rs11465804 — IL23R

IL23R — The Protective Haplotype That Tamps Down the IL-23/Th17 Axis

Your immune system walks a narrow line between fighting infection and attacking its own tissues. One of the most critical molecular checkpoints along that line is the IL-23/Th17 axis¹¹ IL-23/Th17 axis
The signalling pathway in which the cytokine IL-23 binds to the IL-23 receptor (IL23R) on T helper 17 (Th17) cells, sustaining their inflammatory effector function and driving chronic inflammation in the skin, gut, and joints. Dysregulation of this pathway is a root cause of ankylosing spondylitis (AS), Crohn's disease (CD), ulcerative colitis (UC), and psoriasis. The rs11465804 variant in the IL23R gene is a tag SNP that co-segregates with the most studied protective IL23R haplotype — and carries one of the strongest single-locus protective signals identified in immune-mediated disease genetics.

The Mechanism

rs11465804 is an intronic variant located at chromosome 1, position 67,236,843 (GRCh38). It lies in high linkage disequilibrium (LD)²² high linkage disequilibrium (LD)
Linkage disequilibrium means the two variants are inherited together on the same chromosomal segment so frequently that knowing one variant's identity predicts the other; r²=0.84 between rs11465804 and rs11209026 in the IBD case-control dataset with rs11209026, the missense variant encoding the p.Arg381Gln (R381Q) substitution in the cytoplasmic domain of the IL-23 receptor. The R381Q change is the biologically active element: replacing arginine with glutamine at position 381 partially impairs the receptor's ability to transduce IL-23 signals.

Mechanistically, R381Q dampens IL-23-induced STAT3 phosphorylation³³ STAT3 phosphorylation
STAT3 is a transcription factor activated when IL-23 binds its receptor; phosphorylated STAT3 enters the nucleus and drives expression of inflammatory cytokines including IL-17A; lower pSTAT3 means less downstream inflammation specifically in Th17 effector cells. T cells from carriers of the protective allele produced a median of 5.5 pg/ml IL-17A after IL-23 stimulation, compared with 36.0 pg/ml in non-carriers — a 6.5-fold reduction. Crucially, this reduced effector response did not affect Th17 cell differentiation or baseline cytokine production, meaning that protective-allele carriers retain Th17-mediated host defence against pathogens while being protected from the chronic Th17 hyperactivation that drives spondyloarthritis and IBD. This receptor hypomorphism is precisely the mechanism that pharmaceutical anti-IL-23 biologics (guselkumab, risankizumab, mirikizumab) try to recapitulate pharmacologically.

The Evidence

The IL23R locus was first identified as an IBD gene by a landmark GWAS published in Science in 2006⁴⁴ Science in 2006
Duerr et al. Science 313:1461–3; genome-wide discovery in 567 CD cases and 571 controls, with replication in additional Jewish and non-Jewish cohorts. In that study, the G allele at rs11465804 was present in 6.3% of non-Jewish healthy controls but only 2.0% of CD cases — a striking frequency difference. The resulting odds ratio was 0.30 (95% CI 0.18–0.51, P=7.52×10⁻⁷), meaning G allele carriers had roughly 70% lower odds of Crohn's disease. In the Jewish cohort, where G allele frequency is higher (~10%), the protective OR was 0.47 (95% CI 0.31–0.71).

The protective signal extends across inflammatory diseases. A meta-analysis of 25 AS case-control studies⁵⁵ meta-analysis of 25 AS case-control studies
Zhong et al. Expert Rev Clin Immunol 2018; 8,431 AS cases and 8,972 controls from multiple European cohorts confirmed that the G allele frequency was significantly lower in AS patients than controls (P<0.001), placing rs11465804 among the four protective IL23R polymorphisms in ankylosing spondylitis. In ulcerative colitis, a meta-analysis of 33 studies⁶⁶ meta-analysis of 33 studies
Zhong et al. Oncotarget 2016; 10,527 UC cases and 15,142 controls found the G vs T comparison OR=0.76 (95% CI 0.64–0.90, P=0.002), a consistent 24% reduction in UC risk. The protective associations are most robust in European populations; East Asian populations carry the G allele at near-zero frequency (~0.01%) and have not shown significant association.

The protective effect size is consistent with the IL-23/Th17 pathway being a principal driver of these diseases — and with the clinical success of IL-23 inhibitor drugs as highly effective treatments for the same conditions.

Practical Implications

Carriers of the G allele have measurably dampened IL-23-driven Th17 effector responses, which translates to reduced lifetime risk for AS, Crohn's disease, UC, and psoriasis. This is especially relevant for individuals with a family history of spondyloarthritis or inflammatory bowel disease. The protection is partial and additive — GG homozygotes (extremely rare globally at ~0.3%) carry the greatest degree of protection; GT heterozygotes carry intermediate protection.

It is important to understand what this variant does not protect against: conditions driven by IL-12/Th1 pathways or other arms of the immune system remain unaffected. Additionally, the protective signal is strongest for the conditions listed above and should not be extrapolated to all autoimmune diseases.

Interactions

rs11465804 tags the same protective IL23R haplotype block as rs10489629, rs1343151, and rs11209026 (R381Q). These variants are in strong LD and typically co-inherited, so individuals who carry the G allele at rs11465804 will almost always also carry the protective alleles at rs10489629 and rs1343151 — they represent the same underlying biology. The independent functional variant remains rs11209026 (R381Q), with rs11465804 serving as a reliable proxy in genotyping studies.

Within the broader IL-23 pathway, several other IL23R variants (rs2201841, rs1004819) confer increased susceptibility and represent distinct haplotypes; individuals may carry both protective alleles at rs11465804 and susceptibility alleles at these other loci on separate chromosomal copies, making the net haplotype architecture complex. The rs7517847 variant, also intronic in IL23R, marks a susceptibility haplotype and is tracked separately in this database.