Immune system and bone metabolism: Does thymectomy influence postmenopausal bone loss in humans?

Recent studies of animal models have suggested that an increase in the number of T cells due to both peripheral expansion and increased thymic T cell output plays a key role in the regulation of bone loss after ovariectomy. Osteoclastogenic cytokines which are either produced by T cells or activate T cells have also been implicated in ovx induced bone loss. Among them are TNF alpha and IL-7. The present study investigates the role of thymectomy (THX) and IL-7 in bone metabolism in humans. We studied T cells subsets, cytokine production and bone metabolism in 13 women thymectomized for Myasthenia gravis as compared to healthy controls. Our data demonstrate that the number of CD4+ and TNF-producing T cells is lower in THX women as compared to euthymic controls. However in THX women the residual T cells produce higher levels of IL-7 and RANKL. Furthermore, flow cytometry shows that IL-7 is produced by T and B cells. Serum levels of TNF alpha were unaffected by THX and both serum TNF alpha and the RANKL/OPG correlated inversely with BMD. There were no differences in bone turnover and bone mineral density between THX women and the controls.