Macrophage migration inhibitory factor gene promoter polymorphism (−173G/C SNP) determines host susceptibility and severity of leptospirosis

Abstract

The biological mechanisms that are associated with the severity of leptospirosis are far from complete. The aim of the present study was to investigate whether the macrophage migration inhibitory factor (MIF) gene promoter polymorphisms determine susceptibility to and severity of human leptospirosis. MIF is a potent pro-inflammatory cytokine, which has been reported to correlate with the risk of inflammatory disease onset and severity. In the present study, MIF 173G/C single nucleotide polymorphism (SNP) was analyzed by PCR-RFLP (Restriction fragment length polymorphism). A statistically significant increase of MIF -173*C allele related genotypes was observed in leptospirosis patients when compared with healthy control subjects. Genotypes GC (OR: 28.4; 95% CI: 10.9–73.6; p < 0.001) and CC (OR: 40; 95% CI: 2.3–686.5; p < 0.001) of −173 G/C MIF polymorphism was associated with susceptibility and severity of leptospirosis respectively. In leptospirosis cases, 69.8% of leptospirosis patients were GC genotype carriers while 19.8% and 10.4% cases were CC and GG carriers; in severe leptospirosis, 68% cases were CC carriers and 32% were GC carriers; and in healthy controls, 92.5% subjects were GG carriers and 7.5% were GC carriers. MIF -173*C allele was (OR: 15; 95% CI: 6.1–36.8; p < 0.001) significantly associated with the risk of leptospirosis than −173*G allele (OR: 0.06; 95% CI: 0.02–0.16; p < 0.001). The relationship of −173G/C MIF polymorphism with mRNA and serum level of MIF and inflammatory cytokine expression was analyzed by quantitative real-time PCR and MIF ELISA. MIF mRNA expression was significantly increased in carriers of MIF -173*C allele associated genotypes, GC and CC. A substantial increase of serum MIF (Mean ± SD) was found in risk genotypes GC (5.81 ± 0.61 ng/mL) and CC (10.12 ± 0.23 ng/mL) carrying leptospirosis patients than GG genotype (0.86 ± 0.3 ng/mL) carrying healthy controls. Pearson correlation test showed a significant positive correlation between elevated serum MIF and −173*C allele (r = 0.99, p < 0.001). High MIF expression genotypes GC and CC upregulated the mRNA expression of TNF-α, IL-1β and IL-4 whereas downregulated the IL-10 expression. Thus, MIF -173 G/C SNP genotype GC carriers have highly susceptible to leptospirosis and the leptospirosis patients with CC genotype had an increased risk of developing a severe form of the disease. The observations of this study conclude that MIF -173G/C polymorphism is associated with leptospirosis susceptibility and severity and also could be a promising severity predictor of leptospirosis.