HLA-A — Major Histocompatibility Complex Class I A

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HLA-A — Major Histocompatibility Complex Class I A

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HLA-A — Major Histocompatibility Complex Class I A

Introduction

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">HLA-A — Major Histocompatibility Complex Class I A</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>HLA-A</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Major Histocompatibility Complex Class I A</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>6p21.3</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>3105</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000206503</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>P01890</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>142800</td>
</tr>
<tr>
<td class="label">Allele</td>
<td>Association</td>
</tr>
<tr>
<td class="label">HLA-A*02:01</td>
<td>Risk allele</td>
</tr>
<tr>
<td class="label">HLA-A*03:01</td>
<td>Risk allele</td>
</tr>
<tr>
<td class="label">HLA-A*24:02</td>
<td>Protective</td>
</tr>
<tr>
<td class="label">Allele</td>
<td>Caucasians</td>
</tr>
<tr>
<td class="label">A*02:01</td>
<td>~30%</td>
</tr>
<tr>
<td class="label">A*03:01</td>
<td>~20%</td>
</tr>
<tr>
<td class="label">A*24:02</td>
<td>~10%</td>
</tr>
<tr>
<td class="label">A*01:01</td>
<td>~15%</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/alzheimer

...

HLA-A — Major Histocompatibility Complex Class I A

Introduction

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">HLA-A — Major Histocompatibility Complex Class I A</th>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>HLA-A</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Major Histocompatibility Complex Class I A</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>6p21.3</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>3105</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000206503</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>P01890</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>142800</td>
</tr>
<tr>
<td class="label">Allele</td>
<td>Association</td>
</tr>
<tr>
<td class="label">HLA-A*02:01</td>
<td>Risk allele</td>
</tr>
<tr>
<td class="label">HLA-A*03:01</td>
<td>Risk allele</td>
</tr>
<tr>
<td class="label">HLA-A*24:02</td>
<td>Protective</td>
</tr>
<tr>
<td class="label">Allele</td>
<td>Caucasians</td>
</tr>
<tr>
<td class="label">A*02:01</td>
<td>~30%</td>
</tr>
<tr>
<td class="label">A*03:01</td>
<td>~20%</td>
</tr>
<tr>
<td class="label">A*24:02</td>
<td>~10%</td>
</tr>
<tr>
<td class="label">A*01:01</td>
<td>~15%</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">Alzheimer</a>, <a href="/wiki/lymphoma" style="color:#ef9a9a">Lymphoma</a>, <a href="/wiki/ms" style="color:#ef9a9a">Ms</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">36 edges</a></td>
</tr>
</table>

HLA-A (Major Histocompatibility Complex Class I A) is a key gene located on chromosome 6p21.3 within the human leukocyte antigen (HLA) complex. It encodes the alpha chain of the HLA class I molecule, a cell surface glycoprotein essential for immune surveillance and antigen presentation to CD8+ cytotoxic T-lymphocytes[@klein2000][@shiina2009].

HLA class I molecules are expressed on the surface of virtually all nucleated cells and present endogenously synthesized peptide antigens to CD8+ T-cells. This process is fundamental to immune defense against intracellular pathogens ( viruses and some bacteria) and malignant transformation. Beyond this classical function, increasing evidence implicates HLA class I molecules in broader biological processes, including immune regulation in the central nervous system (CNS)[@watanabe2010][@cante2013].

The HLA-A gene is extraordinarily polymorphic, with thousands of documented alleles across global populations. This diversity has significant implications for disease susceptibility, transplant matching, and therapeutic response[@choo2007].

Gene Overview

Molecular Biology

Gene Structure

The HLA-A gene spans approximately 2.6 kb and comprises 8 exons:

Exon 1: 5' untranslated region and signal peptide
Exons 2-4: Encoding the three extracellular domains (α1, α2, α3)
Exon 5: Transmembrane domain
Exon 6: Cytoplasmic tail
Exon 7: 3' untranslated region

Protein Structure

HLA-A encodes a transmembrane glycoprotein consisting of:

Heavy chain (~45 kDa): The polymorphic α-chain encoded by HLA-A

β2-microglobulin (~12 kDa): Non-polymorphic light chain, required for surface expression

Peptide binding groove: Forms from the α1 and α2 domains, accommodates 8-10 amino acid peptides

The peptide binding groove has pockets (B and F being most important) that determine peptide binding specificity. Different HLA-A alleles have distinct peptide binding preferences.

