MPO and infection: Neutrophils are necessary for controlling C. rodentium in mice; for example, mice rendered neutropenic due to anti-Gr-1 antibody treatment or depletion of CXCR2 have higher colonic bacterial burdens compared to wildtype mice.27,29 In the present study, cathelicidin-null (Camp−/-) mice had reduced neutrophil infiltration into the distal colon compared to Camp+/+ mice at peak C. rodentium infection (7 d post-infection; pi), as determined by immunofluorescence (Figure 1a) and myeloperoxidase (MPO) activity (Figure 1b).