TNFSF11 and chronic obstructive pulmonary disease: In fact, tumor necrosis factor a (TNF-α) and interleukin-6 (IL-6) have been reported to be associated with osteoporosis in COPD patients (26), and both factors are known to stimulate osteoclasts and increase bone resorption through RANKL-mediated bone resorption in vitro (27).