Use of recombinant RNP peptides 70K and A in an ELISA for measurement of antibodies in mixed connective tissue disease: a longitudinal follow up of 18 patients.

In a three year prospective study disease activity variables and levels of antibody against the RNP-peptides 70K and A were measured in 18 patients with mixed connective tissue disease. Antibody measurement entailed use of cloned autoantigens in an enzyme linked immunosorbent assay (ELISA). Fluctuations in antibody levels against 70K and A were most commonly noted in patients who also had changes in disease activity, but these changes in serology and disease activity were synchronous in only a minority of the episodes. Even major disease flares were associated with changes in anti-A levels in only a few, and with changes in anti-70K levels in none of the episodes. The data indicate that measurements of anti-70K and anti-A levels are not useful in monitoring disease activity or response to treatment in mixed connective tissue disease, and suggest that these antibody specificities do not play a direct part in the pathogenesis of disease manifestations.