Immunological reconstitution of T-cell-deprived mice: I. Inability of thymosin to restore spleen cell mitogen and tumor allograft response

Abstract

The effect of thymosin fraction-5 therapy on the response of spleen cells to T-dependent mitogens was investigated in adult thymectomized mice (ATx). Although thymosin fraction 5 potentiated thymocyte proliferation in mixed lymphocyte reactions, it failed to restore or maintain spleen cell Con A and PHA responsiveness in ATx mice after therapy using different routes of injection, doses, vehicle, length of treatment, and post-ATx age recipients. Thymosin fraction-3 or -5 therapy also did not restore tumor allograft response in ATx mice depleted of long-lived T-derived lymphocytes by anti-thymocyte serum treatment. By contrast, newborn thymus grafts were completely effective in reconstituting tumor allograft rejection. These results suggest that maturation of the above functional activities of T-derived lymphocytes depends on the thymus microenvironment or that thymosin is deficient in a thymic humoral factor regulating this maturation in the periphery.