Osteoimmunology and aging - a frontier to explore.

Osteoimmunology is an interdisciplinary branch of immunology which studies the interplay of skeletal and immune systems. Both spatial and functional connections exist between the two systems, as most immune cells are generated in the bone marrow microenvironment, which facilitates the communication between the two systems. Moreover, immune cytokines such as RANKL (receptor activating Nf-kB ligand) and non-immune soluble mediators such as osteoprotegrin (OPG), made by immune and bone cells, respectively, interact to influence differentiation and activation of each other. The above interactions become of particular importance in the old age, when dysregulation of both systems yields changes affecting both length and quality of life. This perspective paper will outline both our current understanding as well as general gaps in knowledge, on geriatric osteoimmunology. We will also specifically address two highly prevalent diseases of aging, osteoarthritis and osteoporosis, as major sources of disability, loss of independence and increased morbidity and mortality in older adults, because cellular senescence appears to play a substantial pathogenetic role in both conditions, potentially opening new avenues for diagnosis and treatment.