Immunoglobulin G (IgG) is a kind of monomer immunoglobulin which is developed and secreted by effective B cells and participates in secondary antibody reaction. IgG has four subclasses (IgG1,IgG2,IgG3,IgG4). IgG2 contains two members: IgG2a and IgG2b, both of which belong to the Fc fragments of IgG antibodies. Fc fragments have been shown to mediate phagocytosis, trigger inflammation, and target immunoglobulin Ig to specific tissues. In addition, some studies have shown that protein G or protein An on the surface of some staphylococci and Streptococcus strains can also specifically bind to the Fc region.