MPO and infection: In the hyper-virulent UTI89 infection, MPO localization was monitored by immunofluorescent microscopy using a labeled anti-MPO antibody, revealing a significant reduction in MPO localization in the uroepithelial lining of AKB-4924 treated bladders (Fig 5D). MPO expression is nearly undetectable level in uninfected cells (S6B Fig), confirming the elevated level of MPO expression is not a pre-existing inflammatory condition but occurs specifically in response to UPEC infection.