Cytokine modulation of keratinocyte cytokines

There is increasing evidence that epidermal cytokines may have an important role in mediating inflammatory and immune responses in the skin. A number of cell types in the epidermis are capable of secreting cytokines including keratinocytes, Langerhans cells, melanocytic cells, and even Merkle cells. Keratinocytes are the major source of cytokines in the epidermis and have been reported to secrete IL-1, IL-3, IL-6, IL-8, CSF, TNFα, TGFα, TGFβ, and PDGF. Normally these cytokines are not actively secreted by keratinocytes; however, a number of agents are capable of mediating keratinocyte cytokine production, including cytokines themselves. We examined the effect of a number of cytokines on keratinocyte IL-1, IL-6, GM-CSF, and PDGF production. It was found that these keratinocyte cytokines are all modulated by one or more cytokines, including several that keratinocytes themselves secrete. These effects appear to be mediated by high-affinity cytokine receptors on keratinocytes. We are only beginning to understand the molecular mechanisms underlying the production, regulation, and precise role of keratinocyte cytokines in normal and diseased skin; however, recent studies suggest that cytokines secreted by epidermal cells and lymphoid cells may be important modulators of keratinocyte cytokine production.