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Systemic inflammation is accompanied by profound behavioral and mood changes that resemble symptoms of depression. Findings in animals suggest that pro-inflammatory cytokines released by activated immune cells in the periphery evoke these behavioral symptoms by driving inflammatory changes in the brain. However, experimental data in humans are lacking. Here we demonstrate in healthy male volunteers (10 endotoxin treated, 8 placebo treated) that intravenous administration of low-dose endotoxin (0.8 ng/kg body weight), a prototypical pathogen-associated molecular pattern that activates the innate immune system, not only induces a significant increase in peripheral blood cytokine concentrations (that is, tumor necrosis factor-α, interleukin (IL)-6, IL-10) but also results, with some latency, in a robust and selective increase of IL-6 in the cerebrospinal fluid (CSF). Moreover, we found a strong association between the endotoxin-induced increase of IL-6 in the CSF and the severity of mood impairment, with larger increases in CSF IL-6 concentration followed by a greater deterioration in mood. Taken together, these findings suggest that the appearance of depressive symptoms in inflammatory conditions might be primarily linked to an increase in central IL-6 concentration, identifying IL-6 as a potential therapeutic target in mood disorders.

Activation of the innate immune system is thought to contribute to depression. Multiple social and behavioral factors are also known to instigate depression. Whether these socio-behavioral factors interact with inflammatory stimuli to alter proinflammatory responses and depressed mood is not known. In 115 healthy adults, social, emotional, and behavioral factors were assessed at baseline. A single infusion of endotoxin (Escherichia coli; 0.8 ng/kg of body weight) or placebo (0.9% saline) was administered with hourly assessment of depressed mood and proinflammatory cytokines (interleukin-6 (IL-6); tumor necrosis factor-α (TNF)). Inflammatory gene expression was examined at 30 min after infusion, prior to increase of inflammatory cytokines. As compared to placebo, endotoxin-induced increases of depressed mood were moderated by baseline levels of perceived stress, trait sensitivity to social disconnection, and severity of symptoms of anxiety and depression (all Ps < 0.05) but not early life stress, social status, social support, neuroticism, or sleep disturbance. Anxiety symptoms remained significant in multivariable analyses (P < 0.01). None of these socio-behavioral factors were related to increases in proinflammatory cytokines. Transcriptome profiling analyses indicated that perceived stress, sensitivity to social disconnection, and depressive symptoms were associated with increased activation of pro-inflammatory transcription control pathways (i.e., activator protein-1, nuclear factor-κB) in response to endotoxin (all Ps < 0.05). These results indicate that an array of socio-behavioral factors, which are associated with depression risk, modify vulnerability to inflammation-induced depressed mood. Together, these observations may be used to help target therapeutic interventions to mitigate occurrence of the inflammatory biotype of depression.

We recently indicated that four-week probiotic supplementation significantly reduced depression along with microbial and neural changes in people with depression. Here we further elucidated the biological modes of action underlying the beneficial clinical effects of probiotics by focusing on immune-inflammatory processes. The analysis included a total of N = 43 participants with depression, from which N = 19 received the probiotic supplement and N = 24 received a placebo over four weeks, in addition to treatment as usual. Blood and saliva were collected at baseline, at post-intervention (week 4) and follow-up (week 8) to assess immune-inflammatory markers (IL-1β, IL-6, CRP, MIF), gut-related hormones (ghrelin, leptin), and a stress marker (cortisol). Furthermore, transcriptomic analyses were conducted to identify differentially expressed genes. Finally, we analyzed the associations between probiotic-induced clinical and immune-inflammatory changes. We observed a significant group x time interaction for the gut hormone ghrelin, indicative of an increase in the probiotics group. Additionally, the increase in ghrelin was correlated with the decrease in depressive symptoms in the probiotics group. Transcriptomic analyses identified 51 up- and 57 down-regulated genes, which were involved in functional pathways related to enhanced immune activity. We identified a probiotic-dependent upregulation of the genes ELANE, DEFA4 and OLFM4 associated to immune activation and ghrelin concentration. These results underscore the potential of probiotic supplementation to produce biological meaningful changes in immune activation in patients with depression. Further large-scale mechanistic trials are warranted to validate and extend our understanding of immune-inflammatory measures as potential biomarkers for stratification and treatment response in depression. Trial Registration: www.clinicaltrials.gov , identifier: NCT02957591.

