Immune recognition of the surface associated antigen, Tc- SAA-1, from infective larvae of Teladorsagia circumcincta

SUMMARY A cDNA encoding a surface-associated antigen was amplified by reverse transcriptase polymerase chain reaction (PCR) from RNA extracted from Teladorsagia circumcincta exsheathed third stage larvae (xL3). The protein encoded by this cDNA, Tc -SAA-1, displays 77% identity over 162 amino acid residues to a surface associated antigen from Ancylostoma caninum ( Ac- SAA-1 ). Antiserum raised against a bacterially-expressed recombinant form of Tc -SAA-1 reacted with a native protein in somatic and surface extracts of xL3 but not with L4 or adult parasites. Limited binding of anti -Tc- SAA-1 antibody was observed on the cuticular surface of xL3 s, however, regions of localization underlying the cuticle were observed. Incubation of xL3 T. circumcincta with anti-SAA rabbit serum failed to significantly inhibit penetration of the abomasal mucosa in vitro. IgA in abomasal mucus derived from sheep that had received a trickle infection of T. circumcincta bound recombinant Tc -SAA-1.