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HLA-DM acts as a molecular chaperone and rescues empty HLA-DR molecules at lysosomal pH
H Kropshofer1, S O Arndt, G Moldenhauer
1Department of Molecular Immunology, German Cancer Research Center, Heidelberg, Federal Republic of Germany.
Abstract:
HLA-DM (DM) is a nonclassical MHC class II molecule that interacts with classical MHC II molecules in acidic compartments. During this association DM is supposed to catalyze the release of invariant chain (Ii)-derived CLIP peptides, as well as other peptides bound with low kinetic stability. Here we provide evidence that in lysosomal compartments of B cells a considerable fraction of DM is stably associated with empty DR alphabeta dimers, thereby preventing their functional inactivation and aggregation. Upon encounter with cognate peptide, the DM-associated DR molecules can be rapidly loaded and no longer bind to DM. Thus, DM seems to act as a dedicated class II-specific chaperone. In view of the suggested shortage of DM-resistant self-peptides in the loading compartment, empty class II molecules that are chaperoned by DM may enable the antigen-processing system to respond promptly to the challenge by newly entering antigens.
Insights
Human Leukocyte Antigen-DM (DM) acts as a chaperone for empty MHC class II molecules in B cells. This prevents aggregation and allows rapid peptide loading, enhancing antigen presentation.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Human Leukocyte Antigen-DM (DM) is a nonclassical MHC class II molecule.
- DM interacts with classical MHC II molecules in acidic compartments.
- DM is believed to catalyze the release of peptides from MHC II.
Purpose of the Study:
- To investigate the role of DM in B cell lysosomal compartments.
- To determine if DM associates with empty MHC class II dimers.
- To understand how DM influences MHC class II function and antigen presentation.
Main Methods:
- Analysis of B cell lysosomal compartments.
- Biochemical assays to detect DM-DR associations.
- Functional assays to assess peptide loading kinetics.
Main Results:
- A significant fraction of DM stably associates with empty DR alphabeta dimers in B cells.
- This association prevents functional inactivation and aggregation of DR molecules.
- DM-associated DR molecules are rapidly loaded with cognate peptides and release DM.
Conclusions:
- DM functions as a dedicated class II-specific chaperone.
- DM chaperoning of empty MHC II molecules ensures prompt response to new antigens.
- This mechanism optimizes the antigen-processing system for efficient immune surveillance.