Circulating T helper 17 and IFN-γ positive Th17 cells in Major Depressive Disorder

Peripheral CD4+ T helper lymphocytes alterations in major depressive disorder: A systematic review and meta-analysis

Previous research has shown that patients with major depressive disorder (MDD) develop immune dysfunction. However, the exact alterations of cluster of differentiation (CD)4+ T helper (Th) lymphocytes in MDD remains unclear. This meta-analysis aimed to examine the specific changes in CD4+ Th cells. A comprehensive search of PubMed, EMBASE, Web of Science, and PsycINFO databases was conducted to identify studies investigating CD4+ Th, Th1, Th2, Th17, and T regulatory (Treg) cell counts in the peripheral blood of MDD patients and healthy controls (HCs), covering the period up to June 22, 2024. Our findings revealed that patients with MDD might exhibit higher CD4+ Th cells (SMD=0.26, 95 %CI, 0.02 to 0.50), CD4+/CD8+ cell ratios (SMD=0.51, 95 %CI, 0.14 to 0.89), Th1/Th2 cell ratios (SMD=0.15, 95 %CI, 0.01 to 0.30) and lower Th1 (SMD=-0.17, 95 %CI, -0.30 to -0.03), Th2 (SMD=-0.25, 95 %CI, -0.40 to -0.11), and Treg cells (SMD=-0.69, 95 %CI, -1.27 to -0.11). However, no significant difference was observed in terms of Th17 cells and Th17/Treg cell ratios between MDD patients and the HCs. Heterogeneity was large (I2:18.1-95.2 %), and possible sources of heterogeneity were explored (e.g., age, depression scale, country, and antidepressant use). Our findings indicate that peripheral CD4+ T cells in depressed patients exhibit features of adaptive immune dysfunction, as evidenced by increased CD4+ Th cells and CD4+/CD8+ and decreased Treg cells. These findings offer insights into the underlying mechanism of MDD.

Activation of the interleukin-23/Th17 axis in major depression: a systematic review and meta-analysis

The interleukin-23/Th17 axis is a promising modifiable target for depression. However, its association with depression has not been systematically evaluated. We systematically searched four databases (EMBASE, Web of Science, Pubmed and PsycINFO) for studies comparing patients with major depression and healthy controls for plasma/serum levels of Th17 cells and their canonical cytokines (interleukin-17A [IL-17A], IL-22, granulocyte macrophage colony stimulating factor [GM-CSF]). We also compared counts of Th1, Th2 and Th9 cells between depressed/non-depressed patients and their respective canonical cytokines. We performed random-effects meta-analysis of the standardised mean difference (SMD) in immune measures between groups. Risk of bias was assessed using the Newcastle-Ottawa scale. Of 3154 studies screened, 36 studies were included in meta-analysis. Patients with depression had elevated IL-17A compared to controls (SMD = 0.80 [95% CI 0.03 to 1.58], p = 0.042), an association moderated by antidepressant use (Z = 2.12, p = 0.034). Patients with depression had elevated GM-CSF (SMD = 0.54 [95% CI 0.16 to 0.91], p = 0.0047), and a trend towards higher Th17 counts (SMD = 0.44 [- 0.01 to 0.88], p = 0.052). Whilst the Th2-associated cytokine IL-5 was elevated in depression (SMD = 0.36 [95% CI 0.05 to 0.66], p = 0.02), Th2 cell counts (p = 0.97), Th1 cell counts (p = 0.17) and interferon-γ (p = 0.22) were not. Data for Th9 cells, IL-9 and IL-22 were insufficient for meta-analysis. Respectively, 22, 25 and 5 studies were good, fair and poor in quality. Patients with major depression show peripheral over-activation of the IL-23/Th17 axis. Future interventional studies should test whether this is a modifiable target for depression.

