Rheumatoid diseases are mainly associated with the occurrence of anti-nuclear antibodies (ANA). Some of these ANA are disease-specific and therefore can bes used as serological markers in the diagnosis. They include antibodies against:

• Double-stranded DNA (ds-DNA) and the Sm antigen in Systemic Lupus Erythematodes (SLE)
• Fibrillarin in scleroderma and Scl-70 (Topoisomerase I) are associated with diffuse scleroderma
• Centromere (ACA) for CREST syndrome
• Histidyl-tRNA-Synthetase (Jo-1) in polymyositis
• PM-Scl in polymyositis and scleroderma overlap syndromes

ANA with different prevalence are found in several diseases, including

• anti-Histone in SLE, drug-induced Lupus and nutritive toxic chronic liver diseases;
• anti-RNP in SLE and mixed connective tissue disease (Sharp Syndrome) and
• anti-SS-A (Ro) and anti-SS-B (La) associated with SLE and Sjögren Syndrome (1,2).

Antimitochondrial antibodies (AMA) against the M2 epitope typically react with mitochondrial proteins of the a-keto acid-dehydrogenase complexes and are characteristic markers for primary biliar cirrhosis (PBC), which is a chronic cholestatic liver disease.

The earliest developed method for the detection of ANA and AMA has been the Immunofluorescence test (IFT) utilizing cryostatic tissue sections or cells as substrate.

An important criteria for the selection of the appropriate substrates is the species specificity of relevant antibodies. For some human antibodies it has been demonstrated that they only react with tissue substrates of human or primate origin, whereas other types of autoantibodies also react on tissue sections from rat, mice, rabbit or guinea pig. This indicates that the respective antigens are distinguishable with respect to their phylogenetic development and only those antigens that remained mostly conserved during evolution can be found in species of less close relationship.

Utilization of HEp2 cells, a human Larynx Epithelioma cell line with high specificity for most of the human ANA and ENA antibodies, circumvents the disadvantage and limitation of substrates of animal origin that are not suitable for the detection of several autoantibody specificities.