Autoantibodies and their target antigens in Sjögren's syndrome

The subject of this review is the humoral autoimmune response in Sjögren's syndrome. Autoantibodies in this disease are primarily directed against the Ro/SS-A and La/SS-B autoantigens and against IgG (rheumatoid factor). The Ro/SS-A and La/SS-B autoantigens consist of a number of antigenic proteins coupled to small RNA molecules. These RNA-protein particles are present in all human cells and are strongly conserved throughout various species. Anti-Ro/SS-A and anti-La/SS-B autoantibodies can be detected using counter-immunoelectrophoresis, immunoblotting technique, ELISA or RNA precipitation assays. The preferred method of screening for anti-Ro/SS-A antibodies in human sera is counter-immunoelectrophoresis; anti-La/SS-B antibodies are best detected with the immunoblotting technique. Anti-Ro/SS-A antibodies are found in 60% of patients with Sjögren's syndrome, but are not specific markers for this disease. Anti-La/SS-B antibodies are present in approximately 40% of patients with Sjögren's syndrome; the only other disease where the antibody has been detected is systemic lupus erythematosus (15% positive). The origin and possible pathogenetic role of autoantibodies in Sjögren's syndrome is still unclear. Our view is that the current evidence supports a mechanism whereby autoantibodies are the product of an oligoclonal B-cell proliferation. The only instance where autoantibodies probably play a direct pathogenetic role is the occurrence of congenital heart block in the offspring of anti-Ro/SS-A and anti-La/SS-B positive mothers.