Immunologic Studies on Trypanosoma cruzi. IV. Serial Transfer of Organisms from Immune to Nonimmune Mice

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Abstract
Mice infected with an avirulent strain of T. cruzi-(FH5) for varying lengths of time were challenged with a virulent strain (T. cruzi-Tulahuen). Blood from survivors was serially transferred into non-infected mice. The results of these experiments indicated that recipient mice received organisms which were altered in their virulence. Mice receiving small numbers of T. cruzi-Tulahuen (50-1000 organisms per mouse) and 0.2 ml of normal serum died within an average of 15.3-19.5 days. Mice receiving the same number of organisms but 0.2 ml of immune serum survived for 20.6-29.5 days and 28 percent did not die. The difference in survival time between these two groups of mice is statistically significant. The number of days which mice survive after receiving small numbers of organisms from immune donors and the number of days which mice survive receiving small numbers of virulent organisms and protective antibodies in immune serum are statistically similar. These results suggest that the alteration of virulence of T. cruzi-Tulahuen in the immune animal is due to the presence of antibodies. When T. cruzi-Tulahuen is transferred into a normal recipient the presence of small amounts of antibody in the inoculum may account for the loss in virulence of the strains. After 2 or 3 serial transfers into normal recipient mice, virulence will slowly increase.