rs3790565 — IL12RB2

Intronic IL12RB2 variant associated with IL-12 signaling pathway variation and susceptibility to Th1-mediated autoimmune conditions including primary biliary cholangitis, allergic rhinitis, and endometriosis

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IL12RB2 rs3790565 — Th1 Immune Gating and Autoimmune Risk at the Interleukin-12 Receptor

Interleukin-12 (IL-12)11 Interleukin-12 (IL-12)
A heterodimeric cytokine secreted by dendritic cells and macrophages after pathogen sensing; it drives naive CD4+ T cells toward the Th1 phenotype, activates NK cells, and sustains IFN-γ production — the core of cellular immunity against intracellular pathogens is one of the master switches of adaptive immunity. Its receptor on T and NK cells consists of two subunits: IL-12Rβ1 (encoded by IL12RB1) and IL-12Rβ2 (encoded by IL12RB2). The β2 subunit is the key signaling component — it carries the intracellular domains that activate the JAK2/TYK2-STAT4 cascade, ultimately driving IFN-γ production and Th1 commitment. rs3790565 is an intronic variant within IL12RB2 on chromosome 1p31.3, approximately 11 kilobases from the better-studied rs3790567, which has reached genome-wide significance in primary biliary cholangitis (PBC) GWAS.

The Mechanism

rs3790565 lies within intron sequence of IL12RB2 but is located in a region with regulatory potential. The C allele (the minor allele globally, at ~24% frequency) is the variant of interest. While the intronic position means it does not alter the IL-12Rβ2 protein sequence, intronic variants at this locus are known to influence IL12RB2 expression levels, potentially affecting the density of functional IL-12 receptors on T cell and NK cell surfaces.

IL-12Rβ2 expression is the critical gating step for IL-12 responsiveness22 IL-12Rβ2 expression is the critical gating step for IL-12 responsiveness
Szabo et al. 2000 established that Th1/Th2 polarization is regulated in vivo by differential expression of the β2 subunit — cells without β2 cannot respond to IL-12 regardless of cytokine levels. When β2 expression is altered — whether by intronic regulatory variants, epigenetic modification, or cytokine feedback — the magnitude of IL-12 signaling in responding T cells shifts. This directly adjusts the balance between Th1-dominated responses (targeted at intracellular pathogens, also driving many autoimmune processes) and Th2/Th17 responses (atopic disease, allergy). Variants in this locus are therefore positioned at a central immune decision point with downstream consequences for both protective immunity and autoimmune risk.

The Evidence

The strongest evidence linking IL12RB2 genetic variation to disease comes from genome-wide association studies of primary biliary cholangitis (PBC), an autoimmune liver disease with a hallmark Th1 inflammatory signature. Hirschfield et al. 200933 Hirschfield et al. 2009
536 PBC cases and 1,536 controls; first GWAS to identify non-HLA PBC risk loci including IL12RB2; rs3790567 at the same locus reached p=2.76×10⁻¹¹, OR=1.51 established IL12RB2 as a bona fide PBC susceptibility gene. A follow-up Immunochip study44 Immunochip study
Juran et al. 2012 — 2,426 PBC patients and 5,731 controls confirmed the locus, refined the association signal, and notably identified an epistatic interaction between the IL12RB2 risk locus at 1p31 and the IRF5 locus at 7q32 — suggesting that these two regulatory genes amplify each other's effect on PBC susceptibility.

rs3790565 itself has been directly genotyped in a Chinese Han allergic rhinitis study55 Chinese Han allergic rhinitis study
Wei et al. 2015 — 543 cases and 749 controls; rs3790565 among three IL-12Rβ2 SNPs genotyped by PCR-RFLP and in a study of IL-12/IL-27 receptor variants and endometriosis organ involvement66 IL-12/IL-27 receptor variants and endometriosis organ involvement
Zare et al. 2023 — Iranian patients. Both conditions involve Th1/Th2 imbalance: allergic rhinitis reflects Th2-skewed airway immunity, while endometriosis shows aberrant Th1 signaling contributing to peritoneal inflammation.

The broader IL23R-IL12RB2 intergenic region has been independently implicated in Behçet's disease — Fei et al. 2010 GWAS77 Fei et al. 2010 GWAS
2,430 Behçet's cases, 2,660 controls; rs924080 in the IL23R-IL12RB2 region reached p=6.69×10⁻⁹, OR=1.28 — consistent with the role of this chromosomal neighborhood in multiple Th1-predominant inflammatory conditions.

