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      Cumulative meta-analysis of interleukins 6 and 1β, tumour necrosis factor α and C-reactive protein in patients with major depressive disorder

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          • This meta-analysis confirms a robust link between IL-6, CRP and major depression.
          • The role of TNF-α and IL-1β in major depression remains uncertain.
          • Further mechanistic and immunotherapeutic studies on IL-6 and CRP are needed.


          Cumulative meta-analyses are used to evaluate the extent to which further studies are needed to confirm or refute a hypothesis. We used this approach to assess observational evidence on systemic inflammation in individuals with major depressive disorder. We identified 58 studies of four common inflammatory markers in a literature search of PubMed, Embase and PsychInfo databases in May 2014. Pooled data from the earliest eight studies already showed an association between interleukin-6 concentrations and major depression; 23 more recent studies confirmed this finding ( d = 0.54, p < 0.0001). A significant association between C-reactive protein levels and major depression was noted after 14 studies and this did not change after addition of six more studies ( d = 0.47, p < 0.0001). For these two inflammatory markers, there was moderate heterogeneity in study-specific estimates, subgroup differences were small, and publication bias appeared to be an unlikely explanation for the findings. Sensitivity analyses including only high-quality studies and subjects free of antidepressant medication further verified the associations. While there was a link between tumour necrosis factor-α levels and major depression ( d = 0.40, p = 0.002), the cumulative effect remained uncertain due to the extensive heterogeneity in study-specific estimates and inconsistencies between subgroups. No evidence was found for the association between interleukin-1β levels and major depression ( d = −0.05, p = 0.86). In conclusion, this cumulative meta-analysis confirmed higher mean levels of interleukin-6 and C-reactive protein in patients with major depression compared to non-depressed controls. No consistent association between tumour necrosis factor-α, interleukin-1β and major depression was observed. Future studies should clarify the specific immune mechanisms involved as well as continue testing anti-inflammatory therapies in patients suffering from major depression.

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          Most cited references 74

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          Interleukin (IL)-6, tumour necrosis factor alpha (TNF-α) and soluble interleukin-2 receptors (sIL-2R) are elevated in patients with major depressive disorder: a meta-analysis and meta-regression.

          Many studies have explored the association between soluble interleukin-2 receptor (sIL-2R), cytokines and major depressive disorder (MDD). However, the results of these studies were not consistent. The aim of our study is to compare the levels of sIL-2R and cytokines in the blood between MDD patients and controls by a meta-analysis and to identify moderators accounting for potential heterogeneity in the levels of sIL-2R and cytokines in MDD patients versus controls by meta-regression analyses. A comprehensive literature search was performed to identify studies comparing the levels of sIL-2R and cytokines between MDD patients and controls. We pooled the effect sizes for standardized mean differences (SMD) of the levels of sIL-2R and cytokines. We also performed meta-regression and sensitivity analyses to investigate the roles of age, gender, sample type, ethnic origin and selected studies' quality in explaining potential heterogeneity and differences in results respectively. Twenty-nine studies were selected for this analysis. The levels of sIL-2R, TNF-α and IL-6 in MDD patients were significantly higher than those of healthy controls (SMD=0.555, p<0.001, SMD=0.567, p=0.010; SMD=0.680, p<0.001). Mean age of all subjects was a significant moderator to explain the high heterogeneity of IL-6. Sensitivity analysis found that European but not non-European subjects have higher levels difference of sIL-2R, TNF-α and IL-1β between MDD patients and controls. The severity of MDD was not considered. The blood levels of sIL-2R, TNF-α and IL-6 were significantly higher in MDD patients than controls. Age, samples source and ethnic origins may play a potential role in heterogeneity. Copyright © 2011 Elsevier B.V. All rights reserved.
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            The effect of antidepressant medication treatment on serum levels of inflammatory cytokines: a meta-analysis.

            Serum levels of inflammatory cytokines, for example, tumor necrosis factor alpha (TNFα), interleukin-6 (IL-6), and IL-1 beta (IL-1β), are elevated in subjects with major depressive disorder (MDD). The reason why this occurs is unclear. Elevated levels of inflammatory cytokines could be a result of brain dysfunction in MDD. It is also possible that inflammatory cytokines contribute to depressive symptoms in MDD. If the first assumption is correct, one would expect levels to normalize with resolution of the depressive episode after treatment. Several studies have measured changes in cytokine levels during antidepressant treatment; however, the results vary. The purpose of this study was to pool all available data on changes in serum levels of TNFα, IL-6, and IL-1β during antidepressant treatment to determine whether these levels change. Studies were included if they used an approved pharmacological treatment for depression, patients had a diagnosis of MDD, and serum levels of TNFα, IL-6, and/or IL-1β were measured before and after treatment. Twenty-two studies fulfilled these criteria. Meta-analysis of these studies showed that, overall, while pharmacological antidepressant treatment reduced depressive symptoms, it did not reduce serum levels of TNFα. On the other hand, antidepressant treatment did reduce levels of IL-1β and possibly those of IL-6. Stratified subgroup analysis by class of antidepressant indicated that serotonin reuptake inhibitors may reduce levels of IL-6 and TNFα. Other antidepressants, while efficacious for depressive symptoms, did not appear to reduce cytokine levels. These results argue against the notion that resolution of a depressive episode is associated with normalization of levels of circulating inflammatory cytokines; however, the results are consistent with the possibility that inflammatory cytokines contribute to depressive symptoms and that antidepressants block the effects of inflammatory cytokines on the brain.
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              The macrophage theory of depression.

               R.S. Smith (1991)
              Excessive secretion of macrophage monokines is proposed as the cause of depression. Monokines when given to volunteers can produce the symptoms necessary for the Diagnostic and Statistical Manual of Mental Disorders, Third Edition Revised (DSM-III-R) diagnosis of major depressive episode. Interleukin-1 (IL-1) can provoke the hormone abnormalities linked with depression. This theory provides an explanation for the significant association of depression with coronary heart disease, rheumatoid arthritis, stroke and other diseases where macrophage activation occurs. The 3:1 female/male incidence of depression ratio is accounted for by estrogen's ability to activate macrophages. The extraordinary low rate of depression in Japan is consistent with the suppressive effect of eicosapentanoic acid on macrophages. Fish oil is proposed as a prophylaxis against depression and omega-6 fat as a promoter. Infection, tissue damage, respiratory allergies and antigens found in food are some of the possible causes of macrophage activation triggering depression.

                Author and article information

                Brain Behav Immun
                Brain Behav. Immun
                Brain, Behavior, and Immunity
                Academic Press
                1 October 2015
                October 2015
                : 49
                : 206-215
                [a ]Department of Epidemiology and Public Health, University College London, London, UK
                [b ]Finnish Institute of Occupational Health, Systems Toxicology Unit, Centre of Expertise for Health and Work Ability, Helsinki, Finland
                [c ]Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, UK
                [d ]Université Pierre et Marie Curie, Paris, France
                [e ]Department of Public Health, Faculty of Medicine, University of Helsinki, Helsinki, Finland
                Author notes
                [* ]Corresponding author at: Department of Epidemiology and Public Health, University College London, Torrington Place, WC1E 6BT London, UK. Tel.: +44 (0) 7847285466; fax: +44 (0) 1865 793101. r.haapakoski@
                © 2015 The Authors

                This is an open access article under the CC BY license (



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