Rapid flow cytometric identification of putative CD14- and CD64- dendritic cells in whole blood.

Blood dendritic cells (DCs) may be identified as mononuclear leucocytes with high expression of HLA-DR, but lacking the antigens CD3, CD14, CD16, CD19, and CD56, which are characteristically expressed by T cell, monocytes, B cells, and natural killer cells. However, some DCs have recently been reported to express the monocyte-associated antigen CD14; also some monocytes may shed CD14 and so appear to be CD14-. It is therefore possible that the expression of CD64, which is absent on blood DCs but which is expressed by both CD14+ and CD14- monocytes may better distinguish DCs from monocytes. DCs were identified by flow cytometry as mononuclear leucocytes with the phenotype HLA-DR+, CD2-, CD16-, CD19-, CD57-, and either CD14- or CD64- and hence are described herein as either CD14- DCs or CD64- DCs, respectively. CD14- DCs and CD64- DCs occurred, respectively, at a concentration of 65 +/- 48 x 10(6) cells 1(-1) and 149 +/- 103 x 10(6) cells 1(-1) (mean +/- S.D.) in samples of peripheral blood (corresponding, respectively, to 3.0 +/- 1.8% and 6.6 +/- 3.8% of the mononuclear cells). The expression of CD14 and CD64 on monocytes in blood was also investigated. Cells with the immunophenotype CD14- CD64+ comprised 12.7 +/- 3.3% of the monocyte population and had high expression of HLA-DR. DCs identified as CD14- or CD64- were isolated by flow cytometric sorting, prepared for electron microscopy, and both were found to have the characteristic morphology of resting DCs. We conclude that mononuclear cells with the phenotype HLA-DR+, CD3-, CD16-, CD19-, CD56-, and CD64- are blood DCs that may be CD14+ or CD14-. The method described therefore provides a more accurate and rapid means of identifying circulating DCs.