Systemic immunization with streptococcal immunoglobulin-binding protein Sib35 induces protective immunity against group A Streptococcus challenge in mice

The streptococcal immunoglobulin (Ig)-binding protein Sib35 binds to IgG, IgM and IgA in human, mouse and bovine. Since all group A Streptococcus pyogenes (GAS) strains examined express the sib35 gene, we evaluated the Sib35 as a vaccine candidate against GAS infections. We detected significantly higher anti-Sib35 IgG antibody titers in sera from patients with GAS infections than from healthy volunteers. Immunization of mice with Sib35 induced antigen-specific IgG antibodies in their sera, and rabbit Sib35-specific antiserum showed opsonic activity. Immunization with Sib35 enhanced survival rates in mice challenged with a GAS strain, while exhibiting no toxicity in hosts. We conclude that Sib35 is a promising vaccine for prevention of GAS infections.