Hypercholesterolemia promotes leukocyte-dependent platelet adhesion in murine postcapillary venules

OBJECTIVE: Leukocyte-platelet aggregates form in blood during the development of cardiovascular diseases, including atherosclerosis. The study determined whether leukocytes contribute to the platelet adhesion induced by hypercholesterolemia in postcapillary venules. METHODS: Wild-type (WT) C57Bl/6 or CD18-deficient (CD18-/-) mice were placed on a normal (ND) or high-cholesterol (HC) diet for 2 weeks. Platelets isolated from ND, HC, or CD18-/- mice were fluorescently labeled with CFSE, and administered to either ND, HC, HC-CD18-/- or anti-neutrophil serum (HC-ANS)-treated mice. Rhodamine 6G was administered to label and visualize leukocytes. Intravital fluorescence microscopy was used to quantify leukocyte and platelet adhesion in intestinal postcapillary venules. RESULTS: HC increased both leukocyte and platelet adhesion (relative to ND). Greater than 50% of adherent platelets in HC mice were bound to adherent leukocytes. When HC platelets were examined in HC-ANS-treated or HC-CD18-/- mice, leukocyte-dependent platelet adhesion was significantly attenuated. Conversely, when HC-CD18-/- platelets were observed in HC recipients both leukocyte-dependent and endothelium-dependent platelet adhesion was comparable to HC mice receiving WT platelets. CONCLUSIONS: The findings demonstrate that the pro-thrombogenic phenotype assumed in the microvasculature during hypercholesterolemia is largely attributed to leukocyte-dependent platelet adhesion.