mAb/Tf was bound (4°C) and endocytosed (37°C) by CHO-hTfR cells.

<p>(A) 2×10⁵ CHO-hTfR cells were incubated with anti-hTfR mAb for 1h followed by PE-conjugated donkey anti-mouse Ab staining for 30min at 4°C (upper). Half cells were incubated at 37°C for another 30 min and then rinsed by ice-cold medium 1 (Lower). (B) 2×10⁵ CHO-hTfR cells were incubated with Alexa-Tf (5μg per tube) at 4°C (upper) or 37°C for 1h. Then 37°C incubated cells were rinsed with ice-cold medium 1 (lower). Fluorescence was developed using Olympus fluorescence microscope (60×).