A Review of Monocytes and Monocyte-Derived Cells in Hypertrophic Scarring Post Burn

Pediatric burns remain a common injury after which many patients develop a severe form of scarring known as hypertrophic scarring. The formation of the hypertrophic scar arises from excessive production of collagen during wound healing. Wound repair and regeneration represents a complex process that is accomplished through many biological processes involving various cell types, extracellular matrix proteins, cytokines, and other mediators. One important cell type is the monocyte, which displays an altered profile in many wound models. These profile changes may function as biomarkers, reflecting and/or influencing the clinical outcome of the healing response seen after burn injury. Monocytes circulate in the blood and then enter into the tissue, where they further differentiate into macrophages, which serve various functions, including immune defense and tissue remodeling. More recently, these cells have been characterized in detail based on cell surface markers expressed and genes up-regulated, enabling subpopulations to be identified. Fibrocytes, which are also monocyte-derived cells, have been shown to contribute to collagen production in the burn wound and are associated with hypertrophic scarring. They may represent a unique subpopulation of macrophages that, due to their production of collagen, promote tissue fibrosis rather than wound repair. A better understanding of the relationship among monocytes, fibrocytes, and macrophages may improve our appreciation of the factors influencing scar formation and tissue remodeling.