Antibodies that produce speckled patterns in anti-nuclear antibody (ANA) immunofluorescent tests (IFA) are commonly directed against extractable nuclear antigens found in the cytoplasm of cultured human epithelial cells. Included in this group of ENA’s are Ribonucleoproteins (RNP), Smith (Sm), SS-A (Ro), SS-B (La), histidyl-sRNA synthetase (Jo-1) and topoisomerase (Scl70). The incidence of these antibodies varies according to the population served by a particular laboratory. When a speckled staining pattern is found, further testing is required to determine the exact antibody specificity and thereby aiding differential diagnosis.

Antibodies to Ro are often found in systemic lupus erythematosus (SLE) and Sjögren’s Syndrome (SS) patients. Anti-Ro antibodies in the mother are also strongly associated with congenital heart block. Antibodies to La are common in SS patients and also occur in SLE patients. Antibodies to Sm are present in approximately 30% of patients with SLE are widely regarded as a disease marker. Antibodies to RNP are found in 90% of mixed connective tissue disease (MCTD) patients and are normally present in high levels. They are also found to occur in 35-45% of SLE patients and occasionally in scleroderma, rheumatoid arthritis and drug induced LE patients. Anti-Jo-1 antibodies are classically found in patients with polymyositis. Anti-Scl70 antibodies are very common in patients with scleroderma.

The common method for detecting ENA antibodies is enzyme-linked immunosorbent assays (ELISA).

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