Interleukin 2 acutely induces platelet and neutrophil-endothelial adherence and macromolecular leakage

The acute effects of interleukin 2 (IL-2) were determined in the rat cremaster microcirculation model by intravital, light, and electron microscopy to better understand the pathophysiology of the IL-2-induced vascular leak syndrome. Four groups of rats were studied over a 2-h monitoring period. One group received 1 x 10(6) units of IL-2/kg i.v. (n = 10), while the remaining groups received IL-2 topically applied to the cremaster muscle in dosages of either 1 x 10(5) (n = 9), 1 x 10(6) (n = 5), or 3 x 10(6) (n = 5) units. Each group was compared with controls (n = 9). IL-2 administered i.v. acutely induced platelet and polymorphonuclear leukocyte-endothelial adherence and microvascular macromolecular leakage that occurred synchronous with the development of tachycardia, hypotension, tachypnea, and hypoxemia. Topically applied IL-2 induced similar microvascular alterations but without changes in hemodynamic and respiratory parameters, which suggests that microvascular alterations were not caused by IL-2-induced changes in hemodynamic parameters. Electron microscopy of cremaster muscle sections demonstrated platelet and neutrophil adherence to the endothelium and endothelial injury. We conclude that IL-2 (or a locally generated mediator) acutely induces platelet and neutrophil-endothelial adherence in the rat skeletal muscle microcirculation that is associated with the development of macromolecular leakage from the microcirculation.