Interactions between multipotential stromal cells (MSCs) and immune cells during bone healing

The physiological process of bone healing takes place in three sequential stages: inflammation, repair and remodelling. Multipotential stromal cells (MSCs) are the key progenitor cells for osteoblasts and chondrocytes and are also imbued with immunomodulatory capabilities. Although MSCs are well known to be involved in osteogenesis during the later stages of repair, their role during the inflammatory phase and precise interactions with immune cells remain poorly understood. This chapter describes the current knowledge on cellular interactions during the bone repair as well as cytokines and growth factors mediating these processes. The roles of emerging innate immune cell populations, innate lymphoid cells are also discussed. Based on this current knowledge, we conclude that in addition to their differentiation during later bone repair stages, MSCs are likely to have a substantial involvement in the initial stage of bone healing by controlling the fate of inflammation. An improved understanding of complex cell interactions during bone repair has broad implications on optimising the treatment of the fracture complications including non-union.