Extractable Nuclear Antigens are over 100 different soluble cytoplasmic and nuclear antigens. Autoantibodies to these antigens are associated with particular connective tissue disorders.
Contents
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.
On anti-nuclear antibody tests, these antigens have a speckled pattern.
Terminology
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
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:
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.