The effect of CD44 from APL cells on fibrin clot structure and properties. (A) APL/NB4 cells treated with empty vector and CD44 knockdown (kd) shRNA were incubated with fibrinogen (Fbg) and thrombin, leukemic cells were surrounded by thick fibrin networks (arrow), and CD44 kd cells exhibited thin fibers (arrowheads). Scale bar, 10 µm. (B) Clotting was induced by incubating leukemic cells with PPP. The time to the plateau of the clot was monitored according to turbidity. (C) The permeability of these clots was measured as described in “Methods.” (D-E) Clot lysis assays were performed in the presence of 1 nM tissue-type plasminogen activator. The time was recorded according to clot turbidity at 405 nm. (F) Five minutes after the clot assays began, the level of d-dimer was measured. (G-I) The levels of d-dimer, Fbg, and soluble CD44 (CD44s) in patient plasma were measured. *P < 0.05, **P <0 .01. Each image in panel A was from at least 3 experiments. *P < .05 vs previous data in the APL group, **P < .01 vs previous data in the NB4 group in panel E. Each value was from at least 5 experiments and is shown as the mean ± standard deviation.