PCA of normal human plasma (A) and FVII-deficient plasma (B) of cell extracts from NB4 cells, sensitive to ATRA-induced differentiation, and two NB4-derived cell lines, resistant to ATRA-induced differentiation (ie, NB4.306 and NB4.007/6). Cells were cultured with 10⁻⁶ mol/L ATRA (▪) or the vehicle (□) for 96 hours. Results, expressed as RVV units/mg total proteins, are the mean of at least three experiments. Statistical analysis of PCA of untreated versus treated samples was performed by the paired Student'st-test; *P < .05, **P < .01.