Immunological Evidence for Peptide-Carbohydrate Mimicry with a Group A Streptococcus Polysaccharide-Mimetic Peptide
Silvia Borrelli, Rehana B. Hossany, Susan Findlay and B. Mario Pinto
DOI : 10.3844/ajisp.2006.77.87
American Journal of Immunology
Volume 2, 2006
The immunogenicity of a peptide-protein conjugate developed by linking a peptide mimic DRPVPY of the Group A Streptococcus cell-wall polysaccharide (GAS-CWPS), to tetanus toxoid (TT) was examined. BALB/c mice were immunized three times subcutaneously following homologous or heterologous prime/boost strategies at 4- or 6- week intervals in two different experiments. DRPVPY-TT, CWPS-TT, heat-killed, pepsin-treated GAS bacteria (with exposed polysaccharide) and TT, were used as immunogens with alum as adjuvant. Antibody titers were determined by ELISA with GAS bacteria (with exposed polysaccharide) and DRPVPY-linked to bovine serum albumin (BSA, DRPVPY-BSA) as solid phase antigens. All mice primed with DRPVPY-TT developed high IgG anti-peptide and anti-GAS titers. The binding of polyclonal anti-peptide antibodies to GAS could be inhibited by purified CWPS, synthetic oligosaccharides corresponding to CWPS, DRPVPY-BSA, DRPVPY and DRPVP, as assessed by competitive-inhibition ELISA. Anti-oligosaccharide titers were also obtained upon titration of anti-peptide sera with synthetic oligosaccharide-BSA conjugates. All mice primed with CWPS-TT and mice primed and boosted with GAS developed IgG anti-peptide titers. These data demonstrate conclusively the cross-reactivity of the immune responses and support the hypothesis of antigenic mimicry of the GAS-CWPS by the hexapeptide DRPVPY. However, mice boosted with DRPVPY-TT, after 6-8 weeks, showed a decrease in IgG anti-GAS titers, but an increase in IgG anti-peptide titers, suggesting carrier-induced suppression of the response to polysaccharide. Strategies are outlined for further refinement of a DRPVPY conjugate as a surrogate of the cell-wall polysaccharide for use in vaccines against Group A Streptococcus.
© 2006 Silvia Borrelli, Rehana B. Hossany, Susan Findlay and B. Mario Pinto. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.