CD4+ and CD8+ alpha beta, and gamma delta T cells are cytotoxic effector cells of beta 2-microglobulin-deficient mice against cells having normal MHC class I expression.

Despite original reports that describe the absence of CD8+ CTLs in mice having homozygous deficiency in the beta 2-microglobulin gene, strong cytotoxic activities against cells with normal beta 2-microglobulin expression were observed in these animals. This cytotoxicity was reproducibly induced by immunizations with allogeneic or syngeneic cells. MHC class II expression by the stimulator cells was not required. The effector population contained alpha beta T cells with CD4+ or CD8+ phenotypes, as well as gamma delta T cells with CD8- and CD8+ phenotypes. Both alpha beta T cell types recognized MHC class I molecules. The gamma delta T cells seemed to respond to molecules that are affected by the absence of beta 2-microglobulin, but that are not encoded by classical MHC loci.