Circulating T helper 17 and IFN-γ positive Th17 cells in Major Depressive Disorder

Introduction: Animal models of depression have reported elevated levels of T helper 17 (Th17) and T helper 1 (Th1) cells along with a decrease in T regulatory (Treg) cell percentage. However, there is ambiguity in the results of clinical studies investigating Th17 cells in Major Depressive Disorder (MDD). No studies have investigated the role of Interferon gamma positive Th17 cells (IFN gamma + Th17) in MDD yet. Methods: The study population included 53 patients of first episode, drug naive MDD patients, and 53 non-psychiatric healthy volunteers as healthy controls. Th17, Th1, IFN gamma + Th17 and Treg cell percentages were assessed by flow cytometry. Results: The mean (+/- SD) percentage of Th17 cells in cases (1.87 +/- 1.03) was significantly higher than the mean in controls (1.1 +/- 0.94) (p < 0.001). There was no significant difference in the Treg percentages between the cases (2.1 +/- 2.0) and controls (2.23 +/- 0.95). The Th17:Treg ratio was significantly higher in cases (5.41 +/- 10.84) compared to the controls (0.69 +/- 0.89) (p < 0.05). Further analysis of data has also revealed that IFN gamma + Th17 subsets secreted more IL-17 in cases (515.7 +/- 423.4) compared to controls (509.6 +/- 337.4). Intracellular IL-17 levels in this subset also showed a weak though insignificant positive correlation with HDRS scores in the cases. Conclusion: Elevated circulating Th17 cell percentage and Th17:Treg ratio in MDD cases thus add to the evidence suggesting Th17 mediated pro-inflammatory state in MDD. The study also provides preliminary findings of the more pathogenic IFN gamma + Th17 cell subset in MDD.