Diapedesis across mammary epithelium reduces phagocytic and oxidative burst of bovine neutrophils

The effect of diapedesis on the phagocytic and oxidative burst activity of polymorphonuclear neutrophil (PMN) was examined, using an in vitro cell cul ture model consisting of a monolayer of primary mammary epithelial cells. I solated blood PMN from 10 cows were added to the basal side of the epitheli al cell monolayer. Diapedesis was induced by the addition of complement fac tor C5a to the apical side of the monolayer. PMN phagocytosis of Staphyloco ccus aureus and oxidative burst were measured before diapedesis on PMN that were non-activated and activated by incubation with C5a and on PMN after d iapedesis, using flow cytometry. The percentages of PMN fluorescing due to phagocytosis of S. aureus and oxidative burst were reduced by 21.2 and 14.4 %, respectively, after diapedesis. Pre-incubation in the presence of C5a ha d no effect on percentage PMN fluorescing due to phagocytosis or oxidative burst. The capacity for individual migrated PMN to phagocytose S. aureus an d to produce an oxidative burst, as measured by the intensity of fluorescen ce, decreased by 34.2 and 30.3%. Activation of PMN with C5a increased inten sity due to the oxidative burst, but had no effect on intensity due to phag ocytosis. These data show that PMN diapedesis across mammary epithelium res ults in decreased phagocytosis and oxidative burst of the PMN. (C) 1999 Els evier Science B.V. All rights reserved.