LIPOPROTEINS UP-REGULATE 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 (FcγRI) 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 FcγRI-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 FcγRI 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 FcγRI 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 FcγRI in monocytes and macrophages. © 1993 Academic Press.