MMP3 and rheumatoid arthritis: Serum MMP-3 in RA patients with high grade synovitis was significantly higher than that in patients with low grade synovitis score (median 325 ng/mL, IQR 233~528 ng/mL versus median 207 ng/mL, IQR 141~392 ng/mL, P = 0.024), and serum MMP-3 was also higher in RA patients with high grade group of the resident cells density (Figure 2(b)).