IL1RN

IL1RN Intron 2 VNTR — When the Brake on Inflammation Is Wired Differently

The immune system's inflammatory response is governed not just by the molecules that ignite
inflammation, but equally by those that extinguish it. Interleukin-1 receptor antagonist
(IL-1Ra) | The natural protein inhibitor of IL-1α and IL-1β — it occupies the IL-1 receptor
without triggering signaling, acting as a competitive brake on the entire IL-1 cytokine
axis is one of the most important of these
brakes. Encoded by the IL1RN gene on chromosome 2q14.1, IL-1Ra is the direct target of
anakinra, a recombinant form of the protein used clinically in rheumatoid arthritis and
systemic autoinflammatory diseases. The rs2234663 polymorphism is a variable number tandem
repeat (VNTR) | A type of DNA polymorphism where a short DNA sequence is repeated a
different number of times in different individuals; this particular VNTR consists of an 86
base-pair repeat unit in intron 2 of IL1RN, present in 2, 3, 4, 5, or 6 copies depending
on the allele located in the second intron of
IL1RN. The most clinically relevant distinction is between the A1 allele (4 copies of the
86bp repeat — the common form) and the A2 allele (2 copies — the shorter, risk-associated
form). Together these two alleles account for over 95% of chromosomes studied.

The Mechanism

The intron 2 VNTR does not alter the IL-1Ra protein sequence, but it does alter how the
gene is regulated. The repeated 86bp units contain binding sites for transcription factors
and splicing regulators | These include sites resembling SP1, TCF, and other regulatory
elements; the number of repeat copies changes the chromatin architecture and accessibility
of the intron 2 region, influencing alternative transcript initiation and splicing.
IL1RN produces four distinct protein isoforms through alternative promoter usage and
splicing: the secreted form (sIL-1Ra, the dominant circulating antagonist) and three
intracellular forms (icIL-1Ra I, II, and III). The A2 allele alters the balance between
these isoforms in ways that are cell-type and context-dependent. The net effect in
inflammatory tissues — particularly mucosal surfaces such as gastric mucosa and periodontium
— is an insufficient IL-1Ra response that allows IL-1β-driven inflammation to persist and
amplify unchecked.

This is consistent with a broader principle in IL-1 biology: the critical parameter is not
IL-1β concentration alone, but the IL-1β:IL-1Ra ratio | The relative amounts of the
pro-inflammatory IL-1β and its endogenous antagonist IL-1Ra. When IL-1Ra production is
insufficient relative to the IL-1β signal, even modest IL-1β levels can drive sustained
tissue-destructive inflammation. The A2
allele shifts this ratio toward greater effective IL-1β activity at sites where it matters most.

The Evidence

The landmark connection between the IL1RN VNTR and gastric cancer was established by
El-Omar et al. 2000 | Nature 404:398-402; case-control and cohort studies showing
IL-1 cluster polymorphisms associated with hypochlorhydria after H. pylori infection
and gastric cancer development in Nature,
demonstrating that individuals with certain IL-1 cluster variants who become infected
with H. pylori develop more extensive corpus gastritis, progressing to hypochlorhydria
and atrophy — the recognized precancer sequence. H. pylori activates IL-1β production
in the gastric mucosa; the IL-1RN VNTR modulates how effectively IL-1Ra can contain
this response. In a Brazilian study of 675 individuals, Oliveira et al. 2012 | Mol Biol
Rep 39:7617; 229 gastritis cases, 200 gastric cancer cases, 246 controls
found the IL-1RN A2 allele associated with gastric cancer (OR=3.04, p<0.01) and chronic
gastritis (OR=2.32, p=0.02) in a recessive model. An Omani study of 118 gastric cancer
patients confirmed A2 association (OR=2.2, p=0.04), amplifying to OR=3.5 in H. pylori-positive
individuals.

In the periodontium, Ding et al. 2012 | Arch Oral Biol 57:585; meta-analysis of 19
studies, 2,011 chronic periodontitis cases and 1,719 controls
found the VNTR polymorphism marginally associated with chronic periodontitis overall
(OR=1.47, p=0.05), but strongly associated with severe disease (OR=4.02, 95% CI 1.84–8.80,
p<0.0005). This dose-dependent severity effect is characteristic of a variant that shifts
the threshold for inflammation resolution rather than simply turning on disease.

For systemic lupus erythematosus, a Bulgarian case-control study (55 SLE patients, 112
controls) found Kamenarska et al. 2014 | Dermatol Res Pract; OR=2.5, 95% CI 1.2–5.4
for A2 allele in SLE patients. For COPD, a
systematic review and meta-analysis of 26 studies identified IL1RN rs2234663 as showing a
strong association with COPD susceptibility among interleukin gene variants — consistent
with the variant's role in modulating inflammatory persistence in chronically exposed
airways. For bone infections, a study of 153 trauma patients found the A2/A2 genotype
associated with sevenfold increased osteomyelitis risk (OR=7, p<0.001), particularly for
Staphylococcus aureus infections — likely reflecting inadequate IL-1Ra-mediated control
of IL-1β at the bone-infection interface.

The picture for rheumatoid arthritis is more complex. A meta-analysis of 15 case-control
studies found no significant overall association (A2/A2 OR=0.96, p=0.77), though a
Mexican case-control study of 657 participants found A1/A2 heterozygotes at modestly
elevated RA risk (OR=1.45, p=0.03) with A2/A2 homozygotes showing higher disease activity.
Population heterogeneity in LD structure may explain these inconsistencies.

Practical Actions

The actionable implications concentrate on two areas where the evidence is strongest:
H. pylori-related gastric disease and periodontal inflammation. For A2 carriers, especially
A2/A2 homozygotes, the IL-1β:IL-1Ra imbalance creates a tissue environment where
inflammatory damage at mucosal surfaces is harder to resolve. Catching H. pylori infection
early and treating it decisively is more important for A2 carriers than for the general
population. In the mouth, the severely elevated periodontitis risk for A2 carriers (OR=4+
for severe disease) makes professional dental assessment essential — this is one of the
largest genetic effect sizes documented for periodontitis susceptibility.

Interactions

The IL1RN VNTR does not act in isolation — it is part of the IL-1 gene cluster on
chromosome 2q14.1 alongside IL-1α (IL1A) and IL-1β (IL1B). The functionally critical
pairing is between IL1RN rs2234663 and IL-1B rs1143634 (+3954 C>T) or rs16944 (-511 C>T).
When a carrier has both increased IL-1β production (IL1B risk alleles) AND reduced
effective IL-1Ra response (IL1RN A2), the IL-1β:IL-1Ra ratio is shifted at both ends
simultaneously. This synergy has been documented for gastric cancer, chronic periodontitis,
and COPD — with combined genotype odds ratios substantially exceeding those of either
variant alone. These combinations represent strong candidates for compound actions in
carriers who have been typed at both loci.