Function and Specificity of T Cell Subsets in the Mouse

To deal with intracellular organisms, the immune system has evolved a quite different set of immunocompetent cells, T cells. These cells are imbued with a number of interesting properties. In contrast to B cells and antibody molecules, T cells generally do not manifest specificity. Unlike B cells, T cells do not secrete their antigen-specific receptors. Under physiological conditions, T cells only respond to antigen displayed on the surface of living cells. T cells show the intriguing requirement that, to be immunogenic, antigen has to be aligned on the cell surface in association with gene products of the major histocompatibility complex (MHC), the H-2 complex, in mice. Parasitized cells recognized by T cells, especially in the case of viral infections, are destroyed by cytotoxic T lymphocytes (CTL), a subset of T cells with cytolytic properties. T cells also play a major role in controlling the quantity and quality of specific antibody made by B cells. This function of T cells is controlled by a different subset of T cells, T helper cells. Whereas T killer cells provide a negative (cytotoxic) signal to antigen-bearing cells, T helper cells provide a positive signal. The chapter outlines the way the specificity, function, and induction of T cells and T cell subsets are under the strict control of H-2 molecules.