The binding of 125I-labeled GAT by murine thymocytes was studied by autoradiography. GAT binding was highly temperature dependent. Significantly more thymocytes bound GAT at 37°C than at 4°C. GAT bound at 37°C was usually distributed in a "cap" over one pole of the cell. Preincubation of thymocytes with specific anti-H-2 serum markedly inhibited the subsequent binding of GAT. The frequency of antigen-binding thymocytes was not significantly affected by preincubation of thymocytes with

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... serum or a number of anti-immunoglobulin in sera. The immune response to GAT is controlled by an H-2 linked immune response gene(s). Mice of strains that are H-2p, H-2q or H-2s (non-responders) fail to develop effective T cell helper function necessary for a humoral immune response to GAT under most conditions. However, both responder and non-responder strains had similar numbers of thymocytes capable of binding GAT in vitro, indicating that T cells from non-responder strains of mice do possess a recognition mechanism for GAT.