Antinuclear antibodies in systemic sclerosis

The pattern produced by indirect immunofluorescence using a HEp-2 cell substrate can reliably distinguish anti-centromere (ACA) and anti-fibrillarin (AFA) antibodies; other antibodies associated with particular disease patterns require additional methods. With the exception of ACA, all other antibodies can be identified by radio-immunoprecipitation (RIP) using a ³⁵S-Met labelled cell extract as antigen; from the resulting autoradiograph, protein complexes or individual protein antigens can be identified by molecular weight. All the antibodies with the exception of ACA, AFA and anti-ThRNP can be identified by precipitation-in-gel methods (double diffusion and counter-immunoelectrophoresis) using saline soluble cell extracts or acetone powder antigens commonly used to detect anti-ENAs. The sensitivity of these methods, particularly for detecting ARA, is lower than the radioimmunoprecipitation method and the commercially developed ELISAs that are available for ATA, U1-RNP Ro Jo-1 and the CENP B ACA protein.