Formation of immature cells and their maturation thumb|400px|Diagram of hematopoiesis from HSC, showing a separate dendritic cell lineage via CDP (Common Dendritic-cell Progenitor). Dendritic cells are derived from hematopoietic bone marrow progenitor cells (HSC). These progenitor cells initially transform into immature dendritic cells. These cells are characterized by high endocytic activity and low T-cell activation potential. Immature dendritic cells constantly sample the surrounding environment for pathogens such as viruses and bacteria. This is done through pattern recognition receptors (PRRs) such as the toll-like receptors (TLRs). TLRs recognize specific chemical signatures found on subsets of pathogens. Immature dendritic cells may also phagocytose small quantities of membrane from live own cells, in a process called nibbling. Once they have come into contact with a presentable antigen, they become activated into mature dendritic cells and begin to migrate to a lymph node. Immature dendritic cells phagocytose pathogens and degrade their proteins into small pieces and upon maturation present those fragments at their cell surface using MHC molecules. Simultaneously, they upregulate cell-surface receptors that act as co-receptors in T-cell activation such as CD80 (B7.1), CD86 (B7.2), and CD40 greatly enhancing their ability to activate T-cells. They also upregulate CCR7, a chemotactic receptor that induces the dendritic cell to travel through the blood stream to the spleen or through the lymphatic system to a lymph node. Here they act as antigen-presenting cells: they activate helper T-cells and killer T-cells as well as B-cells by presenting them with antigens derived from the pathogen, alongside non-antigen specific costimulatory signals. Dendritic cells can also induce T-cell tolerance (unresponsiveness). Certain C-type lectin receptors (CLRs) on the surface of dendritic cells, some functioning as PRRs, help instruct dendritic cells as to when it is appropriate to induce immune tolerance rather than lymphocyte activation.
formation of immature cells and their maturation thumb|400px|diagram of hematopoiesis from hsc showing a separate dendritic cell lineage via cdp (common dendritic-cell progenitor) dendritic cells are derived from hematopoietic bone marrow progenitor cells (hsc) these progenitor cells initially transform into immature dendritic cells these cells are characterized by high endocytic activity and low t-cell activation potential immature dendritic cells constantly sample the surrounding environment for pathogens such as viruses and bacteria this is done through pattern recognition receptors (prrs) such as the toll-like receptors (tlrs) tlrs recognize specific chemical signatures found on subsets of pathogens immature dendritic cells may also phagocytose small quantities of membrane from live own cells in a process called nibbling once they have come into contact with a presentable antigen they become activated into mature dendritic cells and begin to migrate to a lymph node immature dendritic cells phagocytose pathogens and degrade their proteins into small pieces and upon maturation present those fragments at their cell surface using mhc molecules simultaneously they upregulate cell-surface receptors that act as co-receptors in t-cell activation such as cd80 (b71) cd86 (b72) and cd40 greatly enhancing their ability to activate t-cells they also upregulate ccr7 a chemotactic receptor that induces the dendritic cell to travel through the blood stream to the spleen or through the lymphatic system to a lymph node here they act as antigen-presenting cells they activate helper t-cells and killer t-cells as well as b-cells by presenting them with antigens derived from the pathogen alongside non-antigen specific costimulatory signals dendritic cells can also induce t-cell tolerance (unresponsiveness) certain c-type lectin receptors (clrs) on the surface of dendritic cells some functioning as prrs help instruct dendritic cells as to when it is appropriate to induce immune tolerance rather than lymphocyte activation