Immunomodulating effect of low density lipoprotein on human monocytes.

Low density lipoprotein (LDL) isolated from sera of healthy volunteers in 50 micrograms protein/ml concentration induced an early adenylate cyclase activation in human monocytes followed by elevation of cGMP level. In addition, a rapid 45Ca2+ influx was also detected on addition of 25-100 micrograms protein/ml concentrations. The monocyte activating effect of LDL under in vitro circumstances was characterized by an enhanced O2 consumption, H2O2 generation and by the increased release of lysosomal enzymes such as beta-glucuronidase and elastase like protease (ELP). On the other hand, LDL diminished markedly the Fc gamma receptor (Fc gamma R) mediated rosette formation, phagocytosis and the antibody dependent cellular cytotoxicity (ADCC) of monocytes without a significant decrease in the IgG binding capability of cells. High levels of serum LDL may play a significant role in the arterial wall injury by elastase like protease as well as biologically active oxygen species released from monocytes of patients suffering from arteriosclerosis.