Introduction: Adult-onset still's disease (AOSD) is a rare systemic inflammatory disorder in which abnormalities in inflammatory cytokines production appear to play a pathophysiological role. Our previous work has reported increased expression of macrophage migration inhibitory factor (MIF) and revealed its correlation with disease severity and activity in AOSD. A -173 G/C single nucleotide polymorphism (SNP) (rs755622) and a -794 CATT₅₋₈ repeat (rs5844572) in the MIF promoter have been reported. In this study, we sought to explore the relationship between functional MIF promoter polymorphisms and MIF expression in AOSD.
Methods: 100 patients and 200 controls were recruited in the study. A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay was utilized to analyze the -173 G/C SNP (rs755622) and PCR-based size discrimination assay was applied to detect the -794 CATT₅₋₈ repeat (rs5844572) in the MIF promoter. Plasma MIF levels were measured by ELISA. MIF mRNA levels were quantified by real-time reverse transcription (RT)-PCR. Bisulfate genomic sequencing was employed to evaluate DNA methylation status within the MIF promoter.
Results: We identified that the frequencies of MIF -794 CATT₅ (P = 0.001) allele and the expression of MIF (P <0.001) were increased in patients compared to healthy controls. Plasma levels of MIF in patients with CC genotype were higher than those of patients with GC or GG genotypes (P = 0.05). In patients with established AOSD, a higher frequency of -794 CATT₇ containing MIF genotypes was observed in those with liver dysfunction (P = 0.009). Haplotype analysis revealed a higher representation of the MIF haplotype defined by -173*C/-794 CATT₅ (C5) in AOSD patients (P = 0.001).
Conclusion: Functional promoter polymorphisms in the MIF gene influence plasma MIF levels in AOSD and may contribute to disease susceptibility or clinical presentation of AOSD.