Expression Pattern

HLA-A is expressed:

Constitutively: All nucleated cells
Inducible: Upregulated by IFN-γ, TNF-α, and other cytokines
High expression: Immune cells (lymphocytes, monocytes)
Brain expression: Neurons, astrocytes, microglia

Function

Classical MHC Class I Function

The primary function of HLA-A involves antigen presentation:

Peptide Processing and Loading

Intracellular proteins are degraded by the proteasome

Peptides are transported to the ER by TAP (transporter associated with antigen processing)

Peptides are loaded onto HLA-A molecules with the assistance of tapasin

The peptide-HLA-A complex is transported to the cell surface

Immune Recognition

Surface HLA-A-peptide complexes are recognized by CD8+ T-cell receptors

This triggers cytotoxic T lymphocyte (CTL) activation

Activated CTLs can eliminate the presenting cell

Non-Classical Functions

HLA-A has additional functions beyond antigen presentation[@cante2013][@morena2017]:

Interaction with NK Cells

HLA-A interacts with killer cell immunoglobulin-like receptors (KIRs)
Can inhibit NK cell cytotoxicity in some contexts

Signaling Functions

HLA-A can signal through multiple receptors
Modulates cell survival and proliferation

CNS Functions

Regulation of neuronal development
Synaptic plasticity modulation
Neuroprotection

Disease Associations

Multiple Sclerosis

HLA-A alleles have been studied in [multiple sclerosis](/diseases/multiple-sclerosis)[@pashenkov2002]:

The HLA region contributes significantly to MS genetic risk, with HLA-DRB1*15:01 being the strongest individual effect.

Parkinson's Disease

HLA-A and the broader HLA class I region have been implicated in [Parkinson's disease](/diseases/parkinsons-disease) susceptibility[@boehme2018][@ham2019][@ich2021]:

Key Findings

HLA region polymorphisms influence PD risk
HLA-DRB1 variants show stronger associations than HLA-A
Some HLA-A alleles may modify disease progression

Proposed Mechanisms

Alpha-synuclein presentation: HLA-A may present α-syn fragments to T-cells[@gate2019]

Microglial activation: HLA class I modulates microglial responses

Autoimmunity: Potential for α-syn-specific T-cell responses

Neuroinflammation: HLA class I influences inflammatory responses

Alzheimer's Disease

HLA class I molecules have complex roles in [Alzheimer's disease](/diseases/alzheimers-disease)[@g ao2020][@lamanna2023]:

Current Understanding

Altered HLA class I expression in AD brain
Potential roles in amyloid clearance
Neuroinflammation modulation

Therapeutic Implications

HLA class I-based immunotherapy approaches
Modulation of antigen presentation pathways

Other Neurological Conditions

Narcolepsy: HLA-DQB1*06:02 is primary association, HLA-A modifies risk
Amyotrophic Lateral Sclerosis (ALS): Some HLA associations reported
Guillain-Barré syndrome: Strong HLA associations

Non-Neurological Diseases

Autoimmune disorders: Type 1 diabetes, rheumatoid arthritis, SLE
Infectious disease: HIV progression, hepatitis outcomes
Transplantation: Graft rejection, graft-versus-host disease

Genetic Polymorphism

Major Alleles

The HLA-A gene has thousands of documented alleles:

Common Alleles by Population

Allele Groups

A*02: Most common group globally
A*03: Common in Europeans
A*24: Common in East Asians
A*01: Variable by population

Therapeutic Implications

Transplantation

HLA-A matching is critical for:

Solid organ transplantation
Hematopoietic stem cell transplantation
Reducing graft rejection risk

Immunotherapy

HLA-A is relevant for[@wen2024]:

Cancer immunotherapy: Peptide vaccines targeting HLA-A
Adoptive T-cell therapy
Checkpoint inhibitor response

Neurodegeneration

Potential therapeutic approaches include:

Modulating HLA class I expression
Targeting specific antigen presentation pathways
Immunomodulatory strategies

Brain-Specific Considerations

CNS Immune Privilege

The brain has specialized immune regulation:

Blood-brain barrier: Limits immune cell entry
Microglial surveillance: Resident immune cells
Limited classical antigen presentation: Compared to peripheral immune

HLA in the Normal Brain

In healthy CNS:

Low basal HLA class I expression
Upregulated in disease states
Roles in development and plasticity

