Cytokines in the cerebrospinal fluid of suicide attempters

Abstract

Previous studies have reported elevated blood levels of cytokines in patients with depression. We investigated, for the first time, cytokine concentrations in the cerebrospinal fluid (CSF) of suicide attempters (n=63) and healthy controls (n=47). Cytokines Interleukin-1β, Interleukin-6 (IL-6), Interleukin-8, Tumor necrosis factor-α (TNF-α) and chemokine Macrophage inflammatory protein-1α (MIP-1α) were analyzed in CSF by means of multiplex sandwich ELISAs. Patients were classified according to diagnosis and violent or non-violent suicide attempt. Suicidal ideation and depressive symptoms were evaluated using the Suicide Assessment Scale (SUAS) and the Montgomery – Åsberg Depression Rating Scale (MADRS). We also analyzed the integrity of the blood brain barrier as reflected by the CSF/serum albumin ratio. We found that levels of IL-6 in CSF were significantly higher in suicide attempters compared to healthy controls. Violent suicide attempters displayed the highest IL-6 levels. Furthermore, there was a significant positive correlation between MADRS scores and CSF IL-6 levels in all patients. MIP-1α correlated significantly with MADRS and SUAS scores. Cytokine levels were not related to increased blood-brain barrier permeability. This study is the first to report elevated CSF levels of IL-6 in suicide attempters compared to healthy controls. We suggest that IL-6 may play a role in suicidal behaviour, and our findings may lead to new insights into how the immune system contributes to suicidality and depressive symptoms.