Role of macrophage polarisation in skin wound healing

Skin wound healing is a complex pathophysiological change that is driven by macrophages and their secreted related factors. Depending on the stimuli, macrophages can be polarised into two subtypes of macrophages with completely different phenotypes and functions, namely M1 and M2. The aim of this study was to explore the role of M1 and M2 macrophages in skin healing in order to develop new drugs for the treatment of refractory wounds. Primary bone marrow-derived macrophages (BMDMs) were isolated from rats and expanded in vitro using macrophage colony stimulating factor. In addition, the BMDMs were polarised into the M1 and M2 subtypes using lipopolysaccharides (LPS) and interleukin-4 (IL-4), respectively. Cytokine levels in the culture supernatants were measured by an enzyme linked immunosorbent assay. Epidermal wounds were made on the dorsal surface of rats, and treated with M1 or M2 cell suspensions or phosphate buffered saline. Wound healing was recorded on days 1, 3, 7, 10, and 14 after stamping, and the wound healing rate was measured by haematoxylin-eosin and Masson staining. A total of 3 to 4 × 10⁷ bone marrow cells were extracted from each rat femur. The BMDM culture had 87.1% CD45⁺ cells, 89.2% CD68⁺ cells, and 86.5% CD45⁺ CD68⁺ cells. Furthermore, IL-12 (P < .05) and IL-10 (P ≥ .05) levels, respectively, increased and decreased in the culture supernatants of the M1 cells after LPS stimulation compared with those in the M0 (unstimulated) group. Likewise, IL-4 stimulation led to a significant increase in IL-10 levels (P < .01) in the conditioned media of M2 cells, while that of IL-12 decreased slightly (P ≥ .05). In the rat model, the infusion of M2 cells accelerated wound healing and tissue regeneration, whereas the M1 cells delayed the recruitment of inflammatory cells, granulation growth, and collagen deposition, which impaired wound healing. Macrophage polarisation and activation are critical for skin wound healing. While exogenous M1 cell infusion delayed wound healing, the M2 cells promoted wound healing in a rat model.