The M-DC8-positive leukocytes are a subpopulation of the CD14+ CD16+ monocytes.

Recently, a population of M-DC8-positive leukocytes has been described as a new subpopulation of human dendritic cells (DC). In view of the expression of the CD16 antigen on these cells, as well as the finding that DC can arise from blood monocytes, we hypothesized that the expression of M-DC8 is mainly associated with the CD14+ CD16+ phenotype of blood monocytes. Immunofluorescence analysis of whole blood showed that the percentage of M-DC8+ cells is about three times lower than the percentage of CD14+ CD16+ monocytes among all leukocytes (0.32% versus 1.10%). Further, in addition to the expression of CD16, these M-DC8+ cells were also positive for CD14 at low density. Multicolor flow cytometric analysis of whole blood revealed that more than one third of the CD14+ CD16+ monocyte population expressed the M-DC8 antigen (42.3%), and almost all M-DC8+ cells were CD14-CD16-double-positive (87.5%). Finally, the M-DC8 antigen was also expressed on alveolar macrophages from healthy individuals, i.e., cells that are phenotypically and functionally related to the CD14+ CD16+ monocytes. Taken together, the data presented here clearly demonstrate that the M-DC8+ leukocytes are a subpopulation of the CD14+ CD16+ monocytes and may represent DC