Antibodies to heterogeneous nuclear ribonucleoproteins in sera from patients with rheumatic autoimmune diseases.

Ribonucleoprotein (RNP) particles sedimenting at 40 S in sucrose gradients were prepared from calf thymus nuclei. They were identified as heterogeneous nuclear RNP (hnRNP) on the basis of size, electron microscopic examination, buoyant density, and protein electrophoretic patterns. Sera from patients with systemic lupus erythematosus, rheumatoid arthritis, and mixed connective tissue disease were found to interact with hnRNP by counter-immunoelectrophoresis and enzyme-linked immunosorbent assay (ELISA). Small nuclear RNP (snRNP) were purified by immunoaffinity using a monoclonal anti-snRNP antibody immobilized on Sepharose beads. Inhibition of the ELISA assay for snRNP with anti-hnRNP Fab fragments and cross-over experiments revealed that the autoantibodies detected in human sera recognize common epitopes present on snRNP and hnRNP.