Autoimmune diseases other than lupus share common anti-DNA idiotypes

We examined the sera of 170 patients with various autoimmune diseases other than systemic lupus erythematosus (SLE) for the presence of an anti-DNA antibody idiotype termed 16/6 and known to occur with high frequency in sera of patients with SLE. The idiotype was found in 6/15 sera from patients with polymyositis (49%), 3/18 with multiple sclerosis (17%), 3/18 with primary Sjögren's syndrome (18%), 9/40 with autoimmune thyroid diseases (23%), 2/35 with myasthenia gravis (6%), and 3/42 patients with rheumatoid arthritis (7%). The idiotype was not detected among 12 patients with scleroderma or 77 normal controls. The presence of the 16/6 idiotype was associated with the presence of another anti-DNA idiotype termed 134-Id. Serum samples were also tested for activity against DNA, various synthetic polynucleotides, and cardiolipin. The serum activity against these antigens was found to be polyspecific, though overlap in reaction against the various polynucleotides was not absolute. The 16/6 idiotype is thought to be coded by a germline gene. The presence of this idiotype in various autoimmune diseases points to a pathophysiologic link between the diseases.