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Detection and quantification of variant specific antigen in the plasma of rats and mice infected with Trypanosoma brucei brucei.

Variant specific antigen (VSA), the principal constituent of the surface coat of salivarian trypanosomes, was detected by gel immunoassays in the plasma of rats and mice infected with Trypanosoma brucei brucei. The quantity of VSA in plasma was measured in radial immunodiffusion tests using a monospecific antiserum and purified VSA as a standard. During the first peak of parasitemia, a statistically significant, linear relationship was determined between the number of parasites in the blood (in the range between 4 x 10(8) and 10(9)/ml) and the concentration of VSA in the plasma (28-320 microgram/ml). The VSA from parasites of the first peak was lost within 2 days of remission. Variant antigens of parasites constituting the second peak then began to appear in the plasma of infected rats. All plasma samples had been separated from parasites and blood cells within 15 min of blood collection. The pH of plasma was controlled with a buffered anticoagulant. No soluble parasite antigens, other than VSA, were detected in the plasma of infected hosts. The results of this study extend the observation that salivarian trypanosomes shed surface coat material during the course of infection. Thus, sloughed VSA may be the parasite product that has been hypothesized to cause the nonspecific lymphocyte proliferation, immunosuppression, and/or hypergammaglobulinemia which occur during African trypanosomiasis.