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. 2020 Feb 7;11:163. doi: 10.3389/fimmu.2020.00163

Figure 1.

Figure 1

Role of MCs in physiological bone turnover and bone disease. (A) In physiological bone turnover, few MCs are located in the bone marrow of the metaphysis, preferentially adjacent to bone surfaces. (B) In osteoporotic bone, more MCs are found in the bone marrow which are frequently co-localized with osteoclasts and influence their resorption activity by releasing mediators including histamine, TNF-α and IL-6. (C) In rheumatoid arthritis, increased MC numbers and concentrations of MC-mediators including histamine, tryptase, IL-6, and IL-17 are found in the inflamed joint, inducing osteoclastic bone resorption and T-cell driven inflammation. (D) In fracture healing, MCs regulate bone-fracture induced inflammation by releasing inflammatory cytokines including IL-6, and influence innate immune cell recruitment. During the repair phase, few MCs are located in the fracture callus mainly near blood vessels; MC numbers increase during callus remodeling, where MCs are found in close proximity to osteoclasts and regulate bone resorption by releasing osteocatabolic mediators including histamine.