Background: The pathophysiology of bipolar disorder is not thoroughly solved. Several studies have investigated the possible role of cytokines in psychiatric disorders considering their place in neuroimmunomodulation. However, findings are still limited and contradictory in bipolar disorder and most of the studies are focused on either manic or depressive episodes. These studies suggest that both of these episodes could be proinflammatory states. We aimed to determine whether there are enduring changes of cytokine levels in euthymic bipolar patients.
Methods: Sixteen medication-free, euthymic and 15 only lithium-treated, euthymic bipolar patients and 16 healthy volunteers were recruited for assesment of serum cytokine levels. All the groups were homogenous regarding age, gender and ethnicity. IFN-γ, TNF-α, IL-2, IL-4, IL-5, IL-10 levels were assessed by using flow cytometry.
Results: There were no differences in cytokine levels between medication-free, euthymic bipolar patients and healthy subjects, only the levels of TNF-α and IL-4 in lithium-treated, euthymic bipolar patients were higher than both medication-free, euthymic bipolar patients and healthy subjects.
Limitations: Small and strictly selected study sample could make it hard to generalize the findings.
Conclusions: Cytokine production in medication-free euthymic bipolar patients is not different from healthy controls. Regarding the studies focusing on mania and depression, this study shows that proinflammatory state resolves in euthymia and current use of medication like lithium has an effect on cytokine profile, which could create a confounding factor.