Dendritic cell

Dendritic cells are immune cells and form part of the mammal immune system. They are present in those tissues which are in contact with the environment: in the skin (where they are often called Langerhans cells) and the lining of nose, lungs, stomach and intestines. They have long spiky arms, called dendrites, whence the name.

Dendritic cells constantly sample the surroundings for viruses and bacteria. Once they have captured such an invader, they cut its proteins into small pieces and present those fragments at their cell surface using MHC molecules. They then 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 the pieces of the invader. Depending on the type of invader, this results in an immune response involving antibodies or killer cells.

Every helper T-cell is specific to one particular antigen. Only dendritic cells are able to activate a helper T-cell which has never encountered its antigen before.

Dendritic cells form from monocytes, white blood cells which circulate in the body and, depending on the right signal, can turn into dendritic cells or macrophages. The monocytes in turn are formed from stem cells in the bone marrow.

How long do they live?

The HIV virus which causes AIDS is attracted by one particular kind of dendritic cell; when these get infected and then travel to lymph nodes, the virus is able to move to helper T-cells, and this infection of helper T-cells is the major cause of disease.

References

• Jacques Banchereau: The Long Arm of the Immune System, Scientific American Vol 287, No. 5 (November 2002), pp. 52 - 59