A preliminary report of increased plasma levels of IL-33 in bipolar disorder: Further evidence of pro-inflammatory status

Background: Recent findings suggest an important role for inflammation in the neurobiology of bipolar disorder (BD). Interleukin 33 (IL-33) is a cytokine with multiple functions and may act as a nuclear factor regulating transcription and as an "alarmin". IL-33 exerts part of its function through the receptor ST2 that also exists in a soluble form (sST2). This study was performed to evaluate IL-33 and sST2 plasma levels in BD patients. Methods: We evaluated IL33 and sST2 plasma levels of 46 BD patients (23 in euthymia and 23 in mania) and 23 healthy controls using enzyme-linked immunosorbent assay (ELISA). BD patients were age and gender matched healthy controls. Results: IL-33 levels were higher in BD patients (p=0.02) but there was no difference in sST2 (p=0.55). IL33 and sST2 plasma levels were not correlated with age, neither was influenced by clinical comorbidities nor medications in use. Conclusion: These findings corroborate the view of BD as a multisystem condition with a proinflammatory profile.