Extractable nuclear antigen
The six main antigens used in immunological laboratories for detection are Ro, La, Sm, RNP, Scl-70 and Jo1, which are screened for by Ouchterlony double immuno diffusion techniques and confirmed by immunoblotting.
ENAs originally referred to proteins found in a saline extract of cell nuclei. 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-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|
Reference for all values: 
- 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.
- 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.
- 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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