EXPRESSION AND ROLES OF INTERFERON REGULATORY FACTOR-5 (IRF5) IN ASTHMATIC AND NON-ASTHMATIC PATIENTS

Abstract

Asthma affects 24% of children in the state of Selangor, Malaysia. It is postulated that an imbalance in the T helper 1 (Th1) and T helper 2 (Th2) immune responses may contribute to the pathophysiology of atopic asthma. Polymorphisms in IRF5 expression had been found to be associated with several autoimmune diseases. Interestingly, asthma was associated with IRF5 SNPs as opposed to those associated with autoimmune diseases amongst the British population. However, the association between IRF5 polymorphisms and asthma in the Asian population has yet to be established. Therefore, this study was conducted to determine the association of IRF5 gene polymorphisms (rs10954213/rs11770589 and rs2004640) and asthma in the Malaysian population. This study also aims to understand how IRF5 single nucleotide polymorphisms (SNPs) might have contributed to atopic asthma. From 189 asthmatic subjects and 189 non-asthmatic subjects, genomic deoxyribonucleic acid (DNA) was isolated and sequenced. From the 189 asthmatic patients, five subjects each with rs10954213 GG and AA genotypes were selected. Skin prick tests were done and their peripheral blood mononuclear cells (PBMCs) cultured and sensitised with crude mite extract. The cytokines produced by the PBMCs were measured via multiplex assay and IRF5 messenger ribonucleic acid (mRNA) expression measured via reverse transcription polymerase chain reaction (RTqPCR). There is no association between IRF5 gene polymorphisms (rs10954213/11770589 and rs2004640) and asthma in the Malaysian population. However, there are significant associations between IRF5 SNPs, rs10954213 and rs11770589, and adult onset asthma (risk genotype: GG; rs10954213: p = 0.043; OR = 3.400; 95% CI: 1.0393 to 11.1231; rs11770589: p = 0.005; OR = 5.4667; 95% CI 1.6520 to 18.0896) and having more than one allergic disease (protective genotype: AA; rs10954213: p = 0.020; OR = 0.1720; 95% CI 0.0389 to 0.7616; rs11770589: p = 0.026; OR = 0.1838; 95% CI: 0.0415 to 0.8145). Sensitised PBMCs with AA genotype at rs10954213 had a significantly higher IL-10/IL-17F ratio compared to those with GG genotype (p = 0.030) indicating that sensitised PBMCs with GG genotype at rs10954213 have a dominant pro-inflammatory profile by IL-17F and less immunosuppressive effect by IL-10, compared to those with AA genotype at rs10954213. Coupled with this, sensitised PBMCs with GG genotype at rs10954213 retained higher levels of IRF5 mRNA expressions compared to those of AA genotype (p < 0.001). Therefore, in contrast to rs10954213-GG, rs10954213-AA might have contributed to the atopic component of asthma by suppressing the asthma-contributing Th1-Th17 immune response. There are significant associations between IRF5 SNP rs2004640 and adult onset asthma (risk genotype: TT; p = 0.012; OR = 3.8571; 95% CI: 1.3490 to 11.0287), the same risk genotype for autoimmune diseases. Therefore, IRF5 SNPs rs2004640 might have contributed to adult asthma via autoimmunity through Th1-Th17 pathways. IRF5 SNP rs41298401 CC genotypes conferred risk to adult onset asthma (p < 0.001; OR = 110.8333; 95% CI: 11.6594 to 1053.5692) and eczema (p = 0.009; OR = 3.3103; 95% CI: 1.3543 to 8.0913) amongst females. This might be due to a dominant Th2 immune response as a result of lack of suppression of allergy by regulatory T cells (T regs) and counterbalance by Th17. Through this study, IRF5 polymorphisms (rs10954213/rs11770589, rs2004640 and rs41298401) may not be applicable biomarkers for the risk of asthma for the Malaysian population. IRF5 SNPs rs10954213/rs11770589 and rs41298401 might have contributed to asthma via atopy whereas rs2004640 may be through autoimmunity. This information may provide insights to tailor treatment plans according to patient’s IRF5 genotypes.