Inhibition of His-ILFAC uptake. His-ILFAC internalization by HSC536 lymphoblasts was inhibited by addition of recombinant human IL-3 (10 μg/mL) to the medium, and inhibited further by pretreatment of intact cells with 0.25% Trypsin for 10 minutes before incubation with His-ILFAC (10 μg/mL). No inhibition was seen with His-FAC at 50 μg/mL (ie, 5-fold higher concentration than His-ILFAC) or with murine IL-3 (WEHI conditioned medium at a concentration 10-fold higher than that required for growth of the IL-3–dependent cell line HCD57). The mean of three independent measurements and standard error of the mean are shown.