MMP9 and rheumatoid arthritis: Furthermore, existing information suggests that YKL-40 could have an active role in the pathogenesis of RA stimulating the production of inflammatory mediators such as chemokines (CCL2 and CXCL2), proinflammatory cytokines, and metalloproteinases (MMP-3 and MMP-9), and activating connective tissue growth factor (CTGF), favoring the formation of pannus, a determinant element in the development of erosions and joint disorganization characteristic of this disease [50,51,52,53,54].