The early events of inflammation within the joints involving protease activity were quantified according to a previously established method using Near-Infrared (NIR)-fluorescence imaging (21 (link)). Briefly, 24 hours prior to the time of imaging, animals were administered an i.v. injection of the protease substrate, Prosense (2 nmol/150 μl volume; ViseEn Medical, Woburn, MA). Prosense is a NIR fluorescent protease substrate that is incorporated into bone tissue and allows us to specifically visualize ongoing in vivo protease activity of cathepsins B, C, D, G, K, L and S, plasmin, and plasma kallikrein. NIR-fluorescence scanning of dissected knees was performed at the time of sacrifice using the Licor-Odessey infrared imaging system with a MousePod attachment. Images were then analyzed using commercially available software (Licore-Odessey, Lincoln, NE) for regions of interest within each knee and the mean differences in fluorescent intensity were quantified. Data are represented as mean fold induction relative the saline controls, which were scanned and analyzed at the same time.