Osteoimmunology and its implications for transplantation.

Osteoimmunology is a field of research dedicated to the study of the interactions between the immune system, the hemopoietic system and bone. Among the cells of the immune system that regulate bone cells and the hemopoietic function are T lymphocytes. These cells secrete inflammatory cytokines that promote bone resorption, as well as Wnt ligands that stimulate bone formation. In addition, T cells regulate bone homeostasis by cross talking with BM stromal cells and osteoblastic cells via CD40 ligand (CD40L) and other costimulatory molecules. This article describes the immune cells relevant to bone and the hemopoietic function, reviews the role of lymphocytes as mediators of the effects of PTH and estrogen in bone and the hemopoietic system and discusses the implication of osteoimmunology for transplant medicine.