The rise and fall of allergic contact dermatitis.

When a simple chemical hapten contacts the skin, it triggers a complex cellular and molecular reaction that eventuates in the cutaneous reaction clinically recognized as allergic contact dermatitis. This review summarizes the crucial role of the cytokines and adhesion molecules that direct the traffic of cells into, and out of, the skin after contact with an allergen. Particularly stressed are the molecular interactions between antigen-bearing Langerhans cells and responding CD4(+) T cells: this interaction results in the amplification of the memory cells that add specificity to the immune response. Finally, negative feedback mechanisms for dampening the response are briefly discussed.