Involvement in the initiation of T cell responses and structural features of an 85-kDa membrane activation antigen

A monoclonal antibody, 7F7, directed at a recently described membrane activation antigen of 85 kDa was found to inhibit the T cell proliferation induced by an anti-CD3 antibody, phytohemagglutinin A and concanavalin A. The T cell response to allogenic stimulator cells was also weakly inhibited. The inhibition of these T cell responses was only obtained if the antibody was added within the first 8 h (first 24 h in the case of the concanavalin A response) of culture. In addition the antibody inhibited the formation of cellular aggregates seen in stimulated cultures when added within the first 8 h. The membrane glycoprotein recognized by 7F7 is shown to have a slightly different molecular mass on cells of different lineage, a protein core of 55 kDa and to contain 30-50% of N-linked as well as a small amount of O-linked carbohydrates and sialic acid residues. This study suggests that the highly glycosylated membrane activation antigen defined by antibody 7F7 could contribute to the contact between those cells which are involved in the initiation of T cell responses.