We have been studying gene expression in cytotoxic immune cells with specific emphasis on large granular lymphocytes (LGLs) and cytotoxic T cells and how a monoclonal antibody to a T-cell ganglioside may enhance cytotoxic function. We have been characterizing a gene which appears to be part of a receptor complex on LGLs and is also expressed in the cytoplasm of T cells. We have also demonstrated that cytotoxic function of T cells can be increased upon treatment with a monoclonal antibody to a ganglioside. These studies begin to define, at the molecular level, the genes involved in the development and maturation of cytotoxic immune effector cells.