Trypanosoma cruzi: Infection of normal and activated mouse macrophages

Normal and BCG-activated mouse peritoneal macrophages were infected with culture forms of Trypanosoma cruzi at 1:1, 10:1, or 100:1 multiplicities of infection (MOI). Secondary lysosomes labeled with thorium dioxide were seen fusing with parasite-containing phago-somes in both normal and activated macrophages. The latter, however, contained larger numbers of secondary lysosomes. Parasites were frequently found in the cytoplasm of normal macrophages infected with high ratios of infection; this permitted the parasite to escape the host cell defense system. While both activated and normal macrophages could control T. cruzi infections, the activated cells could control a significantly greater infection.