T cell dependence of macrophage activation and mobilization during infection with Mycobacterium tuberculosis.

Mice made T cell-deficient as adults by thymectomy and lethal irradiation, and infected with Mycobacterium tuberculosis, showed a greatly reduced capacity to develop nonspecific resistance to challenge with a heterologous bacterium. The capacity to develop nonspecific resistance was restored, however, by an infusion of syngeneic thymocytes. Evidence was presented which showed that the capacity of mycobacteria-infected mice to resist a lethal challenge with a heterologous organism rested on the capacity of macrophages existing at the time of challenge to reduce the number of challenge organisms to a sublethal level within 8 h. This antibacterial activity of macrophages was substantially reduced in T cell-deficient mice but could be restored by an infusion of syngeneic thymocytes. It was concluded that T cell-deficient mice have a reduced capacity to mobilize and activate macrophages because of their reduced capacity to respond immunologically to antigens of M. tuberculosis.