Immunology of skin transplantation

Untreated viable allogeneic skin is highly immunogenic. Epidermal Langerhans migrate after transplantation out of the donor skin into the lymph node of the recipient where they can activate T cells capable to mediate rejection. Allogeneic skin is used as a temporary coverage of burn wounds, often in combination with autologous skin grafts. Several methods to pretreat the allogeneic skin have been used to delay the rejection process. Processing of allogeneic skin in 85% glycerol results in a non-viable skin with a well-preserved structure. Experiments in a full thickness porcine wound model showed that rejection of glycerol treated allogeneic skin grafts was up to six days delayed. Viable, untreated allogeneic skin grafts were rejected predominantly by CD8 positive T cells whereas in the glycerol treated grafts the influx of host cells was lower and the majority of the cells were macrophages. The outgrowth of the autologous skin grafts underneath glycerol treated allogeneic skin was three days earlier completed when compared to grafts in combination with untreated allogeneic skin. Thus, by processing the allogeneic skin into 85% glycerol, the direct route to induce graft rejection is blocked since the Langerhans cells are non-viable. The glycerol-preserved skin grafts are finally rejected via an indirect route mediated by macrophages; this process is less disturbing for the outgrowth of autologous cells.