Novel insights in MHC class II antigen presentation

Abstract

Major Histocompatibility Complex class II (MHC-II) antigen presentation is involved in the regulation of immune responses against infections and tumours and strongly linked to autoimmune diseases. To better understand this process we performed a genome-wide RNAi screen. The effect of downregulation of each human gene on MHC class II expression and antigen loading was analyzed. Genes affecting MHC-II antigen presentation were tested for their involvement in MHC-II transcription and transport. Some genes might function in repositioning MHC-II towards the plasmamembrane upon Dendritic Cell maturation. This was confirmed by silencing these genes in immature Dendritic Cells. The novel GTPase ARF7, ARF7EP and MYO1E play a central role in this transport process. MHC-II antigen loading on intraluminal vesicles of the MHC-II compartment is facilitated by chaperone DM. In a confocal FRET study we investigated whether microdomain-forming tetraspanins CD63 and CD82, interacting with MHC-II and DM, could facilitate the MHC-II/DM interaction. MHC-II and DM preferably interacted with CD63 on the intraluminal vesicles, likely facilitating the MHC-II/DM interaction and antigen loading. MHC-II favoured interactions with CD82 on the limiting- and plasmamembrane suggesting a sorting role for CD82. This knowledge will contribute to development of new methodologies to influence MHC class II presentation in patients.