AOC3 and rheumatoid arthritis: Vascular adhesion protein 1 (VAP-1) is prominently involved in immune cell trafficking in a number of major human diseases, including rheumatoid arthritis, certain cancers, and atherosclerosis.1 VAP-1 was first discovered in inflamed synovial vessels in Turku, Finland, more than two decades ago.2 Since then, the international scientific community has devoted a great deal of research effort to VAP-1 targeting.