Ambient UFP triggers prooxidant effects in-vivo. Representative dorsal photograph of HO-luc transgenic mice that were exposed to concentrated UFP, concentrated PM2.5 or filtered-air (FA) for 5 hours in a mobile exposure laboratory located in downtown Los Angeles, ~300 meters away from the I-110 freeway. Increased bioluminescence was due to a larger HO-1 upregulation response generated in tissues subject to greater oxidative stress. Mice were generated and obtained from Dr. Christopher Contag at Stanford University . They contain a modified coding sequence of the luciferase gene under the control of the full HO-1 promoter. Whole-body images were acquired within 3 hours of the exposure using a cooled charged-couple device (CCD) camera at the Small Animal Imaging Center of the UCLA Crump Institute for Molecular Imaging  as previously described . The bioluminescence signal was recorded as maximum photons/sec/cm2/steradian (p/sec/cm2/sr). Notice that the UFP-exposed mouse displays increased luciferase emissions both in the thorax and abdomen as compared with the PM2.5 or FA-exposed mice.