Purification of Dendritic Cells from Peripheral Blood

It is well established that dendritic cells (DC) exhibit different phenotypes and functions as they progress down the developmental pathway toward interdigitating DC that stimulate T cells in the secondary lymphoid tissue (1 ). In the blood, two populations of DC can be identified based on the expression of the β-intergrin, CD1 1c. For most individuals, the proportion of DC that are CD1 1c⁺ ranges from 30% to 70%. The CD11c^- population was originally proposed to be the precursor of the CD1 1c⁺ cells, but there is now good evidence that they constitute a distinct population of DC that have a separate developmental pathway (2 ,3 ). The CD11c⁺ blood DC give rise to the Langerhans cells located in the epidermal layers of the skin and mucosal tissue, where their function is to capture and process antigens from invading pathogens for presentation. Dermal and interstitial DC are also derived from CD1 1c⁺ blood DC. CD1 1c- DC, on the other hand, are thought to migrate directly to secondary lymphoid tissue and not to take up residence in the tissues. CD11c⁺ and CD11c^- DC were claimed to stimulate Th1 and Th2 types of immune responses, respectively, and hence were termed DC1 and DC2 (2 ). However, other reports suggest that both cell populations can stimulate Th1 and Th2 responses (4 ). The role of the CD11c^- DC is currently unclear but they are potent producers of interferon-α (4 ,5 ) and could therefore be important in antiviral immunity. Elucidating the function of these cells and comparing them with the CD1 1c⁺ population will be a major aim of DC research groups in the future. There is thus a need for techniques to purify these two cell populations.