IL1B and rheumatoid arthritis: Circulating monocytes from RA patients produce elevated levels of IL-1β and IL-6 upon in vitro stimulation (69), IL-6 contributes to joint destruction (70), while IL-1β promotes osteoclastogenesis, induces matrix metalloproteinase (MMP) expression in chondrocytes, and initiates synoviocyte proliferation (71).