C3dg/Epstein-Barr virus receptors (CR2) on human peripheral blood and tonsillar B lymphocytes and Raji cells was quantified by measuring binding of unlabeled monoclonal anti-CR2 antibody (OKB7 and HB-5) in an indirect immunoenzymatic assay. Scatchard analysis of saturation binding curves revealed that Raji cells on the average express about 22,000 and 17,000 binding sites, with mean affinity constants of 9.9 X 10(10) and 8.7 X 10(10) M-1 for OKB7 and HB-5, respectively. Tonsillar mononuclear cells (TMC) expressed 16,700 and 17,600 binding sites for OKB7 and HB-5, respectively, with a significantly lower affinity constant for HB-5 (3.2 X 10(10) M-1) than for OKB7 (9.0 X 10(10) M-1). On the average 34% of E- peripheral blood mononuclear cells (PBMC) from healthy donors and 49% of TMC expressed the CR2 antigen. When correcting for the fraction of CR2-positive cells, the mean CR2 density was 12,600 on E- PBMC (n = 10) and 34,000 on TMC (n = 4).