Anti-nuclear antibodies (ANA) are an important tool for the differential diagnosis of systemic rheumatic diseases. Indirect immunofluorescence test (IFT) on eukaryotic cells like HeLa has been the established method for the detection of ANAs.
Single antibody specificities are distinguished by fluorescence patterns but more specific testing by ELISAs employing the tgarget antigens are available too for a simple and reliable differentiation of ANAs.
ANAs are especially found in active and inactive systemic lupus erythematosus (SLE), mixed connective tissue diseases (MCTD), scleroderma, Sjőgren’s syndrome, polymyositis.
Antibodies against:
- Sm (Smith antigen) are directed against core proteins (B,B’, D1-D3, E,F,G) of small nuclear ribonucleoproteins (snRNPs). Anti-Sm as well as antibodies against double stranded DNA (dsDNA) are highly specific for SLE and thus are included in diagnostic and classification criteria for SLE.
- U1 snRNP is directed to the 70 kDa protein of U1 snRNP. They are patognomic for MCTD but do also occur in SLE. A high titer of antibodies against this antigen is typical for the Sharp-Syndrome.
- snRNP/Sm are directed against Sm and U1-snRNP proteins (70 kDa, A and C). They occur in SLE, Sjogren’s syndrome, scleroderma and polymyositis.
- SS-A (Ro; soluble cytoplasmic and/or nuclear ribonucleoproteins of 52 kDa and 60 kDa) and antibodies against SS-B (La; 48 kDa protein associated with RNA polymerase III) are mainly found in high titers for primary and secondary Sjogren’s syndrome but also in SLE, congenital heartblock and neonatal lupus.
- Scl-70 are directed against DNA-topoisomerase I. They are highly specific for systemic scleroderma and give a hint for a severe course.
- CenpB (80 kDa centromere protein B) are typical for the CREST-Syndrome (69% of CREST.patients) which is a more protracted type of systemic sclerosis.
- Jo-1 are directed against histidyl-tRNA synthetase (cytoplasmic protein involved in protein biosynthesis) and are found in 20-40% of patients with polymyositis and dermatomyositis.
Method:
Immunoenzymatic method for the quantitative determination of IgG antibodies to 8 different nuclear antigens: U1-snRNP 70 kDa, SS-B, SS-A 60/52 kDa, Scl-70, Cenp-B, Jo-1, snRNP complex (snRNP/Sm), Sm (screening) in human serum, using a disposable device applied on the Chorus and Chorus TRIO instruments. The test is based on the ELISA principle (Enzyme Linked ImmunoSorbent Assay) which uses the reaction between the antibodies present in the tested sample and the immobilized antigen bound to solid phases.The immunoglobulins bind to the antigen through incubation with diluted human serum.The disposable devices contain all the reagents to perform the test when applied on the Chorus instruments. The result is expressed as an INDEX (ratio between the OD value of the sample and that of the Cut-off).
