Mediation of immunity to intracellular infection (Toxoplasma and Besnoitia) within somatic cells.

Antigen-treated lymphocytes from immune hamsters specifically protected not only macrophages, but also cultured fibroblasts and kidney cells infected with Toxoplasma gondii or Besnoitia jellisoni. Macrophages were not necessary for the protection of fibroblasts and kidney cells. A mediator that inhibited the intracellular proliferation of these microbes was obtained from immune lymphocytes in contact with specific antigen. Again, macrophages were not necessary for the elaboration of this mediator or its activity in kidney cells or fibroblasts. The mediator was microbe and host specific, had a molecular weight between 4,000 and 5,000, was resistant to heating at 56 degrees C for 30 min, and was sensitive to chymotrypsin, but resistant to ribonuclease and deoxyribonuclease. A single injection of Besnoitia mediator afforded better protection to hamsters infected with Besnoitia than did antibody. Whereas antibody lysed extracellular organisms, the microbe-specific mediators conferred immunity not only on macrophages, but also on other cells of the body, apparently the first such demonstration.