The Immune Microenvironment in Cartilage Injury, Repair and Regeneration

Since articular cartilage lacks blood vessels, nerves, and lymph tissue, its ability to repair itself is limited. Once damaged, it can lead to joint swelling and pain, accelerating the progression of osteoarthritis. Complete regeneration of hyaline cartilage with good mechanical properties remains an elusive goal, despite the many technologies available today. The inflammatory milieu created by cartilage damage is critical for chondrocyte death and hypertrophy, extracellular matrix breakdown, ectopic bone formation, and the progression of cartilage injury to osteoarthritis. In the inflammatory microenvironment, MSCs undergo aberrant differentiation, and chondrocytes begin to convert or dedifferentiate into cells with a fibroblast phenotype, resulting in fibrocartilage with poor mechanical qualities. All of these suggest that inflammatory problems may be a major stumbling block to cartilage repair. To produce a milieu conducive to cartilage regeneration, multi-dimensional management of the joint inflammatory microenvironment in place and time is required. Therefore, it is of great significance to elucidate the immune microenvironment of cartilage repair and regeneration after injury. This review provides a brief overview of:（1）the pathogenesis of cartilage injury（2）immune cells in cartilage injury and repair（3）effects of inflammatory cytokines on cartilage repair;（4）clinical strategies for the treatment of cartilage defects（5）strategies for targeted immunoregulation in cartilage repair and regeneration.