Schematic representation of intracellular trafficking of wild-type and tail-deleted hFcγRIa. In this model, based on our kinetic data and morphologic observations, four types of endocytic compartments are distinguished, ie, small coated and noncoated vesicles and tubules (1), early endosomes (2), multivesicular late endosomes (3), and lysosomes (4). hFcγRIa WT/γY65F,Y76F/IgG-OVA complexes are internalized via type 1 vesicles and transported to the early endosomes. The majority of complexes are sorted to late endosomes and lysosomes for degradation and loading onto MHC class II molecules. Only part of the receptor-ligand complexes recycle back to the cell surface (indicated by the dashed arrow) via type 1 vesicles and tubules. In contrast, the majority of hFcγRIa ▵315/γY65F,Y76F/IgG-OVA complexes is diverted from type 2 early endosomes into the recycling pathway, most likely due to the absence of intrinsic targeting information. Some antigen-receptor complexes are transported further down the endocytic tract to type 3 and 4 compartments (dashed arrows), but this is insufficient for antigen presentation to occur.