Autoimmune thyroid disease (AITD) is a family of classic autoimmune disorders that mainly consists of Hashimoto's thyroiditis (HT) and Graves' disease (GD). 1 The global prevalence of HT is estimated at 2%. 2 A significant sign of HT is loss of self-tolerance to thyroid antigens. 3 HT is characterized by infiltration of thyroid lymphocytes, circulating thyroid autoantibodies, and apoptosis of thyroid cells leading to the destruction of follicles. 3,4 GD is an organ-specific thyroid autoimmune disease with anti-thyroid stimulating hormone (TSH) receptor (TSH-R) autoantibodies in circulation that can cause hyperthyroidism. Lack of immune tolerance to thyroid antigens, especially TSH-R, is the cause of GD. 5 It is estimated that the incidence of AITD in women is significantly higher than that in men. The prevalence of AITD is 2% in women and 0.2% in men. AITD is most common in adults aged 30-50, and the disease occurrence increases with age. 6,7 Cytokines play a crucial role in the induction and action stages of immune and inflammatory responses. Imbalances between preand anti-inflammatory cytokines may play an important role in the occurrence and development of AITD. Several cytokines, including interleukin (IL)-17, IL-23, IL-28, and IL-29, have been implicated in the pathogenesis of HT. [8][9][10][11][12][13][14] Additionally, IL-6, IL-21, IL-23, and IL-37 are all involved in the occurrence of GD. [15][16][17][18][19] IL-12 family plays a key role in immune responses through their functional, unique structural, and immunological characteristics. 20 IL-12, IL-23, IL-27, IL-35, and the recently discovered IL-39 comprise the IL-12 cytokine family. 21 Wang et al. 22,23 first reported that IL-39 is