Differentiation, Multiplication and Control of Bloodstream Form Trypanosoma (Duttonella) vivax in Mice

1550-7408

Blackwell Publishing Journal Backfiles 1879-2005

Biology

.The growth and differentiation of Trypanosoma vivax was studied in intact and irradiated C3H/He and C57B1/6 mice. In irradiated (800 R) or intact C3H/He and irradiated (800 R) C57B1/6 mice, T. vivax parasitaemia increased rapidly then entered a plateau phase and thereafter declined in an antibody-independent remission phase. Throughout the infection, variations were observed in parasite morphology, density, DNA content, number of organisms with 2 nuclei and 2 kinetoplasts and infectivity of parasites for mice. Parasites in exponential phase had the highest number of members in the S, G2 and M phases of the cell cycle as determined by staining with the interchalating dye Chromomycin A, and analysis on a flow cytometer. During this phase there were numerous parasites with 2 nuclei and 2 kinetoplasts and infectivity was high for mice. As the parasitaemia approached and entered the plateau phase, the proportion of organisms in the S, G2 and M phases of the cell cycle as well as the number of those with 2 kinetoplasts decreased slightly; the number of organisms with 2 nuclei decreased rapidly; and parasites had a considerably reduced capacity to infect mice. Organisms from the remission phase contained only 1 nucleus and 1 kinetoplast and were not infective for mice. The study suggests that T. vivax organisms transit from dividing to committed non-dividing forms and that some non-dividing, non-infective T. vivax organisms remain trapped in the S, G2 and M stages of the cell cycle and die without completing binary fission. In contrast to the above, parasite wave remission occurred in T.vivax-infected intact C57B1/6 mice during exponential growth when there were large numbers of dividing form organisms present in the bloodstream as determined by both DNA content and the proportion of parasites with 2 kinetoplasts and 2 nuclei. Clearance of T. vivax from the bloodstream of infected intact C57B1/6 mice coincided with the production of a parasite-specific antibody response. The studies are discussed with reference to the mode of induction of host protective antibody responses to exponentially growing T. vivax.

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