Osteoimmunology--the hidden immune regulation of bone.

Osteoimmunology is an emerging field of research dedicated to the investigation of the interactions between the immune and skeletal systems. These interactions are not only mediated by the release of cytokines and chemokines but also by direct cell-cell contact. Recently, it was proposed that immunoreceptors found in the immune cells are also an essential signal for osteoclasts activation, along with receptor activator NF-kappaB (RANK) ligand (RANKL) and macrophage-colony stimulating factor (M-CSF). In addition, adipose tissue also produces several factors (adipokines) that are known to interfere with the immune system and bone homeostasis. Chronic inflammation strongly influences osteoimmunology determining profound metabolic, structural and functional changes in bone.