Cellules immunocompétentes

The skin provides a complex microenvironment where several cell populations actively participate in the initiation and regulation of inflammatory and immune responses. Cutaneous dendritic cells serve as dominant antigen-presenting cells in the induction of T-cell mediated immune responses and subsequent reactivation of T cells. Under homeostatic conditions, however, dendritic cells are primarily involved in the maintenance of immune tolerance to self- and innocuous non-self antigens. T lymphocytes with specificity for antigens penetrating through the skin acquire the propensity, by virtue of the expression of specific homing receptors, to recirculate in the skin. Keratinocytes have the capacity to secrete an array of cytokines and chemokines very important for the regulation of dendritic cell functions, and the recruitment and activation of inflammatory cells; in addition, keratinocytes can directly modulate T cell activation by expressing on their surface adhesion molecules and major histocompatibility complex class II molecules. Mast cells and peptidergic nerve endings form an integrated unit which can readily release factors involved in the initiation of the vascular phase of acute inflammation, but, together with endothelial cells, they also regulate cell-mediated immune responses.