CD200 Protein

CD200 Protein

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">CD200 Protein</th>
</tr>
<tr>
<td class="label">Strategy</td>
<td>Mechanism</td>
</tr>
<tr>
<td class="label">CD200-Fc</td>
<td>Agonist fusion protein</td>
</tr>
<tr>
<td class="label">CD200R antibodies</td>
<td>Receptor activation</td>
</tr>
<tr>
<td class="label">Gene therapy</td>
<td>AAV-CD200</td>
</tr>
<tr>
<td class="label">Compound</td>
<td>Type</td>
</tr>
<tr>
<td class="label">CD200-Fc</td>
<td>Fusion protein</td>
</tr>
<tr>
<td class="label">Anti-CD200R mAb</td>
<td>Monoclonal antibody</td>
</tr>
<tr>
<td class="label">CD200 mimetic peptides</td>
<td>Small molecules</td>
</tr>
<tr>
<td class="label">NCT ID</td>
<td>Intervention</td>
</tr>
<tr>
<td class="label">(TBD)</td>
<td>CD200-Fc</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

Introduction

CD200 (OX-2 Membrane Glycoprotein) is a critical immune regulatory molecule that plays essential roles in maintaining immunological quiescence in the central nervous system. As a member of the immunoglobulin superfamily, CD200 interacts with its receptor CD200R to deliver inhibitory signals that suppress the activation of microglia and other myeloid cells.[@barclay2002] This CD200-CD200R immune checkpoint is fundamental to understanding neuroinflammation and neurodegenerative disease pathogenesis.

CD200 Protein

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">CD200 Protein</th>
</tr>
<tr>
<td class="label">Strategy</td>
<td>Mechanism</td>
</tr>
<tr>
<td class="label">CD200-Fc</td>
<td>Agonist fusion protein</td>
</tr>
<tr>
<td class="label">CD200R antibodies</td>
<td>Receptor activation</td>
</tr>
<tr>
<td class="label">Gene therapy</td>
<td>AAV-CD200</td>
</tr>
<tr>
<td class="label">Compound</td>
<td>Type</td>
</tr>
<tr>
<td class="label">CD200-Fc</td>
<td>Fusion protein</td>
</tr>
<tr>
<td class="label">Anti-CD200R mAb</td>
<td>Monoclonal antibody</td>
</tr>
<tr>
<td class="label">CD200 mimetic peptides</td>
<td>Small molecules</td>
</tr>
<tr>
<td class="label">NCT ID</td>
<td>Intervention</td>
</tr>
<tr>
<td class="label">(TBD)</td>
<td>CD200-Fc</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>

Introduction

CD200 (OX-2 Membrane Glycoprotein) is a critical immune regulatory molecule that plays essential roles in maintaining immunological quiescence in the central nervous system. As a member of the immunoglobulin superfamily, CD200 interacts with its receptor CD200R to deliver inhibitory signals that suppress the activation of microglia and other myeloid cells.[@barclay2002] This CD200-CD200R immune checkpoint is fundamental to understanding neuroinflammation and neurodegenerative disease pathogenesis.

The CD200-CD200R pathway represents one of the most important endogenous mechanisms for preventing excessive microglial activation.[@choi2018] Dysregulation of this pathway has been implicated in Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), stroke, and amyotrophic lateral sclerosis (ALS).[@walker2014] The therapeutic potential of enhancing CD200 signaling has made it a compelling target for drug development.

This comprehensive review examines the structure-function relationships of CD200, its normal physiological functions in the nervous system, its dysregulation in neurodegenerative diseases, and current therapeutic strategies targeting the CD200-CD200R axis.

Structure

Primary Structure and Biochemistry

CD200 is a type I transmembrane glycoprotein with a molecular weight of approximately 47 kDa. The protein consists of:

• N-terminal extracellular domain: 192 amino acids containing two immunoglobulin-like domains
• Transmembrane region: 27 amino acids
• C-terminal cytoplasmic tail: 31 amino acids containing signaling motifs

Immunoglobulin Domain Architecture

CD200 contains two immunoglobulin (Ig) domains:

• V-set Ig domain: N-terminal domain with characteristic Ig fold
• C2-set Ig domain: Membrane-proximal Ig domain

Receptor Binding Interface

CD200 binds to CD200R through a well-characterized interface involving:

• Contact residues: Hydrophobic and polar residues in the V-set domain
• Epitope specificity: Distinct from other immunoglobulin family members
• Binding affinity: KD ~ 0.5-1 μM for CD200R binding

Post-Translational Modifications

CD200 undergoes several post-translational modifications:

• N-linked glycosylation: Six potential N-glycosylation sites in the extracellular domain
• O-linked glycosylation: Present in the membrane-proximal region
• Palmitoylation: At cysteine residues in the transmembrane domain for membrane anchoring

Normal Function

CD200R Signaling and Immune Suppression

CD200 delivers inhibitory signals through interaction with CD200R on myeloid cells, including microglia in the CNS. The CD200R contains an extended cytoplasmic tail with immunoreceptor tyrosine-based inhibition motifs (ITIMs) that recruit phosphatases (SHP-1, SHP-2) upon receptor clustering.

