Distinct role of T helper Type 17 immune response for Graves' hyperthyroidism in mice with different genetic backgrounds.

T helper type 17 (Th17) cells, a newly identified effector T-cell subset, have recently been shown to play a role in numerous autoimmune diseases, including iodine-induced autoimmune thyroiditis in non-obese diabetic (NOD)-H2(h4) mice, which had previously been thought Th1-dominant. We here studied the role of Th17 in Graves' hyperthyroidism, another thyroid-specific autoimmune disease, in a mouse model. Two genetically distinct BALB/c and NOD-H2(h4) strains with intact or disrupted IL-17 genes (IL-17(+/+) or IL-17(-/-)) were immunized with adenovirus (Ad) expressing the thyrotropin receptor (TSHR) A-subunit (Ad-TSHR289). Both IL-17(+/+) and IL-17(-/-) mice developed anti-TSHR antibodies and hyperthyroidism at equally high frequencies on the BALB/c genetic background. In contrast, some IL-17(+/+), but none of IL-17(-/-), mice became hyperthyroid on the NOD-H2(h4) genetic background, indicating the crucial role of IL-17 for development of Graves' hyperthyroidism in non-susceptible NOD-H2(h4), but not in susceptible BALB/c mice. In the T-cell recall assay, splenocytes and lymphocytes from the draining lymph nodes from either mouse strains, irrespective of IL-17 gene status, produced IFN-γ and IL-10 but not other cytokines including IL-17 in response to TSHR antigen. Thus, the functional significance of Th17 may not necessarily be predictable from cytokine expression patterns in splenocytes or inflammatory lesions. In conclusion, this is, to our knowledge, the first report showing that the role of Th17 cells for the pathogenesis of a certain autoimmune disease depends on the mouse genetic backgrounds.