Percent side population cells in lung before and seven days after bleomycin challenge in wildtype vs. gp91phox-/- and MMP12-gp91phox double knockout mice. At this point, lung parenchyma was digested by dispase and Hoechst dye effluxing cells (side population) were isolated. *P < 0.05 compared to control, averaged from three independent experiments. FACsans and flow sorts were done in triplicate per sample. Abbreviations: WS, saline-treated wildtype mice; WB, wildtype mice treated with bleomycin; NOXS, saline-treated gp91phox null; NOXB, bleomycin-treated gp91phox null; DKOS, saline treated MMP12- gp91phox double knockout; DKOB, bleomycin-treated MMP12- gp91phox double knockout.