The transferrin in the blood is a glycoprotein that can transport iron to cells from the liver and intestine. Generally, the surface transferrin receptor on the cells can readily bind to the ferrotransferrin (transferrin bound with iron) at neutral pH, which then induces receptor-mediated endocytosis of the ferrotransferrin. The iron (Fe3+) ions are taken up inside the cells through the clathrin-coated vesicle into endosome, while the unbound form of apotransferrin is secreted back into the blood for reloading of iron. This pathway is an attractive delivery method for drugs, proteins and therapeutic genes into malignant cells with overexpressed transferrin receptors.
Traditionally, fluorescently-labeled transferrin receptors can be qualitatively inspected via fluorescent microscopy or quantitatively measured by flow cytometry. However, manual microscopy method is time-consuming and non-quantitative and flow cytometry can generate sensitive quantitative results, but requires a highly-trained dedicated user.
By using the Celigo imaging cytometer, antibody or fluorescent protein-labeled receptors can be imaged and the fluorescent intensities of the target cell populations are measured to determine the level of CD71 transferrin receptor expression automatically.