CXCL13 and rheumatoid arthritis: Chemokines like CXCL9, CXCL10, CXCL13, CCL18 and especially alarmins like S100A8/A9 and S100P, which were among the top ranks of RA-ST, demonstrated that their concentration tremendously declined from a high level in the synovial fluid to a much lower level in serum.