rs2070874 — IL4 IL4 C-33T

IL4 C-33T — The 5'-UTR Rheostat of Th2 Immunity

Interleukin-4¹¹ Interleukin-4
IL-4 is the master Th2 cytokine secreted by activated CD4+ T cells, mast cells, basophils, and innate lymphoid cells type 2 (ILC2s); it drives naïve T cell polarization toward the Th2 phenotype, instructs B cells to switch antibody class to IgE, and maintains mast cell and eosinophil survival is the central regulator of the allergy-prone immune state. The IL4 gene sits on chromosome 5q31.1, a region long known to harbour susceptibility loci for atopic disease. rs2070874 is a C-to-T substitution 33 bases into the 5'-untranslated region (5'-UTR) of the IL4 transcript — between the transcription start site and the protein-coding start codon. At this position, the variant does not change the IL-4 protein but alters the RNA sequence in a way that influences how efficiently the mRNA is translated and, indirectly, how much IL-4 protein is ultimately produced.

The Mechanism

The 5'-UTR is not silent. It contains secondary structures (hairpin loops, internal ribosome entry elements, and upstream open reading frames) that regulate ribosome access and translation efficiency. A single-nucleotide change in this region can flatten or deepen a hairpin that otherwise impedes ribosomal scanning, raising the rate at which ribosomes reach the main IL-4 coding sequence. The T allele at position +33 is associated with higher IL-4 plasma levels in genotype-stratified studies — an association documented in multiple genotype-stratified studies — T allele carriers consistently show higher in-vivo IL-4 plasma levels than CC homozygotes, a relationship that is amplified when the T allele at this 5’-UTR site co-occurs with the IL4 VNTR allele-1 on the same haplotype (Bibert et al., Immunogenetics 2015²² (Bibert et al., Immunogenetics 2015
doi:10.1007/s00251-015-0836-3). The rs2070874 variant is also in strong linkage disequilibrium with rs2243250, the -589C>T promoter SNP. The two variants co-segregate on the same haplotype — the T alleles at both sites tend to be inherited together, and together they confer higher IL-4 transcription (rs2243250 effect via NFAT-1 binding) plus potentially higher translation efficiency (rs2070874 5'-UTR effect). The combined haplotype represents the most biologically active IL-4 configuration.

The Evidence

The strongest evidence for rs2070874 comes from a 2020 meta-analysis of 24 publications³³ 2020 meta-analysis of 24 publications
Imani et al., BMC Medical Genetics — 28 studies pooling 6,587 asthma cases and 8,408 controls with searches in Web of Science, Scopus, and PubMed. In the overall population, the T allele was a significant risk factor under all genotype models tested. Ethnicity- specific analysis found the association significant in Europeans across all models except heterozygote comparison, and in Americans and Asians across several models. Age-stratified analysis confirmed T allele risk in pediatric, adult, and mixed-age cohorts under the allelic model. An earlier 2014 meta-analysis⁴⁴ 2014 meta-analysis
Zheng et al. independently confirmed the -33C/T polymorphism as an asthma risk factor across ethnically diverse studies.

For atopic dermatitis, a 2016 pediatric case-control study⁵⁵ 2016 pediatric case-control study
Saadat et al., Allergy Asthma Immunol Res found that IL-4 gene polymorphisms including rs2070874 contribute to elevated atopic dermatitis risk in children, with T allele carriers showing higher serum IL-4 levels. The direct IgE link was established in early work by Howard et al. 2001⁶⁶ Howard et al. 2001, who associated the C+33T polymorphism directly with elevated total serum IgE in atopic cohorts.

Beyond classic atopy, a 2022 haplotype analysis⁷⁷ 2022 haplotype analysis
Junta et al., Genes of 195 patients demonstrated that the IL4 haplotype containing the rs2070874 T allele was significantly associated with NSAID-exacerbated respiratory disease (AERD/N-ERD) — the severe aspirin-sensitive asthma phenotype defined by nasal polyps, eosinophilic inflammation, and reactions to COX-1 inhibitors. This finding extends the IL4 5'-UTR variant's clinical footprint from common atopy to the most refractory eosinophilic asthma phenotype.

Evidence level: strong. Meta-analyses replicate across multiple ethnicities, ages, and atopic disease phenotypes; the biology (5'-UTR regulation of translation, plasma IL-4 elevation, serum IgE elevation) is mechanistically coherent.

Practical Actions

For T allele carriers, the elevated IL-4 output means: (1) total serum IgE is a directly informative biomarker — T allele carriers' IgE trends higher, and periodic measurement reveals whether the IL-4 pathway is biologically active; (2) quercetin and related flavonoids suppress IL-4 and IL-13 gene transcription in activated T cells with mechanistic specificity to this pathway; (3) for TT homozygotes with active moderate-to-severe atopic disease, dupilumab (which blocks the IL-4Rα receptor used by both IL-4 and IL-13) is the biologically best-matched therapy; (4) aspirin and NSAIDs warrant caution in T allele carriers with asthma, given the haplotype association with NSAID-exacerbated respiratory disease.

Interactions

rs2070874 is in strong linkage disequilibrium with rs2243250 (IL4 -589C>T) — the two T alleles co-segregate on the same haplotype. Carriers of both T alleles have the highest constitutive IL-4 output from combined promoter-level (NFAT-1 binding enhancement) and 5'-UTR-level (translation efficiency) effects. Haplotype-level analysis consistently shows stronger disease associations for the T/T haplotype at both sites than for either variant alone.

The rs1801275 variant (IL-4Rα Arg576Gln) alters the cytoplasmic signalling domain of the shared IL-4/IL-13 receptor chain. When elevated IL-4 production (rs2070874 T allele) meets altered receptor signal transduction (rs1801275), Th2 pathway output may be doubly amplified — a biologically plausible interaction that is relevant to dupilumab pharmacogenomics.

The rs20541 variant (IL-13 Arg130Gln) elevates IL-13 output through a separate gene but shares the IL-4Rα signalling chain. Carriers of both rs2070874-T and rs20541-A face combined Th2 cytokine over-activity from both arms of the IL-4/IL-13 axis — the combination that dupilumab is designed to block at the receptor level.