Schistosoma mansoni lung-stage larvae appear to not bind antibodies from radiation vaccine or infection sera in the membrane immunofluorescence test. However, treatment of ex vivo lung-stage schistosomula with methyl-beta-cyclodextrin, a hydrophobic oligosaccharide that specifically extracts cholesterol from plasma membranes, induced readily detectable binding of specific antibodies in a concentration- and time-dependent manner. Surface membrane antigen binding of specific antibodies was also conclusively demonstrated by quantitative absorption of anti-schistosome sera with intact ex vivo larvae. These data together suggest that confinement of lung-stage schistosomula surface membrane antigens in cholesterol-rich sites allows only monovalent antibody binding, which can be detected by absorption and not by direct serology.
Schistosoma mansoni glyceraldehyde 3-phosphate dehydrogenase (SG3PDH) is a target of cellular and humoral immune responses of Brazilian and Egyptian subjects putatively resistant to reinfection with S. mansoni. In an aim to develop a safe, stable and effective vaccine based on this promising molecule, six peptides derived from its primary sequence were selected based on the lowest homology to human G3PDH. The synthetic peptides were tested by ELISA against plasma of humans putatively susceptible or resistant to reinfection with S. mansoni or S. haematobium following chemotherapeutic cure of previous infection. Repeat experiments indicated that the six peptides bear human B-cell epitopes that bind immunoglobulin (Ig)M, IgG1 and IgG3 antibodies. Resistance to reinfection appeared to be significantly associated with humoral immune responses to multiple peptides. This contention was supported by studies in the murine model, whereby we examined the B cell immune responses of Swiss and inbred BALB/c and C57BL/6 mice immunized with recombinant SG3PDH (rSG3PDH) to the six SG3PDH-derived peptides. The serum antibodies of rSG3PDH-immunized Swiss mice were directed to only one of the six peptides tested by ELISA. Antibodies from rSG3PDH-immunized C57BL/6 and BALB/c mice bound, respectively, to four and six out of six peptides. In contrast to Swiss mice, immunization of C57BL/6 and BALB/c mice with rSG3PDH induced protection against challenge cercariae which reached the level of significance (P , 0.05) for BALB/c mice. The data together indicate that host recognition of multiple peptides of a candidate vaccine antigen is necessary for the expression of its ability to contribute to protective immunity against Schistosomiasis.
Four monoepitopic MAPs (MAP A, B, C and E) and one bis-diepitopic MAP B-E derived fromthe primary sequence of Schistosoma mansoni glyceraldehyde 3-phosphate dehydrogenase, previously tested in BALB/c mice, were examined for their immunogenicity and protective capacity in C57BL/6 mice. Despite multimerization into MAPs, MAP Aand MAP C were poorly immunogenic. In contrast toBALB/c mice, MAP E was non-immunogenic in C57BL/6 mice. Peptide B in the form of MAP B orbis-diepitopic MAPB-E elicited immune responses in C57BL/6 mice that were associated with a significant decrease in worm burden. The MAPs were prepared by the stepwise solid-phase peptide synthesis using Boc/Bzl chemistry, successfully purified on the RP-HPLC column and characterized by RP-HPLC, HPCE and MALDI-TOF MS techniques. A general strategy for MAPs purification is discussed here and the purification of MAP Band MAP E is documented in detail.
Six peptides, A, B1, B, C, D and E, derived from the primary sequence of Schistosoma mansoni glyceraldehyde 3-phosphate dehydrogenase (SG3PDH) were selected based on lowest homology to human glyceraldehyde 3-P dehydrogenase (G3PDH), multimerized in dipeptidic multiple antigen peptide
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