Interaction of HLA-DR and CD74 at the cell surface of antigen-presenting cells by single particle image analysis
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Published on: February 28, 2019
Ioannis Karakikes1, Ian E G Morrison, Peter O'Toole
1School of Biological Sciences, University of Essex, Wivenhoe Park, Colchester C04 3SQ, UK.
Insights
CD74 regulates human leukocyte antigen (HLA)-DR molecules, crucial for antigen presentation. This study shows CD74
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Major histocompatibility complex (MHC) class II molecules present antigens to T cells.
- CD74, the invariant chain associated with MHC class II, has a poorly defined role in antigen presentation.
- Human leukocyte antigen (HLA)-DR is a key MHC class II molecule involved in immune responses.
Purpose of the Study:
- To investigate the role of CD74 in the function and trafficking of HLA-DR molecules.
- To quantify the colocalization of CD74 and HLA-DR on antigen-presenting cells.
- To determine the effect of a universal peptide (HA(307-319)) on CD74-HLA-DR interactions and HLA-DR internalization.
Main Methods:
- High-resolution single-particle imaging to quantify molecular colocalization.
- Utilizing human fibroblast cells and monocyte-derived dendritic cells.
- Employing a universal peptide (HA(307-319)) to probe HLA-DR binding groove interactions.
Main Results:
- Significant colocalization observed between CD74 and HLA-DR (25% and 17%, respectively).
- The universal peptide HA(307-319) inhibited both CD74-HLA-DR association and HLA-DR internalization.
- Similar inhibition of HLA-DR internalization was noted in dendritic cells.
Conclusions:
- CD74 plays a critical role in translocating HLA-DR to early endosomes for peptide reloading.
- CD74 regulates the surface expression of peptide-occupied versus peptide-free HLA-DR molecules.
- Understanding CD74's function is key to modulating MHC class II-mediated antigen presentation.
Abstract:
Major histocompatibility complex (MHC) class II-associated antigen presentation involves an array of interacting molecules. CD74, the cell surface isoform of the MHC class II-associated invariant chain, is one such molecule; its role remains poorly defined. To address this, we have employed a high-resolution single-particle imaging method for quantifying the colocalization of CD74 with human leukocyte antigen (HLA)-DR molecules on human fibroblast cells known for their capacity to function as antigen-presenting cells. We have also examined whether the colocalization induces internalization of HLA-DR using HA(307-319), a "universal" peptide that binds specifically to the peptide-binding groove of all HLA-DR molecules, irrespective of their alleles. We have determined that 25 ± 1.3% of CD74 and 17 ± 0.3% of HLA-DR are colocalized, and the association of CD74 with HLA-DR and the internalization of HLA-DR are both inhibited by HA(307-319). A similar inhibition of HLA-DR internalization was observed in freshly isolated monocyte-derived dendritic cells. A key role of CD74 is to translocate HLA-DR molecules to early endosomes for reloading with peptides prior to recycling to the cell surface. We conclude that CD74 regulates the balance of peptide-occupied and peptide-free forms of MHC class II at the cell surface.
