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Antibody introduction

Antibodies are a type of immunoglobulin that can specifically bind to antigens. Antibodies are classified into lectins, settlers, antitoxins, lysins, opsonins, neutralizing antibodies, and complement-fixing antibodies according to their reaction forms. According to the source of antibody production, it is divided into normal antibodies (natural antibodies), such as anti-A and anti-B antibodies in blood type ABO, and immune antibodies such as anti-microbial antibodies.Family Video  According to the source of the reactive antigen, it is divided into heterogeneous antibodies, heterophilic antibodies, homologous antibodies and autoantibodies. According to the aggregation state of the antigen reaction, it can be divided into complete antibody IgM and incomplete antibody IgG. Antibodies are widely used in medical practice. For example, it has a certain role in disease prevention, diagnosis and treatment. Clinically, gamma globulin is used to prevent viral hepatitis, measles, rubella, etc., and anti-Rh immunoglobulin is used internationally to prevent hemolysis caused by Rh blood group incompatibility. For diagnosis, rheumatoid factor is used for rheumatoid arthritis, antinuclear antibody (ANA), anti-DNA antibody is used for systemic lupus erythematosus, antisperm antibody is used for diagnosis of primary infertility, etc.; treatment is like toxin Anti-toxic treatment for poisoning and treatment of immunodeficiency diseases. 

Antibody naming

In the late 19th century, V on Behring and his colleague Kitasato discovered that after immunizing animals with diphtheria or tetanus toxin, a substance that neutralizes the toxin can be produced, which is called antitoxin, and then the term “antibody” is introduced. Refers to anti-toxin substances. Antibody (Ab) is a glycoprotein produced by B cell proliferation and differentiation into plasma cells after receiving antigen stimulation. It mainly exists in body fluids such as serum. It is an important effector molecule for mediating fluid immunity and can specifically bind to the corresponding antigen. Exert immune function. In 1937, Tiselius and Kabat used electrophoresis to separate serum proteins into albumin, α1, α2, β and γ globulin, and found that antibodies mainly exist in the γ region, so the antibody is also called γ globulin. Subsequently, the World Health Organization and the International Federation of Immunological Societies in 1968 and 1972 discussed and decided that globulins with antibody activity or chemical structures similar to antibodies were named as immunoglobulin (Ig). Ig can be divided into secreted Ig (secreted Ig, SIg) and membrane Ig (membrane Ig, mlg). Slg mainly exists in blood and tissue fluid, and performs various functions of antibodies; mlg mainly constitutes the antigen receptor on the surface of B cell membrane 

Antibody antibody structure

1. The heavy chain has a molecular weight of 50 000 to 75,000 and consists of 450 to 550 amino acid residues. The amino acid composition and sequence of the constant region of the heavy chain are different, and their antigenicity is also different. According to this, 12 can be divided into 5 classes, namely IgM, IgD, IgG, IgA and IgE, and their corresponding heavy  respectively. Different types of Ig have different characteristics, such as the number and position of intra-chain and inter-chain disulfide bonds, the number of structural domains, and the length of the hinge region. Even for the same type of Ig, the amino acid composition of the hinge region and the number and position of the heavy chain disulfide bonds are different. According to this, the same type of Ig can be divided into different subclasses. For example, human lgG can be divided into four subclasses, including IgG1, IgG2, IgG3, and IgG4; human IgA can be divided into two subclasses, IgAl and lgA2. 

2. The light chain has a molecular weight of approximately 25,000 and consists of 214 amino acid residues. Light chains can be divided into two types, namely kappa (κ) chain and lambda) chain. According to this, lg can be divided into two types, namely κ type and λ type. The type of the two light chains on an Ig molecule is always the same. There are both kappa and lambda types in different types of Ig. Both κ-type and-type Ig molecules can exist in the same body, and the ratio of the two types of light chains is different in different species. The  of normal human serum Ig is about 2:1, while it is 20:1 in mice. The abnormal ratio of κ to λ in lg can reflect the abnormality of the immune system. According to the difference of individual amino acids in the constant region of the λ chain, the λ chain can be divided into four subtypes:

By analyzing the amino acid sequences of different Ig heavy and light chains, it is found that about 110 amino acid sequences near the N-terminus of the heavy and light chains vary greatly, and the amino acid sequences of other parts are relatively constant. Therefore, the region near the N-terminal amino acid sequence of the Ig light chain and heavy chain with greater changes is called the variable region (V), which accounts for 1/4 and 1/2 of the heavy chain and light chain respectively; The relatively stable region of the C-terminal amino acid sequence is called the constant region (C), which accounts for 3/4 and 1/2 of the heavy chain and light chain, respectively. 

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