Characterization of the domain of fibronectin-binding protein I of Streptococcus pyogenes responsible for elicitation of a protective immune response

Fibronectin-binding protein I (SfbI) represents a major adhesin of Streptoc occus pyogenes. Mice were intranasally immunized with recombinant proteins spanning different portions of SfbI to identify the minimal fragment able t o elicit a protective response against a lethal challenge with S. pyogenes. The strongest cellular responses and the highest levels of antigen-specifi c secretory immunoglobulin A (IgA) were detected in mice immunized with the fibronectin-binding region of SfbI. In contrast, animals vaccinated with a polypeptide spanning the aromatic and proline-rich regions showed the high est titers and fastest Ige response in serum. Vaccination with either SfbI without a membrane anchor and signal peptide or a polypeptide encompassing its fibronectin-binding regions resulted in efficient protection against he terologous challenge (60% and 80%, respectively), whereas the use of a poly peptide lacking this region conferred marginal protection (10%) with respec t to the control group (0%). These results demonstrate that the fibronectin -binding region of SfbI is a promising candidate antigen for developing ant i-S. pyogenes vaccines.