Sera from <i>Thbs1^−/−</i> mice have reduced ability to undergo activation of TGF-β1 by stirring or shear.

<p>(A) Immunoblots of WT and <i>Thbs1^−/−</i> mice sera demonstrate absence of TSP-1 in the <i>Thbs1^−/−</i> mice. (B, C, D) Sera from WT (n = 23) and <i>Thbs1^−/−</i> (n = 23) mice were stirred (S) at 1,200 rpm or left unstirred (US) for 120 min at 37°C and then total (B) and active (C, D) TGF-β1 were measured; the latter was expressed either as an absolute value (ng/mL) (C) or as a percentage of total TGF-β1 (D). Levels of active TGF-β1 increased less in <i>Thbs1^−/−</i> than WT mice with stirring [p = 0.057 (absolute values) and p = 0.016 (percentages of total TGF-β1) for interaction by ANOVA]. The post-stirring values were also higher in WT than <i>Thbs1^−/−</i> mice [p = 0.19 (absolute values) and p = 0.001 (percentages of total TGF-β1) by t-test]. (E, F) Sera from WT (n = 10) or <i>Thbs1^−/−</i> (n = 10) mice were either incubated at 37°C (−) or subjected to shear (+) at 1,800 s⁻¹ at 37°C for 120 min. Active TGF-β1 increased more in WT mice, both in terms of absolute values (p = 0.18 by t-test) (E) and as percentages of total TGF-β1 (p = 0.039 by t-test) (F).