S100A9 and infection: This trend has been observed in human infections where elevated levels of the neutrophil proteins S100A8, S100A9, and S100A12 are detectible in the stool.61 The S100A8 and S100A9 proteins are antimicrobial factors and potent neutrophil chemoattractants;30,62 these proteins also promote neutrophil activation, and S100A9 potentiates IL-8 production from neutrophils in response to other stimuli.63 In addition to these three proteins, our study has uncovered additional host factors that appear in the intestine during C. jejuni infection, including antimicrobial neutrophil related proteins.