Lipoproteins upregulate high affinity Fc receptors in human monocytes

Plasma lipoproteins have been implicated in immunoregulation. Here we report that LDL and VLDL up-regulate high affinity Fc receptors (Fc gamma RI) in normal human monocytes. Adherent monocytes were cultured for 4 days in media containing fetal calf serum or delipidated serum. Immunofluorescence analysis showed a significant decrease in percentage of Fc gamma RI-positive cells from 85 +/- 3 in medium containing normal serum to 54 +/- 9 in medium containing delipidated serum. The decrease in the fraction of cells expressing Fc gamma RI was parallel to a decrease in the average number of receptor molecules per cell as indicated by a decrease in the mean value fluorescence intensity from 234 +/- 20 to 112 +/- 14. The inhibition of Fc gamma RI expression was overcome by addition to the culture medium of LDL or VLDL. Since pure cholesterol is ineffective, it is proposed that these lipoproteins deliver a component(s) such as apolipoprotein B-100 which triggers a signal leading to up-regulation of Fc gamma RI in monocytes and macrophages.