MMP1 and rheumatoid arthritis: To verify gene regulation of the candidate chemokines by these factors, real-time qPCR was performed using cultured RA FLS to assess the mRNA expression levels of CXCL8, CCL2, receptor activator of nuclear factor kappa-B ligand (RANKL), osteoprotegerin (OPG), matrix metalloproteinase 1 (MMP1), and MMP13 (Fig. 3D).