Fig. 4

A novel perspective for axSpA development. Upon external triggering agents, acute-phase proteins (including LCN2 and OSM) are produced by the innate immune system to combat acute infection. Transient elevation of these proteins is thought to play a protective role in host defense. Nevertheless, failure to normalize these self-defense proteins in a timely manner would cause local chronic inflammation. Eventually, it leads to excessive tissue repair, including ankylosis in spondylitis