PTGS2 and rheumatoid arthritis: Notably, ROS, lipoxygenase, pro-inflammatory cytokines (such as tumour necrosis factor-α, interleukin (IL)-1β), prostaglandin-endoperoxide synthase, prostaglandins, cyclooxygenase-2 (COX-2) enzyme and macrophage colony-stimulating factor plays a crucial role in the pathophysiology of rheumatoid arthritis.