P-SELECTIN MEDIATES THE INTERACTION OF CIRCULATING LEUKOCYTES WITH PLATELETS AND MICROVASCULAR ENDOTHELIUM IN RESPONSE TO OXIDIZED LIPOPROTEIN IN-VIVO

BACKGROUND: Oxidized low density lipoprotein (oxLDL) has been demonstr ated to stimulate leukocyte/endothelium interaction, an early feature of atherogenesis. Using the skinfold chamber model for intravital micr oscopy in hamsters and mice, we have shown that oxLDL-induced leukocyt e adhesion to microvascular endothelium shares many characteristics wi th leukocyte adhesion during inflammation and ischemia/reperfusion, in cluding the involvement of beta(2) integrin adhesion molecules. In lig ht of the two-step model of leukocyte adhesion, we have examined the c ontribution of P-selectin to oxLDL-induced leukocyte/endothelium inter action. P-selectin is an inducible adhesion molecule on platelets and endothelium, mediating the initial steps of leukocyte margination and rolling along the endothelial lining, as well as of aggregate formatio n between platelets and leukocytes. EXPERIMENTAL DESIGN: For our studi es, we used the dorsal skinfold chamber model for intravital fluoresce nce microscopy on awake Syrian golden hamsters. Hamsters were treated 10 minutes before oxLDL-injection (oxidized by Cu2+, 4 mg/kg body weig ht, intravenously) with blocking antibodies to P-selectin (2 mg/kg bod y weight intravenously, N = 7). RESULTS: In seven control animals (pre treated with an irrelevant IgG antibody), oxLDL injection elicited leu kocyte rolling and adhesion on both venular and arteriolar endothelium , and also the formation of aggregates tumbling down the microvessels and firmly adhering to the microvascular endothelium. The aggregates c onsisted of leukocytes and activated, dendritic platelets, as assessed by scanning electron microscopy of the buffy coat isolated by density gradient centrifugation of whole blood taken from hamsters 15 minutes after injection of oxLDL. Leukocyte adhesion to venular and arteriola r endothelium, as well as the formation of leukocyte/platelet aggregat es were significantly reduced by pretreatment of the animals with anti -P-selectin antibodies. CONCLUSIONS: These data emphasize the similari ties between leukocyte adhesion in response to oxLDL and in other path ophysiologic conditions, identifying P-selectin as a crucial player in the interaction between leukocytes and microvascular endothelium as w ell as in the formation of circulating leukocyte/platelet aggregates.