Direct evaluation of antigen binding to human T lymphocyte clones: involvement of major histocompatibility complex products in antigen binding.

Cloned human helper T lymphocytes reactive with a defined peptide (p20; residues 306-329) of the HA-1 molecule of influenza virus hemagglutinin were analyzed for their capacity to specifically bind peptide antigen. Three different methods of analyzing antigen binding to T cell receptors were compared. One method involved the binding of radiolabeled T cells to antigen-pulsed populations of sheep erythrocyte rosette-negative (E-) cells (B cells and monocytes). The binding was antigen specific, in that only E- cells pulsed with the appropriate antigen bound the treated T cells, and was inhibitable by free peptide. Furthermore, antigen binding was major histocompatibility complex-restricted in that only E- cells histocompatible at the HLA-D region locus bound the T cells, and monoclonal antibody of the relevant specificity was able to inhibit the binding. Secondly, it was demonstrated that tritiated T cells could bind to insolubilized antigen (p20) in the absence of E- cells. The binding was inhibited by anti-class II antibody suggesting that the interaction of antigen with the T cells involves recognition of T cell major histocompatibility complex class II determinants. Finally, radiolabeled peptides were also used to detect binding to the appropriate clones in the absence of presenting cells. This binding was specific, inhibitable by the appropriate unlabeled peptide and temperature dependent. These studies demonstrate that the process of antigen binding to receptors is analyzable and should in turn facilitate the analysis of the mechanism of T cell activation.