Sjögren’s syndrome (SS) is an autoimmune disease that affects primarily the salivary and lachrymal glands, causing xerostomia and

so-called ‘Sicca syndrome’, and is categorized thus as an organ-specific autoimmune disease. The pathogenetic mechanisms consist of an autoimmune LY294002 molecular weight process leading to the progressive destruction of salivary and lachrymal glands. Therefore, symptoms of SS are chronic and sometimes irreversible. It is well known that autoimmune diseases often overlap with other collagen diseases, and this is also the case for SS. Without overlapping with any other autoimmune diseases, SS is called primary SS, while SS that overlaps with other autoimmune diseases is termed secondary SS. It has been reported that approximately half of SS cases are secondary SS [1]. SS can be seen alone (primary SS) or in association with other autoimmune rheumatic disease, especially rheumatoid arthritis (RA), systemic sclerosis (SSc) and systemic lupus erythematosus (SLE) (secondary

SS). It has not been explained clearly why SS is prone to merge with these autoimmune diseases. Although the essential mechanism of autoimmune diseases is still largely unknown, Daporinad various immune cells are suggested to be involved in their genesis. Among those immune cells, dendritic cells (DCs) have emerged recently as candidates for the master cells that elicit aberrant immune reactions in autoimmune diseases [2–7]. DCs are professional antigen-presenting cells (APCs) that have a unique capacity to prime naive T cells and induce them to develop into effector T cells. Thus, DCs are regarded as being the master regulators of adaptive immune responses. Furthermore, recent progress of DC biology has highlighted the functional plasticity of DCs; DCs can induce not only inflammatory immune responses but also peripheral tolerance, depending upon their subsets, the maturation stage of DCs and microenvironments such as cytokine milieu or stimuli [8,9]. These biological properties of DCs may lead to a

hypothesis that functional alteration of the DC system causes development of autoimmune diseases. Human peripheral blood contains Ketotifen two major subsets of DCs: CD11c+ myeloid DCs and plasmacytoid DCs [10,11]. Blood myeloid DCs are in the immature stage and seem to be en route to peripheral and lymphoid tissues; they may contribute mainly to T helper type 1 (Th1)-mediated adaptive immune responses by producing interleukin (IL)-12 in response to microbial pathogens. On the other hand, blood plasmacytoid DCs are identical to circulating natural type 1 interferon (IFN)-producing cells, which may contribute to anti-viral innate immunity. The analysis of blood DCs may provide a novel and unique perspective in dissecting the pathogenesis of autoimmune diseases. There is evidence that mature DCs infiltrated into the RA joint mediate immunopathology in RA [3,4].