Discussion

Allergies and other disorders of the immune system have recently increased markedly, particularly in economically advanced countries. The 'hygiene hypothesis' ascribes this to reduced exposure to microbial and parasitic infections and consistent with this, some people with helminth infections are protected against allergic disorders. It has been known for some time that glycoproteins of invertebrates and plants are antigenically cross-reactive due to their carrying carbohydrate epitopes in common (cross-reactive carbohydrate determinants - CCDs). In preliminary experiments we found that rabbit IgG antibodies raised against Schistosoma mansoni egg antigens reacted in Western immunoblots with a wide range of molecules in different plants and invertebrates known to be causes of allergy. We have investigated this antigenic cross-reactivity with respect to: (i) determining whether the rabbit anti-S. mansoni antibodies cross-reacted with known allergens in the plant and invertebrate extracts; and (ii) determining which S. mansoni egg antigens may have induced the allergen cross-reactive antibodies. Allergen molecules which have been found to be reactive in immunoblots with rabbit anti-S. mansoni antibodies include: Hev b 7 in rubber latex, Ara h 1 in peanut, 5 different known allergens in Timothy grass and birch tree pollens, Der f 15 from the house dust mite Dermatophagoides farinae, a Per a 3 homologue from cockroach and honey bee venom phospholipase A. The rabbit IgG antibodies reactive with the above-mentioned allergens were purified by elution from immunoblotted allergen using low pH buffer. These acid-eluted antibodies reacted with three immunodominant S. mansoni egg antigens IPSE/alpha-1, omega-1 and kappa-5 (though the reactivity with IPSE/alpha-1 may be due to its ability to complex non-immunologically with immunoglobulins). If the results are substantiated with similar observations using sera from schistosome-infected humans, they may offer an explanation for the hygiene hypothesis in terms of schistosome-induced IgG anti-CCD antibodies 'blocking' the reactivity of allergenic IgE antibodies