Role of skeletal macrophages in fracture repair: A systematic review

In the field of bone research, the importance of the function of skeletal macrophages (sMΦ) and their crucial role in immune homeostasis and bone regeneration has been extensively studied. The aim of the present systematic review was to summarize the role of sMΦ in bone fracture healing and to evaluate their potential for immunoregulatory therapy in bone regeneration. A systematic literature search of PubMed and Embase® was performed to retrieve studies on the role of sMΦ in bone injury repair. The Systematic Review Centre for Laboratory animal Experimentation tool was used to assess the risk of bias of the studies included. A total of four articles were included in the present review. A relatively high risk of bias was identified in the included articles as none of the assessors in these studies were blinded. sMΦ were defined by the surface markers F4/80+, Mac-2- / low, TRAP-, CD169+, Ly6G- and CD115low. All of the studies provided support for the essential role of sMΦ in intramembranous ossification or endochondral ossification during fracture healing. F4/80+Mac-2-CD169+ sMΦ are a promising therapeutic target for immunoregulatory therapy of bone repair due to their essential role in bone formation and homeostasis. Future studies aimed at profiling and modulating sMΦ to promote bone regeneration are required.