Differential effects of monoclonal antibodies anti-L3T4 and anti-LFA1 on the antigen-induced proliferation of T-helper-cell clones: correlation between their susceptibility to inhibition and their affinity for antigen

Recognition by specific T helper (TH) cells of antigen presented by antigen-presenting cells (APC) involves, in addition to the antigen-specific receptor, non-antigen-specific molecules such as L3T4 and LFA1. In the present study, we analyzed the relationship between the avidity for antigen presented by APC of three TH cell lines and the participation of L3T4 and LFA1 cell surface antigens. We found a correlation between the avidity of TH cells for the complex GAT/Ia on APC measured by two independent assays and the participation of the cell-adhesion molecules L3T4 as measured by the ability of corresponding monoclonal antibody (MAb) to block the antigen-induced proliferation of TH cells. In contrast to the situation found with cytolytic T-lymphocyte (CTL) clones, we also found a differential inhibiting effect of anti-LFA1 MAb on the GAT-specific proliferation of the three TH clones. The results indicate a direct correlation between the inhibitory effects of anti-LFA1 and anti-L3T4 MAb and the affinity of TH cells for the complex formed by antigen and Ia.