HLA in Disease

Disease-associated changes include[@kang2022]:

Increased microglial HLA expression
Altered antigen presentation
T-cell infiltration in some conditions

Epigenetic Regulation

DNA Methylation

HLA-A expression is subject to epigenetic regulation:

Promoter methylation: Can repress HLA-A expression in tumors
Tissue-specific patterns: Distinct methylation in immune vs. non-immune tissues
Disease-associated changes: Altered methylation in neurodegenerative conditions

Histone Modifications

Chromatin states affect HLA-A:

Active marks: H3K27ac associated with expression
Repressive marks: H3K27me3 in silenced contexts
Enhancer activities: Distal regulatory elements

Non-coding RNAs

microRNAs modulate HLA-A:

miR-148a: Targets HLA-A 3'UTR
miR-568: Downregulates HLA class I
Let-7 family: Multiple targets in antigen presentation

Molecular Mechanisms in Neurodegeneration

ER Stress Response

HLA-A folding occurs in the endoplasmic reticulum:

Protein synthesis: Heavy chain translation in ER

Quality control: Calreticulin/calnexin system

peptide loading: TAP-mediated peptide transport

Surface expression: Golgi processing and trafficking

ER stress affects HLA-A processing in neurodegeneration.

Autophagy Interplay

Autophagy and HLA-A intersect:

Cross-presentation: Autophagy delivers antigens to HLA class I
IFN-γ effects: Autophagy required for optimal presentation
Disease relevance: Altered autophagy in neurodegeneration

Neuroimmune Signaling

The neuroimmune axis involves HLA-A:

Microglial activation: Triggered by antigen presentation
T-cell infiltration: CD8+ T-cells in PD/AD brain
Cytokine effects: IFN-γ modulates HLA expression

Research Directions

Current Areas of Investigation

Genetic studies: Population-specific HLA effects

Functional studies: Mechanism of HLA-associated risk

Therapeutic development: HLA-targeting approaches

Biomarkers: HLA as disease biomarker

Single-cell analysis: Cell-type specific expression

Future Directions

Personalized medicine applications
Gene therapy approaches
Immunomodulation strategies
Epigenetic therapies
CAR-T cell approaches for neurodegeneration

Interaction Networks

Receptor Interactions

HLA-A interacts with multiple receptors:

T-cell Receptor (TCR): Primary interaction

CD8+ T-cell recognition
Activation of cytotoxic response

Killer Cell Immunoglobulin-like Receptors (KIRs)

NK cell regulation
Inhibition or activation

CD8 Co-receptor

Enhances TCR engagement
Required for optimal signaling

Peptide Presentation

HLA-A presents diverse peptides:

Viral peptides: From infected cells
Tumor antigens: Cancer-specific peptides
Self-peptides: Normal cellular proteins
Mutated peptides: Cancer-associated variants

Clinical Considerations

HLA Matching

Transplantation requires HLA-A matching:

Donor-recipient matching: Minimize rejection

Desensitization protocols: For mismatched transplants

Virtual crossmatching: Pre-transplant assessment

Disease associations

Beyond neurodegeneration:

Type 1 Diabetes: Strong HLA-DR association
Rheumatoid Arthritis: HLA-DR specific
Systemic Lupus Erythematosus: Multiple loci
Celiac Disease: HLA-DQ specific

Research Methods

Detection Methods

Serology: Traditional typing
Sequence-based typing (SBT): DNA sequencing
Flow cytometry: Cell surface expression
Mass spectrometry: Peptide identification

Animal Models

Transgenic mice: HLA-A expression
Knockout models: Loss of function studies
Humanized mice: Immune system models

Summary

HLA-A represents a critical intersection between adaptive immunity and neurodegenerative disease. Its role in antigen presentation, immune regulation in the CNS, and genetic associations with disease risk make it an important target for understanding neurodegeneration. Key implications include:

Disease risk: HLA alleles modify neurodegenerative risk
Immune modulation: Class I pathways in neuroinflammation
Therapeutic potential: Targeting antigen presentation
Biomarker development: HLA as disease marker

Further research into HLA class I biology will provide insights into neurodegenerative disease mechanisms and potential therapeutic approaches.

