Dendritic cells (DCs) are the principal antigen-presenting cells for T lymphocytes, and direct both the quality and the quantity of the immune responses. DCs in peripheral tissues continuously sample the surrounding environment and migrate to regional lymph nodes where they present the antigens captured in the periphery to naïve T lymphocytes. By expressing high levels of co-stimulatory molecules essential for naïve T-cell activation, DCs efficiently direct expansion and then differentiation of antigen-specific effector T cells. In addition DCs, by secreting different cytokines at the time of antigen presentation, provide an additional signal instructing naïve T cells to differentiate into diversely specialised subsets for appropriate adaptive immune response. Given the central role in the activation and regulation of immune responses DCs represent an ideal target for immune system manipulation aimed at either boost responses to pathogens and tumoural cells or reducing self-harmful autoimmune reactions.

Key Concepts:

• Dendritic cells are components of the innate immune system specialised in antigen presentation and cytokine secretion.
  
• Dendritic cells efficiently capture molecules in the surrounding environment including foreign and self-antigens.
  
• Dendritic cells are activated by molecules signalling infection or tissue injury.
  
• Molecules associated with potentially pathogenic organisms are recognised by Toll-like receptors expressed by dendritic cells.
  
• Dendritic cells have the unique ability to prime naïve T lymphocyte to proliferate and differentiate into effector T cells.
  
• Plasmacytoid dendritic cells’ primary task is the rapid and abundant release of type I interferons, in response to viral infection.