CCL13 and rheumatoid arthritis: We observed significantly upregulated expression of CCL13, CCL18, and MMP3. CCL13 was found aberrantly expressed in the serum, synovial fluid, and synovial tissues from RA patients compared with those with osteoarthropathy, which could enhance fibroblast-like synoviocytes (FLS) proliferation, increase macrophage infiltration, and synovial tissue angiogenesis15,16.