CIA affects the expression levels of IL-18 and IL-18Rα in the mouse synovium and lymph node (LN) cells. In the basic research, wild-type (WT) mice were immunized subcutaneously at the base of the tail with collagen type II and Freund’s adjuvant and injected intraperitoneally with 50 μg of lipopolysaccharide (LPS) and sacrificed on days 2 (n = 6), 4 (n = 6), and 14 (n = 6). The gene expressions of IL-18 (A) and IL-18Rα (B) in the synovium were measured by real-time PCR. In each experiment, the expression levels were normalized to the expression of 18SrRNA and are expressed relative to the values of saline-treated control mice. The data are the mean fold-increase and mean ± SEM: * p < 0.05, the WT mice after LPS injection at day 2 and 14 (n = 4 and n = 6) vs. day 4 (n = 4) after the LPS injection. The percentage of IL-18R1+ cells in CD4+ T cells, F4/80+, CD11b+ and F4/80+CD11b+ cells was measured by FACS analysis of LN cells on day 4 (C). The data are the mean ± SEM: ** p < 0.01, *** p < 0.005, and **** p < 0.001, WT vs. IL-18Rα KO mice on day 4 after the LPS injection (n = 10 and n = 15).