Immune Response of Rats and Mice to Trypanosome Infections

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Abstract
In an experiment in which Trypanosoma cruzi was inoculated into the peritoneum of immune and normal mice, the parasites were found in blood of normal mice within 2 hr, but few or none were found in blood of immune animals during the experiment. Immunized rats gave the same response to intraperitoneally inoculated Trypanosoma lewisi, and this parasite was used in the study of the response. The response was not peculiar to the immunity of rats and mice to trypanosomes. Rat blood (labeled with Plasmodium berghei) was found in the blood of normal mice within 2 hr after intraperitoneal inoculation, but was not found in blood of mice previously sensitized with normal rat blood 6 hr after inoculation. Mice (as well as rats) passively immunized with anti-T. lewisi rat serum inhibited the passage of T. lewisi to the blood after intraperitoneal inoculation. When P. berghei-infected mouse blood was inoculated along with trypanosomes into the peritoneal cavity of passively immunized mice, P. berghei-infected cells, but not trypanosomes, were found in the blood within 2 hr. Thus, the failure of antigen (trypanosomes or erythrocytes) to pass from peritoneal cavity to blood of immunized animals does not seem to be attributable to occluded passageways, or to the alteration of sensitized tissues by antigen, and it was shown that the response was specific for the im- munizing antigen. Examination of T. lewisi recovered from the peritoneal cavity of immune and normal rats during a 4-hr period after inoculation indicated that the trypanosomes from immune rats were not killed, immobilized, agglutinated, or phagocytized. The mechanism that prevented passage of trypanosomes from the peritoneal cavity to the blood of immune rats or mice was not apparent. However, it is suspected that this response might be an allergic or sensitivity reaction of sensitized tissue to antigen.