Mechanisms of Disease: primary Sjögren's syndrome and the type I interferon system.

Sjögren's syndrome is a chronic autoimmune disease of largely unknown etiology and pathogenesis. The salivary and lacrimal glands are the main target organs, and key cells and molecules involved in the autoimmune process have been detected in these glands. Chemokines, expressed by epithelial cells, can attract T cells and dendritic cells that produce proinflammatory cytokines, which stimulate the immune response and induce apoptosis in the acinar and ductal epithelial cells. The autoantigens SSA and SSB are translocated to the apoptotic blebs and trigger infiltrating B cells to produce autoantibodies against SSA and SSB. Germinal-center-like structures can form within glandular lymphocyte foci, facilitating the antigen-driven B-cell activation. Many of the autoimmune mechanisms described above can be induced by type I interferon (IFN), and activation of this system in patients with Sjögren's syndrome has been described. A possible scenario is that an initial viral infection induces type I IFN production in salivary glands with a subsequent activation of the adaptive immune system. Resultant autoantibodies form nucleic-acid-containing immune complexes that can trigger prolonged type I IFN production, leading to a self-perpetuating autoimmune reaction. Several potential therapeutic targets for Sjögren's syndrome exist within the type I IFN system.