INCREASED NUMBER OF CYTOTOXIC T-CELLS WITHIN CD4- T-CELLS IN BETA(2)-MICROGLOBULIN, MAJOR HISTOCOMPATIBILITY COMPLEX CLASS I-DEFICIENT MICE(8)

Targeted disruption Of beta2-microgobulin gene results in deficient ma jor histocompatibility complex class I expression and failure to devel op CD4-8+ T cells. Despite this, beta2M-/- mice reject skin grafts and cope with most viral infections tested. We asked whether CD4+8- cytot oxic T cells could play a role in compensating for the defect in CD4-8 + cytotoxic T cell function. We found that the cytotoxic activity agai nst class II+ targets is significantly higher among CD4+8- T cells Of beta2M-/- than among those Of beta2M+/+ mice. In the limiting dilution experiment, we showed that the precursor frequency for the cytotoxic, CD4+8-, class II-specific T cells is at least fivefold higher in beta 2M-/- than in beta2M+/+ mice. These results suggest that CD4+8- cytoto xic T cells could play a major role in carrying out cytotoxic function in beta2M-/- mice.