Co-existent anti-La antibodies and rheumatoid factors bear distinct idiotypic markers.

This study describes the distribution of isotypes and idiotypes of two autoantibody populations, anti-La and rheumatoid factor, which co-exist in both the sera and saliva of patients with primary Sjögren's syndrome. The two autoantibodies are distinguished not only by their antigenic specificity but also by the nature of their idiotypic markers. IgA anti-La antibodies bearing restricted idiotypes are specifically enriched in saliva compared to serum suggesting their local synthesis. In contrast, rheumatoid factors bear cross-reactive idiotypes and may arise as a direct consequence of the secondary immune response.