The presence of citrulline in salivary glands is evidence that nitric oxide is mediator of inflammation in Sjögren acinar epithelia

Aim: The present study addresses the question whether nitric oxide (NO) plays a role in inflammation of salivary glands in Sjögren's syndrome. Methods: The expression of inducible nitric oxide synthase (iNOS) and the presence of citrulline, as a monitor of NO activity were studied by immunohistochemistry, in minor salivary glands from 24 patients with primary Sjögren syndrome. An equal number of control tissues were included. The presence of mRNA of eNOS (endothelial NOS) and iNOS in tissues was studied by fluorescent in situ hybridization. Results: All salivary glands displayed eNOS along the ductal epithelia, blood vessels and acini. In Sjögren disease iNOS enzyme was widely expressed along ductal epithelia, acini and in foci of lymphocyte infiltration; therefore by the extensive citrulline presence and iNOS, we infer that NO is related to inflammation. Control biopsies were negative for iNOS and citrulline. Conclusion: The present data suggest that local production of NO should contribute to salivary gland inflammation in Sjögren disease.