Fig. 8

A novel perspective for r-axSpA development. LCN2 (L) as one of the acute phase proteins of the self-defense mechanism (innate immunity) is produced when triggered by agents such as microbial factors to prevent acute infection. Failure to normalize L in a timely manner would lead to chronic inflammation, reflected by elevation of L (L+) as well as concurrent elevation of L and LM (L+LM+) in the circulation. In HLA-B27-positive male patients, L+LM+ is the predominant pattern, resulting in severe SIJ and spinal inflammation and eventual drastic radiographic damage. In HLA-B27-negative male patients, and female patients (irrespective of HLA-B27 status), L+ is the predominant pattern, resulting in mainly SIJ inflammation and milder radiographic damage in the spine