Characterising a large population of langerin+, MHC-II+ cells in mouse skin wounds

Abstract

Developing a thorough understanding of wound healing is crucial given the importance of the skin and the many challenges medical professionals face when it is damaged. The immune system is very involved in the healing process, and it has been noted that a large part of the healing outcome depends on the types of immune cells present and the size of their populations. Langerin expressing cells were found one day post wounding in mouse skin within the dermis and hypodermis adjacent to the wound by the Wise Laboratory (Wise et al., 2012). All known langerin expressing cells at the wound site are antigen presenting cells. These have been reported to arrive days later in the healing process. This research aims to investigate and characterise the langerin expressing cells of interest at the wound site.

A Langerhans cell depletable langDTR mouse model was used in this study. Langerin depletion failed to eliminate the cells of interest from the wound as it did the Langerhans cells in the epidermis, indicating that the population might be distinct from Langerhans cells. As shown by immunohistochemistry, the cells of interest were found to express markers associated with stem cells (CD34), migrating cells (vimentin), as well as antigen presenting cells (MHC-II), macrophage (F4/80), and dendritic cells (langerin, CD11b, CD11c). A timeline was created of wounds at different time points with langerin and MHC-II expressing cells targeted. This showed a peak in langerin and MHC-II co-stained cells one day post wounding. In order to assess whether the langerin expressing cells were present in other wound environments, burn wounds were created by the Wise Laboratory and immunohistochemistry was used to detect langerin and MHC-II expression for the cells of interest. At Day four the burn wounds did contain a large population of langerin and MHC-II expressing cells which were compared to the population in the biopsy wounded skin and found to be very similar in morphology however the population was smaller in the burned skin. PCR analysis revealed an environment which was generally proinflammatory, with upregulation MCP-1, which is associated with monocytes and facilitates cellular movement into an inflamed area, and MIP2 alpha which is a chemotactic signal in inflammatory environments. To a lesser extent, CCR7, associated with stimulated dendritic cells, including Langerhans cells and CXCL10, a chemokine associated with lymphocyte activation were also upregulated. Confocal and Multiphoton microscopy confirmed the efficacy of the langerin depleted mouse model used as shown with green fluorescent protein expressing Langerhans cells of interest in the epidermis of an undepleted LangDTR mouse.

These findings show that the langerin expressing cells of interest are most likely early Langerhans cells, a group of monocyte derived cells which rapidly infiltrate the wound area and repopulate the epidermis following trauma. These findings demonstrate how rapidly the early Langerhans cells enter the wound area and provide a more in depth characterization of the cells which have only recently been discovered in mouse skin.