Extracellular and cytoplasmic Cu/Zn superoxide dismutases from Haemonchus contortus

S. LIDDELL a1p1 and D. P. KNOX a1c1
a1 Moredun Research Institute, 408 Gilmerton Road, Edinburgh EH17 7JH, Scotland, UK


Full-length cDNAs encoding cytosolic (SODc) and putative extracelluar (SODe) Cu/Zn superoxide dismutases (SODs) from the ovine gastrointestinal parasitic nematode Haemonchus contortus have been isolated and characterized. The predicted sequences of the H. contortus SODs showed strong homology to other helminth SODs, the highest level of sequence similarity was with those of the free-living nematode Caenorhabditis elegans. The predicted amino acid sequence of the putative extracellular form contained an N-terminal extension with the characteristics of a signal sequence including a potential signal peptidase cleavage site. Transcripts of both classes of Cu/Zn SOD were detected in all life-cycle stages examined. The cytosolic SOD mRNA was approximately 6-fold more abundant than that of the extracellular enzyme in adult parasites. Immunoblotting with antisera raised to in vitro-expressed parasite SODs revealed the presence of 2 proteins in extracts of adult H. contortus, with molecular masses of approximately 19·8 and 18 kDa. An additional protein of approximately 16·8 kDa was detected in adult ES material. Immunofluorescent staining showed Cu/Zn SOD was localized in the body wall musculature and the pharynx in adult worms and in the uterine tract of adult females. The immunogenic properties of recombinant H. contortus Cu/Zn SODs was assessed in a challenge infection experiment in lambs.

(Received September 26 1997)
(Revised November 15 1997)
(Accepted November 15 1997)

Key Words: Haemonchus contortus; superoxide dismutase; extracellular; RT–PCR; immunogenicity.

c1 Corresponding author. Tel: +44 131 664 3262. Fax: +44 131 664 8001. E-mail:
p1 Present address: Parasite Immunobiology Laboratory, USDA, ARS, Building 1040, Room 100, BARC, East, Beltsville, MD 20705, USA.