Developmentally regulated expression of a Haemonchus contortus surface antigen

All life cycle stages of Haemonchus contortus were screened with antibody-secreting cell (ASC) probes generated from immune sheep 5 days after a challenge infection. An antigen with an approximate molecular weight of 70-90 kDa was found to be predominantly expressed in the 3rd-stage larvae, while a molecule with an approximate molecular weight of 28-31 kDa was recognised by the ASC-probes in the earlier developmental stages. Antisera generated against the purified 70-90 kDa molecule and antibodies eluted from the 70-90 kDa region in the 3rd-stage larvae were found to react with the 28-31 kDa region in the 2nd-stage larvae. These results suggest that the 70-90 kDa antigen, previously identified as a major 3rd-stage surface antigen, is synthesised as a lower molecular weight molecule in the earlier larval stages and assembled into a higher molecular weight complex through non-reducible covalent bonds.