Immunological heterogeneity of human monocyte subsets prepared by counterflow centrifugation elutriation

Human peripheral blood mononuclear cells were separated into three fractions by means of counterflow centrifugation elutriation (CCE). The first fraction, eluted at a flow rate of 24 ml/min, was composed of lymphocytes with less than 2% contaminating esterase-positive cells. The cells in this fraction were incapable of responding to either soluble antigen (tetanus toxoid) or particulate antigen (cytomegalovirus-infected fibroblasts) unless recombined with accessory cells. The second fraction, eluted at a flow rate of 28 ml/min, was composed predominantly (72%) of small Ia, leu M3, and esterase-positive monocytes, which stained weakly with leu 10 antibody. Cells in this fraction efficiently presented soluble and particulate antigens to monocyte-depleted lymphocytes. Of the remaining cells, 87% were large esterase-positive monocytes that labelled strongly with Ia, leu M3, and leu 10. These cells were less efficient in antigen presentation than the small monocytes. However, lymphocytes activated with antigen-pulsed large monocytes exhibited more suppressor cell activity than those activated with antigen-pulsed small monocytes.