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[The skin as an immunological organ].

BACKGROUND
The skin is our largest organ. Its physico-chemical properties are adapted to its function as a non-specific general defense line against infections and injury from the environment. Through evolution the skin has developed a second line of highly specific immune defense comprising epidermal Langerhans cells, T lymphocytes and keratinocytes as the most distinct cellular elements.


MATERIAL AND METHODS
On the basis of available research data and reviews, an overview on the skin as an immunological organ is presented.


RESULTS AND INTERPRETATION
Antigens penetrating into the epidermis are bound to dendritic Langerhans cells, processed and presented to T lymphocytes. Certain memory T cells are able to remember where they first encountered antigen. Skin homing T cells are CLA+ and circulate between the skin, peripheral blood and skin draining lymph nodes. Keratinocytes produce a wide spectre of cytokines, in particular interleukin-1, which has a key role in the skin immune function. The most common inflammatory skin disorders are mediated by T lymphocytes, usually Th1 cells, as in psoriasis, or Th2 cells, as in atopic dermatitis. Systemic treatment with T cell specific suppressive drugs, such as cyclosporine, has been successful in certain dermatoses. Promising cyclosporine analogues for topical treatment (tacrolimus and pimecrolimus) have been developed and may soon be introduced.