Globulin is a kind of proteinserum albumin, has immune effect.When the human immune system encounters foreign invaders, it will produce different amounts of globulin according to the characteristics of the invaders. If the invaders are difficult to eliminate, it will stimulate the lymphatic system to produce more globulin until the invaders are eliminated.[1]
Chinese name
Globulin[2]
Classification:
IgG、IgM、IgA、IgD、IgE[2]
Normal value
20-35 g/L (the normal values of different kits and laboratories are different)[1]
Features
Specific recognition and binding of antigens, activation of complements, binding of Fc receptors, across placenta and mucosa[2]
X-ray crystal diffraction structure analysis showed that the basic structure of globulin was a monomer composed of four symmetrical polypeptide chains connected by disulfide bonds.Two chains with large molecular weight are called heavy chains.Two chains with smaller molecular weight are called light chains.[2]
1. Heavy chain and light chain
Globulin heavy chain,H chain) is composed of 450~550 amino acid residues, with a molecular weight of 55~75 kDa.According to the difference in antigenicity of constant region of heavy chain Ig, it can be divided into five categories, namely IgGIgM、IgA、IgD、lgE，The corresponding heavy chains are called γμ. α, δ and ε chains.All kinds of Igs can beAmino acid residueThe composition, disulfide bond number and position are different, which can be divided into different subclasses.[2]
Light chain,L chain) usually contains 214 amino acid residues, with a molecular weight of about 25 kDa.According to the different antigenicity of light chainλ two types.The light chains of all kinds of Igs have κ and λ types (the κ: λ of normal human serum Ig is about 2:1).In the same type of Ig, it can be divided into different subtypes according to the difference in the N-terminal amino acid sequence of the light chain C region.In natural Ig monomer, the two heavy chains have the same type, and the two light chains have the same type.[2]
2. Variable area and constant area
The sequence of about 110 amino acids near the amino terminal (N-terminal) of the heavy chain and light chain of globulin varies greatly, called variable re gion,V zone), accounting for 1/4 (or 1/5) and 1/2 of heavy chain and light chain respectively.The H chain and L chain of this region each have three amino acids in composition and sequence.[2]
Globulin
The part with the most severe changes is called hypervariable region,HVR），They are HVR1~HVR3. Because this region is the complementary binding site of Ig and antigen epitopes, it is called the complementary determination region,CDR）。Ig synthesized by different B cell clones in the same body is different in this region, so it is also called idiotype of antibody.The amino acid composition and arrangement order of the V region outside this region are relatively difficult to change, which is called the skeleton region (FR).[2]
The amino acid sequence near the carboxyl end (C end) of heavy chain and light chain is relatively constant, which is called constant region,Zone C), accounting for 3/4 (or 4/5) and 1/2 of heavy chain and light chain respectively.The Ig of different species and individuals will be different in this area, which is manifested in the clinical injection of xenogenic or xenogenic Ig can also cause allergic reactions.[2]
3. Hinge area
The hinge area is located between CH1 and CH2, which is sensitive to protease and easy to be hydrolyzed.It is rich in proline, so it is easy to stretch and bend, which is conducive to the simultaneous binding of both arms to two antigen epitopes at different distances.[2]
Other components of globulin
Joining chain is rich inCysteineThe polypeptide chain of Ig is synthesized by plasma cells. Its main function is to connect Ig monomer to dimer or polymer at the carboxyl end of the H chain, stabilize the structure of the polymer and participate in the operation in the body.[2]
Secretory piece,SP) is a sugar containing peptide chain, which is synthesized and secreted by mucosal epithelial cells, and is bound to IgA dimer in the form of non covalent bond, making itSecretory IgA（SlgA）。The main role of SP is to protect SlgA against the degradation of protease in exocrine fluid and to mediate the active transport of poly lgA to the supradermal mucosa.[2]
Globulin hydrolysate tabletparagraph
Globulin
