EVALUATION OF RECOMBINANT PROTEIN R140, A POLYPEPTIDE SEGMENT OF TEGUMENTAL GLYCOPROTEIN SM25, AS A DEFINED ANTIGEN VACCINE AGAINST SCHISTOSOMA-MANSONI

To investigate the role of tegumental glycoprotein Sm25 in protective immunity against schistosomiasis, codons 43-182 of its gene (GP22) wer e amplified by PCR and cloned in the pET 15b bacterial expression syst em. Recombinant protein r140 was inducibly expressed in the presence o f rifampicin and purified by Ni-affinity chromatography. In different vaccination trials, Balb/c mice and Fischer rats repeatedly immunized with r140 in combination with one of several adjuvants (alum, cholera toxin or complexed into proteosomes) produced high titre anti-r140 res ponses. These antibodies detected an N-glycanase sensitive, 25 kDa ant igen in a detergent solubilized worm fraction using Western immunoblot ting. The choice of adjuvant affected the isotope distribution of the specific anti-r140 antibodies. Despite the presence of high antibody t itres and isotypes which have been shown to correlate with protective immunity protection against subsequent cercarial challenge was not obs erved. In addition, no appreciable effects on worm sex ratios or liber egg yields were detected in mice. Studies involving biotin labelling of membrane proteins in live worms showed that the majority of anti-r1 40 reactive molecules present in adult schistosomes are biotinylated a fter permeabilization of the parasite surface. Several possibilities t o account for the lack of protective immunity are analysed.