IL-17A significantly shifts the MMP-1: TIMP-1 ratio in rheumatoid arthritis synovial explant cultures. Whole rheumatoid arthritis (RA) synovial tissue explants were serum-starved for 24 hours and incubated with TNF-α (10 ng/ml), IL-17A (10 ng/ml) or IL-17A (20 ng/ml) alone and in combination. (a to c) Levels of matrix metalloproteinase (MMP)-1 and tissue inhibitor of metalloproteinase (TIMP)-1 in culture media were measured by ELISA. Values are the mean and standard error results from seven experiments. * P < 0.05 versus baseline (Basal). (d) MMP-2 and -9 activity in the culture supernatants was assessed by gelatin zymography.