MPO+ macrophages contain active MPO that generates HOCl detectable by SNAPF, following stimulation. a) The gene for hMPO is transcribed in bone marrow derived macrophages from hMPO-Tg, but not WT, mice as demonstrated by RT-PCR. This is translated into functionally active MPO, established by a dTNB assay (b). Results are expressed as a percentage decrease in absorbance at 412 nm per μg protein (n=3). Enzymatically active MPO is also present in human MPOhi cells (b, n=4). HOCl generated by hMPO-Tg BM macrophages (c, n=3) or human MPOhi macrophages (d, n=5) is quantifiably detected by SNAPF using a fluorescent plate reader, following cell stimulation with 400 nM PMA. Results are expressed as a percentage change in fluorescence from baseline readings (pre-stimulation) over time.