Extractable nuclear antigen

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Extractable Nuclear Antigens are over 100 different soluble cytoplasmic and nuclear antigens. Autoantibodies to these antigens are associated with particular connective tissue disorders.

The six main antigens used in immunological laboratories for detection are Ro, La, Sm, RNP, Scl-70 and Jo1,[1] which are screened for by Ouchterlony double immuno diffusion techniques and confirmed by immunoblotting.

On anti-nuclear antibody tests, these antigens have a speckled pattern.[2]


ENAs originally referred to proteins found in a saline extract of cell nuclei[citation needed]. Its components have since been more clearly identified and in fact include many cytoplasmic molecules. The misnomer, however, has remained. These proteins are intimately associated with various RNA molecules and are thus called ribonucleoproteins, but the nomenclature used for them is often a source of confusion, Sm, Ro and La were named after the first 2 letters of the surnames of the patients in whom they were first found. Two proteins associated with Sjogren's Syndrome were independently described as antigens A and B, but are now known to be identical to Ro and La respectively. i.e. SS-A = Ro and SS-B = La.


Anti-ENA is a grouping of antibodies often used to screen for mixed connective tissue disease (MCTD), Sjögren's syndrome and systemic lupus erythematosus and commonly is composed of six tests:[3]

  • anti-Sm (for SLE)
  • anti-RNP (for MCTD)
  • anti-La (for Sjögren's)
  • anti-Ro (for Sjögren's)
  • anti-Scl70 (for Scleroderma)
  • anti-Jo (for Dermatomyositis)

Sensitivity and specificity of these tests depends on the type of assay employed, and will therefore vary by lab. The following table illustrates the sensitivity and specificity of ENA antibodies at detecting SLE with the ELISA technique.

Antibody (tested using ELISA) Sensitivity (%) for SLE Specificity (%) for SLE
Anti-Ro (SS-A) 61 80-93
Anti-La (SS-B) 27-35 88-97
Anti-Sm 34-45 88-100
Anti-RNP 39-64 84-97

Reference for all values: [4]


  1. ^ Prince HE, Hogrefe WR (1998). "Evaluation of a line immunoblot assay for detection of antibodies recognizing extractable nuclear antigens". J. Clin. Lab. Anal. 12 (5): 320–4. doi:10.1002/(SICI)1098-2825(1998)12:5<320::AID-JCLA13>3.0.CO;2-X. PMID 9773966.
  2. ^ "Immunopathology".
  3. ^ ENA test (QUANTA Lite) product sheet. inovadx.com. URL: http://www.inovadx.com/Products/di_pdfs/708555/628555rEnglish.pdf ENA. Accessed on: November 5, 2007.
  4. ^ Lock, R.J., Unsworth, D.J. Antibodies to extractable nuclear antigens. Has technological drift affected clinical interpretation? (2001) Journal of Clinical Pathology, 54 (3), pp. 187-190.

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