CXCL8 and rheumatoid arthritis: RA synovial fibroblasts exposed to IL-40 up-regulated the secretion of IL-8 into the supernatants in a dose-dependent manner [250 ng/ml: 34.1 (11.8-62.7) pg/ml, p = 0.004; 200 ng/ml: 16.61 (9.9-51.8) pg/ml, p = 0.049; 100 ng/ml: 18.4 (7.1-41.7) pg/ml, p = ns, compared to the unstimulated control: 15.0 (2.6-24.9) pg/ml] (Figure 5A).