The IL15 +96522 A>T functional polymorphism is related to the differentiation of Th17 cells and the severity of Hashimoto's disease

Summary To clarify the association between the genetic producibility of IL-15, a pro-inflammatory cytokine, and the pathogenesis of autoimmune thyroid diseases (AITDs), we genotyped +96522 A>T and +82889 A>G polymorphisms in the IL15 gene using 127 patients with Hashimoto's disease (HD), including 55 patients with severe HD and 48 patients with mild HD; 130 patients with Graves’ disease (GD), including 52 patients with intractable GD and 44 patients with GD in remission; and 79 healthy volunteers. Both the IL15 +96522 A allele and AA genotype were more frequent in patients with severe HD than in those with mild HD. The serum levels of IL-15 were higher in individuals with the IL15 +96522 AA genotype than in those with the T allele, and they were also higher in patients with severe HD than in those with mild HD. On the other hand, the mRNA levels of IL-15 were not significantly different among individuals with each genotype of both SNPs. After incubation with recombinant human IL-15, the proportions of Th17 cells in CD4+ cells were increased, and those of Treg cells in CD4+ cells were maintained. Our study indicates that the IL15 +96522A/C polymorphism correlates with the severity of HD, most likely by increasing Th17 cells.