PapainThe site where lgG is hydrolyzed is near the N end of two heavy chains connected by disulfide bonds in the hinge area, which splits Ig into two identical antigen binding fragments,Fab segment) and a crystalline fragment,Fc).One Fab segment is univalent and can specifically bind to the antigen without agglutination and precipitation.Fc segment has no antigen binding activity and is the site where Ig interacts with effector molecules or cells.[2]
Pepsin hydrolyzes IgG at the near C end of the two heavy chains connected by disulfide bonds in the hinge region, and after hydrolysis, a F (ab ') that is bivalent with antigen is obtainedtwoSegment and some small segments (pFc ').F(ab')twoThe segment is composed of two Fab segments and hinge regions. It is bivalent and can combine two epitopes at the same time, so it can form agglutination reaction and precipitation reaction.PFc 'was finally degraded and had no biological activity.[2]
Enzymatic hydrolysis of lg is conducive to elucidating the structure andbiological activityIt is also conducive to the production and purification of biological products, such asRefined tetanus antitoxinThe application of this method has greatly reduced the incidence of hypersensitivity reaction.[2]
classification
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Globulins can be divided into a1A2, β and r
1. When the liver is inflamed,The increase of a1 globulin, while the increase of a1 indicates that the disease is mild, and if it is reduced, it usually indicates that the disease is severe.Therefore, the determination of a1 globulin has reference value in judging the severity and prognosis of hepatitis patients.
2、A2 globulin can also reflect the severity of hepatitis.In the initial stage of viral hepatitis, most of them remained normal, and then gradually increased.In the case of severe hepatitis, if a2 globulin is reduced to less than 0.4 g%, it indicates that the patient is about to or has had a liver coma.In case of liver cancer,A2 globulin tends to increase.A2 contains lipoproteins. In case of cholestasis, especially in chronic cases, when blood lipids increase,A2 globulin increased accordingly.In decompensated cirrhosis,A2 globulin mostly decreased.
3、β - globulin is mostly increased in cholestatic liver disease.When hepatocytes are severely damaged, due to the decrease of liver synthesis,β - globulin decreased to less than 6% in some cases.
4、R-globulin is increased in almost all hepatobiliary diseases.In case of viral hepatitis,R-globulin is moderately elevated and is expected to recover within 2-3 months.If the r-globulin continues to increase without other reasons to explain, it often means that the disease has poor prognosis and has turned to chronic hepatitis or cirrhosis.In severe hepatitis,R-globulin can be significantly increased, even up to 2.5 g% - 3 g%.If the r-globulin increases to more than twice the normal value, and the aminotransferase is more than 5 times the normal value, and there is no improvement for 10 weeks, it can be confirmed as subacute severe hepatitis. If not treated, the prognosis is dangerous.In chronic hepatitis,The average value of r-globulin varies with disease type.The r-globulin in cirrhosis is generally increased, especially in advanced or progressive decompensated cirrhosis,R-globulin can be extremely high.
Reasons for high
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Globulin is produced by the immune organs of the body, and most of the globulin is generated outside the liver cells, which is related to the immunity of the human body.The normal value of globulin is 20-30 g/L. The high globulin is usually due to the infection of the body by foreign viruses, and the immune system will fight against foreign viruses, leading to the increase of globulin.
1. When the liver is inflamed,α 1 globulin will increase, indicating that the condition is mild;
2、β - globulin may increase in cholestatic liver disease;
3、Gamma globulin increases in almost all hepatobiliary diseases. If gamma globulin continues to rise without other reasons, it often means that the disease has worsened and has turned into chronic hepatitis or cirrhosis;In severe hepatitis,Gamma globulin may increase significantly
4、α 2-globulin can reflect the severity of hepatitis disease. In the early stage of viral hepatitis,The majority of α 2-globulin remains normal, and will gradually increase with the development of the disease.When liver cancer, cholestasis and blood lipids increase,α 2 will increase accordingly.
