A microsatellite polymorphism in the gamma interferon gene is associated with resistance to gastrointestinal nematodes in a naturally-parasitized population of Soay sheep

Free-living Soay sheep (Ovis aries) on the island of Hirta, St Kilda, Scotl and, are naturally parasitized bq gastrointestinal nematodes, predominantly Teladorsagia circumcincta. In this paper we show that reduced faecal egg c ounts (FEC) are associated with an allele at a microsatellite locus located in the first intron of the interferon gamma gene (o(IFN)-gamma) in Soay sh eep lambs and yearlings, measured at approximately 4 and 16 months of age, respectively. The same allele nas also associated with increased T. circumc incta-specific antibody (IgA) in lambs, but not associated significantly in yearlings. Flanking control markers failed to show; a significant associat ion with either FEC or IgA. These results suggest that a polymorphic gene c onferring increased resistance to gastrointestinal nematode parasites is lo cated at or near the interferon gamma gene, and support previous reports wh ich have mapped a quantitative trait locus (QTL) for resistance to this reg ion in domestic sheep. Our data are consistent with the idea that a functio nal polymorphism leading to reduced expression or efficacy of (IFN)-gamma c ould enhance the immune response to gastrointestinal nematodes by favouring the activity of the Th-2 cell subset and antibody associated immune mechan isms.