Inflammatory mediators in autoimmune lacrimal gland disease in MRL/Mpj mice

PURPOSE. MRL/MpJ-fas⁺/fas⁺ (MRL/+) and MRL/MpJ-fas^lpr fas^lpr (MRL/lpr) mice are congenic substrains of mice that have spontaneously developing lacrimal and salivary gland inflammation and are models for the human disorder Sjögren's syndrome. Nitric oxide (NO) and tumor necrosis factor (TNF)-α are proinflammatory and potential mediators of tissue damage. The presence of the inducible form of nitric oxide synthase (iNOS), which catalyzes the production of NO, and the presence TNF-α in the lacrimal glands of MRL/MpJ mice were assessed. METHODS. Lacrimal glands from MRL/+ and MRL/lpr mice, at ages 1 through 9 months, were evaluated by real-time RT-PCR for iNOS and TNF-α mRNA and by immunohistochemistry for the presence of iNOS and of TNF-α. Age-matched BALB/c lacrimal glands were used as the control. RESULTS. By quantitative real-time PCR (qPCR), mRNA for iNOS was detected in the lacrimal glands in significantly greater amounts in both MRL/+ (median, normalized to 18S rRNA, 2.90; P < 0.0003) and MRL/lpr mice (median 6.84, P < 0.001) than in BALB/c mice (median 0.34). By qPCR, mRNA for TNF-α in the lacrimal glands was detected in significantly greater amounts in aged MRL/+ mice than in BALB/c mice (median, normalized to actin, 221.8 vs. 77.8, P = 0.011) and in MRL/lpr mice than in BALB/c mice (median 136.7 vs. 72.5, P = 0.001). Immunohistochemistry demonstrated both iNOS and TNF-α in scattered mononuclear cells throughout the lacrimal glands and in mononuclear cells at the junction of the focal inflammatory infiltrates and normal acinar tissue in both MRL/+ and MRL/lpr niice. CONCLUSIONS. As demonstrated by the greater presence of iNOS and TNF-α in the lacrimal glands of MRL/MpJ mice than in control glands, both NO and TNF-α are potential mediators of lacrimal gland damage in these murine models of Sjögren's syndrome.