The signaling cascade includes:

Functions in the CNS

CD200-mediated immune suppression is essential for CNS homeostasis:

Cellular Expression Patterns

CD200 Expression:

• Neurons (high expression in cortex, hippocampus)
• [Oligodendrocytes](/cell-types/oligodendrocytes) Endothelial cells
• Some astrocyte populations

• Microglia (highest expression in brain)
• Perivascular macrophages
• Certain T cell subsets
• Some dendritic cells

Role in Neurodegenerative Diseases

Alzheimer's Disease

CD200 Expression Changes in AD

Multiple studies have demonstrated significant alterations in the CD200-CD200R pathway in Alzheimer's disease:

• Reduced CD200 expression: 30-50% decrease in AD brain tissue
• Decreased CD200R: Reduced receptor expression on microglia
• Correlation with pathology: Changes correlate with amyloid burden and cognitive decline

Mechanisms of CD200 Dysfunction in AD

Amyloid-β Effects: Aβ1-42 oligomers directly interfere with CD200-CD200R signaling through:

• Competitive binding with CD200R
• Disruption of receptor clustering
• Induction of CD200 internalization

Neuroinflammation Feedback: Chronic inflammation leads to epigenetic silencing of CD200 gene expression.

Therapeutic Implications for AD

Strategies targeting CD200 in AD include:

Parkinson's Disease

CD200 in PD Pathogenesis

In Parkinson's disease, CD200 dysregulation contributes to neuroinflammation in affected brain regions:

• Reduced CD200: Decreased expression in substantia nigra
• Microglial Activation: Loss of inhibitory signaling correlates with dopaminergic neuron loss
• α-Synuclein Interactions: α-Synuclein oligomers disrupt CD200 signaling

Evidence from Models

• CD200 knockout mice show enhanced vulnerability to MPTP-induced parkinsonism
• CD200 overexpression protects against 6-OHDA toxicity
• CD200R deficiency in microglia leads to increased inflammatory responses

Therapeutic Targeting in PD

Multiple Sclerosis

CD200-CD200R in MS

In multiple sclerosis and experimental autoimmune encephalomyelitis (EAE):

• CD200 expression is reduced in demyelinating lesions
• CD200R on microglia is downregulated during active disease
• Restoration of CD200 signaling ameliorates EAE

Mechanisms

The CD200 pathway limits:

• T cell activation and infiltration
• Pro-inflammatory cytokine production
• Demyelination and axonal loss

Stroke and Brain Injury

CD200 in Ischemic Injury

CD200 plays protective roles after stroke:

• CD200 expression increases after ischemic injury (adaptive response)
• CD200 knockout mice show larger infarcts
• CD200R signaling limits post-injury inflammation

Therapeutic Potential

• CD200-Fc administration reduces infarct size in mouse models
• The pathway promotes neurovascular remodeling

Amyotrophic Lateral Sclerosis (ALS)

CD200 alterations in ALS:

• Reduced CD200 in motor cortex and spinal cord
• Correlation with disease progression
• CD200R microglial expression increases with disease

Signaling Pathways and Mechanisms

CD200R Signaling Cascade

CD200R signaling involves multiple downstream pathways:

Cross-talk with Other Immune Pathways

CD200 signaling intersects with:

• TLR Signaling: CD200R can suppress TLR-induced inflammation
• CX3CR1 Pathway: Synergistic with fractalkine signaling
• TREM2 Pathways: Coordinate microglial regulatory mechanisms
• Complement System: Modulates complement-mediated phagocytosis

Cell-Type Specific Effects

CD200R signaling has distinct effects on different cell types:

• Microglia: Maintains surveillance state, limits cytokine production
• Macrophages: Reduces phagocytic activity and antigen presentation
• Dendritic Cells: Limits T cell activation capacity

Therapeutic Targeting

Agonist Approaches

Gene Therapy Approaches

• AAV-CD200: Adeno-associated virus-mediated gene delivery
• Lentiviral vectors: Ex vivo modification of cells
• Gene editing: CRISPR-based approaches to enhance CD200 expression

Combination Strategies

• CD200 agonist + CSF1R inhibitor: Combined immune modulation
• CD200 + anti-inflammatory drugs: Synergistic effects
• CD200 + neurotrophic factors: Immune modulation + neuroprotection

Clinical Trials

Genetic Variations

The CD200 gene contains several polymorphisms associated with disease risk:

• rs40493: Promoter variant associated with AD risk
• rs1626694: Intron variant linked to PD susceptibility
• rs3181220: 3'UTR variant affecting mRNA stability

Cross-Links to Related Topics

• [CD200 Gene](/genes/cd200)
• [CD200R1 Protein](/proteins/cd200r1-protein)
• [Neuroinflammation](/mechanisms/neuroinflammation)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Microglia](/cell-types/microglia)
• [CX3CR1 Signaling](/mechanisms/cx3cr1-pathway)
• [TREM2 Signaling](/mechanisms/trem2-signaling-pathway)

Key Publications

See Also

• [CD200R1 Protein](/proteins/cd200r1-protein)
• [CX3CR1 Protein](/proteins/cx3cr1-protein)
• [CSF1R Protein](/proteins/csf1r-protein)
• [Neuroinflammation](/mechanisms/neuroinflammation)
• [Microglia](/cell-types/microglia)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)

External Links

• [UniProt: P14210](https://www.uniprot.org/uniprot/P14210)
• [PDB: 1O7Y](https://www.rcsb.org/structure/1O7Y)
• [PDB: 4AD8](https://www.rcsb.org/structure/4AD8)
• [AlphaFold: CD200](https://alphafold.ebi.ac.uk/entry/P14210)
• [GeneCards: CD200](https://www.genecards.org/cgi-bin/carddisp.pl?gene=CD200)
• [IUPHAR: CD200R](https://www.guidetopharmacology.org/GTP/RCDb.html)

Brain Atlas Resources

• [Allen Human Brain Atlas](https://human.brain-map.org/) — protein expression data
• [Allen Cell Type Atlas](https://celltypes.brain-map.org/) — cell type specific expression
• [BrainSpan Atlas](https://brainspan.org/) — developmental transcriptome
• [Allen Mouse Brain Atlas](https://mouse.brain-map.org/) — mouse brain expression

References