Objective  To study the clinical significance of Th17 cell detection in patients with thymoma associated with myasthenia gravis (MG).

  Methods  From October 2015 to October 2017, 78 patients with thymoma who treated in Cardio-Thoracic Surgery of Tianjin Medical University General Hospital and 15 normal controls were collected. Flow cytometry was used to detect the proportion of Th17 cells, and the levels of IL-17, IL-21 and AchR-Ab in peripheral blood were detected before operation. The correlation of Th17 with the corresponding cytokines was analyzed, and the independent risk factor was predicted for thymoma with myasthenia gravis.

  Results  The percentage of Th17 cells in the MG group was 10.33%±1.28%, compared with 7.33%±0.58% for the Con group and 7.67%±2.18% for the Tm group. These differences were statistically significant. The MG group was recorded as having (18.05±7.23) pg/mL IL-17, (180.67±16.17) pg/ml IL-21, and (37.29±7.48) pmol/L AchR-Ab compared to (7.45±3.46) pg/mL, (84.33±5.13) pg/mL, and (15.23±3.32) pmol/L for the Con group and (8.22±1.67) pg/mL, (93.00±7.21) pg/mL, and (16.87±4.89) pmol/L for the Tm group for the same cytokines, respectively. These differences were also statistically significant (P < 0.001). The percentage of Th17/CD4⁺T cells in the MG group was positively correlated with IL-17 (r=0.830, P < 0.001), IL-21 (r=0.734, P < 0.001), and AchR-Ab (r=0.809, P < 0.001). IL-17, IL-21, and AchR-Ab are independent risk factors for predicting the combination of thymoma with MG.

  Conclusions  Th17 cells are involved in the development of thymoma with MG, which promote cell proliferation by secreting IL-21 and regulate MG growth by secreting IL-17.