Contribution of Immune Interferon (IFN-γ) in Lymphokine-Induced Anti-Toxoplasma Activity: Studies with Recombinant Murine IFN-γ

Abstract Recombinant E . coli -derived murine interferon gamma (cDNA IFN-γ) per se induced resident mouse peritoneal macrophages (MPM) and mouse embryo cells to exert marked anti-toxoplasma activity. This capacity of cDNA IFN-γ was abrogated by a specific antiserum to cDNA IFN-γ which could only neutralize the antiviral activity mediated by this product, whereas a rabbit antiserum directed against murine IFN-α/β proved ineffective in neutralizing these functions. It has been found that rabbit antiserum to cDNA IFN-γ could also neutralize IFN-y-mediated antiviral activity present in crude lymphokine-enriched supernatants of antigen-stimulated toxoplasma-sensitized spleen cells (Toxo-LK) but proved ineffective in abolishing the capacity of Toxo-LK to trigger macrophage anti-toxoplasma activity. The data obtained suggest that macrophage anti-toxoplasma activity induced by Toxo-LK may be an interplay of multiple factor(s) and that Toxo-LK preparations contain soluble factor(s) other than IFN-γ, which can induce macrophages to kill intracellular Toxoplasma . Experiments in which crude Toxo-LK preparations were incubated with lectin concanavalin A (Con A) showed that this treatment resulted in a block of anti-toxoplasma arming factor(s) activity, as well as a significant reduction of IFN-γ-mediated antiviral activity present in Toxo-LK. By contrast, no significant difference was observed in the macrophage anti-toxoplasma activity mediated by Con A or untreated cDNA-IFN-γ.