IDENTIFICATION OF THE SCHISTOSOMA-JAPONICUM 22.6-KDA ANTIGEN AS A MAJOR TARGET OF THE HUMAN IGE RESPONSE - SIMILARITY OF IGE-BINDING EPITOPES TO ALLERGEN PEPTIDES

Human resistance to reinfection with Schistosoma mansoni and Schistoso ma haematobium correlates with elevated IEE titers against worm antige ns (soluble worm antigen preparation, SWAP). In S. mansoni infection, low levels of reinfection following chemotherapy are associated with t he recognition of a cloned tegumental protein Sm22.6. Because of poten tial species-specific differences in resistance to schistosomes, we at tempted to identify Schistosoma japonicum antigens recognized by human IgE, Following a survey of 176 infected individuals in Leyte, Philipp ines, we show that IgE antibodies from the majority of older, high-IgE /SWAP responders recognize antigens in the 22 (Sj22)-, 45-, 78- and 97 -kDa range in SWAP. Limited IgE cross-reactivity between Sj22 and Sm22 was observed following a comparison of Filipino IgE responses to thes e antigens. The antigen was cloned from an adult S. japonicum lambda-Z AP cDNA library (Mindoro strain) by immunoscreening with pooled high-t iter IgE antisera and a anti-Sj22 polyclonal antibody. The deduced ami no acid sequence of the identified cDNA clone, MJ-1, showed significan t homology to Sm22.6 (74%) and Sj22.6 (99%). Although the molecular se quence of Sj22.6 has already been reported, this is the first demonstr ation of its recognition by human IgE, thereby strengthening its poten tial as a vaccine candidate. Using an overlapping peptide approach, fo ur IgE-binding epitopes were identified in Sj22.6, two of which exhibi ted similarities to known IEE-binding epitopes from codfish (Gad c 1) and beta-lactoglobulin-related allergens. These findings suggest that allergy and protective immunity to helminth infection may be linked by the structural similarities of epitopes recognized by human IgE.