rs3024505 — IL10 3' downstream variant

IL-10 Downstream Enhancer — The Lead IBD Signal at the IL10 Locus

Interleukin-10 (IL-10) is the immune system's master anti-inflammatory cytokine — the molecular signal that tells an activated immune response to stand down. When IL-10 production is reduced, inflammatory reactions in the gut, joints, and other tissues run longer and harder than they should. rs3024505 sits approximately 5 kilobases downstream of the IL10 gene's 3' end on chromosome 1q32.1¹¹ chromosome 1q32.1
The long arm of chromosome 1, a region with dense immune gene content and one of the most robustly replicated IBD susceptibility loci in the human genome. It is the lead GWAS signal at the IL10 locus for inflammatory bowel disease and has been associated with systemic lupus erythematosus, Sjögren's syndrome, and other autoimmune conditions.

IL10 is encoded on the minus (reverse) strand of chromosome 1. Genome files report alleles on the plus strand — so while published papers describe this as a C/T polymorphism (coding-strand notation), plus-strand genome files use G and A. The common G allele corresponds to the protective C allele in papers; the risk A allele is what papers call the T allele. All genotype keys here use plus-strand notation as reported by genome files.

The Mechanism

rs3024505 lies within an enhancer element²² enhancer element
A non-coding DNA sequence that boosts the transcriptional activity of nearby genes; enhancers can act over long distances by looping toward gene promoters that augments IL10 promoter activity, particularly in B cells. The common G allele (coding-strand C) creates a functional binding site for the transcription factor STAT3, which drives IL10 expression when immune cells are activated. The risk A allele (coding-strand T) disrupts this STAT3 binding site — luciferase reporter assays in stimulated pro-B cell lines confirmed a significant reduction in enhancer activity for the A variant compared to G.

This mechanism explains why rs3024505 is an expression quantitative trait locus (eQTL)³³ expression quantitative trait locus (eQTL)
A genetic variant that predicts the expression level of a nearby gene, confirmed in multiple immune cell types for IL10: carriers of the A allele produce less IL-10 per stimulated B cell. Lower IL-10 shifts the immune environment toward a more pro-inflammatory baseline. In the gut mucosa, inadequate IL-10 allows the normal commensal microbiome to trigger unresolved inflammatory responses — the fundamental driver of both Crohn's disease and ulcerative colitis. In systemic autoimmunity, impaired B cell IL-10 production removes a critical brake on autoreactive immune cell activation.

The Evidence

rs3024505 was first identified as a genome-wide significant UC susceptibility locus in the landmark 2008 GWAS at chromosome 1q32.1 that implicated IL10 in inflammatory bowel disease. The lead signal pointed directly to the IL10 downstream region as central to IBD pathogenesis.

A Danish case-control study of 336 CD patients, 498 UC patients, and 779 healthy controls⁴⁴ of 336 CD patients, 498 UC patients, and 779 healthy controls
Holt et al. 2010, The polymorphism rs3024505 proximal to IL-10 is associated with risk of ulcerative colitis and Crohn's disease in a Danish case-control study, BMC Medical Genetics provided the clearest genotype-level data. Heterozygous CT carriers had OR = 1.31 for CD (p = 0.07) and OR = 1.34 for UC (p = 0.02). Homozygous TT carriers (corresponding to AA on the plus strand) showed substantially higher risk: OR = 2.48 for CD (95% CI 1.27–4.84, p = 0.01) and OR = 2.31 for UC (95% CI 1.27–4.20, p = 0.01). The combined CT+TT group reached OR = 1.40 for CD (p = 0.02) and OR = 1.43 for UC (p = 0.004). The T allele frequency in Danish controls was 18%.

A meta-analysis of 13 studies covering 8,552 IBD cases and 12,830 controls⁵⁵ of 13 studies covering 8,552 IBD cases and 12,830 controls
Gu et al. 2021, Association between IL-10 rs3024505 and susceptibility to inflammatory bowel disease: A systematic review and meta-analysis, Cytokine confirmed strong and consistent association across European populations: OR = 1.37 (95% CI 1.30–1.45) under the allelic model, OR = 2.06 (95% CI 1.74–2.45) under the recessive model, and OR = 2.25 (95% CI 1.89–2.67) for homozygous TT vs. CC (all p < 0.00001).

A Serbian case-control study of 107 CD patients, 99 UC patients, and 255 controls⁶⁶ of 107 CD patients, 99 UC patients, and 255 controls
Simovic et al. 2016, Downstream IL10 polymorphism associated with Crohn's disease in Serbian IBD patients, Inflammatory Bowel Diseases replicated the CD association and added a clinical nuance: carriers of the protective C allele had significantly increased risk of anemia and stricturing or penetrating disease behavior, illustrating how this locus influences not just susceptibility but also disease phenotype.

Beyond IBD, rs3024505 has been associated with systemic lupus erythematosus and Sjögren's syndrome (OR = 1.52, p = 0.025 for Sjögren's susceptibility), consistent with the variant's role in B cell IL-10 regulation across multiple autoimmune contexts.

The 2024 mechanistic study using reporter assays and chromatin immunoprecipitation in human B cell lines⁷⁷ using reporter assays and chromatin immunoprecipitation in human B cell lines
Uvarova et al. 2024, Autoimmunity-Associated SNP rs3024505 Disrupts STAT3 Binding in B Cells, Leading to IL10 Dysregulation, International Journal of Molecular Sciences provided the first direct functional explanation: the variant creates or destroys a STAT3 recognition sequence, giving rs3024505 a clear molecular mechanism — rare for a non-coding GWAS SNP.

Practical Actions

The A allele's functional effect on IL-10 production is concentrated in B cells but has downstream consequences for the entire mucosal and systemic immune environment. Anti-inflammatory nutritional strategies that upregulate IL-10 through independent pathways — particularly omega-3 fatty acids (EPA/DHA) and vitamin D — can partially compensate. EPA and DHA stimulate IL-10 production in macrophages and regulatory T cells via PPAR-γ activation; vitamin D drives IL-10 expression in Treg cells independently of STAT3. Neither substitutes for STAT3-driven B cell IL-10, but they reduce the overall inflammatory burden that low IL-10 producers carry.

For anyone with the AA genotype and gut symptoms, early gastroenterological evaluation is warranted. The diagnostic delay for IBD averages 1–3 years, and genetic risk awareness can prompt earlier endoscopic investigation before complications develop. Calprotectin testing offers a non-invasive first screen to distinguish gut inflammation from functional disorders.

Interactions

rs3024505 operates in parallel with the IL10 promoter haplotype system (rs1800896, rs1800871, rs1800872) and the intronic variant rs3024491, each of which independently regulates IL10 transcription from different regulatory elements. Carriers of both the downstream A allele at rs3024505 and a low-producing promoter haplotype face stacked reductions in IL-10 from multiple regulatory levels — a combined low-producer state that is likely additive for IBD risk and autoimmune susceptibility, though direct compound studies are limited.