Specificity of DF labeling and DF interaction with ECs. (A) Confocal microscopy images show no green staining when SK cells (red staining with wheat germ agglutinin for membranes) were incubated only with Alexa 488 compared with (B) the incubation of SK cells with DF labeled with Alexa 488. (C) Exposure of HUVEC to DF (4 μg/mL) for 4 hours also resulted in the internalization of the drug. (D) Flow cytometry results show that SK and HUVEC follow the same DF interaction kinetics. PBMCs do not interact with DF. Confocal images were taken using a Leica TCS SP5 microscope and a 63× oil immersion objective. Image analysis was performed using Fiji software (National Institutes of Health).