Extractable Nuclear Antigens are soluble cytoplasmic and nuclear components that are antibody targets with over 100 different antigens described.
The main 6 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 Immuno blotting. Antibodies to these antigens have particular associations with various connective tissue disorders.
On anti-nuclear antibody tests, they have a speckled pattern.[2]
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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 stuck. 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.
ENA 4 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 four tests:[3]
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