Immunoglobulin G (IgG) is one of the most abundant proteins in human serum, accounting for about 10–20% of plasma protein. Immunoglobulin G (IgG) is a monomer immunoglobulin, mainly involved in secondary antibody reaction, plasma B cell synthesis and secretion, constitute 75% of human serum immunoglobulin. There are four subtypes of human IgG antibodies: IgG1, IgG2, IgG3, IgG4; mice IgG can be divided into five subtypes; IgG1, IgG2A, IgG2B, IgG2C and IgG3; rats have four subtypes: IgG1, IgG2A, IgG2B and IgG2C. The nomenclature of IgG subtypes of different species is independent, so there is no correlation among different genera. The content of IgG1 in serum accounts for about 60%, and the half-life in serum is about 21 days. After pepsin cleavage, IgG1 is divided into two antigenic binding sites F (ab) s and a highly conserved Fc fragment, and Fc has a highly conserved N-glycosylation site. IgG1 is the most potential subtype in tumor immunotherapy. The active form of IgG1 is bivalent monomer, and human IgG1 can also bind to mouse Fc γ receptor, so the obvious effect can be observed in mouse model.

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