Disruption of Multivesicular Body Vesicles Does Not Affect Major Histocompatibility Complex (MHC) Class II-Peptide Complex Formation and Antigen Presentation by Dendritic Cells*

Berta Bosch,Adam C Berger,Sanjay Khandelwal,Erica L Heipertz,Brian Scharf,Laura Santambrogio,Paul A Roche

doi:10.1074/jbc.m113.461996

Abstract

The antigen processing compartments in antigen-presenting cells (APCs) have well known characteristics of multivesicular bodies (MVBs). However, the importance of MVB integrity to APC function remains unknown. In this study, we have altered the ultrastructure of the MVB by perturbing cholesterol content genetically through the use of a deletion of the lipid transporter Niemann-Pick type C1 (NPC1). Immunofluorescence and electron microscopic analyses reveal that the antigen processing compartments in NPC1(-/-) dendritic cells (DCs) have an abnormal ultrastructure in that the organelles are enlarged and the intraluminal vesicles are almost completely absent and those remaining are completely disorganized. MHC-II is restricted to the limiting membrane of these enlarged MVBs where it colocalizes with the peptide editor H2-DM. Curiously, proteolytic removal of the chaperone protein Invariant chain from MHC-II, degradation of internalized foreign antigens, and antigenic-peptide binding to nascent MHC-II are normal in NPC1(-/-) DCs. Antigen-pulsed NPC1(-/-) DCs are able to effectively activate antigen-specific CD4 T cells in vitro, and immunization of NPC1(-/-) mice reveals surprisingly normal CD4 T cell activation in vivo. Our data thus reveal that the localization of MHC-II on the intraluminal vesicles of multivesicular antigen processing compartments is not required for efficient antigen presentation by DCs.

Highlights

The antigen processing compartments in antigen-presenting cells (APCs) possess a multivesicular morphology
Our data reveal that the localization of MHC class II (MHC-II) on the intraluminal vesicles of multivesicular antigen processing compartments is not required for efficient antigen presentation by dendritic cells (DCs)
Cholesterol Accumulation Alters the Structure of Antigen Processing Compartments and Causes Mislocalization of MHC-II to the Limiting Membrane—To examine whether DC multivesicular bodies (MVBs) morphology is affected by altered lysosomal lipid content, we made use of DCs derived from NPC1Ϫ/Ϫ mice

Summary

Introduction

The antigen processing compartments in APCs possess a multivesicular morphology. Results: APCs lacking multivesicular bodies can effectively process and present antigens to T cells. The mislocalization of MHC-II to the limiting membrane of antigen processing compartments had little effect on the ability of MHC-II to bind antigenic peptides and function as stimulators of naïve CD4 T cells, suggesting that localization of MHC-II on ILVs of MVB is important for a function that is not directly related to efficient antigen processing and presentation.

Results

Conclusion