MPO and chronic granulomatous disease: Specifically, MPO utilizes H2O2 to oxidize chloridion to produce hypochlorous acid (HOCl), which is a strong oxidizing antimicrobial agent.4 However, the absence of any of the three elements of the MPO-H2O2-Cl system, namely the absence of MPO (MPO deficiency), H2O2 (CGD), or Cl (CF), impairs normal host defense and inflammation resolution.