Fig. 5: Analysis of the local macrophage and dendritic cell populations at the site of injury 3 days post-surgery revealed significant differences in macrophage polarization, activation, and dendritic cell subsets.

Macrophages and dendritic cells were analyzed via flow cytometry in the untreated bone marrow and at the fracture site in the immunoaged and aged groups. a Three days post-surgery, significantly more macrophages were present around the fracture gap than in the untreated bone marrow. b The activation state of macrophages at the fracture site differed, as significantly more M1-polarized macrophages could be found in the immunoaged group than in the aged group 3 days post-surgery. Additionally, an increased level of M2a-activated macrophages was observed in the immunoaged group. These data showed an increased activation state in the mice with higher adaptive immune experience and depicted a prolonged inflammatory phase. c Immunoaged mice showed an increased level of plasmacytoid dendritic cells (pDCs) at the fracture site compared to that in aged mice 3 days post-surgery. In contrast, increased levels of specified CD4+ and CD8+ lymphoid tissue-resident classical dendritic cells (lDCs) could be found in aged mice compared to immunoaged mice. d Increased adaptive immune experience significantly altered the innate immune system by increasing CD205+ expression on CD8+ lDCs. Higher expression levels of CD205+ on DCs facilitate communication with CD8+ T cells. N = 4 per group; box-and-whisker plot with a line at the median; Welch’s t-test; black * = between immunological experience groups, gray * = between untreated and osteotomized groups.