Clement Rioux

Identification of Group B Streptococcal Sip Protein, Which Elicits Cross-Protective Immunity

ABSTRACT A protein of group B streptococci (GBS), named Sip for surface immunogenic protein, which is distinct from previously described surface proteins, was identified after immunological screening of a genomic library. Immunoblots using a Sip-specific monoclonal antibody indicated that a protein band with an approximate molecular mass of 53 kDa which did not vary in size was present in every GBS strain tested. Representatives of all nine GBS serotypes were included in the panel of strains. Cloning and sequencing of the sip gene revealed an open reading frame of 1,305 nucleotides coding for a polypeptide of 434 amino acid residues, with a calculated pI of 6.84 and molecular mass of 45.5 kDa. Comparison of the nucleotide sequences from six different strains confirmed with 98% identity that the sip gene is highly conserved among GBS isolates. N-terminal amino acid sequencing also indicated the presence of a 25-amino-acid signal peptide which is cleaved in the mature protein. More importantly, immunization with the recombinant Sip protein efficiently protected CD-1 mice against deadly challenges with six GBS strains of serotypes Ia/c, Ib, II/R, III, V, and VI. The data presented in this study suggest that this highly conserved protein induces cross-protective immunity against GBS infections and emphasize its potential as a universal vaccine candidate.

Intranasal Immunization with Gonococcal Outer Membrane Preparations Reduces the Duration of Vaginal Colonization of Mice by Neissevia gonorrhoeae

Nasal immunization was studied to determine if it could elicit an immune response capable of preventing vaginal colonization by Neisseria gonorrhoeae or of reducing its duration in the estradiol-treated mouse model. Nasal administration of gonococcal outer membrane (OM) preparations induced the development of systemic and vaginal immune responses that were directed mainly against a limited number of gonococcal OM proteins. The impact of nasal immunization on vaginal colonization by N. gonorrhoeae was evaluated by use of an experimental model, in which mice were treated with estradiol to prolong the infection. Bacterial clearance was significantly faster for mice immunized intranasally with N. gonorrhoeae OM preparations (4.0+/-2.5 days) than for control mice (8.5+/-4.3 days). The estradiol-treated mouse model may serve as a useful tool for the evaluation of potential gonococcal vaccine candidates.