Importance of thymus-derived lymphocytes in cell-mediated immunity to infection.

Abstract Mice made T cell deficient by thymectomy and irradiation, and protected with bone marrow cells (THXB mice) have a greatly reduced capacity to develop antituberculous immunity. In contrast, their capacity to develop anti- Listeria immunity is not impaired. Infection-induced lymphoid cell proliferation in the spleen is greatly reduced in THXB mice infected with either organism. The reduced capacity of THXB mice to develop antituberculous immunity and to show increased lymphoid cell proliferation in response to a tuberculous infection can be restored by an intraperitoneal injection of normal syngeneic thymocytes. In contrast, reduced lymphoid cell proliferation in THXB mice infected with Listeria cannot be restored with thymocytes. Nevertheless, the spleen cells from Listeria -infected donors with the capacity to transfer anti- Listeria immunity to normal recipients are destroyed in vitro by anti-θ serum and complement, thus showing they are T cells. The apparent contradiction is explained in terms of a residual T cell population in THXB mice which is large enough to generate anti- Listeria , but not antituberculous immunity.