Innate and adaptive immune system cells implicated in tendon healing and disease

Tendons perform a critical function in the musculoskeletal system by integrating muscle with skeleton and enabling force transmission. Damage or degeneration of these tissues lead to impaired structure and function, which often persist despite surgical intervention. While the immune response and inflammation are important drivers of both tendon healing and disease progression, there have been relatively few studies of the diverse immune cell types that may regulate these processes in these tissues. To date, most of the studies have focused on macrophages, but emerging research indicate that other immune cell types may also play a role in tendon healing, either by regulating the immune environment or through direct interactions with resident tenocytes. The present review synthesises the literature on innate and adaptive immune system cells that have been implicated in tendon healing or disease, in the context of animal injury models, human clinical samples or in vitro experiments.