Differential expression of CD14, CD36 and the LDL receptor on human monocyte-derived macrophages. A novel cell culture system to study macrophage differentiation and heterogeneity.

Macrophages are key players in many aspects of human physiology and disease. It has been hypothesized that in a given microenvironment monocytes differentiate into specific subpopulations with distinct functions. In order to study the role of macrophage heterogeneity in atherogenesis, we established a novel isolation and culture technique for human monocyte-derived macrophages. The present technique does not select for monocyte subpopulations prior to the onset of differentiation. Monocytes were cultured for 2 weeks in the presence of autologous lymphocytes before being plated quantitatively. They differentiated into mature macrophages in terms of morphology, lipid composition, and biological activity. Based on phagocytic activity as well as on the expression of CD14, CD36, and the low-density lipoprotein (LDL) receptor, we have identified macrophage subpopulations that may play distinct roles in atherogenesis. While virtually all adherence-purified monocytes expressed CD14, CD36, and the LDL-R, we characterized three subpopulations of macrophages based on the expression of these antigens: CD36+CD14-LDL-R-(58+/-12%), CD36+CD14+LDL-R+(18+/-5%), the remaining cells being CD36-CD14- LDL-R-. The first two subsets decreased in size during further differentiation (51+/-12% and 8+/-3%, respectively). Our culture technique may also serve as a good model for studying the implications of macrophage heterogeneity in diseases other than atherosclerosis.