Ontogenetic transformation of surface epitope expression, an adaptive immunoevasive strategy of filarial parasites.

Filarial nematodes are highly successful in invading, persisting and propagating in human body and eliciting severe ailments. The exact mechanism by which, filarial nematodes evade the host immunity is still ill-defined. The present investigation on the surface antigens of S. digitata revealed the occurrence of shared antigens in the egg, embryo, mf and adult stages. All these stages showed exposed carbohydrate moieties on their surface. In situ localization studies proved that the egg and embryo have exposed surface epitopes whereas the microfilariae and adults did not have any such epitopes. Based on these observations, a model has been proposed on "the surface epitope hiding", as an immunoevasive strategy of the filarial parasite which explains why the naturally shed surface antigens evoke antifilarial immune response in the host even though the system could not recognize the microfilariae or adult parasite due to lack of exposed surface epitopes, permitting the parasite to escape successfully from immune rejection. As treatment with detergents leads to exposure of surface epitopes of parasites, a safe intervention of parasite surface would be an effective strategy for detection and ultimate control of filariasis.