The supernatant of IL-33–treated human mast cells induces migration of human neutrophils. Human blood neutrophils were obtained from 2 different donors and assayed in triplicates in a chemotaxis assays. Neutrophil migration toward untreated or IL-33–treated CBMCs or IL-33 alone was then quantified by measurement of MPO, and shown as O.D 450-620 nm. Unconditioned medium alone or was used as negative controls, and 1 ng/mL IL-8 and 10% ZAS were used as positive controls. Values are presented as mean ± SEM, **P < .01. CBMCs = cord blood–derived mast cells, ZAS = zymosan activated serum.