Flow cytometric detection of circulating dendritic cells in healthy subjects

Dendritic cells (DCs) are the key antigen-presenting cells controlling the initiation of the T cell- dependent immune response. Currently, two peripheral blood DC subsets have been identified on the basis of their CD11c expression. The CD11c-negative (CD11c–) DCs (expressing high levels of CD123) are designated as lymphoid-derived DCs (DC2), whereas the CD11c+/CD123– cells, do identify the myeloidderived DCs (DC1). A growing number of studies have been conducted in recent years on both the quantitative and functional alterations of DCs and their subsets in different pathological conditions. In the present study we assessed, using two different flow cytometric (FCM) techniques, the normal profile of blood DCs in 50 italian adult healthy subjects (M/F: 25/25, median age 42.5 years, range 20-65). The percentage and the absolute number of DCs and their subsets, were obtained starting from whole blood samples in two ways: 1) by calculating the number of DCs when gated as lineage-negative/ HLA-DR+ and identifing the two subsets as CD11c+ (DC1) and CD123+ (DC2) and 2) by using three specific markers: BDCA.1 (CD11c+ high/CD123+ low, myeloid DCs); BDCA.2 (CD11c-/ CD123+high, lymphoid DCs); BDCA.3 (CD11c+low /CD123–, myeloid DCs). Six parameters, 4-color FCM analysis were perfomed with a BD FACSCanto equipment. The mean values of the percentage and of the absolute number were: 0.5±0.2% and 30±11 cells/?L for DCs; 0.2±0.1% and 15±6 cells/?L for DC1; 0.2±0.1% and 15±7 cells/?L for DC2. The same values were: 0.2±0.1% and 16±7 cells/?L for BDCA.1; 0.2±0.1% and 12±7 cells/?L for BDCA.2; 0.02±0.01% and 2±1 cells/?L for BDCA.3, respectively. Our study confirmes that the two types of FCM analysis are able to identify the DC population. We also provides the first reference values on normal rates and counts of blood DCs in italian adult healthy subjects.