antibody

An antibody is an immunoglobulin that binds to an antigen and is present on the surface of body fluids and lymphocytes. Antibodies are produced by plasma cells differentiated from B cells. The antibody molecule has a binding site (binding cluster) that binds to the corresponding antigenic determinant. Since different antigens specifically bind to antibodies to exhibit various responses, antibodies have various names, such as lectins, precipitins, antitoxins, hemolysins, lysozymes, complement-binding antibodies, and the like. These combinations, under appropriate conditions, can occur directly or indirectly, and can be used as a method of clinical diagnosis. The antibody has a series of biological activities such as corresponding cells, tissues, toxins and enzymes. After binding to the corresponding antigen in the body, the antibody can be phagocytized and excreted to remove the antigen, or the antigen loses its pathogenic effect. Commonly used to prevent certain diseases. This has played a huge role in medical applications. In other cases, an immune complex formed by binding an antibody to an antigen can damage tissues and cells, causing adverse effects such as hypersensitivity or immune diseases. In the past, antibodies were collectively referred to as gamma (gamma) globulin (γG, GG), which was named when the serum was analyzed by electrophoresis in early years and the antibody activity was observed in the γ moiety. It was later shown that the antibodies were not all in the gamma region; conversely, the globulins located in the gamma region did not necessarily have antibody activity. In 1964, the World Health Organization special meeting called antibody-associated and antibody-associated globulins as immunoglobulins (Ig). At present, most scholars believe that the term "antibody" only indicates its biological activity, such as where the target antigen has been identified. It can specifically bind to the target antigen, but it does not indicate its chemical nature. The term immunoglobulin means both immunological activity and more emphasis on its chemical meaning, which refers to a single molecule. When not strictly distinguished, the two words can be mixed. After B lymphocytes are stimulated by antigen, how to become plasma cells capable of secreting antibodies or into memory cells is far from clear. There are certain rules for the production of antibodies. When the antigen enters the body for the first time, after an incubation period, the antibody titer gradually rises, and after reaching the peak, it remains for a short period of time, and then gradually decreases, which is the initial response or the primary antibody response. However, after the second exposure to the same antigen, it initially showed a slight decrease in the amount of the original antibody. This is because a part of the original antibody binds to the re-injected antigen. Subsequently, the increase in antibody titer is faster than the initial one, and the titer at the peak is also higher than the initial one, and the duration is also long. This is called the secondary (antibody) response or the re- (antibody) response. The antibody produced by the antigen stimulation gradually disappears after a period of time, and then contacts the antigen, so that the disappeared antibody rises rapidly and is a response to the recall. A generalized recall response can include a secondary response. If the re-stimulated antigen is the same as the first time, it is a specific recall response, and if it is different from the first time, it is a non-specific recall response. Antibodies that respond non-specifically are only transiently elevated and fall rapidly in a short period of time. The general characteristics of antibodies include: 1 Specificity: Antibodies can only specifically bind to the corresponding antigen, but not to other unrelated antigens. This is determined by the binding site of the antibody and the physical and chemical properties of the antigenic determinant. 2 Heterogeneity: An antibody is composed of a group of different types of immunoglobulin molecules (see "Immunoglobulins"). Their amino acid composition and arrangement as well as the stereo configuration are similar and slightly different, and thus their size, shape and function are also different. For example, the surface of a natural antigenic substance contains many different determinants, and antibodies produced by the body to stimulate the body contain antibodies against these different determinants. For example, antibodies against Salmonella typhimurium should include at least the anti-antibody O antibody, the anti-flagellate H antibody, and the antiviral (Vi) antigen Vi antibody; in fact, the antibody against the cell, due to the bacterial antigen (9, 12) Different, the corresponding antibodies are also different from each other. It is an antibody against a certain determinant, including IgG, IgA, IgM, IgD, and IgE, and their subclasses, although not necessarily in one body at the same time. For a certain type of antibody (such as IgG), the antibodies produced by different germ lines and between different individual animals are also not identical. This difference is determined by genetics. These heterogeneities of antibodies are clinically a concern. 