Figure 2. Role of barrier acquisition in the epidermal response to wound healing.

Under normal conditions the epidermis serves as a barrier to retain water within the body and prevent the entry of infectious agents (e.g., microbes) or chemical agents. Dendritic Langerhans cells, resident in the epidermis, recognize, process, and present antigens to T lymphocytes. In response to trauma to the epidermis, depicted as a full-thickness epidermal wound, keratinocytes increase their proliferation rate and cytokine release. Keratinocytes proliferate and migrate to re-epithelialize the wounded area. T lymphocytes are recruited into the damaged skin. As part of the normal process, keratinocytes initiate the process of terminal differentiation to restore the epidermal barrier. However, if the process of terminal differentiation or barrier recovery is impaired, the skin can enter an inflammatory state.