RELATIONSHIP BETWEEN HELMINTHIC INFECTION AND IGE RESPONSE IN ATOPIC AND NONATOPIC CHILDREN IN A TROPICAL ENVIRONMENT

Background: Although IgE antibody is clearly involved in allergic reac tions to environmental allergens, this immunoglobulin is an important component of host-protective immune responses against the helminthic p arasites that are endemic in the majority of the world population. How ever, these infections not only stimulate the production of antiparasi te IgE antibody but can nonspecifically induce polyclonal IgE synthesi s that results in highly elevated total serum IgE levels. Such polyclo nal stimulation can diminish specific IgE antibody responses and cause saturation of mast cell Fee receptors, thus inhibiting allergic react ivity. This may represent a mechanism of immune evasion by the parasit e.Objective: Because an atopic disposition is generally recognized to be associated with elevated IgE synthesis against environmental allerg ens, the aim of this study was to evaluate the influence of atopy on t he antiparasite response. To this end, we examined two groups of Venez uelan children in whom the intestinal helminth Ascaris lumbricoides is endemic but that differ greatly in their level of atopy. One group wa s from an island population (Coche Island) that has a very strong atop ic background and in which the prevalence of allergic disease is extre mely high. The other was a group of nonatopic children belonging to a mainland population (Barrio Los Erases) that is of comparable socioeco nomic level and has an exposure to helminthic infection similar to tha t of the island group but a relatively low expression of allergic dise ases. Results: Although the living conditions and the prevalence of As caris infection of the two groups were comparable, the intensity of th e parasitic infection was considerably higher in the nonatopic mainlan d children (geometric mean values of eggs per gram of feces: Barrio Lo s Erases, 7621; Coche Island, 1435; p < 0.001). In addition, their tot al serum IgE levels were significantly more elevated than in the atopi c island group (geometric mean: Barrio Los Erasos, 2172; Coche Island, 941 IU/ml; p < 0.001). In contrast, the specific anti-Ascaris respons e was much stronger in the atopic children (geometric mean: Barrio Los Erasos, 0.30; Coche Island, 0.91 PRU/ml; p < 0.001), which resulted i n the ratio of specific to total IgE being nine times higher than in t he nonatopic mainland subjects. These differences were maintained even when the children were matched on the basis of infection intensity, t hus indicating that the atopic children have an intrinsic propensity t o favor specific over polyclonal IgE responses to the parasite. Conclu sions: The children with a strong atopic background demonstrated IgE r esponses concordant with an enhanced protective response against helmi nthic parasites and had significantly lower intensities of infection t han their nonatopic counterparts. These observations support the conce pt that the atopic state has conferred a selective evolutionary advant age that could compensate for its involvement in allergic disease.