الفهرس 
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Abstract
Dendritic cells are potent antigen presenting cells in the immune system with the capacity to regulate immune responses .They represent a heterogenous cell population , residing in most peripheral tissues, particularly at sites of interface with the environment (skin and mucosa).
Dendritic cells arise from distinct bone marrow derived hematopoietic lineages .
Different DCs subsets are described : conventional DC , plasmacytoid and epidermal langerhans cells .In the absence of ongoing inflammatory and immune responses , DCs constitutively circulate through the blood , peripheral tissues, lymph and secondary lymphoid organs. In peripheral tissues , DCs take up self and nonself antigens . Internalized antigens are then processed into proteolytic peptides and these peptides are loaded onto MHC class I and II molecules .This process of antigen uptake , degradation and loading is called antigen presentation. Constitutively , however peripheral DCs present antigen quite inefficiently . Therefore a signal from pathogens , often referred to as a danger signal , is needed to induce DCs to enter a developmental program called maturation , which transforms DC into efficient APC and T cell activators.In addition bacterial and viral products , as well as inflammatory cytokines and other self molecules induce DC maturation through direct interaction with specific DC surface receptors as toll like receptors, cytokine receptors , TNF- R , FcR and sensors for cell death.