Counterregulation of interleukin-18 mRNA and protein expression during cutaneous wound repair in mice.

Recent work has suggested interleukin-18 to represent a proinflammatory cytokine that contributes to systemic and local inflammation. As the process of cutaneous wound healing crucially involves an inflammatory phase of repair, we investigated the regulation of interleukin-18 during the repair process. In non-wounded skin we observed high levels of interleukin-18 mRNA, whereas corresponding interleukin-18 protein was expressed only at low basal levels. Upon injury, we found a rapid and large induction of interleukin-18 protein expression, which is directly correlated with decreasing mRNA levels within the wound. Immunohistochemical analysis revealed different sites of expression in the wounded area, with keratinocytes as one major source of interleukin-18 production. The counterregulation of interleukin-18 mRNA and protein expression during wound repair in vivo might represent a general mechanism for interleukin-18 expressional regulation, as cytokine-stimulated keratinocytes exhibit a similar downregulation of interleukin-18 mRNA that is directly associated with increasing interleukin-18 protein levels in vitro. The rapid induction of interleukin-18 during wound healing suggests a role for interleukin-18 within the early phase of repair rather than a role in costimulation of interferon-gamma release from T cells, which are present in high numbers within the wounded area only during the late inflammatory phase of repair.