EVIDENCE THAT CYTOKINE-MEDIATED IMMUNE INTERACTIONS INDUCED BY SCHISTOSOMA-MANSONI ALTER DISEASE OUTCOME IN MICE CONCURRENTLY INFECTED WITHTRICHURIS-MURIS

In murine models of Schistosoma mansoni infection, egg production is a ssociated with a switch from T helper cell (Th)1- to Th2-type response s to both schistosome-specific and unrelated antigens. Polyparasitism is common in human populations within S. mansoni endemic areas. We hav e, therefore, examined whether coinfection with S. mansoni could affec t the outcome of a second parasitic infection, through Th2 cytokine-de pendent modifications to the host immune response. We find that when m ice susceptible to infection with the gut nematode Trichuris muris are coinfected with S. mansoni, they acquire the capacity to resolve T. m uris infection, thus demonstrating a resistant phenotype. This ability to expel T. muris is associated with the production of Th2-associated cytokines, and corresponding antibody isotypes, in response to S. man soni egg antigens. The Th2 response shows that there is no compartment alization between spleen and mesenteric lymph nodes, and that the expu lsion of T. muris is not caused by any changes in the host intestine a ssociated with excretion of schistosome eggs. This influence of schist osome infections may be important, not only for the outcome of infecti ons with unrelated pathogens in endemic areas, but also for the effica cy of vaccines in such areas.