Changes in cell density induced by Isopaque

Abstract

Incubation in culture medium at 37 °C of normal mononuclear leukocytes, isolated on Ficoll-Isopaque, resulted in a general decrease in the specific gravity of these cells. Monocytes and lymphocytes could then be recognized as separate populations in the density distribution profile. This decrease of the cell density was inhibited by lowering the temperature to 0 °C or by the addition of Ficoll-Isopaque to the incubation medium. After pre-incubation at 37 °C, renewed contact between mononuclear leukocytes and Ficoll-Isopaque induced a general increase of the cell density. Monocytes and thymidine-incorporating lymphocytes were affected to a greater extent than small lymphocytes. The increase of the specific gravity of monocytes was time and temperature dependent. The density shift of the thymidine-incorporating lymphocytes was only time dependent. The change in the density of small lymphocytes was dependent on the combination of contact with Ficoll-Isopaque and centrifugal stress. Isopaque was the agent responsible for the effects. It is concluded that the use of small molecular substances such as Isopaque as a constituent of density gradients may introduce reversible changes of the specific gravity of mononuclear leukocytes which may limit the separation of mononuclear sub-populations.