TGF-β1 quantification in plasma.

Bars indicate TGF-β1 levels after acidification of the samples: ▪ indicate levels in mice engrafted with TGF-β1^+/+hematopoietic cells; ■, levels in hosts engrafted with TGF-β1^−/− hematopoietic cells; ▨, constitutive level in WT adult hosts. No spontaneously active TGF-β1 was detected prior to acidification of the samples. Results of statistical analysis with the 2-tailed Student t test: WT versus TGF-β1^−/−, ^★P < .05 and^★★P < .001.