Objectives: To characterize the immunological variations of patients with a bipolar disorder (BD) diagnosis in manic (BDm) and depressive (BDd) phases, by the quantification of the serum levels of interleukin (IL)-1β, -2, -4, -6 and tumor necrosis factor alpha (TNF-α).
Methods: Twenty physically healthy patients with a BD type I diagnosis and 33 matched controls were studied, after giving informed consent. The inclusion criteria included at least three weeks without any kind of psychopharmacological treatment, Young Mania Rating Scale score ≥20 for BDm (n = 10) and Hamilton Depression Rating Scale score ≥21 for BDd patients (n = 10). Exclusion criteria included any infectious diseases, allergies or any other kind of medical illness that required treatment with immunosuppressors, as well as any other diagnosis in Axis I. Physical and laboratory examinations were performed to rule out any clinical illness. Enzyme-linked immunosorbent assay (ELISA) was used to analyze the serum cytokines concentration.
Results: BD patients, when compared to controls, showed significant differences (p ≤ 0.05) in the serum levels of the measured cytokines. The sub-group of BDd patients showed an increase in IL-6 and TNF-α, as well as a decrease in IL-2 concentration. The BDm sub-group, on the other hand, showed an increase in TNF-α and IL-4 values, with a low concentration of IL-1 and IL-2. The comparison between both sub-groups suggests that there is a distinctive cytokine pattern for the specific phases of the disorder: for mania, we found a high IL-4 and low IL-1β and IL-6 concentration, while in the depressive phase, the inverse pattern was found.
Conclusions: Our results show the existence of phasic differences in the serum levels of cytokines in BD.