Counts and characteristics of macrophage precursors in human peripheral blood.

A method is described for counting the number of macrophages which develop from a sample of human venous blood. Because the macrophages are nondividing cells under these conditions of culture, it is possible to use the count to describe the size of a population of macrophage precursors in the blood. Counts on 43 healthy individuals show that on average there are some 200,000/ml of blood, which is 5–6% of the total white cell count. The precursor cells are mononuclear and the majority of them will adhere to plastic. These characteristics suggest that monocytes are the precursor cells.