Studies on production of biologically active substance which inhibits the intracellular multiplication of Toxoplasma within mouse macrophages.

In vitro assessments were carried out to study some biological aspects of immune lymphocytes producing a new lymphokine, called by the authors Toxoplasma growth inhibitory factor (Toxo-GIF), which inhibits the intracellular multiplication of Toxoplasma gondii within nonimmune mouse macrophages. Concanavalin A and phytohemagglutinin-P were found to induce vigorous production of Toxo-GIF, whereas bacterial lipopolysaccharide did not. In vitro treatment of splenic lymphocytes with rabbit anti-mouse thymocyte serum plus complement abolished almost completely their ability to produce Toxo-GIF. Treatment of splenic lymphocytes with inhibitors of protein synthesis, cycloheximide or puromycin resulted in a remarkable reduction of the ability of sensitized lymphocytes to produce this lymphokine. Thus the production of Toxo-GIF seems to be dependent on the cellular metabolic events of sensitized T-lymphocytes. The significant activity of Toxo-GIF was demonstrable even in the supernate of lymphocyte cultures incubated in serum-free medium and was also evident after immune lymphocytes and homologous antigen were incubated for the relatively short period of 10 h.