CCL21 and rheumatoid arthritis: CCL21, also known as secondary lymphoid tissue chemokine, is a potent inflammatory chemokine that regulates dendritic cell migration and has been implicated in various chronic inflammatory, fibrotic, and pain conditions, including rheumatoid arthritis, neuropathic pain, idiopathic pulmonary fibrosis, chronic hepatitis C, and primary biliary cirrhosis [25], [26], [27], [28].