PILRB

PILRB encodes an activating paired immunoglobulin-like receptor that signals through the adaptor DAP12 and recognizes CD99 as a ligand, functioning broadly in innate immune regulation, cancer signaling, and photoreceptor physiology (PMID:22479310, PMID:16926269). On myeloid cells, PILRB engagement promotes pro-inflammatory cytokine production (IL-1β, TNF-α, IL-6) while suppressing the IL-27/IL-10 anti-inflammatory axis; genetic deletion in mice improves bacterial clearance during S. aureus infection and limits immunopathology during Toxoplasma gondii infection (PMID:20065029, PMID:22479310). In gastric cancer cells, PILRB stabilizes IRS4 by recruiting the deubiquitinase OTUB1, relieving K48-linked ubiquitination and thereby hyperactivating PI3K/AKT signaling and reprogramming cholesterol metabolism (PMID:39227585). In photoreceptors, PILRB localizes to outer segments where its loss causes early-onset dysfunction with reduced expression of calcium-regulated phototransduction proteins, and a causal 3′UTR variant at the PILRB locus alters mRNA abundance and is associated with age-related macular degeneration (PMID:39532089, PMID:34534445).

1. 2006 Medium

   Establishing PILRB as an activating receptor with a defined ligand: comparative genomics identified PILRB at 7q22 as the activating member of a paired receptor family, and mouse studies identified CD99 as its ligand, framing PILRB as an immune receptor with a concrete signaling partner.

   Evidence Comparative genomic analysis and mRNA profiling across tissues and cell types in mouse and human

   PMID:16926269

   Open questions at the time

   • Direct biochemical reconstitution of PILRB–CD99 binding not performed in this study
   • Signaling adaptor for PILRB not yet demonstrated
2. 2010 High

   Defining PILRB as a pro-inflammatory activating receptor on myeloid cells: Pilrb knockout mice showed improved S. aureus clearance with reduced IL-1β/TNF-α/IL-6 and increased IFN-γ/IL-12, establishing that PILRB skews macrophage responses toward pro-inflammatory cytokine production at the expense of protective antimicrobial immunity.

   Evidence Pilrb knockout mouse, agonistic antibody, BMDM stimulation, cytokine measurement in BAL and serum

   PMID:20065029

   Open questions at the time

   • Downstream signaling cascade from PILRB to cytokine transcription not mapped
   • Whether PILRB directly binds S. aureus surface molecules or acts through indirect recognition not resolved
3. 2012 High

   Connecting PILRB to the DAP12-dependent signaling axis and the IL-27/IL-10 regulatory circuit: loss of PILRB in T. gondii infection models revealed that PILRB normally suppresses IL-27 (p28) from APCs, which in turn limits IL-10 from T cells, establishing a specific immunoregulatory pathway downstream of DAP12.

   Evidence Pilrb knockout mice challenged with T. gondii in chronic encephalitis and IBD models, cytokine quantification

   PMID:22479310

   Open questions at the time

   • Molecular mechanism by which DAP12-PILRB signaling represses IL-27 transcription unknown
   • Whether CD99 engagement is required for this pathway in vivo not tested
4. 2016 Medium

   Implicating PILRB in leukemia stem cell expansion independent of DNA damage repair: knockdown of Pilrb in Fanca-/- pre-leukemia stem cells improved survival without correcting genomic instability, placing PILRB in a DDR-parallel pathway that promotes malignant stem cell expansion.

   Evidence shRNA knockdown in Fanca-/- hematopoietic stem cells, in vivo leukemia transplant and survival analysis

   PMID:27568523

   Open questions at the time

   • Downstream effectors of PILRB signaling in LSCs not identified
   • Whether DAP12 is required for this leukemogenic role not tested
   • Knockdown rather than knockout; residual PILRB activity possible
5. 2021 Medium

   Linking PILRB expression regulation to retinal disease: a causal 3′UTR variant at the PILRB locus was shown by endogenous allelic replacement to alter PILRB mRNA abundance, nominating PILRB as a functional gene underlying age-related macular degeneration risk.

   Evidence Massively parallel reporter assay for 3′UTRs, CRISPR endogenous allelic replacement

   PMID:34534445

   Open questions at the time

   • Effect on PILRB protein level and retinal cell function not demonstrated
   • Causal path from altered PILRB abundance to AMD pathology not established
6. 2024 High

   Revealing a non-immune oncogenic mechanism: PILRB was shown to stabilize IRS4 by recruiting OTUB1 to remove K48-linked ubiquitin chains, preventing proteasomal degradation and hyperactivating PI3K/AKT signaling in gastric cancer, demonstrating a direct scaffolding/adaptor function beyond classical immune receptor activity.

   Evidence Co-immunoprecipitation of PILRB–IRS4–OTUB1, ubiquitination assays, loss/gain-of-function in vitro and xenograft models

   PMID:39227585

   Open questions at the time

   • Whether DAP12 is involved in this cancer signaling context unknown
   • Structural basis of PILRB–IRS4 and PILRB–OTUB1 interactions not resolved
   • Generalizability to cancers beyond gastric cancer not tested
7. 2025 High

   Establishing a photoreceptor-intrinsic role: CRISPR deletion of Pilrb1/2 in mice caused early-onset photoreceptor dysfunction with loss of calcium-regulated phototransduction proteins, and PILRB was localized to outer segments, demonstrating a cell-autonomous sensory function distinct from its immune role.

   Evidence CRISPR germline deletion of Pilrb1/2, electroretinography, immunohistochemistry with cell-type markers

   PMID:39532089

   Open questions at the time

   • Direct mechanism by which PILRB maintains calcium homeostasis in outer segments unknown
   • Whether PILRB signals through DAP12 or an alternative adaptor in photoreceptors not determined
   • Ligand for PILRB in the retinal context not identified

• The unifying signaling logic of PILRB across immune, cancer, and sensory contexts remains unresolved: whether DAP12-dependent and DAP12-independent pathways coexist, what ligands engage PILRB in non-immune tissues, and how PILRB's adaptor/scaffolding function for OTUB1–IRS4 relates to its canonical receptor activity are open questions.
• No structural model of PILRB signaling complex exists
• Tissue-specific adaptor usage (DAP12 vs. alternatives) not systematically assessed
• Retinal and cancer ligands for PILRB not identified