931 J. Exp. Med.  The R ockefeller University Press • 0022-1007/ 99/ 03/ 931/ 08 $2.00 Volume 189, Number 6, March 15, 1999 931–938 http:/ / www.jem.org Essential Role of P-Selectin in the Initiation of the Inflammatory Response Induced by Hemorrhage and Reinfusion By R osario Scalia, Valerie E. Armstead, Alexander G. Minchenko, and Allan M. Lefer From the Department of Physiology, Jefferson Medical College, T homas Jefferson University, Philadelphia, Pennsylvania 19107 Summary R esuscitation from hemorrhage induces profound pathophysiologic alterations and activates in- flammatory cascades able to initiate neutrophil accumulation in a variety of tissues. This process is accompanied by acute organ damage (e.g., lungs and liver). We have previously demon- strated that significant leukocyte–endothelium interactions occur very early in other forms of ischemia/ reperfusion (i.e., splanchnic ischemia/ reperfusion and traumatic shock) which are largely mediated by increased expression of the adhesion molecule, P-selectin, on the vascular endothelium. Here we postulated that increased endothelial expression of P-selectin in the mi- crovasculature would play an essential role in initiating the inflammatory signaling of hem- orrhagic shock. Using intravital microscopy, we found that hemorrhagic shock significantly increased the number of rolling and adherent leukocytes in the mouse splanchnic microcircula- tion. In contrast, mice genetically deficient in P-selectin, or wild-type mice given either an anti–P-selectin monoclonal antibody or a recombinant soluble P-selectin glycoprotein ligand (PSGL)-1 immunoglobulin, exhibited markedly attenuated leukocyte–endothelium interaction after hemorrhagic shock. Thus, activation of P-selectin protein on the microvascular endothe- lium is essential for the initial upregulation of the inflammatory response occurring in hemor- rhagic shock. Moreover, endogenous levels of PSGL-1 mR NA were significantly increased in the lung, liver, and small intestine of wild-type mice subjected to hemorrhagic shock. Since PSGL-1 promotes adhesive interactions largely through P-selectin expressed on the vascular endothelium, this result further supports the crucial role played by P-selectin in the recruitment of leukocytes during hemorrhagic shock. Key words: mRNA • leukocyte • endothelium • immunohistochemistry • intravital microscopy H emorrhagic shock initiates an inflammatory response characterized by the upregulation of cytokine expres- sion (1) and emigration of neutrophils into a variety of tissues (2). The accumulation of neutrophils in splanchnic and tho- racic organs is likely to contribute to end-organ damage and resultant dysfunction after this form of shock. The mecha- nism by which hemorrhage triggers this inflammatory re- sponse remains poorly understood. Heightened adrenergic activity (3), increased production of reactive free radicals (4), and systemic release of proinflammatory agents from the gut (5, 6) have been hypothesized to contribute to acute organ injury after hemorrhage. Nevertheless, none of these studies has clarified the specific pathway that promotes leukocyte re- cruitment into visceral organs during hemorrhagic shock. Before transmigration into inflamed tissue, leukocytes must initially interact with the vascular endothelium (7), as demon- strated during ischemia/ reperfusion (8) and in several experi- mental models of circulatory shock (9). Moreover, we have reported that under shock conditions very early endothelial dysfunction (i.e., 2.5–5 min) is associated with increased en- dothelial dysfunction (10, 11) and expression of the cell adhe- sion molecule, P-selectin (12). P-selectin is able to initiate the cascade of events that increases cell adherence and leukocyte infiltration into injured tissues by first promoting leukocyte rolling along the vascular endothelium (13, 14). Therefore, we hypothesized that increased surface expression of P-selec- tin in the microvascular endothelium would exert an essential role in recruitment of leukocytes in the case of hemorrhagic shock. Hemorrhage was therefore carried out in control wild-type mice, in wild-type mice treated with anti–P-selec- Downloaded from http://rupress.org/jem/article-pdf/189/6/931/1120384/98-1803.pdf by guest on 17 June 2022