Nonimmune Interaction of the SfbI Protein of Streptococcus pyogenes with the Immunoglobulin G F(ab′)(2) Fragment

Fibronectin-binding protein I (SfbI) of Streptococcus pyogenes binds to mouse immunoglobulin G (IgG) but not to IgA or IgM in a nonimmune fashion. The fibronectin-binding domains of SfbI were responsible for this activity, which was targeted to the IgG F(ab′)(2) fragment. SfbI also binds to B cells but not to CD4(+) or CD8(+) lymphocytes.