Anti-nuclear antibody

Anti-nuclear antibodies (ANAs, also known as anti-nuclear factor or ANF) are antibodies directed against contents of the cell nucleus.

They are present in higher than normal numbers in autoimmune disease. The ANA test measures the pattern and amount of autoantibody which can attack the body's tissues as if they were foreign material. Autoantibodies are present in low titres in the general population, but in about 5% of the population, their concentration is increased, and about half of this 5% have an autoimmune disease.

Autoimmunity

Normal titer of ANA is 1:40. Higher titers are indicative of an autoimmune disease. The presence of ANA is indicative of lupus erythematosus (present in 80-90% of cases), though they also appear in some other auto-immune diseases such as Sjögren's syndrome (60%), rheumatoid arthritis, autoimmune hepatitis, scleroderma and polymyositis & dermatomyositis (30%), and various non-rheumatological conditions associated with tissue damage. ANA are also directed to the nuclear pore complex in primary biliary cirrhosis. Other conditions with high ANA titre include Addison disease, Idiopathic thrombocytopenic purpura (ITP), Hashimoto's, Autoimmune hemolytic anemia, Type I diabetes mellitus, Mixed connective tissue disorder.

Antinuclear antibodies

Antinuclear antibodies (ANAs) are unusual antibodies, detectable in the blood, that have the capability of binding to certain structures within the nucleus of the cells. The nucleus contains DNA, the genetic material. ANAs are found in patients whose immune system may be predisposed to cause inflammation against their own body tissues. Antibodies that are directed against one's own tissues are referred to as auto-antibodies. The propensity for the immune system to work against its own body is why ANAs indicate the possible presence of autoimmunity and provide, therefore, an indication for doctors to consider the possibility of autoimmune illness.

Following detection of a high titer of ANAs (e.g. 1:160), various subtypes are determined. This is typically done on cells of the HEp-2 cell line. Examples include:

• Anti-ENA (Extractable nuclear antigen)
  • Anti-Ro (SS-A)
  • Anti-La (SS-B)
  • Anti-Sm (Smith antigen)
  • Anti-nRNP (nuclear ribonucleoproteins)
  • Anti Scl-70 (topoisomerase I)
  • Anti-Jo
• Anti-gp-210 (nuclear pore gp-210)
  
• Anti-p62 (Nucleoporin 62)
• Anti-dsDNA (double-stranded DNA)
• Anti-centromere

History

The LE cell was discovered in bone marrow in 1948 by Hargraves et al. This was the first indication that processes affecting the cell nucleus were responsible for lupus erythematosus (LE). In the 1950s, progressively more sensitive and specific ANA serology tests became available.