Monoclonal antibodies against leucoagglutinin-reactive human T-lymphocyte surface components. I. Characterization of cellular binding sites.

The binding specificities of three biologically active anti-lymphocyte monoclonal antibodies (MoAb) (K46M, K3G, and 3-19-2) produced against human T-cell surface components reactive with the mitogenic lectin leucoagglutinin from Phaseolus vulgaris (La) were analysed. K46M is a strong T-cell mitogen, while K3G and 3-19-2 inhibited cell-mediated cytotoxicity. Resting peripheral blood lymphocytes (PBL) contained 4-16% K46M+ cells, 8-35% K3G+ cells, and less than 0.3-4% 3-19-2+ cells. After stimulation with T-cell mitogens the proportion of K46M+ and 3-19-2+ cells increased markedly (mean 59 and 30% positive cells, respectively), while the increase in K3G+ cells was less prominent (38%). K46M-reactive structures were expressed on mature T cells and probably also on B cells. K3G reacted with B and T cells while 3-19-2 showed a broader specificity reacting also with erythrocytes. All three MoAb reacted with lipid extracts of resting and activated PBL as well as with purified neutral glycolipids of lymphoid origin. In addition 3-19-2 reacted with lipid extracts of erythrocytes. K46M immuno-precipitated four surface peptides from lectin-stimulated PBL. Their apparent molecular weights were 53,000, 42,000, and 16,000 (doublet). The 53,000 and 42,000 MW peptides were identified as the alpha and beta chains of the T-cell antigen receptor. The identity of the 16,000 MW peptides is presently unknown. K3G and 3-19-2 did not specifically precipitate any lymphocyte surface peptide.