Monoclonal gammopathies in Japanese patients with Sjögren's syndrome.

We report 10 Japanese patients with Sjögren's syndrome (SS) who developed monoclonal gammopathies (MG). One was of the IgG class, five of IgA, three of IgM, and one of IgG/IgM. The monoclonality of 7 of 10 M proteins was studied using antiidiotypic (Id) antibodies against M proteins. Four (three IgA and one IgM) of 10 M proteins had rheumatoid factor (RF) activity. Hemagglutination inhibition tests and enzyme-linked immunosorbent assays (ELISA) showed that the RF activity was inhibited by anti-Id antibodies in all four monoclonal RFs. In two patients examined, many cells infiltrating into the salivary glands were stained with anti-Id antibodies. Our review of 19 Japanese SS patients with MG revealed that the non-IgM class predominated (13/19). This contrasts with 19 reported non-Japanese SS patients, among whom 14 were IgM. In both Japanese and non-Japanese patients there was a higher incidence of MG in primary than in secondary SS. The difference in the dominant heavy-chain class may reflect a difference in the genetic factors affecting B cell differentiation in immunologically disordered states.