TNFSF11 and osteoporosis: The immune system can regulate bone metabolism through B-cell, T-cell and many cytokines, as well as osteoblast development and bone turnover through the RANKL/RANK/OPG pathway, but when activated abnormally it can disrupt the balance between osteoblasts and osteoclasts, leading to an imbalance between bone formation and bone resorption (Weitzmann and Ofotokun, 2016; Bozec and Zaiss, 2017; Zhao et al., 2018), which in turn induces osteoporosis.