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 depression. Cytokines and T regulatory (Treg) cells may play an important role in the development of depression. This study investigates the levels of cytokines and Treg cells, as well as the concentration of serotonin (5-HT) in the blood of 89 patients suffering from depression 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-alpha, and INF-gamma) and 5-HT levels in the blood were measured by enzyme-linked immunosorbent assays. The levels of CD4(+)CD25(+) Treg cells were determined by flow cytometric analysis. Patients with depression showed significantly higher serum levels of IL-6 and INF-gamma, no altered serum levels of IL-10 and TNF-alpha, and decreased platelet and serum 5-HT levels compared with healthy participants at the first acquisition. In addition, the symptoms of depression and anxiety, the TNF-alpha 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 depression and an association of the serotonergic system and cytokines were observed. These results indicate that the development of depression might be related to several interacting proteins, including cytokines and 5-HT, and the treatment affects imbalances of these factors.