Ex vivo characterization of human thymic dendritic cell subsets

Interactions between thymic dendritic cells (DC) and thymocytes are critical for proper development of T-cells. We identified human thymic DC populations on the basis of CD123, CD11c and CD14 expression. High levels of CD123 (IL-3R) and CD45RA defined the plasmacytoid DC (pDC) subset. Human thymic CD11c+ DC expressed CD45RO and myeloid-related markers (CD13, CD33 and CD11b). CD11c+ DC could be separated into two main subsets based on differential expression of CD14: CD11c+ CD14− and CD11c+ CD14+ cells. Spontaneous production of IL-10 and IFNγ without exogenous stimulation, was observed in the three DC subsets. Important phenotype modifications were observed in pDC cultures supplemented with IL-3. A down-regulation of CD123 and appearance of myeloid markers such as CD11b and CD11c on CD45RA+ cells was noticed within the first 48 h; at a later time there was a shift from CD45RA to CD45RO expression, as well as appearance of CD14 expression. CD11c+ cells emerging in pDC culture did not express high levels of HLA-DR, CD83 and co-stimulatory molecules. This suggests an in vitro evolution of human thymic pDC toward a myeloid phenotype found in the CD11c+ subset of thymic DC.