Extractable nuclear antigen

small nuclear ribonucleoprotein (snRNPS). The location in the nucleus and association with spliceosomes or nucleosomes results in these ENAs being associated with additional RNA and proteins such as polymerases. This quality of ENAs often makes it difficult to purify and quantify their presence for clinical use.^[1]

Autoantibodies to these antigens are associated with particular connective tissue disorders. Indeed, in 84.3% of positive anti-ENA samples, ANA reagents were also found.^[1] The use of anti-ENA autoantibody tests can serve as additional verification of an autoimmune disorder, because a positive ANA test alone does not suffice for diagnosis. In fact, low levels of ANAs can be found in healthy patients. The applications of anti-ENA testing varies from excluding patient groups from specific groups, connective tissue diseases, and to monitor disease activity. In essence, it allows clinicians to exclude specific autoimmune disorders if a particular autoantibody is not present, and allows clinicians to track progression of a disease if the levels of these autoantibodies increase or decrease. To confirm the presence of anti-ENAs, it is currently recommended to use two or more methods to confirm anti-ENAs to avoid false positives. The diagnosis of autoimmune connective tissue diseases (CTDs) is done through analysis of clinical symptoms and signs, but also through the identification of the autoantibodies directed against nuclear antigens. A 2002 paper also seeks to compare the diagnostic tests used in immunology laboratories to measure anti-ENAs and ways to improve this testing and reporting. Double immunodiffusion (DID) and counterimmunoelectrophoresis (CIEP), two forms of gel-based techniques, are used to gain information on the clinical significance and the role of these antibodies in those with CTDs.^[2]

Systemic lupus erythematous (SLE), only 8–40% have detectable anti-SM when using gel-based assays. CIEP has been shown to be more sensitive than DID.^[5]

Enzyme linked immunosorbent assay (ELISA) has become the most widely used technique for testing for anti-ENAs due to them being simple to perform, quantitative, and high volume output. While this method has increased assay sensitivity and is efficient for high volume labs, they have a much lower disease specificity than alternative techniques. This is due to the inability to properly isolate the ENAs without large costs due to their association with complexes in the nucleus of the cell. Another worry with the ELISA technique is that anti-Sm antibodies have been reported in patients without SLE which would lead to over-investigating, but could be due to the quality of the antigen source used.^[5] Western blotting has a major disadvantage in that antibodies targeted against conformational epitopes can not be detected. On top of that, false positive can occur and the disease specificity is lower than other techniques. While each technique has their advantages and disadvantages, ELISA has the least severe disadvantages of potential for false positives (which are less dangerous than false negatives) and expensive.^[5]

anti-nuclear antibody tests, these antigens have a speckled pattern.^[8]

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 Sjögren syndrome

systemic lupus erythematosus and commonly is composed of six tests:^[10]