rs1800925 — IL13 -1112C>T

IL-13 -1112C>T — The Promoter Switch That Amplifies Allergic Inflammation

IL-13¹¹ IL-13
Interleukin-13, a 12.5 kDa cytokine secreted primarily by activated Th2 CD4+ T cells, mast cells, and basophils is one of two master regulators of allergic disease — the other being IL-4. While IL-4 orchestrates the initial Th2 commitment and IgE class switching, IL-13 executes the downstream tissue effects: airway smooth muscle contraction, mucus hypersecretion by goblet cells, subepithelial fibrosis, and IgE amplification. Together they form the axis that makes allergic asthma, atopic eczema, and allergic rhinitis chronic rather than self-limiting.

The rs1800925 variant, also written as IL13 -1112C>T, sits in the IL13 gene promoter region on chromosome 5q31 — not in the protein-coding sequence, but upstream of it, in the DNA elements that control when and how much IL-13 gets made. The C allele is the reference and common form. The T allele, carried by about 20% of Europeans and 38% of Africans, silently rewires a key regulatory node in Th2 immune cells.

The Mechanism

The -1112 region of the IL13 promoter normally contains a STAT6 binding motif²² STAT6 binding motif
Signal transducer and activator of transcription 6 — the transcription factor activated downstream of IL-4 and IL-13 receptor signaling, which feeds back to suppress further IL-13 transcription. When STAT6 binds this site in Th2 cells, it partially represses IL13 gene expression, creating a negative feedback brake.

The T allele change at position -1112 disrupts the STAT6 binding motif and simultaneously creates a Yin-Yang 1 (YY1)³³ Yin-Yang 1 (YY1)
A zinc-finger transcription factor with context-dependent activating or repressing functions, named for its ability to act as both activator and repressor depending on cofactors present binding site that overlaps the STAT6 motif. YY1 then competes with STAT6 for binding to this locus. In polarized Th2 cells — exactly the context of active allergic disease — this competition tips in favor of YY1, attenuating STAT6-mediated repression and selectively boosting IL13 transcription⁴⁴ attenuating STAT6-mediated repression and selectively boosting IL13 transcription. The effect is Th2-selective: the same variant has opposing effects in non-polarized T cells, where the nuclear milieu favors STAT6 binding.

The consequence is increased IL-13 production at the tissue level in allergic individuals, which drives goblet cell hyperplasia and mucus secretion in airways, enhances IgE production by B cells (via IL-4Rα/IL-13Rα1 type II receptor), reduces airway responsiveness by altering smooth muscle physiology, and promotes subepithelial fibrosis in chronic disease. Individuals homozygous for the T allele produce measurably more IL-13 from activated Th2 cells.

The Evidence

The -1112C>T functional mechanism was established in 2006 by Cameron et al., who used ChIP assays and EMSA in primary human Th2 cells to show allele-specific STAT6 and YY1 binding at the -1112 locus and confirmed increased IL-13 secretion in TT homozygous subjects⁵⁵ Cameron et al., who used ChIP assays and EMSA in primary human Th2 cells to show allele-specific STAT6 and YY1 binding at the -1112 locus and confirmed increased IL-13 secretion in TT homozygous subjects. This remains the definitive mechanistic study.

Clinical associations span asthma, COPD, and atopic disease. A 2023 meta-analysis (Gaceja et al.) of 11 studies including 2,895 asthma cases and 2,914 controls⁶⁶ 2023 meta-analysis (Gaceja et al.) of 11 studies including 2,895 asthma cases and 2,914 controls found the TT genotype significantly associated with allergic asthma risk in Asian populations under the recessive model (OR 1.48, 95% CI 1.14–1.93) and codominant model (TT vs CC: OR 1.66, 95% CI 1.27–2.17). West Asian populations (Iranian and Saudi) showed the strongest effect (OR 2.17).

For lung disease, a 2017 meta-analysis of 9 studies (Liao et al., 3,077 participants) found the T allele associated with COPD risk overall⁷⁷ 2017 meta-analysis of 9 studies (Liao et al., 3,077 participants) found the T allele associated with COPD risk overall with OR 1.57 (95% CI 1.21–2.04), driven by both Asian (OR 1.88) and Caucasian (OR 1.30) subgroups.

A particularly important pharmacogenomic finding emerged from the CAMP childhood asthma study: Hunninghake et al. (2007) found that the T allele was associated with increased asthma exacerbations specifically in children on inhaled corticosteroids⁸⁸ Hunninghake et al. (2007) found that the T allele was associated with increased asthma exacerbations specifically in children on inhaled corticosteroids (P=0.02) — the first report of a potential negative gene-ICS interaction for this locus. This suggests T carriers may have attenuated corticosteroid benefit from standard inhaled therapy.

The variant also interacts with environmental exposures. Choudhry et al. (2008) demonstrated that IL13 rs1800925 genotype modifies the effect of prenatal tobacco smoke exposure on persistent wheeze in childhood⁹⁹ Choudhry et al. (2008) demonstrated that IL13 rs1800925 genotype modifies the effect of prenatal tobacco smoke exposure on persistent wheeze in childhood, and the NSHD cohort found evidence for smoking-rs1800925 interaction on allergy risk across the life course¹⁰¹⁰ evidence for smoking-rs1800925 interaction on allergy risk across the life course. T carriers who smoke face compounded risk beyond either factor alone.

Practical Actions

For T allele carriers — particularly those with existing atopic disease — the key intervention targets are the IL-4/IL-13 Th2 axis and mucus pathway, alongside monitoring of corticosteroid effectiveness. Since IL-13 itself is now a validated biologic drug target (tralokinumab, lebrikizumab), the biology underlying this SNP is clinically actionable at the therapeutic level.

Total and specific IgE measurement quantifies the downstream consequence of enhanced IL-13 signaling and helps identify the specific allergens being amplified by your Th2 bias. Monitoring IgE trends over time provides objective feedback on whether dietary, supplement, or medication interventions are effective.

For CT carriers with asthma managed on inhaled corticosteroids, the possible ICS-rs1800925 interaction warrants attention to whether current treatment is achieving expected control. If asthma remains poorly controlled despite standard ICS therapy, discussing add-on therapies (LABA, leukotriene modifiers, or biologic options) with a specialist is appropriate.

Interactions

The most important interaction partner is [rs20541 | IL13 R130Q coding variant — the Q130 minor allele (A) directly increases IL-13 protein activity], which is in moderate LD with rs1800925. The -1112T allele increases the amount of IL-13 made; the Q130/rs20541-A allele increases the activity of the protein made. Carrying risk alleles at both loci compounds IL-13 pathway amplification through independent mechanisms — the TA haplotype (rs1800925-T + rs20541-A) is consistently the highest-risk haplotype for atopic disease.

The [rs1801275 | IL4R Q576R — gain-of-function variant in the shared IL-4/IL-13 receptor alpha chain] from the same Th2 pathway amplifies signaling from both IL-4 and IL-13. A carrier of rs1800925-T (more IL-13 produced) with rs1801275-G (more IL-13 signal transduced) faces dual amplification of the same pathway.

Smoking exposure warrants particular attention: multiple studies show that tobacco smoke interacts with rs1800925 genotype to amplify wheeze and allergy risk beyond what either factor alone predicts, likely because smoke-induced airway inflammation further activates Th2 cells that are already primed to over-produce IL-13.