Immunologic crosstalk in synovium cartilage and bone under inflammatory stress

• Author Details:   
• Madhan Jeyaraman ^*
• Swaminathan Ramasubramanian
• Naveen Jeyaraman

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Inflammatory joint diseases involve a complex interplay among synovial membrane, articular cartilage, and subchondral bone. In rheumatoid arthritis, immune?mediated processes in synovium drive pannus formation that invades cartilage and bone, with fibroblast?like synoviocytes adopting aggressive phenotypes. In osteoarthritis, synovitis can precede gross cartilage degradation, with innate immunity and damage?associated ligands activating Toll?like receptors; this amplifies catabolic cytokines that disrupt cartilage homeostasis. Fibroblast?like synoviocytes govern matrix metalloproteinases and RANKL production for osteoclast differentiation, influencing bone remodeling. Synovial macrophages and T cells engage in reciprocal activation loops, promoting hyaluronan?dependent leukocyte adhesion and sustaining inflammation. Chondrocytes also contribute immunologically by secreting cytokines and presenting antigens to infiltrating immune cells. Bone cells, including osteoclasts and osteoblasts, further engage via RANK/RANKL and other factors to amplify joint destruction. Understanding this tri?tissue dialogue informs novel therapeutic avenues to interrupt destructive circuits and restore joint homeostasis.

Keywords: Synovial inflammation, Chondrocyte immunomodulation, Osteoimmunology, Fibroblast-like Synoviocytes (FLS), Cartilage-Bone Crosstalk, Rheumatoid and Osteoarthritis pathogenesis.