Stage-specific expression of surface molecules by the larval stages of Haemonchus contortus.

Three monoclonal antibodies, Hc2, Hc22 and Hc6, were produced against a surface extract of L3 Haemonchus contortus and screened against both free living and parasitic stages of the parasite. Hc2 and Hc22 were of IgG2c isotype and their target epitopes were insensitive to periodate treatment. Hc6 was of IgM isotype and its reactivity was sensitive to periodate treatment of the antigen, suggesting that Hc6 is specific for a carbohydrate epitope. Western blotting of larval extracts and staining of live worms demonstrated that Hc2 was specific for the surface of second stage larvae and that the epitope was still present on the protective sheath of third stage larvae but absent from the L3 cuticle itself. Hc22 was found to be specific for a 70-90 kDa antigen on the surface of third stage infective larvae and cross reacted with a higher molecular weight species present on the surface of third stage Teladorsagia circumcincta. Hc6 showed strong binding to three high molecular weight proteins on immunoblots of third stage larvae only, but in contrast to Hc2 and Hc22, showed no binding to the surface of live larvae. These studies demonstrate unique expression patterns of stage specific antigens on the surface of free living and parasitic H. contortus larvae.