The Immunological Facets of Chondrocytes in Osteoarthritis: A Narrative Review

. Osteoarthritis (OA) is a disease in which the pathogenesis affects the joint and its surrounding tissues. Cartilage degeneration is the main hallmark of OA, and chondrocytes within the cartilage regulate matrix production and degradation. In patients with OA and in animal models of OA, the pathology of the disease relates to disequilibrium between anabolic and catabolic states of the cartilage. Moreover, chondrocyte phenotype and function are also immunologically altered. Under inflammatory conditions, chondrocytes increase production levels of inflammatory cytokines and cartilage-degrading enzymes, which further drive cartilage destruction. Chondrocytes also have an innate immune function and respond to damage-associated molecular patterns (DAMPs) and cartilage fragments by innate immune receptors. In addition, chondrocytes play a role in adaptive immune responses by acting as antigen-presenting cells and presenting cartilaginous antigens to T cells. Indirectly, chondrocytes are stimulated by pathogen-associated molecular patterns (PAMPs) present in the joints, a result of the microbiota of the host. Chondrocytes have both direct and indirect relationships with immune cells and the immune compartment of patients with OA. Therefore, chondrocytes serve as a target for immunotherapeutic approaches in OA. In this narrative review, we cover the aforementioned immune-related aspects of chondrocytes in OA.