Enumeration and phenotypic assessment of human plasmacytoid and myeloid dendritic cells in whole blood.

Traditionally, flow cytometry analysis of dendritic cells (DC) has followed a negative selection procedure, often limiting the characterization of individual DC subsets to enumeration. We demonstrate the development, evaluation, and clinical application of a novel 6 color/8 parameter flow cytometry panel to allow enumeration and monitoring of activation status of circulating human myeloid (MDC1) and plasmacytoid (PDC) dendritic cells in human whole blood. Enumeration showed a trend of greater numbers of MDC1s and PDCs being collected for fresh whole blood than frozen PBMCs, with this difference being statistically significant (P = 0.04) for unstimulated PDC enumeration. Intra-assay variation had a coefficient of variation <10% and interassay results between operators showed good correlation (r > 0.95). Our results on fresh whole blood showed a significant up regulation of CD83 on both MDC1 and PDC at 4 h post Toll-like ligand stimulus and this activity was comparable in frozen PBMC samples. Comparison for the late activation marker CCR7 showed a significant difference (P <0.05) in expression between fresh and frozen samples, precluding its use for batch analysis of frozen samples. In addition, the level of activation is dependent on the anticoagulant used for sample collection. For CD83 expression at 4 h both EDTA and lithium heparin samples are comparable for MDC1 and PDC populations. Whereas for CCR7 expression, lithium heparin is preferable as EDTA increases the background expression in PDC, preventing further functional assessments. We demonstrate the importance of establishing the kinetic profile of activation marker expression and the importance of evaluating sample collection tubes and sample type before application of novel cytometry panels to a clinical study. We have shown that this DC enumeration flow cytometry panel is a robust analysis system that allows the flexibility of including activation markers.