Immunoglobulin G (IgG) belongs to the immunoglobulin family and is a widely expressed serum antibody. A immunoglobulin has two heavy chains and two light chains connected by a disulfide bond. It mainly helps in immune defense. It is a glycoprotein. IgG is a major class of immunoglobulin. Mouse consists of five immunoglobulin classes- IgM IgG IgA IgD and IgE. Mouse IgG is further divided into five classes- IgG1 IgG2a IgG2b and IgG3.