QUANTITATION OF ANTI-RNP AND ANTI-SM ANTIBODIES IN MCTD AND SLE PATIENTS BY IMMUNOBLOTTING

Abstract

A quantitative immunoblotting assay (QIBA) for the determination of specific antibody titers in human autoimmune sera is described. In this assay, a total HeLa nuclear protein fraction, immobilized on nitrocellulose blot strips, was used as source of antigens and immunoreactive species of autoantibodies were quantitated by an enzyme linked 2nd antibody procedure. Besides being more discriminative, QIBA appeared to be up to 500 times more sensitive than immunodiffusion or immunoelectrophoresis. In this study, 21 sera from patients with systemic lupus erythematosus or mixed connective tissue disease were quantitatively analyzed for their specific autoantibody content. Within this group, a very diverse spectrum of antibody populations was observed; anti-RNP sera appeared to contain, among others, high titered antibody 70 kilodalton (70K) and 31K polypeptides while all 6 anti-Sm sera recognized a 25K protein doublet. In a follow-up study of 2 mixed connective tissue disease patients, significant flares in specific antibody content could be observed.