THYMECTOMY AT WEANING - AN ACCELERATED AGING MODEL FOR THE MOUSE IMMUNE-SYSTEM

Mouse thymectomy at weaning induces a long lasting immunodepression which can be measured by in vivo and in vitro experiments. Lymphocyte proliferation and IL2 production in response to a T cell mitogen are greatly diminished during the whole life of the animals, on the contrary B cell proliferation in the presence of lipopolysaccharide is not modified. The lack of effect of surgery on the in vitro T cytotoxic activity compared to the total abolition of in vivo graft versus host reaction shows that these two phenomena are under the control of different immunocompetent cell subsets. Thymectomy induces a stabilization of natural killer cell activity, while during normal aging, this parameter decreases regularly. Suprisingly, the thy 1+ cell level is normal 8-10 months after thymectomy compared to sham operated animals showing that phenotypically normal cells can be dysfunctional. Macrophage activity is not modified either by aging or by thymectomy. So, thymectomized mice can be used after less than 1 year to study immunopharmacology of aging.