The effect of E2 on OC formation and bone resorption in BMC and Treg cell cocultures. BMCs were cocultured with Treg cells in cell-contact transwells at a ratio of 2∶50 on slides (a) and dentine slices (b), with BMC and Treg cell monocultures as controls. E2 was added at the indicated concentrations, with solvent alone included as a control. The data are expressed as mean±SD (n=5). *P<0.05, **P<0.01, compared with controls. BMC, bone marrow cell; E2, 17β-estradiol; OC, osteoclast; TGF, transforming growth factor; TRAP, tartrate-resistant acid phosphatase; Treg, regulatory T.