Sjögren's syndrome. Autoimmune epithelitis.

Sjögren's syndrome is a chronic autoimmune disorder characterized by mononuclear cell infiltration proximally to epithelial cells of exocrine glands. In recent years, several studies have tried to address the function of the components of the immunopathologic lesion in Sjögren's syndrome. The majority of the mononuclear infiltrating cells are CD4 positive T lymphocytes (60-70%) whereas B cells constitute one fourth of the infiltrating cells. Macrophages and natural killer cells are poorly represented in the lesion. Epithelial cells of minor salivary glands of patients with Sjögren's syndrome express proinflammatory cytokines (IL-1 beta, IL-6), protooncogenes (c-myc) and costimulatory molecules (B71, B72). The destruction of epithelial cells of Sjögren's syndrome patients is probably due to activation of several apoptotic pathways since epithelial cells express different apoptosis related molecules such as Fas, FasL, Bax, while mononuclear cells express Bcl-2, Perforin and Granzymes. Finally epithelial cells seem to exert a regenerative effort since they express trefoil proteins (pS2). The above properties give epithelial cells a significant role in the pathophysiology of the syndrome but the exact events which drive the immune system towards an autoimmune reaction remain obscure.