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CD8+ T cell epitope-flanking mutations disrupt proteasomal processing of HIV-1 Nef
Anita Milicic1, David A Price, Peter Zimbwa
1James Martin 21st Century School and Nuffield Department of Clinical Medicine, The Peter Medawar Building, University of Oxford, Oxford, United Kingdom. anita.milicic@medawar.ox.ac.uk
Journal of Immunology (Baltimore, Md. : 1950)
|September 24, 2005
Summary
Human immunodeficiency virus (HIV) evades immune detection by altering viral proteins, leading to reduced antigen processing and immune escape. This study reveals how HIV mutations impair proteasomal epitope generation, impacting T-cell responses.
Area of Science:
- Immunology
- Virology
- Molecular Biology
Background:
- Cytotoxic T-lymphocytes (CTL) are crucial for controlling human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV).
- Viruses like HIV can evade CTL detection through mutations in antigenic sites, affecting epitope binding to MHC class I or T-cell receptor recognition.
- Immune escape can also occur through mutations affecting antigen processing, even without direct changes to the epitope sequence.
Purpose of the Study:
- To investigate the impact of specific mutations in the HIV Nef protein on cytotoxic T-lymphocyte (CTL) recognition during primary infection.
- To determine if mutations outside of the core epitope sequence can lead to immune evasion by altering antigen processing.
Main Methods:
- Analysis of viral genetic sequences during primary HIV-1 infection.
- Characterization of mutations in the Nef protein, specifically R69K, A81G, and H87R.
- Assessment of the effect of these mutations on the processing of the HLA B*35-restricted VY8 epitope by the proteasome.
- Evaluation of the activation of VY8-specific CTL by the variant Nef protein.
Main Results:
- Three coincident mutations (R69K, A81G, H87R) emerged in a conserved region of the HIV Nef protein during primary infection.
- These mutations persisted and became fixed as the early CTL response to the VY8 epitope waned.
- The variant Nef protein exhibited reduced capacity to activate VY8-specific CTL, despite unchanged protein stability and expression.
- Altered proteasomal processing of the variant Nef led to partial destruction of the VY8 epitope, diminishing antigen generation.
Conclusions:
- Variant HIV genotypes can significantly impair proteasomal epitope processing, leading to immune evasion through reduced antigen generation.
- Immune escape by HIV may be underestimated if only direct variations within epitopes are considered, as altered antigen processing represents a significant mechanism.
- These findings highlight the complex strategies employed by HIV to evade host immune responses.