To investigate the role of IRG1/ITA in the pathogenesis of RA, we generated a crossbreed of TNF-Tg mice with Irg1-deficient mice and monitored four groups of mice—Irg1+/+, Irg1−/−, Irg1+/+/TNF-Tg, and Irg1−/−/TNF-Tg mice—for the incidence of arthritis, arthritis scores, and paw thickness starting at 6 weeks of age. The gene discussed is TNF; the disease is arthritic joint disease.