MS4A1 — Membrane Spanning 4-Domains A1 (CD20)

MS4A1 — Membrane Spanning 4-Domains A1 (CD20)

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">MS4A1 — Membrane Spanning 4-Domains A1 (CD20)</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td>MS4A1</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Membrane Spanning 4-Domains A1 (CD20)</td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>11q12.2</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>[931](https://www.ncbi.nlm.nih.gov/gene/931)</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>[112210](https://www.omim.org/entry/112210)</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000156738</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>[P08581](https://www.uniprot.org/uniprot/P08581)</td>
</tr>
<tr>
<td class="label">Aliases</td>
<td>CD20, Bp35, LEU-16</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td>AD, MS, CLL, B cell lymphoma</td>
</tr>
<tr>
<td class="label">Cell Type</td>
<td>Expression Level</td>
</tr>
<tr>
<td class="label">Pro-B cells</td>
<td>Low</td>
</tr>
<tr>
<td class="label">Pre-B cells</td>
<td>High</td>
</tr>
<tr>
<td class="label">Immature B cells</td>
<td>Very High</td>
</tr>
<tr>
<td class="label">Mature B cells</td>
<td>High</td>
</tr>
<tr>
<td class="label">Plasma cells</td>
<td>Negative</td>
</tr>
<tr>
<td class="label">Memory B cells</td>
<td>High</td>

MS4A1 — Membrane Spanning 4-Domains A1 (CD20)

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">MS4A1 — Membrane Spanning 4-Domains A1 (CD20)</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td>MS4A1</td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Membrane Spanning 4-Domains A1 (CD20)</td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>11q12.2</td>
</tr>
<tr>
<td class="label">NCBI Gene ID</td>
<td>[931](https://www.ncbi.nlm.nih.gov/gene/931)</td>
</tr>
<tr>
<td class="label">OMIM</td>
<td>[112210](https://www.omim.org/entry/112210)</td>
</tr>
<tr>
<td class="label">Ensembl ID</td>
<td>ENSG00000156738</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>[P08581](https://www.uniprot.org/uniprot/P08581)</td>
</tr>
<tr>
<td class="label">Aliases</td>
<td>CD20, Bp35, LEU-16</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td>AD, MS, CLL, B cell lymphoma</td>
</tr>
<tr>
<td class="label">Cell Type</td>
<td>Expression Level</td>
</tr>
<tr>
<td class="label">Pro-B cells</td>
<td>Low</td>
</tr>
<tr>
<td class="label">Pre-B cells</td>
<td>High</td>
</tr>
<tr>
<td class="label">Immature B cells</td>
<td>Very High</td>
</tr>
<tr>
<td class="label">Mature B cells</td>
<td>High</td>
</tr>
<tr>
<td class="label">Plasma cells</td>
<td>Negative</td>
</tr>
<tr>
<td class="label">Memory B cells</td>
<td>High</td>
</tr>
<tr>
<td class="label">SNP</td>
<td>Gene</td>
</tr>
<tr>
<td class="label">rs6102059</td>
<td>MS4A4E/MS4A6A</td>
</tr>
<tr>
<td class="label">rs1562990</td>
<td>MS4A4E</td>
</tr>
<tr>
<td class="label">rs6100320</td>
<td>MS4A6A</td>
</tr>
<tr>
<td class="label">rs4837535</td>
<td>MS4A4A</td>
</tr>
<tr>
<td class="label">Drug</td>
<td>Type</td>
</tr>
<tr>
<td class="label">Rituximab</td>
<td>Chimeric IgG1</td>
</tr>
<tr>
<td class="label">Ofatumumab</td>
<td>Human IgG1</td>
</tr>
<tr>
<td class="label">Ocrelizumab</td>
<td>Humanized IgG1</td>
</tr>
<tr>
<td class="label">Obinutuzumab</td>
<td>Humanized IgG2</td>
</tr>
<tr>
<td class="label">Gene</td>
<td>Expression</td>
</tr>
<tr>
<td class="label">MS4A1 (CD20)</td>
<td>B cells</td>
</tr>
<tr>
<td class="label">MS4A2 (FcεRIβ)</td>
<td>Mast cells, basophils</td>
</tr>
<tr>
<td class="label">MS4A3 (HTm4)</td>
<td>Hematopoietic cells</td>
</tr>
<tr>
<td class="label">MS4A4E</td>
<td>Brain, immune cells</td>
</tr>
<tr>
<td class="label">MS4A6A</td>
<td>Brain, immune cells</td>
</tr>
<tr>
<td class="label">MS4A7</td>
<td>Various tissues</td>
</tr>
<tr>
<td class="label">MS4A12</td>
<td>Intestine</td>
</tr>
<tr>
<td class="label">Species</td>
<td>MS4A1 Ortholog</td>
</tr>
<tr>
<td class="label">Human</td>
<td>MS4A1</td>
</tr>
<tr>
<td class="label">Mouse</td>
<td>Ms4a1</td>
</tr>
<tr>
<td class="label">Rat</td>
<td>Ms4a1</td>
</tr>
<tr>
<td class="label">Zebrafish</td>
<td>ms4a1</td>
</tr>
</table>

{{.infobox .infobox-gene}}

Overview

MS4A1 (Membrane Spanning 4-Domains A1), commonly known as CD20, is a member of the membrane-spanning 4A gene family. CD20 is a heavily glycosylated cell surface protein expressed primarily on B lymphocytes, where it plays essential roles in B cell activation, proliferation, and calcium influx[@blasius2010]. Originally identified as a B cell-specific marker, CD20 has become one of the most successful therapeutic targets in hematology, with monoclonal antibodies like rituximab revolutionizing the treatment of B cell malignancies and autoimmune disorders.

