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antinuclear antibody
Antinuclear antibodies (ANAs, also known as antinuclear factor or ANF)〔(【引用サイトリンク】title=Medical Subject Headings (MeSH) )〕 are autoantibodies that bind to contents of the cell nucleus. In normal individuals, the immune system produces antibodies to foreign proteins (antigens) but not to human proteins (autoantigens). In some individuals, antibodies to human antigens are produced.
There are many subtypes of ANAs such as anti-Ro antibodies, anti-La antibodies, anti-Sm antibodies, anti-nRNP antibodies, anti-Scl-70 antibodies, anti-dsDNA antibodies, anti-histone antibodies, antibodies to nuclear pore complexes, anti-centromere antibodies and anti-sp100 antibodies. Each of these antibody subtypes binds to different proteins or protein complexes within the nucleus. They are found in many disorders including autoimmunity, cancer and infection, with different prevalences of antibodies depending on the condition. This allows the use of ANAs in the diagnosis of some autoimmune disorders, including systemic lupus erythematosus, Sjögren's syndrome, scleroderma, mixed connective tissue disease, polymyositis, dermatomyositis, autoimmune hepatitis and drug induced lupus.
The ANA test detects the autoantibodies present in an individual's blood serum. The common tests used for detecting and quantifying ANAs are indirect immunofluorescence and enzyme-linked immunosorbent assay (ELISA). In immunofluorescence, the level of autoantibodies is reported as a titre. This is the highest dilution of the serum at which autoantibodies are still detectable. Positive autoantibody titres at a dilution equal to or greater than 1:160 are usually considered as clinically significant. Positive titres of less than 1:160 are present in up to 20% of the healthy population, especially the elderly. Although positive titres of 1:160 or higher are strongly associated with autoimmune disorders, they are also found in 5% of healthy individuals.〔(【引用サイトリンク】url=http://www.lupus.org/webmodules/webarticlesnet/templates/new_empty.aspx?articleid=402 )〕 Autoantibody screening is useful in the diagnosis of autoimmune disorders and monitoring levels helps to predict the progression of disease.〔 A positive ANA test is seldom useful if other clinical or laboratory data supporting a diagnosis are not present.
==Immunity and autoimmunity==
The human body has many defense mechanisms against pathogens, one of which is humoral immunity. This defence mechanism produces antibodies (large glycoproteins) in response to an immune stimulus. Many cells of the immune system are required for this process, including lymphocytes (T-cells and B-cells) and antigen presenting cells. These cells coordinate an immune response upon the detection of foreign proteins (antigens), producing antibodies that bind to these antigens. In normal physiology, lymphocytes that recognise human proteins (autoantigens) either undergo programmed cell death (apoptosis) or become non-functional. This self-tolerance means that lymphocytes should not incite an immune response against human cellular antigens. Sometimes, however, this process malfunctions and antibodies are produced against human antigens, which may lead to autoimmune disease.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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