Anti-DNA antibody idiotypes in primary biliary cirrhosis

A significant increase in 16/6 Id--a major cross-reactive idiotype of anti-DNA antibodies (Ab) derived from a patient with systemic lupus erythematosus (SLE) and hitherto identified in SLE patients and their relatives, was found in 16/17 patients with primary biliary cirrhosis (PBC). The increased serum level of Ab with the 16/6 idiotype (16/6 Id) in PBC patients (median 50 ng/ml) was not found in 6/7 of the patients' spouses nor among 27/28 healthy controls or most patients with other types of cirrhosis. The quantity of 16/6 Id was not correlated to either the stage of disease or the presence of antimitochondrial, antinuclear, or anti-dsDNA antibodies. However, 16/6 Id could be shown to be associated with anti-ssDNA antibodies. The high frequency of the lupus-derived 16/6 Id in PBC may accompany the polyclonal B-cell activation seen in that disease. Of 14 healthy first-degree relatives of the PBC patients, 4 (29%) also had elevated serum 16/6 Id (20-25 ng/ml) and the cluster of 3 of them in a single family may indicate a genetic predisposition to develop PBC.