ABSTRACT
Contact allergy (allergic contact dermatitis) is a form of delayed-type hypersensitivity reaction and as such is dependent upon cell-mediated immune function and the activity of T lymphocytes. For the purposes of this chapter, the events that lead to contact sensitization of the susceptible individual, and which later result in the appearance of contact hypersensitivity reactions following subsequent exposure to the inducing allergen, can be separated into a number of stages. Following first encounter with the chemical sensitizer a pattern of changes is provoked in the skin which serves to modulate the movement and function of cutaneous dendritic cells. It is the responsibility of these cells to transport allergen in sufficient quantity and in an immunogenic form to the lymph nodes draining the site of exposure. Here responsive T lymphocytes are activated and induced to divide and differentiate. The daughter cells resulting from the proliferation of responsive lymphocytes provide immunological memory and ensure that after subsequent contact with the same chemical allergen an accelerated and more aggressive immune response will be mounted. Such secondary immune responses are stimulated in the skin and the local activation of allergen-specific T lymphocyte initiates the cutaneous inflammatory process that is recognized clinically as allergic contact dermatitis.
