Identification and Immunophenotypic Analyses of Peripheral Blood Dendritic Cells

Dendritic cells (DC) form a complex network of cells that are distributed throughout the body and whose primary function is the stimulation of antigen-specific immune responses (1 ). DC are derived from CD34⁺ progenitor cells located in the bone marrow (2 ) and undergo a complex process of maturation as they migrate first to peripheral tissues and then to the secondary lymphoid tissue. The vascular tree provides an ideal system for the distribution of DC from where DC were first isolated in 1982 (3 ). It is presumed, although not proven, that these peripheral blood DC (PBDC) are migrating from the bone marrow to peripheral tissues. More recent studies have demonstrated that at least two subsets PBDC exist that have distinct phenotypic (4 ,5 ), functional (6 -9 ), and developmental (10 ) characteristics. These two subpopulations of PBDC are characterized by an absence of surface markers for other lineages and the phenotypes CD11c^- CD2^- CD13^- CD33^DIM HLA-DR⁺⁺ and CD11c⁺ CD2⁺ CD13^- CD33^Bright HLA-DR⁺⁺⁺ respectively (5 ,6 ,10 ). The cellular morphology of these PBDC subsets differs from one another and from that of mature DC in that the CD11c^- population possesses a lymphoid appearance and the CD11c⁺ population possesses a monocytoid morphology (5 ,10 ). Furthermore, both subsets lack expression of both the Langerhans cell marker CD 1a and the DC maturation marker CD83 and express only low levels of adhesion and costimulatory molecules CD80, CD86, CD40 suggesting that these cells are relatively immature DC. However, when cultured, both populations develop into cells with typical dendritic cell morphology that express high levels of adhesion and costimulatory molecules and that possess potent allostimulatory function (5 ,6 ,10 ).