Epidermal cytokines and their roles in cutaneous wound healing.

Cytokines are small proteins or glycoproteins which are synthesized and secreted by a variety of cell types. Through binding to specific receptors on target cells, these hormone-like products regulate many normal cell activities, including growth and differentiation, migration and immune functions. Within the epidermis, keratinocytes are the major source of cytokines along with melanocytes and Langerhans cells. In response to a variety of injurious stimuli, including ultraviolet irradiation and cutaneous wounding, epidermal keratinocytes may release a number of these regulatory molecules which can then interact directly with receptors on inflammatory cells. Epidermal cytokines can therefore play an important role in the wound-healing process by recruiting polymorphs and monocytes and in encouraging deposition of extracellular matrix proteins by fibroblasts. Keratinocytes can themselves respond to keratinocyte-derived cytokines by dividing and migrating over the wound surface before differentiating into a new stratified epidermis. This review presents the evidence of the production of cytokines by human keratinocytes and their role in the healing of skin wounds.