Lipoproteins modify the macrophage uptake of triacylglycerol emulsion and of zymosan particles by similar mechanisms

The uptake of lipids and formation of foam cells are key events in atherosc lerosis and in eruptive xanthomata formation in primary hyperchylomicronemi a. Here we have compared the influence of low density lipoprotein (LDL), ox idized LDL (oxLDL), high density lipoprotein (HDL), and delipidated:HDL (ap oHDL) on the uptake by macrophages of zymosan tan insoluble fraction of yea st cell walls) and of triglyceride rich emulsion (EM) particles that resemb le chylomicrons, but, like zymosan, are equally devoid of protein component s. Zymosan internalization is known to occur through unspecific phagocytosi s,whereas natural chylomicrons are taken up by several specific lipoprotein receptors. We found that phagocytosis is not promoted as much by oxLDL as by normal LDL. HDL-coated zymosan was found to be inert and apoHDL slightly enhanced phagocytosis. LDL and apoHDL promoted the uptake of EM while oxLD L and HDL significantly inhibited the uptake. Therefore, the data support t hat HDL, and not apoHDL, particles inhibit EM uptake. We concluded that by using lipoprotein-coated zymosan particles, we could demonstrate different biological effects of LDL, oxLDL, HDL, and apoHDL on macrophage phagocytosi s and that this method could be useful to delineate components of the vario us lipoproteins important for the propagation or inhibition of the formatio n of foam cells.