Sustained elevation in plasmatic TGF-β1 levels in hosts repopulated with WT or

opg^−/− TPO virus–infected BM cells. TGF-β1 was measured in PPP by ELISA after acidification of the samples. Each bar represents the mean ± SD of 7 to 10 animals per experimental group as indicated under the x-axis. The mice receiving transplants were analyzed at 1 month (open bars), 2 months (hatched bars), and 3 months (dotted bars), except for the WT/opg^−/− group where samples were lost accidentally. Independently of the graft/host combination, levels of latent TGF-β1 were significantly (P < .01) increased over control levels (black bars) in the 4 experimental groups.