Dendritic Cells

Dendritic cells play a key role in both innate and adaptive immune responses. They not only function as antigen-presenting cells and express co-stimulatory and co-inhibitory molecules that regulate T cell activation, but they also produce cytokines that direct the differentiation of specific effector T cell subsets. Dendritic cells are a heterogeneous cell population that develops primarily from macrophage-dendritic cell precursors (MDPs) in the bone marrow. MDPs develop into common DC progenitors (CDPs), which give rise to both plasmacytoid dendritic cells (pDCs) and classical dendritic cell precursor cells known as pre-DCs. Both pDCs and pre-DCs migrate through the blood to different tissues, where pre-DCs then differentiate into classical dendritic cells. In mouse lymphoid tissue, two classical dendritic cell subsets have been characterized that express either CD8 alpha or CD11b, while in mouse non-lymphoid tissue, three additional classical dendritic cell subsets have been identified that are either CD103-CD11b⁺, CD103⁺CD11b^-, or CD103⁺CD11b⁺. Additionally, five subsets of dendritic cells have been found in mouse skin including Langerhans cells, and four dermal dendritic cell subsets that are either CD103⁺CD11b^-CD207⁺, CD103^-CD11b^-CD207⁺, CD103^-CD11b^-D207^-, or CD103^-CD11b⁺CD207^-. In humans, two classical dendritic cell subsets have been identified in the blood, spleen, and tonsils that are either CD141/BDCA-3⁺ or CD1c/BDCA-1⁺. These two subsets are thought to correspond to mouse CD8 alpha⁺ and CD11b⁺ dendritic cells, respectively. In addition to these, four other dendritic cell subsets have been characterized in human skin including Langerhans cells, and CD1a^-CD14⁺, CD1a⁺CD1c/BDCA-1⁺, and CD1a⁺CD141/BDCA-3⁺dermal dendritic cells.