Monoclonal antibodies to the Sjögren's syndrome associated antigen SS-B (La)

The nuclear autoantigen SS-B (Sjögren's syndrome B antigen) was purified from rabbit thymus extract by immunoaffinity chromatography with human autoantibodies, and used to immunise BALB/c mice for production of monoclonal antibodies. Fusion of spleen cells from an immunised mouse with NS-1 myeloma cells resulted in the isolation of 3 clones secreting anti-SS-B antibody. Subclasses were shown to be IgG2b by immunodiffusion. Specificity of the monoclonal antibodies (MCA) was determined by ELISA and indirect immunofluorescence. By immunoblotting all 3 MCA identified a single 45 K immunoreactive polypeptide in rabbit thymus, identical with the major polypeptide recognised by human sera containing anti-SS-B. Affinity columns prepared from the 3 MCA all bound SS-B from rabbit thymus extract, without binding other nuclear antigens. Immunofluorescence studies on standard substrates showed that SS-B was located predominantly in the nucleoplasm but in cells transformed by EBV or phytohaemagglutinin more prominent nucleolar and cytoplasmic staining was seen.