Systemic immunization with streptococcal immunoglobulin-binding protein Sib 35 induces protective immunity against group: a Streptococcus challenge in mice.

The streptococcal immunoglobulin (Ig)-binding protein Sib 35 binds to IgG, IgM and IgA in human, mouse and bovine. Since all group A Streptococcus pyogenes (GAS) strains examined express the sib 35 gene, we evaluated the Sib 35 as a vaccine candidate against GAS infections. We detected significantly higher anti-Sib 35 IgG antibody titers in sera from patients with GAS infections than from healthy volunteers. Immunization of mice with Sib 35 induced antigen-specific IgG antibodies in their sera, and rabbit Sib 35-specific antiserum showed opsonic activity. Immunization with Sib 35 enhanced survival rates in mice challenged with a GAS strain, while exhibiting no toxicity in hosts. We conclude that Sib 35 is a promising vaccine for prevention of GAS infections.