The evidence level for rs3790565 specifically is moderate: the SNP sits in a locus with strong mechanistic and GWAS support, but the specific variant has not yet reached genome-wide significance in any single study. Its association signals in allergic rhinitis and endometriosis are suggestive but not yet definitively replicated at scale.

Practical Implications

C allele carriers (CC or CT at rs3790565) carry the minor allele at a locus where the disease-associated haplotype has been linked to IL-12 pathway dysregulation and Th1 autoimmune conditions. The most clinically meaningful associations at the IL12RB2 locus center on conditions with strong Th1 immune signatures: primary biliary cholangitis, Behçet's disease, and potentially other autoimmune liver and mucosal conditions. No supplement or dietary intervention has been shown to specifically modify IL-12Rβ2 expression in carriers of intronic variants. The actionable response is surveillance — knowing which conditions carry elevated risk and recognizing early symptoms.

Interactions

rs3790565 is in the same IL12RB2 locus as rs379056788 rs3790567
The neighboring IL12RB2 SNP approximately 11kb away that reached p=2.76×10⁻¹¹ for PBC in the Hirschfield GWAS; carriers of rs3790567 risk allele show elevated anti-mitochondrial antibody titers in PBC (PMID 28299343) and rs6679356 — both of which have been more extensively studied in PBC natural history. The IL12RB2 risk locus at 1p31 shows documented epistasis with IRF599 IRF5
Interferon regulatory factor 5, a key transcription factor downstream of innate immune sensing; its interaction with IL12RB2 identified in Immunochip PBC analysis (PMID 22936693) at 7q32, suggesting that combined risk at both loci amplifies autoimmune liver disease susceptibility.

rs2104286 (IL2RA) is a related T-cell regulation SNP that overlaps in the autoimmune spectrum and may combine with IL12RB2 variants through convergent effects on T-cell activation thresholds.

Genotype Interpretations

What each possible genotype means for this variant.

TT T/T — Common Genotype Normal

Common genotype — typical IL12RB2 function and population-average Th1 autoimmune risk

You carry two copies of the T allele at rs3790565, which is the major allele at this IL12RB2 intronic position. Approximately 57% of people globally share this TT genotype (approaching 66% in European and East Asian populations). This is the reference genotype associated with typical IL-12Rβ2 function and population-average risk for IL12RB2-associated autoimmune conditions. No variant-specific actions are indicated.

CT C/T — Heterozygous Intermediate

One copy of the minor C allele — modestly elevated IL12RB2 locus autoimmune risk

The IL12RB2 locus encompasses multiple intronic variants in moderate to strong linkage disequilibrium. rs3790565 and the better-studied rs3790567 (approximately 11kb away) both tag the C-allele risk haplotype. rs3790567's C allele (minor allele) has been associated with elevated anti-mitochondrial antibody titers and cirrhosis risk in PBC patients (PMID 28299343), and the IL12RB2 locus overall reached genome-wide significance in PBC GWAS (PMID 19458352).

Carrying one C allele places you in the intermediate risk group. This is the most common genotype involving the C allele (~37% globally), reflecting the locus's additive architecture where each C allele contributes incrementally to altered IL-12Rβ2 expression and Th1 immune bias. At the heterozygous level, the absolute increase in risk for any specific autoimmune condition remains modest.

CC C/C — Minor Allele Homozygous High Risk

Two copies of the minor risk allele — highest IL12RB2-associated autoimmune susceptibility at this locus

The IL12RB2 locus at 1p31.3 has been implicated by GWAS in primary biliary cholangitis (PBC) — an autoimmune bile duct disease with a characteristic Th1 immune signature — with the neighboring rs3790567 variant reaching OR=1.51, p=2.76×10⁻¹¹ in a cohort of 536 PBC patients (PMID 19458352). A subsequent Immunochip study in 2,426 PBC patients confirmed the locus and identified an epistatic interaction with the IRF5 locus (PMID 22936693).

rs3790565 has been directly studied in allergic rhinitis (Wei et al. 2015, PMID 24997981) and endometriosis (Zare et al. 2023, PMID 36328955), both conditions where Th1/Th2 immune balance plays a mechanistic role. While per-SNP effect sizes for rs3790565 are not yet established at genome-wide significance, the biological plausibility is high: intronic IL12RB2 variants in this region are positioned to modulate IL-12Rβ2 expression and, consequently, the magnitude of Th1 immune polarization.

Note that the African ancestry population shows substantially higher C allele frequency (~67%) compared to European (~19%), East Asian (~22%), and South Asian (~15%) populations. Risk interpretation and population prevalence estimates should be considered in this ancestry context.