PILRB Protein
Overview
<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">PILRB Protein</th>
</tr>
<tr>
<td class="label">Protein Name</td>
<td>Paired Immunoglobulin-Like Type 2 Receptor Beta</td>
</tr>
<tr>
<td class="label">Gene Symbol</td>
<td>[PILRB](/genes/pilrb)</td>
</tr>
<tr>
<td class="label">UniProt ID</td>
<td>[Q9H7E4](https://www.uniprot.org/uniprot/Q9H7E4)</td>
</tr>
<tr>
<td class="label">Protein Length</td>
<td>264 amino acids</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~29 kDa</td>
</tr>
<tr>
<td class="label">Chromosomal Location</td>
<td>7q22.1</td>
</tr>
<tr>
<td class="label">Subcellular Localization</td>
<td>Cell surface, plasma membrane</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/alzheimer" style="color:#ef9a9a">Alzheimer</a>, <a href="/wiki/dementia" style="color:#ef9a9a">Dementia</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">14 edges</a></td>
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</table>
PILRβ (Paired Immunoglobulin-Like Type 2 Receptor Beta) is an activating immune receptor encoded by the [PILRB](/genes/pilrb) gene on chromosome 7q22.1. It forms a functional receptor pair with its inhibitory counterpart [PILRα](/proteins/pilra-protein), together modulating innate immune cell activation in both peripheral tissues and the central nervous system. PILRβ engagement generates activating signals through association with the [DAP12](/proteins/dap12-protein) signaling adaptor, counterbalancing the inhibitory tone set by PILRα. In [microglia](/cell-types/microglia) and myeloid cells, the PILRα/β balance influences phagocytic activity, cytokine production, and neuroinflammatory responses relevant to [Alzheimer's disease](/diseases/alzheimers-disease) and other neurodegenerative conditions[@tabata2008][@fournier2000].
Structure
PILRβ is a type I transmembrane glycoprotein containing a single V-type immunoglobulin-like extracellular domain, a transmembrane segment with a positively charged lysine residue, and a short cytoplasmic tail lacking intrinsic signaling motifs. The charged transmembrane residue enables non-covalent association with the ITAM-bearing adaptor protein [DAP12](/proteins/dap12-protein) (also called TYROBP), which transduces activating signals upon PILRβ ligand engagement[@tabata2008]. The Ig-like domain adopts a canonical β-sandwich fold and recognizes sialylated O-glycan structures (particularly the Tn and sialyl-Tn antigens) presented on cell surface glycoproteins, including CD99[@sun2020]. Unlike PILRα, which contains an ITIM in its cytoplasmic tail for inhibitory signaling, PILRβ relies entirely on DAP12 for signal transduction[@fournier2000].
Normal Function
Immune Cell Activation
PILRβ functions as an activating receptor on myeloid lineage cells including monocytes, macrophages, dendritic cells, neutrophils, and [microglia](/cell-types/microglia). Upon engagement with sialylated glycoprotein ligands, PILRβ recruits DAP12, which becomes phosphorylated on its ITAM tyrosines by Src family kinases. This triggers recruitment and activation of [Syk](/proteins/syk-protein) kinase, initiating downstream signaling cascades including PI3K/Akt, PLCγ, and MAPK pathways that promote phagocytosis, cytokine release, and cell survival[@tabata2008][@salminen2022].
Paired Receptor Balance
The PILRα/PILRβ receptor pair constitutes a paired receptor system common in immune regulation. Both receptors recognize overlapping O-glycan ligands, but their opposing signaling outputs (inhibitory vs. activating) create a tunable activation threshold. The relative expression levels of PILRα and PILRβ on individual cells determine the net outcome of ligand engagement, providing fine-grained control over immune activation[@fournier2000][@sun2020].
HSV-1 Entry Receptor
PILRα (but not PILRβ) has been identified as an entry receptor for herpes simplex virus 1 (HSV-1) through binding to viral glycoprotein B. However, PILRβ may modulate HSV-1 susceptibility indirectly by competing for shared glycan ligands and altering PILRα-mediated viral entry efficiency[@satoh2008].
