Crucial Role of Tissue-specific Apoptosis on the Development of Primary Sjögren's Syndrome

AbstractPrimary Sjögren's syndrome is an autoimmune disorder characterized by lymphocytic infiltrates and destruction of the salivary and lacrimal glands, and systemic production of autoantibodies to the ribonucleoprotein (RNP) particles SS-A/Ro and SS-B/La, leading to clinical symptoms of dryness of the mouth and eyes (sicca syndrome). Autoreactive T cells bearing the CD4 molecule may recognize an unknown self antigen, triggering autoimmunity in the salivary and lacrimal glands. Although several candidate autoamigens including α fodrin have been reported in Sjögren's syndrome, the pathogenic roles of the autoantigens in initiation and progression of SS are still unclear. It is possible that individual T cells activated by an appropriate self antigen can proliferate and form a restricted clone. Recent evidence suggests that the apoptotic pathway plays a central role in making T cells tolerant to tissue-specific self antigen, and may drive the autoimmune phenomenon. We recently reported that tissue-specific apoptosis in estrogen-deficient mice may contribute to autoantigen cleavage, leading to the development of autoimmune exocrinopathy. The studies reviewed imply that tissue-specific apoptosis and caspase-mediated α fodrin proteolysis are involved in the progression of autoimmune lesions in Sjögren's syndrome. Moreover, Fas ligand (FasL) and its receptor Fas are essential in the homeostasis of the peripheral immune system. It is considered that a defect in activation-induced cell death (AICD) of effector T cells may result in the development of autoimmune exocrinopathy in Sjögren's syndrome