External Links

[NCBI Gene: HLA-A](https://www.ncbi.nlm.nih.gov/gene/3105)
[UniProt: HLA-A](https://www.uniprot.org/uniprot/P01890)
[IMGT/HLA Database](https://www.ebi.ac.uk/ipd/imgt/)
[PubMed](https://pubmed.ncbi.nlm.nih.gov/)

References

[Klein & Sato, The HLA system (2000)](https://pubmed.ncbi.nlm.nih.gov/10974132/)

[Shiina et al., HLA complex: from gene to function (2009)](https://pubmed.ncbi.nlm.nih.gov/19301028/)

[Choo, The HLA system: genetics and disease association (2007)](https://pubmed.ncbi.nlm.nih.gov/17580788/)

[Pashenkov et al., HLA in multiple sclerosis (2002)](https://pubmed.ncbi.nlm.nih.gov/11872614/)

[Watanabe et al., HLA class I and immune regulation in the brain (2010)](https://pubmed.ncbi.nlm.nih.gov/20699246/)

[Cante et al., HLA class I molecules couple to multiple receptor tyrosine kinases (2013)](https://pubmed.ncbi.nlm.nih.gov/24227734/)

[Morena et al., The emerging role of HLA class I in neurodegenerative disease (2017)](https://pubmed.ncbi.nlm.nih.gov/28361916/)

[Boehme et al., Microglial HLA-DR and CD4 T cells in Parkinson's disease (2018)](https://pubmed.ncbi.nlm.nih.gov/29594288/)

[Gate et al., HLA genotype influence on alpha-synuclein aggregation (2019)](https://pubmed.ncbi.nlm.nih.gov/31185892/)

[Gao et al., HLA class I in Alzheimer's disease brain (2020)](https://pubmed.ncbi.nlm.nih.gov/32303325/)

[Ham et al., HLA-DRB1 and Parkinson's disease risk (2019)](https://pubmed.ncbi.nlm.nih.gov/30626653/)

[Ich et al., Common genetic variation in HLA region affects PD risk (2021)](https://pubmed.ncbi.nlm.nih.gov/34134982/)

[Kang et al., HLA class I-mediated neuroprotection in neurodegeneration (2022)](https://pubmed.ncbi.nlm.nih.gov/35817342/)

[Lamanna et al., HLA expression in microglia (2023)](https://pubmed.ncbi.nlm.nih.gov/37093421/)

[Wen et al., Targeting HLA-class I pathways for neurodegenerative disease therapy (2024)](https://pubmed.ncbi.nlm.nih.gov/39182847/)

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Related Entities

HLAA

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slug	genes-hla-a
kg_node_id	HLAA
entity_type	gene
origin_type	v1_polymorphic_backfill
source_table	wiki_pages
wiki_page_id	wp-f49818890e9d
__merged_from	{'merged_at': '2026-05-13', 'unprefixed_id': 'genes-hla-a'}
_schema_version	1

📊 Evidence Profile

Evidence Balance

+0%

Certainty

25%

Debates

0

Incoming

5

Outgoing

14

0 supporting 0 contradicting 0 neutral

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📗 Cite This Artifact

HLA-A — Major Histocompatibility Complex Class I A

HLA-A — Major Histocompatibility Complex Class I A

Introduction

HLA-A — Major Histocompatibility Complex Class I A

Introduction

Gene Overview

Molecular Biology

Gene Structure

Protein Structure

Expression Pattern

Function

Classical MHC Class I Function

Peptide Processing and Loading

Immune Recognition

Non-Classical Functions

Interaction with NK Cells

Signaling Functions

CNS Functions

Disease Associations

Multiple Sclerosis

Parkinson's Disease

Key Findings

Proposed Mechanisms

Alzheimer's Disease

Current Understanding

Therapeutic Implications

Other Neurological Conditions

Non-Neurological Diseases

Genetic Polymorphism

Major Alleles

Common Alleles by Population

Allele Groups

Therapeutic Implications

Transplantation

Immunotherapy

Neurodegeneration

Brain-Specific Considerations

CNS Immune Privilege

HLA in the Normal Brain

HLA in Disease

Epigenetic Regulation

DNA Methylation

Histone Modifications

Non-coding RNAs

Molecular Mechanisms in Neurodegeneration

ER Stress Response

Autophagy Interplay

Neuroimmune Signaling

Research Directions

Current Areas of Investigation

Future Directions

Interaction Networks

Receptor Interactions

Peptide Presentation

Clinical Considerations

HLA Matching

Disease associations

Research Methods

Detection Methods

Animal Models

Summary

See Also

External Links

References

💬 Discussion