Stability of G28-5 sFv-PE40 in SCID mouse serum. G28-5 sFv-PE40 was incubated at 37°C in mouse serum at 20 μg/mL for 0 (□), 2 (♦), 4 (○), 6 (▿), or 24 hours (•) and then analyzed for protein synthesis inhibition activity on Ramos cells. Dilutions of serum (+) were used as a control. Data shown are the averages of three samples per time point.