Bone Abstracts

Introduction: We have recently shown that T cells play a key role in postmenopausal bone loss, here we investigate the influence of estrogen replacement therapy in the control of the immune system and osteoclastogenesis.

Description of methods: We enrolled in the study 30 women with postmenopausal osteoporosis randomized to estrogen replacement therapy (HRT) or raloxifene (RLX) associated with calcium and vitamin D or calcium and vitamin D alone.

Osteoclast precursors (OCP) in peripheral blood, regulatory T cells (Tregs) and cytokines production were evaluated at basal level and after 3, 6 and 12 months of therapy.

Results: OCP were significantly reduced by the sole RLX.

Tregs were reduced by HRT, and not by other therapies. HRT ameliorates T cells immune response. TNFα, IL7, and IFNγ and RANKL:OPG ratio were significantly reduced by HRT.

Conclusion: Here we demonstrate that estrogens have an immunomodulatory effect on T cells, reduce Tregs and ameliorates T cells response to immune stimulation.

HRT reduce the production of pro-inflammatory cytokines as TNFα, IL7, and IFNγ. These cytokines are also responsible for increased osteoclastogenesis.

HRT reduces the RANKL/OPG which is the main driver of osteoclast formation and activity, whereas it has no direct effect on OCP number.

In conclusion our data suggest that the effect of estrogen on bone turnover is mainly mediated by T cells.