Isolation of human monocytes on re-orienting gradients of Percoll.

We have developed a rapid and simple method for isolating monocytes from peripheral blood. After mononuclear cells are isolated on a Ficoll-Hypaque gradient, the monocytes are purified by sedimentation for 5 min through a re-orienting gradient of Percoll. The method is easily reproducible and yields approximately half of the monocytes in staring blood, with minimal contamination by lymphocytes. Although both monocytes and lymphocytes have similar densities, separation occurs because these cells migrate at differing rates through the gradient to reach their equilibration point. The recovered monocytes are viable and functional; over 95% of them exclude trypan blue and they adhere to glass and plastic and ingest latex particles normally. By virtue of the rapidity and gentle nature of its centrifugation steps, the method exposes cells to only very limited non-physiologic conditions. For this reason and because the monocytes are maintained in suspension, opportunities for functional alterations are minimized.