FN-null MFs were incubated with 50 μg/mL α5 inhibitory antibodies (5H10-27), or 100 μg/mL αv inhibitory antibodies (H9.2B8), or isotype control IgG at 4°C for 30 minutes. 10 μg/mL TR-fibronectin (A-D) or AF488-fibronectin (E) was added to the media. After 2 hours chase, cells were either fixed for imaging analysis (A, α5 inhibition; B, isotype control of α5; C, αv inhibition; D, isotype control for αv), or processed for flow cytometry (E) to quantitate internalized fibronectin. The numbers over the peaks in E are the MFI of internalized AF 488-fibronectin. Scale bar, 10μm.