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Altered antigen presentation in mice lacking H2-O
M Liljedahl1, O Winqvist, C D Surh
1The R.W. Johnson Pharmaceutical Research Institute, San Diego, California 92121, USA.
Abstract:
HLA-DM catalyzes the release of MHC class II-associated invariant chain-derived peptides (CLIP) from class II molecules. Recent evidence has suggested that HLA-DO is a negative regulator of HLA-DM in B cells, but the physiological function of HLA-DO remains unclear. Analysis of antigen presentation by B cells from mice lacking H2-O (the mouse equivalent of HLA-DO), together with biochemical analysis using purified HLA-DO and HLA-DM molecules, suggests that HLA-DO/H2-O influences the peptide loading of class II molecules by limiting the pH range in which HLA-DM is active. This effect may serve to decrease the presentation of antigens internalized by fluid-phase endocytosis, thus concentrating the B cell-mediated antigen presentation to antigens internalized by membrane immunoglobulin.
Insights
Human Leukocyte Antigen (HLA)-DO acts as a negative regulator of HLA-DM in B cells. This study reveals HLA-DO/H2-O limits HLA-DM activity to specific pH ranges, influencing antigen presentation by B cells.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Human Leukocyte Antigen (HLA)-DM facilitates the release of peptides from MHC class II molecules.
- The role of HLA-DO as a negative regulator of HLA-DM in B cells is suggested but not fully understood.
- The physiological function of HLA-DO in antigen presentation remains unclear.
Purpose of the Study:
- To elucidate the physiological function of HLA-DO in B cell antigen presentation.
- To investigate the regulatory mechanism of HLA-DM by HLA-DO.
Main Methods:
- Analysis of antigen presentation in B cells from H2-O knockout mice (lacking the mouse equivalent of HLA-DO).
- Biochemical assays using purified HLA-DO and HLA-DM molecules.
Main Results:
- HLA-DO/H2-O influences the peptide loading of MHC class II molecules.
- HLA-DO/H2-O limits the pH range in which HLA-DM is enzymatically active.
- This regulation potentially reduces the presentation of antigens acquired through fluid-phase endocytosis.
Conclusions:
- HLA-DO/H2-O acts as a modulator of HLA-DM activity by restricting its function to a specific pH.
- This mechanism may fine-tune B cell-mediated antigen presentation, favoring antigens internalized via membrane immunoglobulin over those from fluid-phase endocytosis.