Exploring the mechanisms of antigen processing by cell fractionation.

It is becoming increasingly clear that most of the intracellular compartments that contain MHC class II products in antigen-presenting cells simply represent the conventional endosomes and lysosomes that are expressed in all cell types. Data from recent cell fractionation studies, however, predominantly those using electrophoresis techniques, show that a population of class-II-containing vesicles exists that may comprise a class of endosomes that are specialized for antigen processing. Strong support for this possibility comes from the observation that such specialized structures, designated class II vesicles (CIIV), are particularly abundant in mature dendritic cells.