CXCL12 and rheumatoid arthritis: IL-17 participates in the joint inflammation of RA via activation of T cells and FLSs by secreting cytokines and chemokines such as IL-6, IL-8, 1L-16, stromal cell-derived factor-1 (SDF-1), matrix metalloproteinase (MMP)-3 and MMP-1 [8-11].