Antigen perception by T lymphocytes. Influence of the major histocompatibility complex

There is considerable evidence that T cell activation to soluble antigens occurs only if this is processed by macrophages and displayed appropriately on the plasma membrane in association with products of the genes of the major histocompatibility complex. The genes responsible differ according to the antigens involved. For cytotoxicity, targets and killer T cells must share K or D region gene products. For delayed type hypersensitivity to fowl gammaglobulin in mice, I-A identity is necessary; for dinitrofluorobenzene, identity at either the I, K or D region is sufficient. Experiments using three different approaches do not support the notion that these genetic constraints are due to the necessity for the T cell and stimulator cell to match an identical gene product or "cell interaction molecule." Rather they favour the hypothesis that activated T cells recognize antigen and products of genes of the major histocompatibility complex. The implications of the results are discussed in terms of the mode of action of immune responsiveness (Ir) genes and of the possible parallel evolution of T cell receptors for antigen and gene products of the major histocompatibility complex.