PEPTIDES THAT MIMIC THE GROUP-B STREPTOCOCCAL TYPE-III CAPSULAR POLYSACCHARIDE ANTIGEN

Microbial polysaccharides are notably poor immunogens. We have develop ed an alternate route for the production of Abs to important carbohydr ate epitopes, mAb S9, a protective mAb against the type III capsular p olysaccharide of group B streptococci (GBS), was used to select epitop e analogues from a peptide display phage library, Depending upon desor ption conditions, two populations of phage were identified with displa yed sequences of WENWMMGNA and FDTGAFDPDWPA. ELISA results demonstrate d that these phage bound to S9 and no other Abs. Phage blocked the bin ding of S9 to type III GBS, but did not block binding by another anti- GBS mAb, Phage displaying the latter peptide sequence showed greater i nhibition, Ab S9 and other monoclonal and polyclonal anti-GBS type III antisera bound the synthetic peptide FDTGAFDPDWPAC. The binding of S9 to GBS was inhibited by the free peptide with an IC50 of 30 mu g/ml. The binding of polyclonal anti-GBS antibodies to peptide could be bloc ked by intact GBS as well as purified capsular polysaccharide. The pep tide was conjugated to three different carriers and was used to immuni ze mice. All mice produced a significant antibody response to GBS and to the purified capsular polysaccharide following a single immunizatio n, These data demonstrate that a peptide mimetic of the GBS capsular p olysaccharide is both antigenic and immunogenic. The incorporation of such peptides into vaccine preparations may enhance the efficacy of va ccines in inducing Ab responses to important carbohydrate epitopes.