Quantitation of Major Histocompatibility Complex Antigen Endocytosis Using Capture ELISA

Major histocompatibility class I and II (MHC-I and MHC-II) antigens (Ags), as well as a variety of cell surface receptors, have been shown to enter the endocytic pathway of antigen-presenting cells (APCs). MHC Ags endocytose into clathrin-coated pits, which pinch off from the plasma membrane and form clathrin-coated vesicles (1-4). These vesicles rapidly uncoat and fuse together or with pre-existing vesicular structures called “early endosomes.” Selected molecules within early endosomes return to the plasma membrane, possibly via carrier vesicles (5). This pathway has been best described for endocytosed transferrin receptors (TfR) (6).