Immunoglobulins are a class of globulins with antibody activity or chemical structure similar to antibody molecules synthesized and secreted by plasma cells, which can be divided into five major categories: Immunoglobulin G, Immunoglobulin A, Immunoglobulin M, Immunoglobulin D, and Immunoglobulin E, as follows: 1. Immunoglobulin G: It is the most abundant and major immunoglobulin in the body, which can pass the placental barrier against viruses, bacteria and Immunoglobulin M: mainly present in serum, it is the earliest antibody in humoral immune response and can be used for early diagnosis of infection. 3, Immunoglobulin A: can be divided into serotype and secretory type, and the secretory type can participate in local mucosal immunity. 4, Immunoglobulin D: is a sign of cell differentiation and maturation. 5, Immunoglobulin E: is the least abundant in normal human serum. Immunoglobulin E: it is the least amount of immunoglobulin in normal human serum, it can cause type I hypersensitivity reaction, in addition, it is also related to parasite immunity.