HP and viral infectious disease: Consequently, we are inclined to think that productive viral infection only requires membranous FcRn and CD163 in early endosomes, although these facts that the CD163 cytoplasmic tail endocytic motif is necessary for the endocytosis of the hemoglobin-haptoglobin complex (56), and CD163 normally circulates between the cell surface and early endosomes (57), and the FcRn cytoplasmic tail is crucial for FcRn-mediated endocytosis and intracellular trafficking (47).