A rheumatic disorders constitute a diverse those of patients with rheumatoid arthritis (RA) and SS has shown similarities and differences. Consequently, group of illnesses with significant clinical and immunological variability. Their clinical presentation and the terms ‘primary’and ‘secondary’SS were proposed for the former and the latter groups of patients. course vary, ranging from subclinical and mild to severe and life-threatening, and from slow and indolent Compared to patients with secondary SS, patients with primary SS present significantly more often parotid to acute and catastrophic. Some of these disorders can be manifested simultaneously in the same individual gland enlargement and systemic manifestations, such as Raynaud’s phenomenon, lymphadenopathy, splenoor, alternatively, one nosological entity may evolve into another. For instance, Sjögren’s syndrome (SS) megaly, purpura and renal tubular acidosis. In addition, primary SS, but not secondary SS, is characterized frequently co-exists with various other rheumatic conditions, whereasapatientwithanorgan-specificdisease by the occurrence of serum autoantibodies against Ro (SSA)(in 60%) and La (SSB)(in 40%) ribonucleo-(eg myasthenia gravis or thyroiditis) can progress to a systemic autoimmune disorder, such as systemic proteins, andisassociatedwithdistinctHLAhaplotypes [5, 6]. Although the incidence, clinical expression and lupus erythematosus (SLE) or SS. A multi-faceted activation of the immune system occurs in these dis- serology of SS in various autoimmune diseases have been evaluated [7], comparative studies of well-defined orders, as illustrated by the presence of autoantibodies directed against one or multiple autoantigens and/or groups of patients with SS co-expressed with autoimmune rheumatic diseases other than RA have never mononuclear inflammatory infiltrates in the affected tissues. The interplay of genetic factor (s) and environ- been performed. Despite this fact, during the present decade, the term ‘secondary SS’has been arbitrarily mental agent (s) is thought to account for the development and clinical course of these diseases. The nature granted to SS occurring in patients with any autoimmune disorder [3]. of such factors, however, remains obscure, whereas the implication of microorganisms has been speculative Today, 20 yr after the original classification, clinical, histopathological and serological evidence implies the for the last three decades [1]. In an effort to establish an avenue of communication existence of at least two additional SS groups.