Although research has demonstrated a relationship between proinflammatory cytokine activity and depressive symptoms, the neurocognitive processes underlying this relationship have remained largely unexplored. Here, we examined the effect of proinflammatory cytokine activation on the neural correlates of socially painful experience and associated depressed mood. Participants received either low-dose endotoxin or placebo through intravenous injection. Levels of the proinflammatory cytokine, IL-6, were repeatedly assessed through hourly blood draws; self-reported depressed mood was assessed hourly as well. Two hours post-injection, participants completed a neuroimaging session in which they were socially excluded during an online ball-tossing game. Replicating previous research, individuals exposed to endotoxin, compared to placebo, showed increases in IL-6 levels and depressed mood. Although there were no meaningful differences between the endotoxin and control groups in neural responses to social exclusion, there were sex differences in the relationships between IL-6 increases and neural responses to exclusion among subjects exposed to endotoxin. Among females, but not males, exposed to endotoxin, increases in IL-6 were associated with increases in social pain-related neural activity (dorsal anterior cingulate cortex, anterior insula) that mediated the relationship between IL-6 increases and depressed mood increases. Implications of these sex differences in the neural correlates of cytokine-associated depressed mood and social pain are discussed.

Inflammation plays a significant role in the pathophysiology of depression. However, not all individuals exposed to inflammatory challenge develop depression, and identifying those at risk is necessary to develop targeted monitoring, prevention, and treatment strategies. Within a randomized double-blind placebo-controlled study (n = 115), we examined whether leukocyte transcriptome profiles predicted inflammation-induced depressed mood in volunteers who received low-dose intravenous endotoxin (n = 58; aged 18–50). At baseline, transcription factor (TF) activities were assessed using genome-wide transcriptional profiling of peripheral blood mononuclear cells and promoter-based bioinformatic analyses. Then, participants were administered endotoxin. Self-reported depressed mood was assessed using the Profile of Mood States. Based on extant studies linking transcriptional profiles to depressive disorder, we examined whether post-endotoxin depressed mood is predicted by baseline activity of TFs related to immune activation, sympathetic activation, and glucocorticoid insensitivity: respectively, nuclear factor kappa B (NF-kB), cAMP response element-binding protein (CREB), and glucocorticoid receptor (GR). Twenty-one participants (36%) experienced an increase in depressed mood from baseline to 2 h post endotoxin, when depressive response peaks. Bioinformatics analyses controlling for age, sex, ethnicity, body mass index, and physical sickness response revealed that post-endotoxin depressed mood was predicted by increased baseline activity of TFs related to inflammation (NF-kB) and beta-adrenergic signaling (CREB) and by decreased activity of GR-related TFs (P’s < 0.001). Inflammation-induced depressed mood is predicted by peripheral transcriptome profiles related to immune activation, sympathetic activation, and glucocorticoid insensitivity. With further replication, these stress-related molecular profiles could be used for a novel genomic approach for identifying individuals at high-risk for the inflammatory subtype of depression.

Depression is associated with systemic inflammation, and the systemic inflammation caused by endotoxin administration elicits mild depressive symptoms such as fatigue and reduced interest. The neural correlates of depressive symptoms that result from systemic inflammation are poorly defined. The aim of this study was to use (18)F-FDG PET to identify brain regions involved in the response to endotoxin administration in humans. Nine healthy subjects received double-blind endotoxin (0.8 ng/kg) and placebo on different days. (18)F-FDG PET was used to measure differences in the cerebral metabolic rate of glucose in the following regions of interest: insula, cingulate, and amygdala. Serum levels of tumor necrosis factor-α and interleukin-6 were used to gauge the systemic inflammatory response, and depressive symptoms were measured with the Montgomery-Åsberg Depression Rating Scale and other scales. Endotoxin administration was associated with an increase in Montgomery-Åsberg Depression Rating Scale, increased fatigue, reduced social interest, increased levels of inflammatory cytokines, higher normalized glucose metabolism (NGM) in the insula, and, at a trend level, lower NGM in the cingulate. Secondary analyses of insula and cingulate subregions indicated that these changes were driven by the right anterior insula and the right anterior cingulate. There was a negative correlation between peak cytokine levels and change in social interest and between peak cytokine levels and change in insula NGM. There was a positive correlation between the change in NGM in the insula and change in social interest. Systemic inflammation in humans causes an increase in depressive symptoms and concurrent changes in glucose metabolism in the insula and cingulate-brain regions that are involved in interoception, positive emotionality, and motivation.

The aim of this study was to evaluate the effects of moderate aerobic exercise training on sleep, depression, cortisol, and markers of immune function in patients with chronic primary insomnia. Twenty-one sedentary participants (16 women aged 44.7 ± 9 years) with chronic primary insomnia completed a 4-month intervention of moderate aerobic exercise. Compared with baseline, polysomnographic data showed improvements following exercise training. Also observed were reductions in depression symptoms and plasma cortisol. Immunologic assays revealed a significant increase in plasma apolipoprotein A (140.9 ± 22 to 151.2 ± 22 mg/dL) and decreases in CD4 (915.6 ± 361 to 789.6 ± 310 mm3) and CD8 (532.4 ± 259 to 435.7 ± 204 mm3). Decreases in cortisol were significantly correlated with increases in total sleep time (r=-0.51) and REM sleep (r=-0.52). In summary, long-term moderate aerobic exercise training improved sleep, reduced depression and cortisol, and promoted significant changes in immunologic variables.

