Schistosomiasis Mansoni in Baboons

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Abstract
The enzyme-linked immunosorbent assay (ELISA) with anti-baboon-µ, -γ, and -α chain conjugates, and the radioallergosorbent test (RAST) with an anti-human-ε chain conjugate were used to measure class-specific antibody responses in six baboons exposed once percutaneously to 1,000 Schistosoma mansoni cercariae. ELISA with egg, adult, and cercarial antigens revealed highest IgM and IgG class antibody levels to be against egg antigens in both acute and chronic stages of infection. In acute infections, IgM class antibodies to cercariae exceeded those to adult worms, whereas in older infections IgG class anti-adult antibodies predominated. Antibody isotype is thus at the basis of the reversal in anti-cercarial and anti-adult antibody levels in baboons. The induction of primary response anti-cercarial IgM antibodies, cross-reactive with soluble egg antigen (SEA), probably explains the anomalous appearance of anti-SEA antibodies 2 weeks before oviposition occurred. IgM, IgG, and IgA anti-adult antibody responses were followed by ELISA for 32 months in the baboons. IgM antibodies appeared at 3 weeks post-infection (p.i.), peaked at 7 weeks, then declined rapidly to very low but persisting levels. IgG and IgA class antibodies nearly paralleled each other, but IgA antibody levels were much the lower. They both appeared between weeks 5–6 p.i., reached their peaks between weeks 10 and 13, and persisted virtually undiminished for IgG antibodies, but with a tendency toward gradual decay after 1 year for IgA antibodies. No relationships were found between the levels of anti-adult IgM, IgG, or IgA class antibodies and fecal egg excretion patterns. Anti-adult indirect hemagglutination titers were a composite of IgM and IgG antibody responses. RAST measurements of anti-adult worm IgE class antibodies revealed wide individual variation. One of six baboons never developed measurable IgE anti-adult antibodies, and it was also notable in maintaining the highest fecal egg output of the six. The other five showed the IgE anti-adult antibody response to parallel IgG and IgA anti-adult antibodies. Additional data on antibody responses to eggs and cercariae, measured by circumoval precipitin and slide flocculation tests respectively, in other groups of singly-infected baboons are discussed in relation to ELISA data.