Immunological clearance of 75Se-labelled Trypanosoma brucei in goats.

An experiment was conducted to determine, under different conditions, the capacity of young adult East African goats to eliminate intravenously inoculated [75Se]selenomethionine-labelled Trypanosoma brucei from the bloodstream. Over 80% of labelled trypanosomes, preincubated for 1 h in inactivated normal goat serum, were detectable in the circulation 1 h after inoculation into normal goats. By contrast, after incubation in serum from goats which had been immunised against the homologous trypanosome clone, parasites were largely removed from the bloodstream within 5 min after inoculation. When the goats were necropsied 1 h after the inoculation of radiolabelled trypanosomes, 50% of the injected activity was found in the liver and lungs, the contribution of each organ being dependent to some extent on whether the inoculum was via a mesenteric or the jugular vein. The same result was obtained when labelled parasites were incubated in normal goat serum, and then inoculated into immunised goats; thus, rapid blood clearance occurred, and high activity was detected in the lungs and liver. The results confirm those of previous studies in laboratory mice in which the removal of trypanosomes from the circulation of an immune animal was achieved primarily by uptake of opsonised trypanosomes by elements of the mononuclear phagocytic system.