CIA-induced arthritis resulted in increased proportions of IL-18R1+ on these cells in WT mice compared to the proportions in IL-18Rα KO mice: CD4+ T cells, 2.4 ± 0.1 vs. 0.0 ± 0.0; F4/80+ cells, 0.2 ± 0.0 vs. 0.0 ± 0.0; CD11b+ cells, 1.7 ± 0.2 vs. 0.0 ± 0.0; and F4/80+CD11b+ cells, 0.1 ± 0.0 vs. 0.0 ± 0.0, respectively. This evidence concerns the gene IL18R1 and arthritic joint disease.