Background:In recent years, a role for the immune system in the pathogenesis of psychiatric diseases has gained increased attention.Although bipolar disorder appears to be associated with altered serum cytokine levels, a putative immunological contribution to its pathophysiology remains to be established. Hitherto, no direct analyses of cerebrospinal fluid (CSF) cytokines in patients with bipolar disorder have been performed. Methods: We analyzed CSF cytokine concentrations in euthymic patients with diagnosed bipolar dis order type I (n = 15) or type II (n = 15) and healthy volunteers (n = 30) using an immunoassay-based protein array multiplex system. Results: The mean interleukin (IL)-1β level (4.2 pg/mL, standard error of the mean [SEM] 0.5) was higher and the IL-6 level (1.5 pg/mL, SEM 0.2) was lower in euthymic bipolar patients than in healthy volunteers (0.8 pg/mL, SEM 0.04, and 2.6 pg/mL, SEM 0.2, respect ively). Patients with 1 or more manic/hypomanic episodes during the last year showed significantly higher levels of IL-1β (6.2 pg/mL, SEM 0.8; n = 9) than patients without a recent manic/hypomanic episode (3.1 pg/mL, SEM 1.0; n = 10). Limitations: All patients were in an euthymic state at the time of sampling. Owing to the large variety of drugs prescribed to patients in the present study, influence of medication on the cytokine profile cannot be ruled out. Conclusion: Our findings show an altered brain cytokine profile associated with the manifestation of recent manic/hypomanic episodes in patients with bipolar disorder. Although the causality remains to be established, these findings may suggest a pathophysiological role for IL-1β in bipolar disorder. In recent years, a role of the immune system in the pathogenesis of psychiatric diseases has gained increased attention. In this regard, many investigators have focused on cytokines, proteins that directly initiate and control immunological responses. We recently demonstrated a selective activation of brain interleukin (IL)-1β in schizophrenia, 2 a disease that appears similar to bipolar disorder with regard to symptomatology, treatment and risk genes. 3,4 Interestingly, a polymorphism in the promoter region of the IL1B gene has been suggested to comprise a shared genetic susceptibility for bipolar disorder and schizophrenia. 5 Indeed, bipolar disorder appears to be linked to inflammation, as indicated by genetic polymorphisms, gene expression and cytokine activation, 6 although direct evidence for a pathophysiological involvement of the immune system of the brain is still sparse. This may be 115 related to the fact that evaluation of cytokine levels in patients with bipolar disorder has been restricted to serum analyses. The bidirectional communication between the immune system of the brain and that of peripheral organs is complex, 7 and serum cytokines do not predict brain cytokine activation in healthy volunteers. 8 Hence, the immune system of the brain, including local cytokine release from microglia and astrocytes, may be independent of the immune sys...

Elevated cerebrospinal fluid (CSF) levels of the glia-derived N-methyl-d-aspartic acid receptor antagonist kynurenic acid (KYNA) have consistently been implicated in schizophrenia and bipolar disorder. Here, we conducted a genome-wide association study based on CSF KYNA in bipolar disorder and found support for an association with a common variant within 1p21.3. After replication in an independent cohort, we linked this genetic variant—associated with reduced SNX7 expression—to positive psychotic symptoms and executive function deficits in bipolar disorder. A series of post-mortem brain tissue and in vitro experiments suggested SNX7 downregulation to result in a caspase-8-driven activation of interleukin-1β and a subsequent induction of the brain kynurenine pathway. The current study demonstrates the potential of using biomarkers in genetic studies of psychiatric disorders, and may help to identify novel drug targets in bipolar disorder.