Fig. 1

In vivo imaging of neutrophil elastase enzyme activity in MIA-injected knee joints and the effect of neutrophil elastase inhibition with sivelestat (50 mg/kg i.p., 20 h post-injection of MIA, i.e., 4 h before imaging) or serpinA1 (10 μg i.p., administered 15 min before and 12 h after MIA injection, i.e., 12 h before imaging). a Representative fluorescence images showing the area of interest analyzed for MIA-injected knees (red arrow) vs. contralateral naïve knee joints. b Intra-articular injection of MIA produced an increase in proteolytic activity on day 1 that was not present by day 14; treatment with sivelestat or serpinA1 caused a significant decrease in day 1 neutrophil elastase activity (n = 5–7 per group). ***P < 0.001, ****P < 0.0001 compared to the MIA control, one-way ANOVA