Effects of muramyl dipeptide treatment on resistance to infection with Toxoplasma gondii in mice.

Studies were carried out to determine whether treatment of mice with the synthetic adjuvant muramyl dipeptide afforded any resistance to infection with the obligate intracellular protozoan Toxoplasma gondii. Marked resistance to lethal challenge infection was observed in CBA but not C57BL/6 mice pretreated with muramyl dipeptide. In CBA mice, a single muramyl dipeptide treatment administered 14, 7, or 4 days before Toxoplasma challenge did not afford protection, whereas mice treated at -1 day were highly resistant. Additional studies carried out to investigate the mechanisms underlying the enhanced resistance to Toxoplasma in muramyl dipeptide-treated mice failed to reveal either enhanced cytolytic antibodies to the parasite or evidence that peritoneal macrophages from treated mice were activated as determined in vitro by their microbicidal capacity for Toxoplasma or cytotoxic capacity for tumor target cells.