What Is an Immunoglobulin?

Immunoglobulin (Ig) refers to a globulin with antibody (Ab) activity or chemical structure similar to an antibody molecule. Immunoglobulin is a tetrapeptide chain structure composed of two identical light chains and two identical heavy chains connected by interchain disulfide bonds. There are five types of immunoglobulins, namely, immunoglobulin G (IgG), immunoglobulin A (IgA), immunoglobulin M (IgM), immunoglobulin D (IgD), and immunoglobulin E (IgE).

Basic Information

nickname

Immunoglobulins

English name

immunoglobulins

Ig Immunoglobulin antibodies and Ig

Antibodies are immune globulins that are specifically synthesized and secreted by B cells after they have been activated by antigens and differentiated into mature plasma cells. Antibodies are biological functional concepts, while immunoglobulins are chemical structural concepts. The chemical basis of all antibodies is immunoglobulin, but not all immunoglobulins have antibody activity.

Ig Function of immunoglobulin Ig

Immunoglobulins can be divided into antibodies and membrane immunoglobulins. Antibodies are mainly found in serum and can also be found in other body fluids and exocrine fluids. Their main function is to specifically bind antigens. Membrane immunoglobulin is an antigen receptor on the B cell membrane and can specifically recognize antigen molecules. In vivo, antibodies and antigens can directly exert effects after binding, such as antitoxins can neutralize exotoxin, virus neutralizing antibodies can prevent the virus from infecting target cells, and secreted IgA can inhibit bacteria from attaching to host cells. In vitro, agglutination and precipitation can occur after the antibody binds to the antigen. Immune globulin can activate complement; bind Fc receptors on the cell surface, (Fc can crystallize fragments. Hydrolyze IgG molecules with papain to get two Fabs and one Fc segment. This fragment can interact with effector molecules and effector cells , But can not bind to antigens.) Thus show different biological effects, such as opsonization, antibody-dependent cell-mediated cytotoxicity, mediate type hypersensitivity; through human placenta and mucosa, IgG is The only type of Ig that can pass through the placenta, the transfer of maternal IgG to the fetus through the placenta is an important natural passive immunity, which is of great significance for anti-infection in newborns. Secreted IgA can pass through the digestive and respiratory tract mucosa, and is the main factor for local mucosal immunity. In addition, antibodies have positive and negative regulatory effects on the immune response.