CXCL8 and rheumatoid arthritis: In line with these findings, Morita et al. observed that IL-4 inhibited both secretion of proinflammatory cytokines, such as IL-1β, TNF, IL-6, and IL-8, as well as proliferation of fibroblast-like synoviocytes (FLS) obtained from synovial tissue of RA patients [123].