Role in Neurodegeneration
Microglial Activation in Alzheimer's Disease
In [Alzheimer's disease](/diseases/alzheimers-disease), the PILRα/PILRβ axis has emerged as a modulator of microglial responses to [amyloid-β](/proteins/amyloid-beta) plaques. Genome-wide association studies identified the PILRA/PILRB locus as an AD risk locus, with a protective missense variant (G78R) in PILRα reducing sialic acid binding affinity and altering microglial activation[@jansen2019][@rathore2018]. PILRβ-mediated activating signals may promote beneficial microglial phagocytosis of amyloid deposits, while excessive PILRα inhibitory signaling could impair clearance. The balance between these paired receptors likely determines whether [microglia](/cell-types/microglia-neuroinflammation) adopt a neuroprotective or neurotoxic phenotype in the AD brain[@salminen2022].
TREM2 Pathway Crosstalk
PILRβ shares the DAP12 signaling adaptor with [TREM2](/proteins/trem2-protein), a major AD risk gene product. Competition for limiting DAP12 molecules may create functional interactions between PILRβ and [TREM2](/proteins/trem2) signaling. In microglia where TREM2 is highly expressed, PILRβ activation could either synergize with or compete against TREM2-DAP12 signals depending on cellular context and ligand availability[@ulland2018].
Neuroinflammatory Modulation
In [Parkinson's disease](/diseases/parkinsons-disease) and [frontotemporal dementia](/diseases/frontotemporal-dementia), chronic neuroinflammation mediated by activated microglia contributes to neuronal damage. PILRβ's activating function may amplify inflammatory cytokine production (TNF-α, IL-1β, IL-6) through DAP12-Syk-[NF-κB](/entities/nf-kb) signaling when microglial activation becomes dysregulated[@salminen2022].
Therapeutic Targeting
The PILR receptor system represents a potential immunotherapeutic target for neurodegeneration. Strategies under investigation include:
- PILRα blockade: Antibodies blocking PILRα inhibitory signaling to enhance microglial phagocytosis of pathological protein aggregates
- PILRβ agonists: Activating PILRβ to promote beneficial microglial functions
- Glycan-based modulators: Sialylated glycan mimetics that selectively engage PILRβ over PILRα
These approaches must be carefully balanced, as excessive microglial activation can exacerbate neuroinflammation[@rathore2018].
See Also
- [PILRα Protein](/proteins/pilra-protein)
- [TREM2 Protein](/proteins/trem2-protein)
- [DAP12/TYROBP](/proteins/dap12-protein)
- [Microglia](/cell-types/microglia)
- [Neuroinflammation](/mechanisms/neuroinflammation)
External Links
- [UniProt: Q9H7E4](https://www.uniprot.org/uniprot/Q9H7E4)
- [NCBI Gene: PILRB](https://www.ncbi.nlm.nih.gov/gene/29990)
- [GeneCards: PILRB](https://www.genecards.org/cgi-bin/carddisp.pl?gene=PILRB)
References
[Tabata S, Kuroki K, Wang J, et al, Biophysical characterization of O-glycosylated CD99 recognition by paired Ig-like type 2 receptors (2008)](https://pubmed.ncbi.nlm.nih.gov/18292562/)
[Fournier N, Chalus L, Durand I, et al, FDF03, a novel inhibitory receptor of the immunoglobulin superfamily, is expressed by human dendritic and myeloid cells (2000)](https://pubmed.ncbi.nlm.nih.gov/10860984/)
[Sun Y, Senger K, Bhatt DK, et al, Innate immune receptor PILRA mediates HSV-1 entry through recognition of viral glycoprotein B sialylation (2020)](https://pubmed.ncbi.nlm.nih.gov/32661338/)
[Salminen A, Kaarniranta K, Kauppinen A, Innate immunity meets neuroinflammation: the immunoregulatory role of PILR family in Alzheimer's disease (2022)](https://pubmed.ncbi.nlm.nih.gov/35218553/)
[Satoh T, Arii J, Suenaga T, et al, PILRα is a herpes simplex virus-1 entry coreceptor that associates with glycoprotein B (2008)](https://pubmed.ncbi.nlm.nih.gov/18246067/)
[Jansen IE, Savage JE, Watanabe K, et al, Genome-wide meta-analysis identifies new loci and functional pathways influencing Alzheimer's disease risk (2019)](https://pubmed.ncbi.nlm.nih.gov/30617256/)
[Rathore N, Bhatt DK, et al, Paired immunoglobulin-like type 2 receptor alpha G78R variant alters ligand binding and confers protection to Alzheimer's disease (2018)](https://pubmed.ncbi.nlm.nih.gov/30069002/)
[Ulland TK, Colonna M, TREM2 — a key player in microglial biology and Alzheimer disease (2018)](https://pubmed.ncbi.nlm.nih.gov/29703995/)