rs3806933 — TSLP

TSLP's Second Switch: The Promoter Variant That Turns Up the Alarm

Your immune system's response to allergens, viruses, and skin-barrier disruptions begins with a deceptively simple signal: the release of thymic stromal lymphopoietin (TSLP)¹¹ thymic stromal lymphopoietin (TSLP)
An epithelial cytokine released by skin, airway, and gut lining cells in response to damage; triggers dendritic-cell-mediated Th2 inflammation from epithelial cells. TSLP is the "break-glass" alarm that tells the immune system an environmental threat has breached a body barrier. The rs3806933 variant sits directly in the promoter of the TSLP gene and determines how loudly that alarm rings.

This variant is distinct from the more widely studied rs1837253 (already on the platform). While rs1837253 is an upstream regulatory site that modulates baseline inducibility of TSLP across tissues, rs3806933 sits in the TSLP core promoter at position −847 and operates through a completely different mechanism. The two variants are not in strong linkage disequilibrium with each other, meaning they segregate independently in the population and can stack their effects.

The Mechanism

The rs3806933 C-to-T substitution at position −847 of the TSLP promoter does something structurally precise: it creates a de novo binding site for activating protein-1 (AP-1)²² creates a de novo binding site for activating protein-1 (AP-1)
AP-1 is a transcription factor complex (typically FOS-JUN heterodimers) activated by inflammatory cytokines, viral dsRNA, and stress signals — it amplifies gene transcription when bound to its target sequence. The C allele at this position does not support AP-1 binding; the T allele does. When an airway epithelial cell is stimulated by a viral signal (poly I:C, mimicking double-stranded RNA from respiratory infections), the T allele dramatically amplifies TSLP transcription through this new AP-1 site. The result is greater TSLP protein output during exactly the kind of infections that most commonly trigger asthma exacerbations.

The TSLP protein released then acts on plasmacytoid dendritic cells³³ plasmacytoid dendritic cells
Immune sentinels that, when activated by TSLP, express OX40L and prime naive T-cells to differentiate into Th2 cells rather than regulatory T-cells — the foundation of allergic inflammation, mast cells, and basophils — driving the full Th2 cascade of IL-4, IL-5, and IL-13 production that underlies asthma, allergic rhinitis, and atopic dermatitis. Critically, TSLP released from damaged skin also drives the atopic march: skin-barrier disruption → TSLP surge → airway Th2 sensitisation → asthma.

The Evidence

The functional and clinical evidence for rs3806933 rests on a multi-step foundation. The mechanistic work, published in the American Journal of Respiratory Cell and Molecular Biology⁴⁴ American Journal of Respiratory Cell and Molecular Biology, demonstrated the AP-1 binding gain-of-function directly: luciferase reporter assays in normal human bronchial epithelial cells showed that the T-allele promoter construct produced substantially more TSLP protein after poly(I:C) stimulation than the C-allele construct. This is a clean causal mechanism with experimental validation, not merely statistical association.

Clinically, the same study found the T allele associated with childhood atopic asthma (OR 1.25, 95% CI 1.07–1.47) and adult asthma (OR 1.37, 95% CI 1.12–1.67) in Japanese case-control cohorts totalling 1,280 cases and 1,214 controls. A subsequent meta-analysis pooling four independent studies⁵⁵ meta-analysis pooling four independent studies yielded a combined OR of 1.32 (95% CI 1.14–1.54, p<0.01) — consistent with a moderate but reproducible effect on asthma susceptibility. The variant's associations have been reported in Japanese, Korean, and Turkish populations, though effect sizes vary by ethnic background and disease phenotype.

The disease spectrum extends beyond the airways. A Taiwanese study of 470 Graves' disease patients found rs3806933 T-allele carriership associated with Graves' ophthalmopathy (GO)⁶⁶ associated with Graves' ophthalmopathy (GO) in female patients specifically (OR 1.79, 95% CI 1.16–2.77), consistent with TSLP's role in thyroid autoimmunity. In the 2017 Nature Genetics GWAS of 360,838 individuals⁷⁷ GWAS of 360,838 individuals analysing the shared genetic architecture of asthma, hay fever, and eczema, the TSLP locus was among the 136 independent signals identified — confirming that TSLP genetic variation contributes to the full allergic disease spectrum.

Pharmacogenomic relevance: Tezepelumab (Tezspire), the anti-TSLP monoclonal antibody approved by the FDA in 2021 for severe asthma, neutralises the TSLP protein directly. Individuals with the TT genotype — who overproduce TSLP through the AP-1 gain-of-function — represent the biological population with the strongest rationale for TSLP-targeted therapy. However, because tezepelumab works downstream of the variant (blocking the protein regardless of which genotype produced it), the drug's efficacy is not formally stratified by rs3806933 genotype in current labelling.

Practical Implications

Maintaining the skin and airway epithelial barrier is the most direct way to reduce TSLP release, regardless of genotype — but it is especially important for T allele carriers, who overproduce TSLP when epithelial cells are stressed. For TT carriers, the threshold at which infections and irritants trigger a Th2 storm is lower, making proactive barrier protection more consequential.

Skin barrier maintenance reduces TSLP release from keratinocytes. Emollient use in eczema-prone individuals has been shown in randomised trials to delay and reduce TSLP-driven atopic sensitisation. This mechanism is especially relevant for rs3806933 T carriers.

Interactions

rs3806933 and rs1837253 are independent TSLP locus signals that can compound. rs1837253 (already on the platform in the innate-immunity category) controls TSLP inducibility at a different regulatory element; rs3806933 controls AP-1-driven promoter activity. Carrying the high-TSLP genotype at both loci — CC at rs1837253 and TT at rs3806933 — would be expected to produce additive increases in TSLP output. rs2289276, a third TSLP promoter variant in high LD with rs3806933 (D′=0.97), is also in the related_snps list. TSLP pathway variants in downstream genes (IL7R, IL1RL1/ST2, TSLPR/CRLF2) can modulate the biological consequences of increased TSLP production.