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H. L. Rosenzweig, T. M. Martin, S. R. Planck, M. M. Jann, K. Galster, M. P. Davey, J. T. Rosenbaum; NOD2 Mediates MDP-Induced Inflammation Independently of IL-1β in a Mouse Eye Model of Uveitis. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1997. doi: https://doi.org/.
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As part of the innate immune system, NOD2 plays an important role in responses to intracellular bacteria. NOD2 has evolved to specifically sense muramyl dipeptide (MDP), a component of bacterial cell walls. Notably, mutations in the gene NOD2 cause Blau syndrome/Jabs disease (autosomal dominant form of uveitis, arthritis and dermatitis), and distinct polymorphisms are linked to Crohn’s disease. Here we sought to test the role of NOD2 in IL-1β production and whether IL-1β contributes MDP-induced uveitis in mice.
Female, BALB/c mice or mice deficient for NOD2, IL-1-receptor-1 (IL-1R1) or caspase-1 and their wild-type controls were treated with an intravitreous injection of 100 µg MDP, 80 ng of recombinant mouse IL-1β or saline. The intravascular inflammatory response within the iris was assessed by intravital microscopy at 6 hours following treatment and the numbers of rolling, adherent and infiltrating cells within the iris were quantified. IL-1β and IL-1-receptor-antagonist (IL-1RA) were measured by ELISA.
We recently described a mouse model of MDP-induced uveitis, wherein mice treated with an ocular injection of MDP develop inflammation in a NOD2-dependent fashion. Here, we measured IL-1β production in response to MDP treatment and found that IL-1β was significantly increased in the eye and that NOD2 was necessary for IL-1β production. MDP-induced IL-1β production in the eye was impaired in caspase-1 knockout mice. This indicates that MDP-induced IL-1β production requires both NOD2 as well as caspase-1, a component of the inflammasome. Unexpectedly, IL-1β does not appear to be a predominant mediator of MDP-induced uveitis, as deletion of either IL-1R1 or caspase-1 had no impact on the intravascular inflammatory response to MDP as measured by intravitral quantification of leukocyte rolling and sticking. Moreover, both control and NOD2 knockout mice were capable of triggering an intravascular inflammatory response to treatment with a high dose of IL-1β. Assessment of ocular IL-1RA levels revealed that IL-1RA was present at concentration greater than 10-fold that of IL-1β in the eye in response to MDP. This suggests that IL-1RA may be a regulator of intraocular inflammation and explain why IL-1β is not critical in MDP-induced uveitis.
Our studies shed light onto the role of NOD2 as a key regulator of IL-1β production. Despite clinical similarities with other NLR-associated autoinflammatory diseases, NOD2 may contribute to inflammation as in the case of Blau syndrome, in an IL-1β-independent mechanism.
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