Cells of the immune system, probably of myeloid origin, though some evidence suggest at least some types may be derived from lymphoid precursors.

Discovered by Ralph Steinman, these cells are exquisite antigen presenting cells (APC). They are able to stimulate T-cells to a much greater extent (given similar doses of antigen) than other APCs.

The current model of how dendritic cells, or DC, function in T-cell responses:

  1. Immature DC encounters antigen, takes up antigen through phagocytosis and/or pinocytosis.
  2. As the DC matures, it moves to the lymph node.
  3. In it's mature state, DC do not take up additional antigen, and have high levels of MHC molecules and co-stimulators on their surface.
  4. In the lymph node, T-cells are activated by the mature DC, proliferate, exit the lymph node, and traffic to the site of infection, presumably where the DC originally came from.

The discovery of the DC has somewhat marginalized the function of the macrophage, which was previously thought to be the master APC. Now, it seems that DC are most important in the initiation of T-cell-mediated immune responses, and that the macrophage functions at sites of infection.