HLA-DM stabilizes empty HLA-DR molecules in a chaperone-like fashion

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Major histocompatibility complex (MHC) class II molecules present antigens to T cells.
• HLA-DM (DM) is a non-classical MHC class II molecule involved in peptide loading onto classical MHC II molecules.
• The role of DM in stabilizing MHC II molecules during peptide scarcity was previously unknown.

Purpose of the Study:

• To investigate the fate of MHC class II (DR) molecules in lysosomal compartments under conditions of peptide scarcity.
• To determine the stabilizing effect of HLA-DM (DM) on empty DR molecules.
• To elucidate the chaperone-like function of DM in preserving MHC II functionality.

Main Methods:

• Incubation of DR molecules at lysosomal pH with and without DM.
• Assessment of DR molecule functional inactivation and aggregation.
• Analysis of DM-DR complex formation and stability.
• Evaluation of peptide loading capacity of DM-associated DR molecules.

Main Results:

• Empty DR molecules rapidly inactivate and aggregate at lysosomal pH without DM.
• DM stabilizes empty DR molecules, maintaining their peptide-loading receptivity.
• The stabilizing effect of DM varies among different DR alleles.
• DM forms stable complexes with empty DR alpha beta dimers, preserving their function.
• DM-associated DR molecules are rapidly loaded with antigenic peptides and subsequently release DM.

Conclusions:

• HLA-DM functions as a dedicated chaperone for MHC class II molecules, rescuing uncharged alpha beta dimers.
• DM prevents the inactivation and aggregation of empty DR molecules in peptide-limited environments.
• This chaperone activity ensures that MHC class II molecules remain receptive for prompt antigen loading, enhancing immune response efficiency.