Functional polymorphisms affecting Th1 differentiation are associated with the severity of autoimmune thyroid diseases

The prognosis for autoimmune thyroid diseases (AITDs), such as Hashimoto’s disease (HD) and Graves’ disease (GD), varies among patients. Interleukin (IL)-12 and IL-18 also induce Th1 differentiation, and SOCS1 (Suppressor of cytokine signaling 1) and TIM-3 (T cell immunoglobulin and mucin domain-3) are known to be negative regulators of Th1 cells. To clarify the association of functional polymorphisms in the IL12, IL12Rβ1, IL18, SOCS1 and TIM3 genes with the intractability and severity of autoimmune thyroid disease (AITD), we genotyped these polymorphisms in 151 GD patients, including 61 patients with intractable GD and 51 patients with GD in remission, in 140 HD patients, including 59 patients with severe HD and 55 patients with mild HD, and in 74 healthy controls. The frequency of the IL18 -607CC genotype which correlates with a high production of IL-18, was significantly higher in patients with GD in remission than in those with intractable GD (p=0.0178). The -607C allele was significantly higher in patients with severe HD than in those with mild HD (p=0.0050). The -607CC genotype in IL18 gene may be protective against the intractability of GD, and the -607C allele may enhance the severity of HD.