Rationale An increasing body of evidence links the occurrence of sleep continuity disturbances with increased inflammation and both sleep disturbances and inflammation are associated with clinical depression. Typhoid vaccination results in a mild inflammatory response that significantly increases levels of the proinflammatory cytokine, interleukin (IL)-6. Objectives The present exploratory study aimed to enhance our understanding of the link between inflammation, sleep and depression by examining the effects of typhoid vaccine on the sleep polysomnogram. Methods We studied the effects of a single injection of typhoid polysaccharide vaccine and placebo (saline solution) on sleep in 16 healthy male and female participants aged 20–38 years, sleeping at home in a randomized, double-blind, balanced order, crossover design. Subjective measures of mood, sleep and adverse effects were elicited and plasma samples analysed for IL-6 levels. Results IL-6 levels (in picogramme per millilitre) significantly increased 2 h post vaccine compared to placebo (0.90 vs 0.53, p  = 0.026, r  = 0.55). Relative to placebo, typhoid vaccination produced significant impairment in several measures of sleep continuity. Total sleep time (in minute) (426.1 vs 410.7, p  = 0.005, r  = 0.62) and sleep efficiency percent (94.3 vs 91.5, p  = 0.007, r  = 0.65) were decreased; with increases in wake after sleep onset (in minute) (25.5 vs 38.8, p  = 0.007, r  = 0.65), total wake (in minute) (34.9 vs 50.3, p  = 0.005, r  = 0.67), sleep stage transitions (155.9 vs 173.1, p  = 0.026, r  = 0.56), number of awakenings (27.2 vs 36.1, p  = 0.007, r  = 0.64) and awakening index (3.8 vs 5.3, p  = 0.005, r  = 0.67) (means, significance level and effect size). Conclusions Inflammatory mechanisms may underlie the impairment in sleep efficiency which is a hallmark of major depression. Because impaired sleep is also a predictor of major depression, there may be a role for suitable anti-inflammatory approaches in strategies designed to prevent the onset of depression. ClinicalTrials.gov ( http://www.clinicaltrials.gov ): NCT02628054

Background Depression is one of the most frequently missed diagnoses in elderly people, with obvious negative effects on quality of life. Various studies have shown that long chain omega-3 polyunsaturated fatty acids (n-3 PUFA) may be useful in its management. Our objective was to evaluate whether a supplement containing n-3 PUFA improves depressive symptoms in depressed elderly patients, and whether the blood fatty acid pattern is correlated with these changes. Methods The severity of depressive symptoms according to the Geriatric Depression Scale (GDS), blood fatty acid composition and erythrocyte phospholipids were analyzed in 46 depressed females aged 66-95y, diagnosed with depression according to DSMIV, within the context of a randomized, double-blind, placebo-controlled trial. 22 depressed females were included in the intervention group (2.5 g/day of n-3 PUFA for 8 weeks), and 24 in the placebo group. We also measured immunological parameters (CD2, CD3, CD4, CD8, CD16, CD19 and cytokines (IL-5, IL-15). Results The mean GDS score and AA/EPA ratio, in whole blood and RBC membrane phospholipids, were significantly lower after 2 months supplementation with n-3 PUFA. A significant correlation between the amelioration of GDS and the AA/EPA ratio with some immunological parameters, such as CD2, CD19, CD4, CD16 and the ratio CD4/CD8, was also found. Nevertheless, omega-3 supplementation did not significantly improve the studied immunological functions. Conclusions n-3 PUFA supplementation ameliorates symptoms in elderly depression. The n-3 PUFA status may be monitored by means of the determination of whole blood AA/EPA ratio.

Despite the importance of mental illness and the high prevalence of HIV in Africa, few studies have documented depressive symptoms among HIV-infected persons in Africa. We assessed factors associated with depression among HIV-infected adults undergoing anti-retroviral eligibility screening in Eastern Uganda. Depressive symptoms were measured using the Center for Epidemiologic Studies Depression Scale (CES-D). Univariate and multiple regression analyses were conducted to identify socio-demographic characteristics and disease-related factors associated with depression. Among 1017 HIV-infected participants assessed for depression, 47% (476/1017) reported depressive symptoms (CES-D >/= 23). Adjusting for age, gender, education, and source of income, patients with CD4 counts <50 cells/microl were more likely to be depressed (odds ratio 2.34, 95% confidence interval, 1.39-3.93, P = 0.001). Women, participants >50 years, and those without an income source were more likely to be depressed. Depression was common among HIV-infected persons in rural Uganda and was associated with low CD4 cell counts. Appropriate screening and treatment for depression should be considered for comprehensive HIV care.