Strain- and age-dependent natural and activated in vitro cytotoxicity in athymic nude mice.

The defect in athymic nude mice with respect to T-lymphocyte number and function is accompanied by increased levels of natural cytotoxicity as well as other immune reactions with potential antitumor effects. With increasing age of immunodeficient mice the take rate of xenotransplanted tumors decreases while the number of cells with T-lymphocyte markers increases and some T-lymphocyte-associated functions become detectable. In the present study the natural cytotoxicity of nonadherent splenocytes from young (4-6 weeks) and aged (about 1 year) BALB/c nu/nu mice was analyzed and compared with that of splenocytes from normal euthymic young and old Balb/c mice on the one hand, and with Bar nu/nu and NCr nu/nu young and old mice on the other. To investigate a possible contribution of T lymphocytes to the cytotoxic effect in athymic mice, LAK cells were generated. For this purpose, the nonadherent splenocytes were exposed in vitro either to IL-2 or to anti-CD3 mAb, specifically to activate T lymphocytes expressing TcR-CD3 in the latter case. Cytotoxic in vitro assays were applied using YAC-1 (NK-sensitive) and P-815 (NK-resistant, LAK-sensitive) target cells in parallel experiments in which splenocytes from young and old donors were used as effector cells. Splenocytes from young immunodeficient mice showed consistently high cytotoxicity with YAC-1 cells. In aged athymic mice, splenocytes stimulated in vitro with anti-CD3 mAb showed cytotoxicity to P-815 (LAK-sensitive) cells. FACS analyses of antigenic markers revealed an increased number of T cells in spleens of aged immunodeficient mice, with differences between mice of the examined strains and a decrease in the number of NK cells in aged mice.