Background/Purpose: During a gout flare monosodium urate (MSU) crystals induce, in the presence of a secondary stimulus, acute joint inflammation characterized by the recruitment of predominantly neutrophils. These neutrophils release chemokines and inflammatory mediators, further amplifying the inflammation. IL37 emerges as a fundamental inhibitor of the innate immune response and inhibits MSU-crystal induced inflammation in cell lines and murine models of gout. To further elucidate the role of IL37 in gout, we examined DNA of people with gout for genetic variations in IL37 and assessed the functional consequences of these mutations.

Methods: Exons of the IL37 gene were sequenced using Molecular Inversion Probes (MIPs) in 677 people with crystal-proven gout. The frequency of rare genetic variants in IL37 was compared to a cohort of 469 healthy controls and a cluster analysis was performed.
Neutrophils were isolated from healthy Dutch donors, pretreated with IL37, a genetic variant of IL37 or IL37Fc (the tail region of an antibody to IL37) and stimulated with opsonized MSU crystals. Reactive oxygen species (ROS) and IL8 production were measured.
For the validation of genetic variants, a total of 2202 clinically-ascertained gout cases and 2295 controls (further stratified into 424 hyperuricemic (≥0.41mmol/L) controls) of European and NZ Māori and Pacific (Polynesian) ancestry were utilized. Taqman® genotyping was carried out, followed by multivariate-adjusted association analysis with gout as the outcome.

Results: MIP-sequencing identified 4 non-synonymous rare variants in exon 5 of IL37 in 6 gout patients, whereas none were detected in the healthy controls (fisher’s exact test; p=0.043). Two variants (p.H172HX; p.N182S), present in two individuals, were observed in the Exome Aggregation Consortium database; the private variants (p.A144P; p.C181*) were not. Cluster analysis showed the rare variants in IL37 significantly cluster (p= 5.71 E10^-5).
To elucidate the effect of mutations in IL37, a recombinant protein was produced based on the p.C181* mutation. In vitro, full length IL37(46-218) significantly decreased ROS and IL8 production. The IL37 mutant demonstrated diminished anti-inflammatory effects compared to the full-length protein.
In our validation cohort, the rs752113534 variant (p.N182S) was monomorphic in people of European ancestry, but the minor G-allele exhibited a frequency of 0.05 in people of Eastern and Western Polynesian ancestry. A meta-analysis of people of Eastern and Western Polynesian ancestry showed a significant association of the G-allele with gout risk using hyperuricemic controls (OR= 1.81, P_OR=0.03). As a potential therapeutic, IL37Fc was tested in vitro and strongly inhibited ROS and IL8 production.

Conclusion: Rare genetic variants in IL37 clustering in exon 5 were found in people with gout. One of these IL37 mutants demonstrated a loss of the anti-inflammatory function in vitro. Moreover, the association of IL37 rare variant rs752113534 in prevalent gout in people of Polynesian ancestry supports a role for IL37 in an inflammatory pathway leading to gout in the presence of hyperuricemia. Furthermore, IL37Fc was identified as a potential new therapeutic in the treatment of gout.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/genetic-variants-identify-interleukin-37-as-an-important-anti-inflammatory-cytokine-in-gout-in-humans/