Characterization, cloning and immunogenicity of antigens released by lung-stage larvae of Schistosoma mansoni

R. HARROP a1c1, P. S. COULSON a1 and R. A. WILSON a1
a1 Department of Biology, University of York, P.O. Box 373, York YO1 5YW


Lung-stage schistosomula are the target of protective immunity in mice vaccinated with attenuated cercariae of Schistosoma mansoni. Therefore, proteins present at this developmental stage, and in particular those which are secreted, are a potential source of novel vaccine candidates. However, little information is available about such molecules. Here we describe the cDNA clones identified by screening expression libraries with serum raised against proteins released by lung-stage schistosomula. In total, 11 different cDNA species were identified, 6 of which have been described previously in S. mansoni; these included fructose 1,6-bisphosphate aldolase and Sm21.7 which together accounted for two-thirds of all positive clones. Of the 5 newly described schistosome genes, 1 cDNA had a high degree of homology to the s5a subunit of 26S proteasomes, most significant being with the human protein. The remaining 4 clones showed no significant homologies to any genes sequenced previously. Fructose 1,6-bisphosphate aldolase, Sm21.7, the proteasome homologue and 1 unknown clone (A26) have been expressed in a bacterial expression system and serum produced against each recombinant protein. Immunolocalization showed fructose 1,6-bisphosphate aldolase, Sm21.7 and the proteasome homologue to be most abundant in muscle cells whilst clone A26 was distributed throughout many tissues, but was most abundant in the tegument. Analysis of the cellular immune responses of vaccinated mice showed 3 of the 4 expressed clones to be highly immunogenic, inducing the secretion of large quantities of the Th1-type cytokine interferon gamma.

(Received September 28 1998)
(Revised January 6 1999)
(Accepted January 6 1999)

Key Words: Schistosoma mansoni; released proteins; sequence analysis; immunolocalization; immune response.

c1 Corresponding author: The Edward Jenner Institute for Vaccine Research, Compton, Newbury, Berkshire RG20 7NN. Tel: +01635 577928. Fax: +01635 577901. E-mail: