IL18 and Arthritis: The 1,407 genes with increased expression in DA and reciprocally decreased expression in DA.F344(Cia5a) congenics included pro-inflammatory cytokines and chemokines implicated in arthritis pathogenesis such as Il1b (5.17-fold on microarray, and 2.46-fold on qPCR), Il18, Mif, Ccl2, Ccl7 and Cxcl13 (Table 3 and Additional file 1: Table S3 and Additional file 2: Table S4).