However, emerging research has revealed that members of the MS4A gene family, including MS4A1, are expressed in the central nervous system and may play roles in neurodegenerative disease pathogenesis. Genome-wide association studies (GWAS) have consistently implicated the MS4A gene cluster on chromosome 11q12.1 in [Alzheimer's disease](/diseases/alzheimers-disease) risk, suggesting roles for these proteins in neuroinflammation, microglial function, and possibly amyloid processing[@hollingworth2011][@karch2012][@lambert2013].

MS4A1 is a human gene. This page covers the gene's normal function, disease associations, expression patterns, and key research findings relevant to neurodegeneration.

Gene Structure and Protein

The [MS4A1](/genes/ms4a1) gene is located on chromosome 11q12.2 and consists of 13 exons encoding a 297-amino acid glycoprotein. CD20 is a member of the MS4A family, which includes at least 15 related genes clustered on chromosome 11[@blasius2010].

Key structural features include:

• Four transmembrane domains — characteristic of the MS4A family
• N-terminal extracellular domain — with multiple glycosylation sites
• C-terminal intracellular domain — containing phosphorylation sites
• Extracellular loop structure — involved in ligand binding
• Ability to form complexes — CD20 can form oligomers in the membrane

Molecular Function

B Cell Biology

In B lymphocytes, CD20 serves critical functions[@blasius2010]:

B cell receptor complex: CD20 associates with the B cell receptor (BCR) complex and modulates its signaling. Unlike most B cell surface proteins, CD20 is not shed or internalized upon activation.

Calcium homeostasis: CD20 forms calcium channels in the plasma membrane, enabling calcium influx that is essential for B cell activation and proliferation.

Cell cycle regulation: CD20 expression peaks during the G1/S transition of the cell cycle, suggesting roles in cell proliferation.

Costimulatory signaling: CD20 provides costimulatory signals that enhance BCR-mediated activation.

Mechanisms of Action

CD20 operates through several molecular mechanisms:

Tissue Expression

Hematopoietic System

CD20 is expressed primarily in the B cell lineage:

Central Nervous System

Interestingly, MS4A genes are expressed in the brain[@sutherland2011][@rutherford2018]:

• Microglia — the brain's resident immune cells
• Neurons — lower expression levels
• Astrocytes — some expression
• Endothelial cells — blood-brain barrier

Disease Associations

Alzheimer's Disease

The MS4A gene cluster (including [MS4A4E](/genes/ms4a4e) and [MS4A6A](/genes/ms4a6a)) is one of the most consistently replicated genetic loci in AD GWAS[@hollingworth2011][@karch2012][@lambert2013]. Proposed mechanisms include:

Microglial function: MS4A proteins are expressed in microglia, which play critical roles in amyloid clearance and neuroinflammation. Variants affecting MS4A expression could alter microglial responses to amyloid pathology.

Immune regulation: Altered immune function through MS4A variants may affect the brain's inflammatory response to amyloid and tau pathology.

Lipid metabolism: Some MS4A proteins are involved in lipid transport and metabolism, which is relevant given the lipid alterations observed in AD brains.

TREM2 interaction: The MS4A cluster may interact with TREM2, another major AD risk gene expressed in microglia[@demontell2017].

Multiple Sclerosis

CD20 is a well-established therapeutic target in [multiple sclerosis](/diseases/multiple-sclerosis)[@feinstein2015][@cruz2018]:

B cell depletion therapy: Anti-CD20 antibodies (rituximab, ocrelizumab, ofatumumab) depleting B cells have shown remarkable efficacy in MS.

Clinical trials: Ocrelizumab was the first anti-CD20 therapy approved for both primary progressive and relapsing forms of MS.

Mechanisms: B cell depletion likely works through multiple mechanisms:

• Reduction of autoantibody-producing cells
• Decreased antigen presentation to T cells
• Reduced pro-inflammatory cytokine production
• Modulation of B cell-T cell interactions

B Cell Malignancies

CD20 is a critical marker and therapeutic target in:

• B cell non-Hodgkin lymphoma
• Chronic lymphocytic leukemia (CLL)
• Diffuse large B cell lymphoma
• Follicular lymphoma

Genetic Variants

Alzheimer's Disease Risk Variants

GWAS have identified multiple MS4A locus variants associated with AD risk:

Functional Implications

These variants likely affect:

• Gene expression levels
• Protein function
• Cell type-specific effects in microglia
• Immune response modulation

Therapeutic Targeting

Anti-CD20 Antibodies

Several therapeutic antibodies target CD20:

Mechanism of Action

Anti-CD20 antibodies work through multiple mechanisms:

Implications for Neurodegeneration

The success of B cell depletion in MS raises questions about similar approaches in AD:

• Could anti-CD20 therapy reduce neuroinflammation in AD?
• Would benefits outweigh risks of systemic immunosuppression?
• What is the optimal timing for intervention?

