[Rheumatoid factor idiotypes in patients with Sjögren's syndrome]

Sjögren's syndrome (SS) is a systemic as well as an organ-specific autoimmune disease, characterized by multiple organ damages, autoantibody production such as rheumatoid factor (RF), and also by the development of lymphoproliferative disorders such as monoclonal gammopathy or malignant lymphoma. We produced two monoclonal anti-idotypic (ld) antibodies (A-SF 18/2 and A-AMB 1/5) against monoclonal RFs (IgA-L and IgM-K) derived from patients with SS. Expression of the cross-reactive idiotype (CRI) of these monoclonal RFs was studied in 101 patients with SS, 71 with rheumatoid arthritis (RA) without complication of SS and 93 normal subjects. The results showed the followings: (1) By the enzyme-linked immunosorbent assay (ELISA), 17.8% and 15.8% of patients with SS and 15.5% and 21.7% of patients with RA showed CRI of SF 18/2 and AMB 1/5, respectively, whereas 6.5% and 5.7% of normal subjects showed these CRIs, respectively, (2) In the SF 18/2 Id system, there was one group (45%) in SS patients who showed weak positive CRI, whereas there was no such group in the AMB 1/5 Id system, (3) Out of 15 patients with SS, there were 4 patients whose peripheral blood lymphocytes had a significant amount of surface membrane Id of SF 18/2 (9.1-37.7%), suggesting the existence of a monoclonal population in the blood. These data suggest that clones with one particular SF 18/2 Id were markedly activated in SS patients and these may be related to the monoclonal proliferation of RF Id-positive B cells in patients with SS.