Globulin belongs to one kind of human serum proteins, which can be divided into five types, namely, IgG, IgA, IgM, IgD and IgE, with different roles. 1. IgG: the most abundant globulin in serum, mainly plays the role of anti-infection, such as anti-bacteria, anti-virus, anti-toxin, etc., and can also be involved in type II and III hypersensitivity reactions. 2.IgA: it can be divided into serum type and secretion type, it does not show important immune function in serum, the elevation and decrease of IgA can indicate certain diseases, but it is not specific. 3. IgM: also known as macroglobulin, often associated with recent infections, especially viral infections, can be used for early diagnosis of infectious diseases. 4. IgE: the least abundant globulin in serum, often associated with allergy and parasitic infection, its elevation suggests that there may be allergy or parasitic infection. 5.IgD: the content is also very small, often as an important surface marker of B cell differentiation and maturation.