Evaluation of recombinant protein r140, a polypeptide segment of tegumental glycoprotein Sm25, as a defined antigen vaccine against Schistosoma mansoni

Abstract

To investigate the role of tegumental glycoprotein Sm25 in protective immunity against schistosomiasis, codons 43-182 of its gene (GP22) were amplified by PCR and cloned in the pET 15b bacterial expression system. Recombinant protein r140 was inducibly expressed in the presence of 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 responses. These antibodies detected an N-glycanase sensitive. 25 kDa antigen in a detergent solubilized worm fraction using Western immunoblotting. The choice of adjuvant affected the isotype distribution of the specific anti-r140 antibodies. Despite the presence of high antibody titres and isotypes which have been shown to correlate with protective immunity, protection against subsequent cercarial challenge was not observed. In addition, no appreciable effects on worm sex ratios or liver egg yields were detected in mice. Studies involving biotin labelling of membrane proteins in live worms showed that the majority of anti-r140 reactive molecules present in adult schistosomes are biotinylated after permeabilization of the parasite surface. Several possibilities to account for the lack of protective immunity are analysed.

Enzymatic Shaving of the Tegument Surface of Live Schistosomes for Proteomic Analysis: A Rational Approach to Select Vaccine Candidates

“…It was then cloned and designated as an N-glycosylated integral membrane protein [27] but later characterized as a palmitoylated protein with the implication that it was on the cytosolic leaflet of the plasma membrane [28]. Further immunocytochemical studies suggested it was distributed throughout the tegument syncytium but not associated with the surface membranes [29] and it could only be biotinylated when parasites were permeabilized by Triton X-100 [30]. It was not found in either our compositional or biotinylation studies on the tegument surface.…”

Cloning and characterization of an orphan seven transmembrane receptor from Schistosoma mansoni

“…Indeed, it has been shown that protective immunity can be induced in mice by immunization with purified adult worm surface membranes (Smithers et al 1989) and, more recently, recombinant forms of the membrane and/or membrane-associated proteins, Sm -TSP-2 (Tran et al 2006), Sm14 (Tendler et al 1996), Sm23 (Da'dara et al . 2001) and Sm25 (Suri et al 1997). Recent studies have explored the tegument proteome of S. mansoni (see Braschi et al 2006; Braschi and Wilson, 2006), but Sm -7TM had not been identified using this approach.…”

“…Given its tegumental location, particular motifs of Sm-7TM are likely to be exposed to the host environment, making this receptor an attractive candidate for intervention strategies against schistosomiasis. Indeed, it has been shown that protective immunity can be induced in mice by immunization with purified adult worm surface membranes (Smithers et al 1989) and, more recently, recombinant forms of the membrane and/or membrane-associated proteins, Sm-TSP-2 (Tran et al 2006), Sm14 (Tendler et al 1996), Sm23 (Da'dara et al 2001 and Sm25 (Suri et al 1997). Recent studies have explored the tegument proteome of S. mansoni (see , but Sm-7TM had not been identified using this approach.…”

Altered Patterns of Gene Expression Underlying the Enhanced Immunogenicity of Radiation-Attenuated Schistosomes

“…Indeed, this particular tetraspanin, identified using a signal sequence trap [25], elicited protective immunity when the major extracellular loop was used to vaccinate mice [26]. Conversely Sm25, or its decorating glycans, may actually protect the parasite by subverting the host immune response as, despite eliciting high antibody titres, the recombinant protein does not protect vaccinated animals [27]. On the basis of membrane association and immunofluorescence studies it has been suggested that the actin binding protein JF-2 may be available at the tegument surface [28].…”