Background/Purpose Type-I interferon (IFN), a central mediator of innate immunity, has been shown to be the hallmark peripheral blood gene expression pattern in lupus (SLE) and a similar type-I IFN signature has been noted in systemic sclerosis (SSc). Interferon regulatory factor 5 and 7(IRF5/IRF7) and tyrosine kinase 2(TYK2) are important genes involved in this signalling cascade. The purpose of this work was to investigate the association and interaction of IRF5, IRF7, TYK2 polymorphisms with SSc.

Methods We performed SNP genotyping for IRF5(Rs20024640), IRF7(Rs1061502), TYK2(Rs2304256) genes using the Taqman Assay in 4 large cohorts comprising of North-American Caucasian, Dutch, Italian and Spanish samples totaling to 2,091 SSc patients and 1,434 race-matched controls. All SSc patients fulfilled ACR criteria or had at least 3 of the 5 CREST features. HWE testing, chi-square, logistic regression(LR) were used for statistical comparisons. Mesoscale assays were used for cytokine detection.

Results LR analysis after controlling for gender and cohorts the association was confirmed in all cohorts {IRF5: P < 0.0001, OR(CI)–0.68(0.6–0.8); IRF7: P = 0.006, OR(CI)–0.80(0.7–0.9); TYK2:P = 0.05, OR(CI)–0.85(0.7–0.99)}. The association was stronger with anti-centromere subset {IRF5:P = 0.0002, OR(CI–0.59(0.5–0.8); IRF7:P = 0.0008, OR(CI)–0.69(0.6–0.9); TYK2:P = 0.04, OR(CI)– 0.79(0.6–0.9)}.

The data was modelled based on mode of inheritance for the 3 SNPs and LR analysis performed controlling for gender and cohorts and revealed an extremely protective effect for the combination of mutations versus the wildtype {IRF5 ^M/IRF7 ^M/TYK2 ^M versus IRF5 ^WT/IRF7 ^WT /TYK2 ^WT:P < 0.0001; OR(CI)–0.39(0.3–0.6)}.

In the IRF5 ^WT/IRF7 ^WT/TYK2 ^WT group, the SSc patients had increased levels of TNF-α and IL-6 as compared to controls and there was no difference amongst the patients and controls in the IRF5 ^M/IRF7 ^M/TYK2 ^M group.

Conclusions We demonstrate association of IRF5, IRF7 and TYK2 SNPs with SSc.

We demonstrate a gene-gene interaction in SSc between three non-linked loci- IRF5, IRF7 and TYK2.

The 3 gene-SNPs have a protective effect in SSc patients and the presence of the 3 mutations simultaneously has the most protective effect.

Plasma TNF-α and IL-6 levels were increased in the SSc patients wildtype for the 3 SNPs versus controls, whereas there was no difference in TNF-α and IL-6 levels in the SSc patients having mutations for the 3 SNPs versus controls.

In summary, IRF5, IRF7, TYK2 SNPs have a protective effect in SSc which is stronger when there are polymorphisms on all of the genes as compared to each of them alone.

This suggests an important role of interferon pathway polymorphisms in susceptibility to SSc and the exact role of these interactions and their function in SSc susceptibility needs to be elucidated experimentally.