IgG is an abbreviation for Immunoglobulin G . Immunoglobulins are classified into five types depending on the structure. IgG is one of human immunoglobulins, and others include lgA, lgM, IgD, and lgE.
IgG is the major antibody component of serum, accounting for approximately 75% of serum Ig. 40–50% of them are distributed in serum, and the rest are distributed in tissues.
Human IgG has four subtypes based on the difference in antigenicity of the r chain in IgG molecules: IgG1, IgG2, IgG3, IgG4.
IgG is mainly synthesized and secreted by plasma cells in the spleen and lymph nodes, and exists in a monomeric form. During the development of the body, the body’s synthesis of IgG is later than IgM, and synthesis begins in the third month after birth, and is close to the adult level at 3 to 5 years old. After the age of 40, it gradually declined.
Physiological action
The function of IgG mainly plays a protective role in the body’s immunity. Most antibacterial and antiviral drugs can cope with measles, hepatitis A, etc., and can effectively prevent the corresponding infectious diseases.
IgG is the only immunoglobulin that can pass through the placenta. The IgG from the mother plays an important role in the defense against infections such as diphtheria, measles and polio for several months after birth. The IgG delivered to the fetus by the mother is almost completely disappeared 6 months after birth, while the infant produces IgG from 3 months. It gradually increased, so it is susceptible to infection after 6 months. At the age of 3–5, it is getting closer to the adult level.
Physiological change
The IgG can be obtained from the mother before birth. During the pre-pregnancy period, the fetal blood IgG concentration is equal to the maternal blood IgG concentration. The maternal IgG is gradually reduced after birth, and the fetal blood IgG is reduced to the lowest in the third and fourth months. The fetus gradually begins to synthesize IgG, and serum IgG gradually increases to reach adult levels by the age of 16.
Age
Content
Umbilical cord
7.6～17g/L (760～1700mg/dl)
New born
7～14.8g/L (700～1480mg/dl)
0.5～6 month
3～10g/L (300～1000mg/dl)
6 months～2years
5～12g/L (500～1200mg/dl)
2～6 years
5～13g/L (500～1300mg/dl)
6～12 years
7～16.6g/L (700～1660mg/dl)
12～16 years
7～16.6g/L (700～1660mg/dl)
Adult
7～16.6g/L (700～1660mg/dl )
Single-phase immunodiffusion assay
Clinical significance
Raise
1 connective tissue disease: systemic lupus erythematosus, rheumatoid arthritis, scleroderma, Sjogren’s syndrome, Sjogren’s syndrome, and the like.
2 IgG type multiple myeloma, primary monoclonal gamma globulinemia.
3 liver disease: chronic viral active hepatitis, concealed cirrhosis, lupus-like hepatitis and the like.
4 infectious diseases: tuberculosis, leprosy, kala-azar, infectious mononucleosis, sexually transmitted diseases, lymphogranuloma, radiation sickness, malaria, trypanosomiasis, etc.
5 types of sarcoma.
Reduce
1 various congenital and acquired antibody deficiency, immunodeficiency syndrome, heavy chain disease, light chain disease, nephrotic syndrome, viral infection and administration of immunosuppressive agents.
2 non-IgG type multiple myeloma, some leukemia.
3 metabolic diseases: muscular dystrophy, hyperthyroidism
4 burns, allergic eczema, pemphigus
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