Influence of Infection with Toxoplasma on Macrophage Function, and Role of Macrophages in Resistance to Toxoplasma

In 1968 and during the subsequent 9 years, studies in our laboratory have revealed that mice infected with Toxoplasma gondii are resistant to a number of phylogenetically unrelated organisms, including bacteria, fungi, and viruses. In studies designed to explore the mechanisms of this resistance it was noted that peritoneal macrophages of mice infected with Toxoplasma gondii and Besnoitia jellisoni could inhibit or kill Listeria monocytogenes, Cryptococcus neoformans, and Trypanosoma cruzi, as well as T. gondii and B. jellisoni (R. McLeod and J. Remington, manuscript in preparation). Studies in tumor models revealed that infection with the latter two protozoa leads to increased resistance to tumors in vivo, and that peritoneal macrophages of the infected mice can inhibit or kill certain tumor cells in vitro. We review here certain of the recent results from our laboratory concerning the influence of in vivo infection with Toxoplasma on macrophage function and the role of macrophages in resistance to Toxoplasma, and attempt to place these results into perspective with results obtained by others.