The study was undertaken to investigate whether the two major monocyte subsets defined by the surface markers CD14(+)CD16(+) and CD14(++)CD16(-) show differences in their responses to hypercholesterolemia. Monocytes were rapidly isolated from the blood of hypercholesterolemic, low-density lipoprotein (LDL) receptor-defective familial hypercholesterolemia (FH) patients and from control persons. Using flow cytometry and uptake, adhesion, and phagocytosis assays as well as laser scanning microscopy, we found significant differences between the monocyte subsets. FH-CD14(+)CD16(+) monocytes exhibit an increased uptake of oxidized LDL (oxLDL) via CD36, whereas FH-CD14(++)CD16(-) monocytes preferentially take up native LDL (nLDL). FH-CD14(+)CD16(+) monocytes have an increased expression of surface proteins CD68, stabilin-1, and CD11c and a higher adherence to activated endothelial cells in response to oxLDL and nLDL stimulation. In addition, all CD14(+)CD16(+) monocytes have an increased ability for phagocytosis and a higher resistance to phagocytosis impairment by oxLDL compared with CD14(++)CD16(-) monocytes. We conclude that FH-CD14(+)CD16(+) monocytes have specialized functions in the uptake of oxLDL at activated endothelial cell surfaces, and we hypothesize that these functions are critical for the clearance of oxLDL deposits and apoptotic cells from the vessel wall under hyperlipidemic conditions.

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SummaryTissue factor (TF) is the most important initiator of intravascular coagulation. Platelets contribute to TF exposure on monocytes, but the mechanism is not completely understood. Here we examined the possibility that platelets may release TF that can be transferred to monocytes by platelet-derived microvesicles. When human citrated platelet-rich plasma was incubated with collagen there was an increase in the plasma levels of TF and CD62P. Incubation of plasma obtained from collagen-stimulated PRP with a sediment of red and white blood cells resulted in an increase in the number of monocytes that express TF, CD62P and the platelet-specific antigen CD42a on their surface. This transfer of platelet-derived antigens to monocytes was reduced when CD62P was blocked by a specific antibody or when platelet-derived microvesicles were removed from the plasma either by high speed centrifugation (17,500 X g for 30 min) or by filtration (pore size 0.2 µm). The data indicate that platelet-derived microvesicles that are released from collagen-stimulated platelets may carry TF, CD62P and CD42a and may transfer these antigens to the surface of monocytes. The interaction of platelet-derived microvesicles with monocytes and the transfer of TF to monocytes strongly depend on CD62P.

This study indicates that treatment of periodontitis significantly reduces the serum activity of Lp-PLA(2), which is believed to be an independent cardiovascular risk factor.

Background: Elevated plasma cholesterol promotes the formation of atherosclerotic lesions in which monocyte-derived lipid-laden macrophages are frequently found. To analyze, if circulating monocytes already show increased lipid content and differences in lipoprotein metabolism, we compared monocytes from patients with Familial Hypercholesterolemia (FH) with those from healthy individuals.