Cellular immunity to secretory IgA (as a common duct antigen of exocrine glands) in Sjögren's syndrome.

Autoimmunity to salivary duct cells has been suggested in Sjögren's symdrome (SjS). We were interested in the secretory component (SC) of secretory IgA (s-IgA) as a common duct cell antigen of systemic exocrine glands because of the possible analogy between SC in SjS and thyroglobulin in Hashimoto's thyroiditis. Therefore, we isolated s-IgA as a source of SC from human milk and investigated lymphocyte responses to s-IgA in patients with SjS. Higher mitogenic indices against s-IgA were demonstrated in SjS than in rheumatoid arthritis, other autoimmune diseases and normal persons. In addition, mitogenic indices in patients with SjS alone were significantly higher than those in SjS patients with associated diseases. These results suggest both the role of SC as a common antigen of exocrine glands in the pathology of SjS, and the presence of an etiologically different subgroup in patients with SjS.