IgE rheumatoid factor. Occurrence and diagnostic importance in comparison with IgM rheumatoid factor and circulating immune complexes.

The sera of 80 patients suffering from rheumatoid arthritis (RA)--30 of them with extraarticular manifestations (EAM) and 50 patients with articular disease only--of 25 patients with other joint diseases and of 30 normal healthy subjects, were analyzed for the presence of 1) IgE rheumatoid factors (IgE RF) by means of a solid phase radioimmunoassay and an ELISA, 2) IgM rheumatoid factors by using solid phase radioimmune techniques, and 3) circulating immune complexes (CIC) with the C1q binding test (C1q BT) and the solid phase conglutinin binding test (SPCBT). The best technique to discriminate RA patients with EAM from RA patients without EAM and patients with other articular diseases was the determination of IgE RF (73.3%, 38.0%, 0%, resp.) compared to IgM RF (86.7%, 78.0%, and 56.0%) and CIC (C1q BT: 80.0%, 66.0% and 45.0%; SPCBT: 46.7%, 22.0%, and 20.0%). The results suggest a certain role of IgE RF for diagnosis and a possible development of extraarticular manifestations in rheumatoid arthritis.