Macrophage polarity and wound age determination

We investigated the dynamics of the gene expression of M1 and M2 macrophage markers during skin wound healing in mice. Expression of M1-macrophage markers, such as Il12a, Tnf, Il6, Il1b , and Nos2 was upregulated after wounding and peaked at 1 or 3 days after injury, and that of M2-macrophage markers such as Mrc1, Cd163, Ccl17, Arg , and Tgfb1 , peaked at 6 days after injury. Consistent with these findings, using double-color immunofluorescence analysis revealed that CD80-positive M1 macrophages were more abundant than CD206-positive M2 macrophages on day 3 in mouse wound specimens, and that M2 macrophages were prominently detected in day 6 wounds. For application in forensic practice, we examined macrophage polarization using human wound specimens. The average ratios of HLA-DRα-positive M1 macrophages to CD163-positive M2 macrophages (M1/M2 ratios) were greater than 2.0 for the wounds aged 2–5 days. Furthermore, six of the eight samples individually exceeded the M1/M2 ratio of 2.0 in the range of 1.88–4.30. Therefore, an M1/M2 ratio significantly above 2.0 strongly indicates a wound age of 2–5 days. This study showed that M1 and M2 macrophages in human skin wound might be a promising marker for wound age determination.