T Lymphocyte-Mediated Cytolysis — A Comprehensive Theory II. Lytic vs. Nonlytic Interactions of T Lymphocytes

Abstract

In the model for CTL-mediated lysis presented in the preceding paper, we postulated that the binding of CTL to target cells through interaction of an array of MHC-specific T cell receptors with a corresponding array of TC MHC antigens is sufficient, under permissive environmental conditions, to cause TC destruction. However, a variety of other T cell subsets interact with target or partner cells in an MHC-restricted fashion, implying the existence of MHC-specific receptors on these T cells as well. In the mouse, T cells displaying Ly 1 antiens but not Ly 2,3 antigens recognize I region associated (Ia) antigens, and serve as amplifying cells in the differentiation of B cells to plasma cells, and in the activation of pre-CTL to mature, functional CTL. Cells with reduced levels of Ly 1 and high levels of Ly 2,3 serve effector functions as CTL and as suppressors of Ly 1 amplifier cells. Ly 2,3 CTL bear receptors for K/D antigens, whereas Ly 2,3 suppressor cells have receptors for determinants coded for by genes in the I-J subregions. Ly 1 T cells do not normally function as CTL; whether Ly 2,3 suppressor T cells utilize a cytotoxic mechanism in their function is uncertain.