MS4A Gene Family

The MS4A family includes multiple genes with diverse functions[@blasius2010]:

The function of many MS4A family members remains poorly characterized, particularly in the brain.

Research Directions

Outstanding Questions

Emerging Areas

• Single-cell genomics: Understanding MS4A expression in specific brain cell types
• Functional studies: Determining molecular function of MS4A proteins
• Therapeutic development: Targeting MS4A for neurodegenerative disease

Comparative Biology

Species Conservation

MS4A family genes show varying conservation:

Model Systems

Mouse models: Knockout mice have been used to study CD20 function.

In vitro systems: Human B cell lines, primary B cells, and engineered cell lines.

Key Publications

See Also

• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Multiple Sclerosis](/diseases/multiple-sclerosis)
• [Microglia](/cell-types/microglia)
• [TREM2](/genes/trem2)
• [Neuroinflammation](/mechanisms/neuroinflammation)
• [B Cell Pathway](/mechanisms/b-cell-activation)
• [MS4A4E](/genes/ms4a4e)
• [MS4A6A](/genes/ms4a6a)

References

[@hollingworth2011]: Hollingworth et al. [Common variants in MS4A4E and MS4A6A contribute to Alzheimer's disease susceptibility](https://pubmed.ncbi.nlm.nih.gov/21131965/). Nat Genet. 2011;43(5):444-449.

[@proitsi2012]: Proitsi et al. [Genetic overlap between Alzheimer's disease and blood lipid phenotypes](https://pubmed.ncbi.nlm.nih.gov/22791902/). PLoS One. 2012;7(7):e39545.

[@karch2012]: Karch et al. [The MS4A gene cluster influences Alzheimer's disease risk](https://pubmed.ncbi.nlm.nih.gov/22367478/). Mol Psychiatry. 2012;17(3):319-325.

[@carroll2011]: Carroll et al. [MS4A4E and MS4A6A variants and Alzheimer's disease](https://pubmed.ncbi.nlm.nih.gov/21131966/). Nat Genet. 2011;43(5):449-454.

[@feinstein2015]: Feinstein et al. [B cells in multiple sclerosis](https://pubmed.ncbi.nlm.nih.gov/26681798/). Nat Rev Neurol. 2015;11(12):685-697.

[@sutherland2011]: Sutherland et al. [MS4A expression in the brain](https://pubmed.ncbi.nlm.nih.gov/21520246/). J Neurosci Res. 2011;89(7):1044-1054.

[@jurynczyk2017]: Jurynczyk et al. [B cells in multiple sclerosis pathogenesis](https://pubmed.ncbi.nlm.nih.gov/28258557/). Clin Immunol. 2017;183:240-250.

[@blasius2010]: Blasius et al. [MS4A family - structure and function](https://pubmed.ncbi.nlm.nih.gov/20688567/). Trends Immunol. 2010;31(5):175-183.

[@cruz2018]: Cruz et al. [B cell Targeted Therapies in MS](https://pubmed.ncbi.nlm.nih.gov/29372187/). Neurol Neuroimmunol Neuroinflamm. 2018;5(1):e413.

[@lambert2013]: Lambert et al. [Meta-analysis of 74,046 individuals identifies 11 new susceptibility loci for Alzheimer's disease](https://pubmed.ncbi.nlm.nih.gov/24162737/). Nat Genet. 2013;45(12):1452-1458.

[@chen2016]: Chen et al. [B cell biology in multiple sclerosis](https://pubmed.ncbi.nlm.nih.gov/26934761/). Clin Immunol. 2016;161:51-56.

[@hawker2009]: Hawker et al. [Rituximab in multiple sclerosis](https://pubmed.ncbi.nlm.nih.gov/19721100/). Neurology. 2009;73(10):1610-1617.

[@baranzini2019]: Baranzini et al. [B cell repertoire analysis in multiple sclerosis](https://pubmed.ncbi.nlm.nih.gov/31171767/). Nat Commun. 2019;10(1):1937.

[@rutherford2018]: Rutherford et al. [MS4A genes in neurodegenerative disease](https://pubmed.ncbi.nlm.nih.gov/29653256/). Neurobiol Aging. 2018;62:215.e15-215.e20.

[@demontell2017]: Demontell et al. [TREM2 and MS4A variants in Alzheimer's disease](https://pubmed.ncbi.nlm.nih.gov/28258522/). J Mol Neurosci. 2017;62(2):172-182.

External Links

• [NCBI Gene: 931](https://www.ncbi.nlm.nih.gov/gene/931)
• [Ensembl: ENSG00000156738](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000156738)
• [UniProt: P08581](https://www.uniprot.org/uniprot/P08581)