Effect of exogenous IL-17 on type I collagen metabolism by RA bone explants. Bone samples from RA patients were incubated for 7 days in the presence of IL-17 (50 ng/ml) and/or IL-1 (100 pg/ml). (a) PICP levels (n = 3) in supernatants were measured by ELISA. Results are expressed as mean ± SEM of % induction of PICP production. Spontaneous production of PICP was 433 ± 133 ng/ml. (b) CTX levels in supernatants were measured by ELISA. Bone samples were incubated with IL-17 (n = 5), IL-1 (n = 5), and IL-17 + IL-1 (n = 2). Results are expressed as mean ± SEM. Spontaneous production of CTX was 104 ± 55 ng/ml. *P < 0.05 compared with control (medium alone).