TNF and rheumatoid arthritis: Synovial fluid concentrations of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-17 (IL-17) [24, 25], calcitonin gene-related peptide (CGRP) [26, 27], and nerve growth factor-β (NGF-β) [28] are increased in RA patients, which can directly alter the responses of nociceptive neurons [12].