Isolation of human monocytes according to volume and density

Human peripheral blood monocytes were obtained in very pure preparations by using buoyant density gradient centrifugation followed by velocity sedimentation. We introduced several modifications in the experimental procedure in order to take advantage of the minimal differences in cell density and size between monocytes and lymphocytes. Previous methods used to isolate monocytes based on their physical properties are reviewed, and the theory of velocity sedimentation is discussed with regard to the differences in the methodology used, which account for the different results we obtained.