Elevated IL-17 and TGF-beta Serum Levels: A Positive Correlation between T-helper 17 Cell-Related Pro-Inflammatory Responses with Major Depressive Disorder

Introduction: Depression is a mental disorder that highly associated with immune system. Therefore, this study compares the serum concentrations of IL-21, IL-17, and transforming growth factor beta (TGF-beta) between patients with major depressive disorder and healthy controls. Methods: Blood samples were collected from 41 patients with major depressive disorder and 40 healthy age-matched controls with no history of malignancies or autoimmune disorders. The subjects were interviewed face to face according to DSM-IV diagnostic criteria. Depression score was measured using completed Beck Depression Inventory in both groups. The serum concentrations of IL-21, IL-17, and TGF-beta were assessed using ELISA. Results: The mean score of Beck Depression score in the patient and control groups was 35.4 +/- 5.5 and 11.1 +/- 2.3. IL-17 serum concentrations in the patients and the control group were 10.03 +/- 0.6 and 7.6 +/- 0.6 pg/mL, respectively (P=0.0002). TGF-beta level in the patients group was significantly higher than compare to the control group; 336.7 +/- 20.19 vs. 174.8 +/- 27.20 pg/mL, (P<0.0001). However, the level of IL-21 was not statistically different between the two groups 84.30 +/- 4.57 vs. 84.12 +/- 4.15 pg/mL (P>0.05). Conclusion: Considering pro-inflammatory cytokines, current results support the association of inflammatory response and depressive disorder. So, it seems that pro-inflammatory factors profile can be used as indicator in following of depression progress and its treatment impacts.