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LD Hazlett, X Huang, XL Rudner, RP Barrett, SM McClellan; IL-18 Contributes to Host Resistance Against Infection with P. aeruginosa Through Induction of IFN-gamma and TNF-alpha Production . Invest. Ophthalmol. Vis. Sci. 2002;43(13):941.
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Purpose: Pseudomonas aeruginosa (P. aeruginosa) keratitis develops rapidly, destroying the cornea in susceptible (B6) but not resistant (BALB/c) mice. Mechanisms contributing to development of the resistance response, particulary the roles of IL-18 and IFN-gamma remain untested. Thus, we conducted a series of studies in BALB/c mice to determine their roles in this response. Methods: RT-PCR analysis, mAb neutralization, and IFN-gamma knockout (-/-) mice were used. Results: RT-PCR analysis detected constitutive expression of IL-18 mRNA in cornea and at 1-7 days p.i., levels were elevated significantly. Corneal IFN-gamma mRNA levels also were significantly increased at 3-7 days p.i. Treatment with IL-18 mAb decreased corneal IFN-gamma mRNA levels, while bacterial load and disease increased/worsened, compared with IgG-treated mice. To more stringently examine the role of IFN-gamma in bacterial killing, -/- vs. wild type (wt) mice were tested. All corneas perforated and bacterial load was increased significantly in -/- vs. wt mice at 5 days p.i. Because disease severity was increased in IFN-gamma -/- vs. IL-18 neutralized mice, and since IL-18 also induces production of TNF, we tested for TNF-alpha in cornea in IFN-gamma -/- and IL-18 neutralized mice. ELISA analysis demonstrated significantly elevated corneal TNF-alpha protein levels in IFN-gamma -/- vs. wt mice at 3 and 5 days p.i. In contrast, in the IL-18 neutralized mice, RT-PCR revealed decreased TNF-alpha mRNA expression at similar times. Conclusion: These data provide evidence that in BALB/c cornea, IL-18 contributes to host resistance by induction of IFN-gamma and TNF-alpha production and that both cytokines are required for bacterial killing. The data from the IFN-gammma -/- study also suggest that TNF-alpha, without IFN-gamma is insufficient for bacterial killing. Support: NIH RO1EY02986 and P30EY04068.
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