Sjögren's syndrome salivary gland immunopathology: increased laminin expression precedes lymphocytic infiltration

Previous studies have demonstrated increased expression of a laminin-like protein in labial salivary glands from Sjögren's syndrome (SS) patients. The objective of the present study was to verify the identity of this protein and to compare lymphocytic infiltration and laminin expression in minor salivary gland ductal epithelium. This was carried out by comparing laminin protein and laminin mRNA expression in 13 SS patients, 11 normal controls, and 12 patients with non-specific sialoadenitis. Laminin protein and laminin mRNA expression was determined using immunoperoxidase (IP) and in situ hybridization (ISH) techniques, respectively. In addition, the relationship between lymphocytic infiltration and laminin expression was evaluated on adjacent serial salivary gland sections from SS patients, using routine histological methods and IP immunohistochemistry. Biopsies from SS patients showed significant increases in staining for both laminin protein and laminin mRNA compared to normal controls. On seven of the eight SS samples that showed significant laminin protein staining, the ductal epithelial staining occurred in the absence of periductal lymphocytic foci. Results of the ISH assay strongly suggest that the increased expression of the laminin-like protein is laminin, since the cDNA probe was specific for the B1 chain of laminin. In addition, this increased expression in ductal epithelial cells occurs without significant lymphocytic infiltration. These studies provide further evidence that altered laminin expression is an early event associated with salivary gland pathology in SS, since these data demonstrate a potential pathologic event prior to the arrival of lymphocytes. Further studies are underway to examine the relationship between laminin and lymphocytic infiltration in salivary gland pathology.