Immunological function in osteoporosis.

An imbalance of osteoblastic bone formation and osteoclastic bone resorption is thought to be responsible for the osteoporotic condition. The pathological events leading to this disorder are, in most instances, uncertain. A defect in the ability of osteoporotic patients to respond to foreign histocompatibility antigens in a mixed leukocyte reaction is reported here. The results further show that this defect is due both to a poorly responding lymphocyte population as well as to a suppressor factor in osteoporotic sera. In addition, there is a significant increase in the relative and absolute numbers of T cells in the patients' peripheral blood, while serum IgG, IgA, and IgM remain within the normal range. These findings are discussed in the light of a common immunopathological pathway regulating osteoclastic activity and leading to the osteoporotic condition.