Immunoglobulins (immunoglobulins) are globulins that have antibody activity or are chemically similar to antibodies in structure. In the electrophoretic analysis of immune sera, most of the antibody activity is present within g globulin, so this type of protein used to be called g globulin. Biological significance: IgG is the predominant immunoglobulin in serum, accounting for approximately 80% of total adult serum immunoglobulins. IgG is the only immunoglobulin that can pass through the placenta and has antibacterial and antiviral effects. IgM is a 5-membered monomer made up of five 7S monomers linked by J-chains and is mainly found in serum. IgM is produced before IgG after artificial immunization or infection with pathogens. IgM cannot be passed through the placenta but can be obtained from breast milk. IgA is mainly found in secretions from the mucosal surfaces of the digestive and respiratory tracts. IgE plays an important role in allergic reactions even though it is found in very small amounts in serum. IgE binds to basophils and mast cells through its unique FC fragment, and when certain antigens re-enter the body and bind to the corresponding IgE on the cells, it can degranulate these cells and release a variety of active substances, resulting in a series of allergic symptoms. The IgD content in normal human serum is minimal, structurally unstable and easily degraded by fibrinolytic enzymes in the serum. IgD and IgM exist on the surface of mature B lymphocytes, while immature B lymphocytes have only IgM but no IgD on their surface.