High numbers of circulating activated T cells and raised levels of serum IL-2 receptor in bipolar disorder

Background Previously, we found an increased prevalence of thyroid autoantibodies in patients with bipolar disorder. In the present study, we investigated other signs of immune activation in bipolar patients, in particular an activation of the T cell system. Methods Fluorescence activated cell scanning (FACS) analysis was performed on lymphocytes of 64 outpatients with DSM-IV bipolar disorder using the T cell marker CD3 in combination with the activation markers MHC-class II, CD25, CD69 or CD71. In 34 patients, these assays were repeated after an interval of 2 years. In addition, T cell activation was determined by measuring serum soluble IL-2 receptor (sIL-2R) in 172 bipolar outpatients. Outcomes were compared with a healthy control group. Results Significantly higher numbers of circulating activated T cells and raised sIL-2R levels were found in euthymic, manic, and depressed bipolar patients when compared with healthy controls. In general, these abnormalities were stable over time. Manic patients showed significantly higher levels of sIL-2R in comparison with depressed patients. Conclusions The T cell system was found to be activated in both symptomatic and euthymic patients with bipolar disorder. The pathophysiological significance of these findings remains to be explored.