Induction of resistance to Toxoplasma gondii in human macrophages by soluble lymphocyte products.

Autoradiography and light microscopy were used to study the effects of lymphocyte culture supernatants, prepared under a variety of conditions, on the course of intracellular Toxoplasma gondii infection in human monocyte-derived macrophages in vitro. Supernatants prepared by incubating lymphocytes of dye test- (DT) positive subjects with T. gondii lysate antigen (TLA), lymphocytes of DT/negative subjects with streptokinase-streptodornase (SK-SD), or both populations of lymphocytes with concanavalin A (Con A) were capable of activating macrophages to inhibit or kill intracellular T. gondii. Supernatants prepared with the homologous antigen (TLA) to the target organism appeared more active in conferring resistance to infection with T. gondii on macrophages than those prepared with a heterologous antigen (SK-SD) or mitogen (Con A). The number of lymphocytes was critical in preparing active supernatants. These results suggest that soluble lymphocyte mediators can activate human macrophages in vitro to inhibit or kill T. gondii.