Effect of low-density lipoprotein on the expression of high affinity Fcγ receptors

Identification of low density lipoprotein as a regulator of Fc receptor-mediated phagocytosis.

“…Cells and Growth Conditions. A strain of human monocyte cell line U-937 that is a cholesterol auxotroph (10)(11)(12)(14)(15)(16) was grown at 37°C in suspension cultures in RPMI 1640 with 10% heat-inactivated FCS (RPMI/FCS), as described (10). To establish the effect of IFN-y on phagocytosis, U-937 cells were incubated at 2 x 105 per ml in 50 ml of RPMI/FCS per 75-cm2 culture flask (Falcon) for 24 hr in the presence (500 units/ml) or absence of IFN-y prior to measurement of phagocytic activity.…”

“…LDL (density, 1.019-1.063 g/ml), very low density lipoprotein (VLDL; density, <1.006 g/ml), and high density lipoprotein fraction 3 (HDL3; density, 1.125-1.21 g/ml) were isolated from plasma of healthy male donors by sequential floatation in KBr solution (10). Prior to use, the lipoprotein fractions were dialyzed once or twice at 4°C against 200 volumes ofRPMI 1640 for 4 hr and against 200 volumes of RPMI 1640 overnight.…”

High-Density Lipoprotein Inhibits the Uptake of Modified Low- Density Lipoprotein and the Expression of CD36 and FcγRI

“…In an attempt to further delineate other possible effects that can explain the well-known anti-atherogenic role of HDL, we aimed to analyze the influence of HDL on the uptake of mLDL and the expression of two known receptors, CD36 and Fc RI, in this process 19,23) . This was accomplished using LDL molecules modified by either transition-metal oxidation (Cu 2 ) or trypsin proteolysis 14,19,24) .…”

“…Since studies based on human monocytes/macrophages often face the problem of a limited amount of cells, and further and most importantly their different stages of maturation, we used two monocytic cell lines, THP-1 and U-937. These cell lines mimic native monocytederived macrophages concerning the expression of receptors and antigens 4,25) , and have different expressions of scavenger receptors (SR) 11,23,25,26) . Further, they represent different stages of monocytic cell differentiation and in physiopathologic studies in atherosclerosis they are usually used in the differentiated stage with different stimuli.…”

“…Moreover, Fc RI mediates the clearance of immune complexes composed of LDL or oxLDL that can enhance foam cell formation 23,48) . Here, we have shown that HDL impairs the expression of Fc RI in THP-1 cells incubated with oxLDL or enzLDL, and in U-937 cells incubated with oxLDL.…”