Immunopathology of Sjögren's syndrome

Sjögren's syndrome is a chronic autoimmune disorder characterized by mononuclear cell infiltration around epithelial cells of exocrine glands. In recent years, several studies have tried to elucidate the components of the immunopathologic interaction in Sjögren's syndrome as well as the function of these components. 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 several cytokines (IL-1 beta, IL-6, NO), protooncogenes (c-myc), autoantigens (Ro, La, Fodrin) and costimulatory molecules (B71, B72). The characteristic 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 Perforin and Granzymes. Finally epithelial cells seem to exert a regenerative effort since they express trefoil proteins (pS2). The above mentioned properties give epithelial cells the leading role in the pathophysiology of the syndrome but the exact causative agent which drives the immune system towards an autoimmune reaction still remains obscure.