Antigen presentation in the skin: modulation by u.v. radiation and chemical carcinogens.

The skin provides an excellent model to investigate antigen presenting cells (APC) particularly using contact hypersensitivity responses. The skin has its own distinct APC of which Langerhans cells (LC) are the best characterized. Fluorescein isothiocyanate (FITC) has proved a useful reagent with which to follow antigen-labeled APC to draining lymph nodes, where they bind to T lymphocytes. Cluster formation appears to be a necessary component of the APC-T cell interaction. Both u.v. radiation and chemical carcinogens are able to alter LC in the skin, resulting in immunological tolerance when antigen is presented through such treated sites. The changes in APC function are linked mainly to the tumor promoting action of carcinogens. The nature of the APC that trigger suppressor circuits and the potential chemical mediators involved are discussed. These studies have important implications for the immunobiology of the skin and for cutaneous carcinogenesis.