Immune Cells and Bone Resorption

The concept of interactions between cells of the immune system and bone in the control of bone turnover is far from new. The relationship between haematopoietic precursor cells and the osteoclast has long been recognised and studies on animals with congenital bone diseases such as osteopetrosis have identified defective components of the immune system as causing or contributing to the disease. For example, the op/op (osteopetrotic) rat exhibits thymic atrophy and the disease can be cured by either administration of normal bone marrow cells or by thymus transplant l. Several mutant rodents have been described in which the osteopetrosis can be cured by injection of bone marrow, spleen or thymocytes l. These studies suggest that a functioning immune system is necessary for the normal activity of the bone resorbing cells.