Osteoclastogenesis and osteoimmunology.

Bone is continuously renewed through a dynamic balance between bone resorption and formation and is the fundamental basis for maintaining normal bone mass and architecture by osteoclasts (bone resorption) and osteoblasts (bone formation). Bone resorption is an elementary cellular activity in the modeling of the skeleton during growth and development. Later in life, bone remodeling occurs, and is locally initiated by resorption. During remodeling, bone resorption is coupled to new bone formation, that ensures bone renewal with only minor and temporary local bone loss. Osteoclasts play a crucial role in both physiological and pathological bone resorption, and receptor activator of nuclear factor-κB ligand is the key cytokine that induces osteoclastogenesis. At the same time, various factors produced during immune responses are capable of profoundly affecting bone regulation; bone and immune systems share an abundance of molecules and regulatory mechanisms. We summarize the new insights on the link between osteoclastogenesis and osteoimmunology.