Identification of a trypanocidal factor againstTrypanosoma equiperdumin normal human serum

Abstract

SUMMARYNormal human serum (HS) contains trypanolytic activity and agglutinins toTrypanosoma equiperdum, while such activities are not found in sera from a range of animals susceptible to infection. HS given toT. equiperdum-infected mice caused a rapid decrease in the number of circulating trypanosomes and protection from lethal infection. Trypanolytic activity of human serum was found to be associated, after DEAE chromatography and Sephadex G-200 gel filtration, with the fraction containing 19S antibodies. Immunofluorescence assays confirmed a binding of human IgM and C1qcomplement component onto the surface ofT. equiperdum. Anti-T. equiperdumactivity of HS was specifically directed toT. equiperdumsurface components and not to some mouse serum components adsorbed on parasites during the growth in the host, because HS adsorbedin vivoin CD-1 mice retained full protective and agglutinating properties. Trypanocidal activity appears in human serum about the 7th month after birth and persists until late in life. On the contrary, human purified high-density lipoprotein had no significantin vitroorin vivotrypanocidal activity. In conclusion, strong natural anti-T. equiperdumactivity in human serum was mainly mediated by natural antibodies of the IgM class. The presence of natural IgM active againstT. equiperdumin HS could represent one of the natural mechanisms of resistance of refractory hosts against trypanosome infections. This phenomenon provides further evidence that host specificity of trypanosomes may be partly conditioned by the presence of natural antibodies.