The role of macrophages in skin homeostasis

The skin and its appendages comprise the largest and fastest growing organ in the body. It performs multiple tasks and maintains homeostatic control, including the regulation of body temperature and protection from desiccation and from pathogen invasion. The skin can perform its functions with the assistance of different immune cell populations. Monocyte-derived cells are imperative for the completion of these tasks. The comprehensive role of macrophages and Langerhans cells in establishing and maintaining skin homeostasis remains incompletely defined. However, over the past decade, innovations in mouse genetics have allowed for advancements in the field. In this review, we explore different homeostatic roles of macrophages and Langerhans cells, including wound repair, follicle regeneration, salt balance, and cancer regression and progression in the skin. The understanding of the precise functions of myeloid-derived cells in the skin under basal conditions can help develop specific therapies that aid in skin and hair follicle regeneration and cutaneous cancer prevention.