Double labelling of major histocompatibility complex molecules and lysosomal protein lamp-1 on human dendritic cells

In this study, double labelling for major histocompatibility complex (MHC) class I and class II molecules and for MHC molecules and the lysosomal membrane protein lamp-1 on ultrathin cryosections of dendritic cells isolated from human peripheral blood was performed. The plasma membrane proved to be positive for both MHC class I and MHC class II molecules and was labelled for only a very few lamp-1 molecules. MHC class I and MHC class II molecules did not co-localize intracellularly except in some peripherally located vesicles. However, many MHC class II-labelled vesicles were present in a juxtanuclear position but only some of them were co-labelled for lamp-1. These results indicate the presence of a separate, non-lysosomal compartment for class II molecules in dendritic cells.