Preparative isolation of p67, A, B, B' and D from nRNP/Sm and Sm antigens by reverse-phase chromatography. Use in a polypeptide-specific ELISA for independent quantitation of anti-nRNP and anti-Sm antibodies.

The p67 (67 kDa) and A (33 kDa) polypeptides of nRNP/Sm antigen and the B, B' (28 and 29 kda) and D (16 kDa) polypeptides of 'free' Sm antigen were isolated and used in enzyme-linked immunoadsorbent assays (ELISA) for human autoantibodies. ELISA specificity was demonstrated using monoclonal antibodies. The ELISA using HPLC-purified polypeptides was found to be more sensitive than immunoblotting for detecting antibody. 86% of sera with precipitating anti-nRNP antibodies were positive in the ELISA, as were all sera with precipitating anti-Sm antibodies. Patients with rheumatoid arthritis (RA), Sjögrens syndrome (SS) and undifferentiated connective tissue disease (UCTD) had low levels of anti-p67 with a prevalence 11.6% and 18%, respectively, whilst patients with systemic lupus erythematosus (SLE) and mixed connective tissue disease (MCTD) had high levels and prevalence rates of 55.2% and 80%, respectively. Anti-B or anti-D antibodies were detected at high levels in SLE (prevalence 30%) but were found rarely in UCTD and MCTD (prevalence 7% and 10%) and not at all in RA or SS sera.