Proteomic approaches to Sjögren's syndrome: A clue to interpret the pathophysiology and organ involvement of the disease

Sjögren's syndrome (SS) is a chronic, inflammatory, autoimmune disease characterized by lymphocytic infiltration of the exocrine glands leading to qualitatively altered and diminished or absent salivary and lachrymal secretion, and by marked B-cell hyperreactivity. Many efforts have been made to define a panel of salivary and lachrymal markers helpful to design diagnostic tests able to replace blood tests and tissue biopsies for the diagnosis of primary and secondary SS. Several proteomic-based studies have indicated that a number of proteins and peptides can be considered SS biomarkers, being 2–3-fold up- or down-regulated compared to normal subject or having an exclusive presence in the saliva or tears of SS patients. Unfortunately, several factors make it difficult to define a comprehensive salivary and lachrymal panel of markers of SS, as the lack of a comprehensive proteomic analysis of human tears and saliva of healthy subjects, the lack of uniform protocols to collect and treat these samples, and the high grade of posttranslational modification of the proteins in these fluids.