CIE cargo molecules label the newly formed endothelial lumen.

<p>(A) HUVECs were placed in three-dimensional collagen gels for 4 h to allow lumen formation. Newly formed lumens were identified using CD31 (PECAM) and rhodamine-phalloidin to label F-actin and DIC. (B) GFP-tH expressing or non-transfected cells were placed in three- dimensional collagen gels and allowed to internalize Alexa-647 conjugated antibodies against MHCI or Alexa-594 Tfn for 4 h. Cells were fixed and labeled with a polyclonal against GFP (B upper panel) and a monoclonal against the transferrin receptor (TfR) (B lower panel). MHCI was associated with the newly formed lumen membrane while internalized Tfn and the TfR were not. Bar, 10 μm.