Role of adult worm antigen-specific immunoglobulin E in acquired immunity to Schistosoma mansoni infection in baboons

Allergic-type immune responses, particularly immunoglobulin E (IgE), correl ate with protective immunity in human schistosomiasis. To better understand the mechanisms of parasite elimination we examined the immune correlates o f protection in baboons (Papio cynocephalus anubis), which are natural host s for Schistosoma mansoni and also develop allergic-type immunity with infe ction. In one experiment, animals were exposed to a single infection (1,000 cercariae) or were exposed multiple times (100 cercariae per week for 10 w eeks) and subsequently were cured with praziquantel prior to challenge with 1,000 cercariae. Singly and multiply infected animals mounted 59 and 80% r eductions in worm burden, respectively (P < 0.01), In a second experiment, animals were inoculated with S. mansoni ova and recombinant human interleuk in 12 (IL-12), This produced a 37 to 39% reduction in adult worm burden aft er challenge (P < 0.05). Parasite-specific IgG, IgE, IgM, and peripheral bl ood cytokine production were evaluated. The only immune correlate of protec tion in both experiments was levels of soluble adult worm antigen (SWAP)-sp ecific IgE in serum at the time of challenge infection and/or 6 weeks later . Baboons repeatedly infected with cercariae or immunized with ova and IL-1 2 developed two- to sixfold-greater levels of SWAP-specific IgE in serum th an did controls, and this correlated with reductions in worm burden (r(2), -0.40 to -0.64; P, <0.01). Thus, in baboons and unlike mice, adult worm-spe cific IgE is uniquely associated with acquired immunity to S. mansoni infec tion. This similar association of parasite-specific IgE and protection amon g primates infected with schistosomiasis, along with similar pathology, ana tomy, and genetic make-up, indicates that baboons provide an excellent perm issive experimental model for better understanding the mechanisms of innate and acquired immunity to schistosomiasis in humans.