Cell surface MHC class II (MHC-II) is known to internalize and can recycle back to the plasma membrane from endosomes in antigen presenting cells. We now describe a simple protocol that allows one to follow the internalization kinetics of proteins from the surface of cells. Furthermore, a simple adaptation of this assay allows one to monitor the rate of appearance of internalized proteins back to the plasma membrane. This assay allows for quantitation of trafficking of proteins on even rare subsets of cells, something that is not possible with traditional biochemical assays.
Keywords: Endocytosis; FACS; MHC class II; Recycling; Transmembrane proteins.