Immunoglobulin (Ig) is a type of immunoglobulin widely present in mammalian serum, lymphatic fluid, tissue fluid, and exocrine fluid, which has antibody activity or a chemical structure similar to antibodies. It plays an important role in the body's defense against diseases, as well as in disease research, drug development, and vaccine evaluation. Antibody (Ab) is an immunoglobulin secreted by B cells after receiving antigen stimulation, which has immune function and can specifically bind to antigens. Therefore, all antibodies are immunoglobulins, and not all immunoglobulins are antibodies. Ig molecules are composed of two identical light chains (L chains) and two identical heavy chains (H chains). The L and H chains are connected by disulfide bonds to form a tetrapeptide molecule, known as the monomer of Ig molecules, which is the basic structure of immunoglobulin molecules. Immunoglobulin is classified into five types based on the different structures of the H chain constant region: IgG, IgA, IgM, IgD, and IgE.

IgG: The main component of serum immunoglobulin, accounting for approximately 75% of the total immunoglobulin. It is mainly synthesized and secreted by plasma cells in the spleen and lymph nodes, and exists in monomeric form. During individual development, the age at which the body synthesizes IgG is later than that of IgM, which plays a protective role in the body's immunity and responds to most antibacterial and antiviral agents; Measles, hepatitis A, etc. can effectively prevent the corresponding infectious diseases. IgG is an immunoglobulin that can pass through the placenta. It begins to be synthesized in the third month after birth, approaches adult levels at 3-5 years old, and gradually decreases after 40 years old.

Clinical significance of IgG

Significance of elevation:

①Connective tissue diseases: systemic lupus erythematosus, rheumatoid arthritis, scleroderma, etc;

②IgG type multiple myeloma and primary monoclonal gammaglobulinemia;

③Liver diseases: chronic viral active hepatitis, occult cirrhosis, lupus like hepatitis, etc;

④Infectious diseases: tuberculosis, leprosy, black fever, etc;

⑤Sarcoma like disease.

Reduced significance:

①Various congenital and acquired antibody deficiencies, immunodeficiency syndromes;

②Metabolic disorders: muscular dystrophy, hyperthyroidism;

③Burns, allergic eczema, pemphigus vulgaris, etc;

Approximately 5% -10% of the total serum immunoglobulin, monomeric IgM is expressed on the cell surface in membrane-bound form (mIgM), forming the B cell antigen receptor (BCR). Secreted IgM is a pentamer, which is the largest molecular weight Ig, called macroglobulin. It mainly exists in the blood and is the earliest antibody to appear in the initial humoral immune response. The detection of IgM in serum indicates a recent infection and can be used for early diagnosis of infection.

Clinical significance of IgM

Elevated: fetal intrauterine infection, chronic or subacute infection, malaria, mycoplasma pneumonia, macroglobulinemia, etc;

Reduction: Hereditary or acquired antibody deficiency, mixed immunodeficiency syndrome, selective IgM deficiency, protein loss bowel disease, burns, immunosuppressive therapy, etc.

The content of IgA in normal human serum is second only to IgG, accounting for 10-20% of the serum immunoglobulin content. There are two types: serotype and secretory type, but serotype IgA does not show significant immune function in serum. Secretory IgA is the main antibody for local anti infective immunity in the body's mucous membranes. It mainly exists in secretions such as saliva, tears, colostrum, nasal and bronchial secretions, gastrointestinal fluids, urine, sweat, etc. IgA cannot pass through the placenta. There is no IgA in the serum of newborns, but secretory IgA can be obtained from breast milk. IgA begins to appear in the blood after 4-6 months of birth. It can initiate an immune response on its own and produce secreted antibodies, namely SIgA.

Clinical significance of IgA

Elevated: Related to severe infections and autoimmune diseases, especially the inflammatory process of the liver, which can increase serum IgA levels;

Reduction: In primary and secondary immunodeficiency syndrome, protein loss from the intestine and through burned skin can also cause a decrease in IgA concentration.

IgE：A secreted immunoglobulin that is the main antibody causing type I hypersensitivity reactions and has immune function that can bind to mast cells and eosinophils. Among the five immunoglobulins, IgE has the shortest half-life, the highest degradation rate, and the lowest synthesis rate, resulting in the lowest serum content.

Elevated: IgE levels in the serum are too high, often indicating a genetic predisposition to allergies or the presence of type I hypersensitivity reactions.

Decrease: The decrease in serum IgE levels is generally caused by ataxia telangiectasia, severe composite immune dysfunction, chronic lymphocytic leukemia, silicosis, and asbestosis.

IgD：The content in serum is very low, accounting for about 1% of the total Ig, and the individual differences in content are significant. It can exist as a membrane receptor on the surface of B cells. Some studies have suggested that IgD may be involved in initiating B cell antibody production and may also be related to certain hypersensitivity reactions, but functional research is still unclear.

The content in serum is very low, accounting for about 1% of the total Ig, and the individual differences in content are significant. It can exist as a membrane receptor on the surface of B cells. Some studies have suggested that IgD may be involved in initiating B cell antibody production and may also be related to certain hypersensitivity reactions, but functional research is still unclear.

The above article is excerpted from the internet

All articles reposted on this website are for the purpose of conveying more information. Media or individuals who do not wish to be reposted can contact us and we will immediately delete them. All articles only represent the author's viewpoint and do not represent our company's position.