IL6 and rheumatoid arthritis: IL-6 and TNF-α also are pro-inflammatory cytokines that can be measured in the serum and the arthritic synovial fluid of patients with RA after synovial inflammation develops [42,43], hence playing a significant role in the occurrence and development of RA, more specifically in bone erosion and osteoclastogenesis (formation of bone-resorbing osteoclasts) [44,45].