The Role of Inflammatory Cytokines in Adolescent Bipolar Disorder: A Systematic Review

Bipolar spectrum disorders (BSD) are neuropsychiatric conditions that involve manic symptoms and depression symptoms. The prevalence of Bipolar Disorder (BD) is 1% to 3% in youth, which is known to undermine their cognitive, emotional, and social functions. Among the many biological mechanisms underlying BD, pro-inflammatory cytokines are small proteins that are active in the immune system, which can affect neuronal activity by altering blood-brain permeability, neurotransmitter activeness, and causing damage to the neuronal cells. This systematic review examines different types of cytokines and how their level varies in adolescent BD. Specifically, the review examined pro-inflammatory cytokines IL-6, IL-8, TNF-α, and IL-1β and an anti-inflammatory cytokine IL-10. A total of 9 studies were included from screening two databases, PsycInfo and PubMed. Overall, the levels of IL-6, IL-8, TNF-α, and IL-1β positively correlated with BD symptoms. While these findings have implications for treatment, counseling, medication, and prevention strategies specific to adolescent patients, future research must address the inconsistency around IL-10 levels as well as other biomarkers such as Brain-Derived Neurotrophic Factors (BDNF).