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The spontaneous non obese diabetic (NOD) mouse model of Sjögren's syndrome provides a valuable tool to study the onset and progression of both autoimmune response and secretory dysfunction. Vasoactive intestinal peptide (VIP) is a neuro and immunopeptide with prosecretory effect in salivary glands and anti-inflammatory actions in various models of autoimmune disease. Our purpose was to analyze the response of peritoneal macrophages to an inflammatory stimulus during the decline of salivary secretion in NOD mice and the potential anti-inflammatory effect of VIP. We present evidence of an increased nitric oxide production by peritoneal macrophages of NOD mice in basal and lipopolysaccharide (LPS)+IFN-gamma-stimulated conditions and a lower IL-10 response to LPS compared with normal BALB/c mice. VIP inhibited LPS-induced TNF-alpha, IL-12 and nitrites accumulation in NOD macrophages while it increased IL-10 production. VIP effect was prevented by an anti-IL-10 monoclonal antibody and it showed an additive effect on exogenously added IL-10 only in NOD mice. The inhibitory effect of VIP-induced IL-10 on nitrites was mediated by COX metabolites mostly in NOD cells as indomethacine inhibited both the increase in IL-10 and the reduction of nitrites exerted by VIP. We conclude that both PGE2 and VIP inhibit nitric oxide production and increase IL-10 induced by LPS in NOD macrophages and VIP effect is mediated through an increase of COX metabolites and IL-10.

The non-obese diabetic (NOD) mouse is chosen among other experimental models to study autoimmune sialadenitis resembling Sjögren's syndrome (SS), because of its unique characteristic of developing salivary dysfunction. Based on the deep loss of nitric oxide synthase (NOS) activity in parotid glands of NOD mice observed from early stages of disease and the inhibitory effect of nitric oxide (NO) donors on amylase secretion in normal salivary glands, our goal was to investigate whether parotid glands from NOD mice lacking NOS activity presented this regulatory mechanism of amylase secretion. We found that parotid glands from NOD mice lack nitric oxide-mediated regulation of amylase secretion in response to VIP stimulation. The lack of regulation might be assigned to the loss of NOS activity as derived from the results with NOS inhibitors and increasing concentrations of VIP. These functional differences observed in NOD vs. BALB/c parotid glands occur in the absence of immune infiltrates in exocrine tissue, and it is not related to cAMP accumulation. NO-mediated regulation of amylase secretion was not observed in BALB/c submandibular glands to the same extent as described in parotid glands and was absent in submandibular glands of NOD mice.