The number of immune cells is lower in healthy oral mucosa compared to skin and does not increase after scarring

• The number of several immune cells was compared between human skin and oral mucosa.
• Oral mucosa had significantly fewer immune cells than skin.
• More blood vessels were present in the oral mucosa compared to skin.
• Scars contained similar numbers of immune cells compared to healthy tissues.
• Less immune cells in the healthy oral mucosa could improve repair.

ObjectiveDepending on the location of injury, wounds can heal with different outcomes. In addition foetal wounds heal fast without scar formation, while scars are a common feature of regular skin repair. Since inflammation is very limited in these wounds reduced numbers or even absence of immune cells might be responsible for scarless foetal wound healing. It is thought that various immune cells, such as macrophages, neutrophils and T-cells, play a role in aberrant wound healing and the fibrotic process seen in scar formation in the adult skin. Similar to the foetus, oral wounds show comparable healing properties by means of accelerated reepithelialization and negligible scar formation. It is possible that reduced inflammatory reaction as a result of lower numbers of immune cells are present in oral wounds compared to skin wounds.DesignHere we investigated the presence of various immune cells in human skin and oral mucosa, with or without scars. The presence or absence of these cells may play a role in the different modes of healing observed between the two types of tissue. Mast cells, neutrophils, M1/M2 macrophages, T-cells and blood vessels were localized in healthy and scarred skin and oral mucosa (scars >1 year old).ResultsOral mucosa had significantly fewer neutrophils, macrophages, mannose receptor-positive M2 macrophages, but more blood vessels. Scars contained similar numbers of immune cells compared to healthy tissues.ConclusionsLess immune cells in the healthy oral mucosa may induce a diminished immune reaction when wounding occurs, and could explain the better healing capacity of the oral mucosa.