3 Duality: On the one hand, the antibody can specifically bind to the antigen to exert its immune function; on the other hand, since it is a high molecular protein, it has the dual role of antibody and antigen when injected into a heterologous animal. When repeatedly injecting antisera from xenogenic animals to prevent disease, it is necessary to pay attention to the possibility of an allergic reaction. There have been many assumptions and doctrines about the mechanism of antibody production. Five kinds of human immunoglobulins have been identified, which are: IgG, IgA, IgM, IgD and IgE, which differ in the H chain and are composed of H chains called γ, α, μ, δ and ε, respectively. IgG is the major immunoglobulin in human serum. The main type of antibody produced after antigen challenge is this monomer. Although the fetus does not produce IgG, it can quickly pass through the placenta, so the maternal IgG can be detected in the fetal and neonatal serum. Depending on the heavy chain, IgG can be divided into four subclasses: γ1, γ2, γ3, γ4. Some antigens provoke antibody responses, and 4 subclasses are comparable, but some antigens are dominated by one of them. The antibody acting on carbohydrates is often IgG2; the anti-DNA antibodies are mainly IgG1 and IgG3. Among the various subclasses, IgG3 has the lowest synthesis rate, the highest rate of decomposition, and the shortest serum half-life. See Tables 1 and 2 for the various biological and physical properties of IgG. IgA has monomers as well as dimers. It is the major immunoglobulin in the secretion and exists as a dimer interconnected by a polypeptide linker (J chain) and a disulfide bridge. In addition, secretions (dimers in sputum, tears, intestinal fluids, also contain a polypeptide chain called secretory component (SC) or secret piece. SC seems to protect dimeric IgA, free of Digestion of gastrointestinal proteolytic enzymes, which are produced by topical serous secretory epithelial cells, located in the surface of these cells, which suggests that SC may be a receptor for dimeric IgA. When it passes between these cells, it is increased. It is believed that the ability of the molecule to pass through the mucosal epithelium by cellulogenesis (as opposed to pinocytosis) is due to this. Therefore, the production of secretory IgA can be considered unusual. Because it is a collaborative product of two different types of cells (ie, antibody-secreting plasma cells and serosal epithelial cells). IgA can be divided into two subclasses, IgA1 and IgA2, depending on its alpha heavy chain. According to its genetic markers, it is divided into two subtypes, A2m(1) and A2m(2). IgM is the largest immunoglobulin (molecular weight 890,000), which is a pentameric composed of 5 identical subunits. Body, each with two K or λ light chains and two μ heavy chains. In addition, IgM has one A similar J chain of dimeric IgA makes molecular binding more robust. IgM is effective for complement binding, and agglutination and bactericidal action against red blood cells and bacteria is also much more effective than IgG. Monomeric IgM is found on the surface of B cells. It is believed to act as an antigen receptor. After the initial administration of one dose of antigen, after a period of initial delay, the first antibody that appears is IgM, which usually reaches the peak on the 7th. However, IgG antibodies can also be detected at this time, generally 10 The highest titer was reached on the 14th. During the growth of IgG titer, the IgM titer began to decline, and it was difficult to detect it after 4 to 5 weeks of the initial antigen dose. IgM when the second reaction (recall reaction or enhanced reaction) Both IgG and IgG titers increased exponentially, but the IgG response was apparently stronger and lasted longer; the IgM titer was the same as that of the first reaction, or slightly increased. IgM cells produced poor memory, although 2 times. Antigen challenge, there is no typical recall response. Therefore, the presence of IgM helps to determine whether it is a new infection. There is evidence that IgG or IgA lymphocytes are developed from IgM or IgM/IgD lymphocyte precursors. From two delta heavy chains and two kappa or lambda light chains Monomer. In serum immunoglobulin, the content is very small, the synthesis rate is less than 1/100 of IgD. The decomposition rate of IgD is also high, and the plasma half-life is only 3 days. IgD does not bind to complement and is not sensitive to skin. Most umbilical cord and adult B cell surface have IgD, and some people think that IgD may be an early antigenic cell receptor. IgE is a macromonomer composed of two ε heavy chains and two κ or λ light chains. The serum content is minimal, the plasma half-life is the shortest, the synthesis rate is the lowest, and the decomposition rate is also the fastest among various immunoglobulins. IgE plays a major role in the immediate hypersensitivity reaction. It binds tightly to mast cells and alkalis in the Fc part. On the receptor of sex cells. The antigen (allergen) then interacts with adjacent di-IgE molecules to form an antigen bridge. The resulting local membrane changes promote media release (histamine, slow-reacting substances, acidic cell chemokines), triggering immediate hypersensitivity reactions. Allergen-specific IgE levels were increased in atopic individuals. IgE is thought to have a protective effect on parasites, but no specific data have been confirmed. [Reference] Editorial Board of Chinese Medical Encyclopedia; edited by Xie Shaowen. Encyclopedia of Chinese Medicine · Twenty-one Immunology. Shanghai: Shanghai Science and Technology Press. 1983. 7-8. Edited by Zhao Kejian. Handbook of Modern Pharmaceutical Nouns. Beijing: China Medical Science and Technology Press. 2004. pp. 273-274. Wang Xiancai's main translation; Liao Youmou, Guo Leiqi et al. Clinical Medicine Dictionary. Qingdao: Qingdao Press, 1994. pp. 1415-1419.