Analysis of cytokine levels, T regulatory cells and serotonin content in patients with depression

Alterations in peripheral serotonin concentrations and an imbalanced immune system have been reported in patients with a depressive disorder. Cytokines and T regulatory (Treg) cells may play an important role in the development of depression. This study investigates levels of cytokines and Treg cells, as well as the concentration of serotonin (5-HT) in the blood of 89 patients suffering from a depressive disorder and 89 healthy participants between two acquisitions. We investigated the state of health before (T1) and after (T2) psychological and pharmacological therapy. Both cytokine (IL-6, IL-10, TNF-α, and INF-γ) and 5-HT levels in the blood were measured by enzyme-linked immunosorbent assays (ELISAs). The levels of CD4+ CD25+ Treg cells were determined by flow cytometric analysis (FACS). Patients with a depressive disorder showed significantly higher serum levels of IL-6 and INF-γ, no altered serum levels of IL-10 and TNF-α, and decreased platelet and serum 5-HT levels compared to healthy participants at the first acquisition. In addition, the symptoms of depression and anxiety, the TNF-α level, and the amount of CD4+ CD25+ cells in the blood were decreased from the first to the second acquisition. Further, a correlation between IL-6 and platelet 5-HT has been observed in patients. An imbalance of the immune system in patients with a depressive disorder and an association of the serotonergic system and cytokines were observed. These results indicate that the development of a depressive disorder might be related to several interacting proteins, including cytokines and 5-HT, and the treatment affects imbalances of these factors.