A simple method of obtaining monocytes in suspension.

Relatively pure monocyte suspensions may be obtained by density flotation after simple conditioning of leukocytes. This consists of incubating blood or buffy coat cells in plasma containing NaCl at a higher than physiological concentration. As a result the density of granulocytes and lymphocytes increases greatly, but the density of monocytes changes very little. It is possible with one centrifugation on a slightly modified density gradient to obtain 90% pure monocyte suspensions with 55% yield. More than 95% purity but lower yield is obtained simply by increasing the NaCl concentration. The membrane characteristics of monocytes and their capacity to function normally remain unaltered by this treatment and cells so obtained develop in culture into macrophages normally. This method is much cheaper and simpler than others described, and is applicable equally to either small or large numbers of leukocytes.