Elimination of a primary schistosome infection from rats coincides with elevated IgE titres and mast cell degranulation.

Abstract

Schistosomes are eliminated from laboratory rats around 28 days post-infection, whilst they are still resident within the hepatic portal distributaries of the liver. We have previously shown that their presence in this location is accompanied by an intense mastocytosis. We have investigated the potential relationships between IgE responses, the allergenicity of schistosome antigens, mast cell responsiveness, and worm elimination. Total and specific IgE were measured using an ELISA and a functional assay based on 3H serotonin release from activated rat basophilic leukemia cells (RBL-SRA), respectively. Both assays revealed that infected rats produced elevated IgE titres relative to naive animals. At days 28 and 35, mixed-sex infections stimulated a higher total IgE than male-only infections. IgE was affinity purified from rat infection serum and used to probe a fractionated soluble worm antigen preparation (SWAP) by Western blotting. Two allergenic products were detected of M(r) 67 and 36-38 kDa, the former having the same molecular weight as a previously identified secretory protein. IgE from mixed-sex schistosome infections bound strongly to the 36-38 kDa molecule, compared to the relatively weak binding exhibited by IgE from male-only infection serum. Since eggs were not recovered from the infected rats, this reactivity was attributed to the greater release of allergens from female worms. Results from the RBL-SRA showed that female SWAP was a more effective trigger of mast cell degranulation in vitro, for equal amounts of protein. This enhanced allergenicity was ascribed to the relative abundance of carbohydrate moieties. Our results support a role for IgE, and mast cell degranulation in the elimination of a primary schistosome burden from rats.