rs3134883 — IL2RA

IL2RA rs3134883 — A Second Independent Signal at the Autoimmune Thermostat

The IL2RA locus¹¹ IL2RA locus
IL2RA on chromosome 10p15.1 encodes CD25, the alpha subunit of the high-affinity interleukin-2 receptor, essential for Treg development and maintenance is one of the most replicated non-HLA autoimmune susceptibility regions in the human genome. While rs2104286 is the most commonly cited variant at this locus, fine-mapping studies have established that multiple independent genetic signals coexist in the same region, each tagging distinct regulatory effects on IL-2 receptor expression and immune tolerance. rs3134883 is one of these independent signals — it anchors a five-variant haplotype block with its own disease associations and its own relationship to soluble IL-2 receptor biology.

The Mechanism

rs3134883 sits in an intron of IL2RA at chromosome 10, position 6,058,762 (GRCh38). The IL2RA gene lies on the minus strand, but the variant is always reported in plus-strand notation (G/A) as per the GRCh38 reference. It is not a coding change; rather, it is an intronic tag SNP²² intronic tag SNP
Intronic variants can influence gene expression through effects on transcription factor binding, RNA splicing, chromatin accessibility, or enhancer activity within introns that marks a haplotype block in strong linkage disequilibrium with functional regulatory elements.

The five-variant protective haplotype H5 — comprising rs3134883 (G allele), rs3118470, rs7072793, rs4749955, and rs12251307 — tags a protective IL2RA regulatory state³³ tags a protective IL2RA regulatory state
The H5 haplotype was in perfect LD (r²=1.0) with the minor allele of ss52580101 in CEU populations, a variant associated with altered IL-2RA expression and soluble receptor shedding. The G allele at rs3134883 is the protective allele: carriers of the G-containing haplotype have lower autoimmune disease risk. Conversely, the A allele tags a haplotype block associated with altered IL-2 receptor biology — specifically, with changes to the balance between membrane-bound and soluble IL-2RA that reduce effective IL-2 signaling to regulatory T cells.

Mechanistically, impaired IL-2 signaling through the high-affinity receptor complex (CD25/IL-2Rβ/γc) reduces STAT5 phosphorylation⁴⁴ reduces STAT5 phosphorylation
pSTAT5 is the master downstream signal in Tregs; its reduction impairs FoxP3 expression and Treg suppressive capacity in CD4+CD25+ regulatory T cells, lowering their suppressive capacity. A study in genotype-selected healthy donors confirmed that susceptible IL2RA haplotypes reduce IL-2 responsiveness⁵⁵ susceptible IL2RA haplotypes reduce IL-2 responsiveness
Cerosaletti et al. measured lower pSTAT5a and reduced FOXP3 expression in susceptibility-haplotype carriers versus protective-haplotype carriers and reduce FoxP3 expression, directly linking locus-level genetic variation to Treg function.

The Evidence

The Type I Diabetes Genetics Consortium study⁶⁶ Type I Diabetes Genetics Consortium study
5,003 T1D-affected sib-pair families from a large international consortium, 69 SNPs spanning ~88 kb of IL2RA established rs3134883's place in the IL2RA haplotype architecture. The protective H5 haplotype carrying the G allele showed OR 0.699 (95% CI 0.602–0.811, p=3.2×10⁻⁵) for T1D protection. Crucially, rs3134883 retained independent statistical significance (p=4.29×10⁻³) after conditioning on the full H5 haplotype, suggesting it tags both haplotype-level and potentially position-specific regulatory effects.

For rheumatoid arthritis, rs3134883 is among the lead variants at the IL2RA locus in large-scale GWAS. A multi-ancestry RA GWAS⁷⁷ multi-ancestry RA GWAS
Ishigaki et al. meta-analysis across European and East Asian populations, confirming multiple independent IL2RA signals with OR ~1.1 per A allele at rs3134883 confirmed the A allele at rs3134883 reaches genome-wide significance (p as low as 2×10⁻¹⁵ in the Ha et al. 2020 analysis) with OR approximately 1.1 per allele for seropositive RA. This effect is independent from rs2104286, reflecting the well-established multi-signal architecture⁸⁸ multi-signal architecture
Fine-mapping of IL2RA identifies at least three independent association signals affecting T1D and MS through different molecular pathways of the IL2RA locus.

In vitiligo, a GWAS of Chinese Han participants⁹⁹ GWAS of Chinese Han participants
6,857 vitiligo cases and 12,025 controls in a two-stage replication study confirmed the 10p15.1 locus — encompassing rs3134883 — as a susceptibility locus (OR 1.11, p=1.01×10⁻⁵), demonstrating that the IL2RA risk haplotype extends beyond European-ancestry autoimmune diseases. Lymphocyte count modulation by rs3134883 has also been reported in GWAS (p=2×10⁻²¹), consistent with the locus's role in regulating the size and activation state of T-cell populations.

Practical Implications

The A allele at rs3134883 marks a modest but independently established increase in autoimmune disease susceptibility across multiple diseases — RA, T1D, and vitiligo. Its effect is additive: AA homozygotes carry approximately twice the incremental risk of a single A allele. Because this variant reflects impaired IL-2-driven Treg signaling, the same compensatory strategies relevant to rs2104286 apply here: strategies that shore up Treg function through IL-2-independent pathways.

Vitamin D is particularly relevant because 1,25-dihydroxyvitamin D3 promotes Treg differentiation through the VDR/TGF-β1 pathway independently of IL-2 signaling. Clinical evidence¹⁰¹⁰ Clinical evidence
Prietl et al. demonstrated that vitamin D supplementation increases Treg percentages in healthy subjects through the VDR/PLC-γ1/TGF-β1 axis confirms this pathway directly increases FoxP3+ Treg numbers and function, directly addressing the Treg deficit caused by impaired IL-2 signaling.

For RA specifically, knowledge of IL2RA genotype has implications for treatment response monitoring. IL2RA variation influences lymphocyte counts and immune activation set-points, potentially affecting responsiveness to biologics targeting the TNF or IL-6 pathways. Carriers of the A allele should be attentive to early joint symptoms (morning stiffness, bilateral symmetric joint pain) that may signal early RA before structural damage develops.

Interactions

rs3134883 operates in the same IL2RA locus as rs2104286 and rs2256774, but fine-mapping studies¹¹¹¹ fine-mapping studies
Todd et al. and subsequent work confirm at least three independent signals at IL2RA, with distinct effects on sIL-2RA production, surface CD25 expression, and downstream T-cell signaling establish these as distinct signals with partially non-overlapping effects. Carrying risk alleles at multiple IL2RA variants likely compounds Treg signaling impairment beyond what any single variant predicts. Interactions with CTLA4 rs3087243 (immune checkpoint) and PTPN22 rs2476601 (T-cell activation threshold) are biologically plausible as parallel pathways to Treg and effector T-cell dysregulation.