Related Experiment Videos
Recycling MHC class I molecules and endosomal peptide loading.
M Grommé1, F G Uytdehaag, H Janssen
1Department of Tumor Biology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
Summary
MHC class I molecules can bind antigens in acidic compartments, a pathway previously thought exclusive to MHC class II molecules. This finding reveals a shared antigen loading mechanism between MHC class I and II.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- MHC class I molecules typically present endogenous peptides in the endoplasmic reticulum.
- The mechanism and location for exogenous antigen loading onto MHC class I molecules, particularly during cross-priming, remain unclear.
- This study investigates an alternative pathway for MHC class I antigen loading.
Purpose of the Study:
- To determine the intracellular location where exogenous antigens interact with MHC class I molecules.
- To investigate whether MHC class I molecules can access and utilize acidic compartments for antigen loading.
- To explore a potential shared pathway for antigen loading between MHC class I and MHC class II molecules.
Main Methods:
- Utilized measles virus F protein as a model antigen for presentation by MHC class I.
- Investigated antigen presentation in a transporters associated with antigen processing-independent manner.
- Employed NH(4)Cl treatment to assess the role of acidic compartments.
- Tracked intracellular transport of green fluorescent protein-tagged MHC class I molecules in living cells.
- Performed fractionation studies to analyze peptide content within MHC class I complexes in specific compartments.
Main Results:
- Measles virus F protein is presented by MHC class I molecules in a manner independent of transporters associated with antigen processing and sensitive to NH(4)Cl.
- MHC class I molecules can access and bind antigens within acidic compartments, similar to MHC class II molecules.
- A fraction of MHC class I molecules was observed to enter and traffic through MHC class II compartments (MIICs).
- MHC class I complexes isolated from MIICs were found to contain peptides.
- The acidic pH within MIICs (around 5.0) supports efficient peptide exchange.
Conclusions:
- MHC class I molecules can load antigens in acidic compartments, challenging the traditional view of their antigen processing pathway.
- A novel pathway for MHC class I antigen loading, shared with MHC class II molecules, has been identified.
- This shared pathway involves MHC class I molecules entering MIICs and potentially exchanging peptides in an acidic environment.