Antinuclear antibodies (ANA) generally refer to antibodies against various nuclear components, and are a widely existing autoantibody. The nature of ANA is mainly IgG, but also IgM and IgA, even IgD and IgE. ANA can react with nuclei from different sources without organ-specific and species-specific. ANA mainly exists in serum, but also in other body fluids such as synovial fluid, pleural effusion and urine.
ANA has a higher titer in SIE patients, but it also appears in many other autoimmune diseases. In many research reports, the detection of ANA is used as the basis for the existence of autoimmunity or even autoimmune diseases. The mechanism of this phenomenon is unclear and needs further study.
(1) Type and significance of ANA
Due to the complexity of the nuclear components, the antigenicity of different components is also different; therefore there will be many different ANAs.
1. Antinuclear protein antibody Nuclear protein antigen (DNP) consists of DNA and histones. Due to the insoluble and soluble parts of DNP antigen, the corresponding antibodies can be produced separately. Insoluble DNP antibodies are usually not completely absorbed by DNA and histones. It is a factor that forms lupus cells; soluble antigens exist in the synovial fluid of various arthritis patients, and their corresponding antibodies also appear in the synovial fluid of RA patients. .
2. Anti-DNA antibodies can be divided into two categories: â‘ anti-natural DNA (nDNA) antibodies, or anti-double-stranded DNA (dsDNA) antibodies; â‘¡ anti-denatured DNA antibodies, or anti-single-stranded DNA (ssDNA) antibodies. Anti-dsDNA antibodies have high specificity for SLE. 70% to 90% of active SLE patients have positive antibodies with high titer and are related to their condition. Anti-ssDNA antibodies can be found in many diseases and have poor specificity.
3. Anti-ENA antibody extractable nuclear antigen (ENA) is mostly extracted from animal thymus. The thymus is homogenized and the cells are broken up to separate the nucleus; after being treated with saline or phosphate buffer, it can be easily extracted from the nucleus. ENA does not contain DNA and is sensitive to ribonuclease. Recent studies have shown that ENA can be divided into dozens of types, and now only a few main types of ENA and their corresponding antibodies are introduced.
(1) Anti-PNP antibody: PNA is ribonucleoprotein, sensitive to ribonuclease and trypsin, denatured by heating for 561h. Anti-PNP antibodies are more common in mixed connective tissue diseases. Highly potent anti-PNP antibodies have diagnostic significance for mixed connective tissue diseases,
The low titer anti-PNP antibody can be found in SIE patients.
(2) Anti-Sm antibody: This antibody was first discovered in the blood of a patient with the surname Smith, and was named after the first two letters of his name. Sm antigens are non-nucleic acid glycoproteins, which are not sensitive to DNase and RNase, but can be hydrolyzed after being treated with iodate and trypsin. Anti-Sm antibody is one of the specific signs of SLE, but the positive rate is low, about 30% to 4%; it may be a recalling antibody of SIE, so it can also be detected in the inactive period. If the anti-dsDNA and anti-Sm antibodies are detected at the same time, the diagnosis rate of SLE can be improved.
(3) Anti-SS-A antibody: SS-A is the A antigen of Sjögren's syndrome (SS), which can be extracted from the cytoplasm of animal thymus. Anti-SS-A antibodies are mainly found in SS, but can also be found in other autoimmune diseases such as SLE.
(4) Anti-SS-B antibody: SS-B is SS B antigen, which can also be extracted from animal thymus or mouse hepatocyte cytoplasm, which can be destroyed by trypsin, mild heating or changing the pH of the solution. 13% of SLE and 30% of SS patients have anti-SS-B antibodies.
(5) Anti-Histone Antibody (AHA): Histone is a basic protein containing a large amount of lysine and arginine. It has been found that histone antigens can be divided into 5 subunits: H-1, H2A, H-2B, H-3, H-4. Anti-histone antibodies and anti-subunit antibodies are found in SLE and drug-induced LE. The detection rate of anti-histone subunit antibody in the serum of SLE patients is: anti-H-2B, anti-H-1, anti-H-3, anti-H-2A and anti-H-4, with anti-H-2B and anti-H -1 mainly, and related to the activity of SLE.
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