Low density lipoprotein receptor activity in freshly isolated human blood monocytes and lymphocytes

Circulating human monocytes and lymphocytes were isolated by counterflow and density gradient centrifugation. Binding and degradation of low density lipoprotein (LDL) occurred predominantly in monocytes and to a much lesser extent in lymphocytes. The findings were consistent with greater LDL receptor activity in freshly isolated monocytes than lymphocytes, in keeping with differences in other cell surface receptors between these two cell types. Therefore, when freshly isolated mixed mononuclear cells are used to study LDL receptor activity in vivo in humans, careful attention needs to be given to the proportions of monocytes and lymphocytes, or alternatively, relatively pure preparations of monocytes should be used.