Identification of a cell-surface glycoprotein mediating cell adhesion in EBV-immortalized normal B cells

Phorbol ester treatment markedly enhanced aggregation of Epstein-Barr virus (EBV)-immortalized normal B cells. Monoclonal antibody (MAb) 60.3, recognizing a leukocyte common antigen, completely inhibited intracellular adhesion, whereas MAbs reacting with leukocyte common antigen T200, C3b receptor, T-cell-associated antigen TA-I, C3d (EBV) receptor, brain-granulocyte/T-lymphocyte antigen, transferrin receptor, surface immunoglobulin, Class-I or Class-II transplantation antigens or a B-cell-specific antigen (BI) showed no inhibitory effect. Both the spontaneous and phorbol-ester-enhanced cell aggregations were similarly inhibited by Fab fragments made from antibody 60.3. Phorbol esters also enhance binding between EBV-immortalized normal B cells and autologous or allogeneic blood mononuclear cells depleted of B lymphocytes. This process, which is independent of immunity to EBV, was similarly blocked by the antibody fragments. Antibody 60.3 precipitated 3 non-covalently associated surface glycopolypeptides with apparent MW of 90, 130 and 160/kDa from EBV-infected B cells. Although dissociation of a similar protein complex from granulocytes by sodium dodecyl sulfate treatment clearly indicated the presence of the epitope on the smallest component, the same treatment did not dissociate the protein complex from EBV-immortalized normal B cells. It is thus concluded that the 90-kDa glycopolypeptide, either alone or associated with the larger glycopolypeptides, mediates cell adhesion of the B cells.