Analysis of epitope expression and the functional repertoire of recombinant complement receptor 2 (CR2/CD21) in mouse...

We transfected human complement receptor 2 (CR2/CD21) cDNA containing eukaryotic expression constructs into CR2-negative mouse L cells and human K562 erythroleukemia cells. We subsequently selected stably transformed cells that expressed human CR2, as assessed by flow microfluorimetry analysis and immunoprecipitation of 125I-labeled surface membranes using the monoclonal anti-CR2 antibody, HB5. Utilizing flow microfluorimetry analysis, epitopes recognized by anti-CR2 mAb HB5, OKB7, B2, and four other anti-CR2 antibodies were detected on CR2 expressing transfectants but not parental cells. In addition, CR2 expressing transfected cells efficiently formed rosettes with sheep erythrocyte intermediates bearing human C3bi and C3d, but not C4b or C3b, consistent with the known ligand specificity of CR2. CR2 containing transfectants were also demonstrated to specifically bind EBV. Infection with EBV of CR2 expressing L cells and K562 cells resulted in mean expression of Epstein-Barr nuclear Ag (EBNA) at 48 h in 0.35% of CR2 expressing L cells and 3.7% of CR2 expressing K562 cells. Parental L cells and K562 cells did not express EBNA after EBV infection. These results indicate that CR2 alone is sufficient to transfer both C and EBV receptor functions to heterologous cells. In addition, expression of EBNA was found to be significantly higher in human K562 than mouse L cells, both expressing the same recombinant receptor. These results suggest that mechanisms other than CR2 binding lead to inefficient EBV infection and/or EBNA synthesis in mouse fibroblasts.