Neutrophil-dependent mediation of microvascular permeability.

Macromolecular extravasation induced by the chemoattractants N-formyl-methionylleucylphenylalanine (FMLP), complement fragment C5a, and leukotriene B4 (LTB4) has been reported to be neutrophil dependent. A review of experimental evidence argues against mechanical disruption of the endothelial barrier as a likely mechanism for enhanced microvascular permeability. Other proposed mechanisms attribute macromolecular efflux to extracellular liberation of granule constituents or granule-independent neutrophil release products (e.g., oxygen radicals) that can undermine vascular integrity by direct or indirect actions on endothelial cells or other components of vascular walls (glycocalyx, basement membrane). The cytotoxic potential of neutrophil-release products on endothelial cells prompts consideration of a transcellular pathway for macromolecular transport. Further studies are needed to clarify the precise nature of endothelial injury and its resolution to better understand the physiology behind the transient effects of these mediators on vascular permeability.