Immunotherapy for depression: Recent insights and future targets

Depression stands as a prominent contributor to global disability, entailing an elevated risk of suicide. Substantial evidence supports the notion that immune dysregulation may play a role in the development of depression and impede responses to antidepressant treatments. Immune dysregulation may cause depression in susceptible individuals through raising inflammatory responses. Differences in immune cell types and the release of pro-inflammatory mediators are observed in the blood and cerebrospinal fluid of patients with major depressive disorder, which is associated with neuroimmune dysfunction. Therefore, the interaction of peripheral and central immune targets in depression needs to be understood. Urgent attention is required for the development of innovative therapeutics directed at modulating immune responses for the treatment of depression. This review delineates the immune mechanisms involved in the pathogenesis of depression, assesses the therapeutic potential of immune system targeting for depression treatment, and deliberates on the merits and constraints of employing immunotherapy in the management of depression.

Neurological and metabolic related pathophysiologies and treatment of comorbid diabetes with depression

BACKGROUND

The comorbidity between diabetes mellitus and depression was revealed, and diabetes mellitus increased the prevalence of depressive disorder, which ranked 13th in the leading causes of disability-adjusted life-years. Insulin resistance, which is common in diabetes mellitus, has increased the risk of depressive symptoms in both humans and animals. However, the mechanisms behind the comorbidity are multi-factorial and complicated. There is still no causal chain to explain the comorbidity exactly. Moreover, Selective serotonin reuptake inhibitors, insulin and metformin, which are recommended for treating diabetes mellitus-induced depression, were found to be a risk factor in some complications of diabetes.

AIMS

Given these problems, many researchers made remarkable efforts to analyze diabetes complicating depression from different aspects, including insulin resistance, stress and Hypothalamic-Pituitary-Adrenal axis, neurological system, oxidative stress, and inflammation. Drug therapy, such as Hydrogen Sulfide, Cannabidiol, Ascorbic Acid and Hesperidin, are conducive to alleviating diabetes mellitus and depression. Here, we reviewed the exact pathophysiology underlying the comorbidity between depressive disorder and diabetes mellitus and drug therapy.

METHODS

The review refers to the available literature in PubMed and Web of Science, searching critical terms related to diabetes mellitus, depression and drug therapy.

RESULTS

In this review, we found that brain structure and function, neurogenesis, brain-derived neurotrophic factor and glucose and lipid metabolism were involved in the pathophysiology of the comorbidity. Obesity might lead to diabetes mellitus and depression through reduced adiponectin and increased leptin and resistin. In addition, drug therapy displayed in this review could expand the region of potential therapy.

CONCLUSIONS

The review summarizes the mechanisms underlying the comorbidity. It also overviews drug therapy with anti-diabetic and anti-depressant effects.

Circulating T-cell subsets discrepancy between bipolar disorder and major depressive disorder during mood episodes: A naturalistic, retrospective study of 1015 cases

AIMS

We aimed to investigate whether peripheral T-cell subsets could be a biomarker to distinguish major depressive disorder (MDD) and bipolar disorder (BD).

METHODS

Medical records of hospitalized patients in the Department of Psychiatry, the First Affiliated Hospital, Zhejiang University School of Medicine, from January 2015 to September 2020 with a discharge diagnosis of MDD or BD were reviewed. Patients who underwent peripheral blood examination of T-cell subtype proportions, including CD3+, CD4+, CD8+ T-cell, and natural killer (NK) cells, were enrolled. The Chi-square test, t-test, or one-way analysis of variance were used to analyze group differences. Demographic profiles and T-cell data were used to construct a random forest classifier-based diagnostic model.

RESULTS

Totally, 98 cases of BD mania, 459 cases of BD depression (BD-D), and 458 cases of MDD were included. There were significant differences in the proportions of CD3+, CD4+, CD8+ T-cell, and NK cells among the three groups. Compared with MDD, the BD-D group showed higher CD8+ but lower CD4+ T-cell and a significantly lower ratio of CD4+ and CD8+ proportions. The random forest model achieved an area under the curve of 0.77 (95% confidence interval: 0.71-0.83) to distinguish BD-D from MDD patients.

CONCLUSION

These findings imply that BD and MDD patients may harbor different T-cell inflammatory patterns, which could be a potential diagnostic biomarker for mood disorders.

Understanding the Biological Relationship between Migraine and Depression

Migraine is a highly prevalent neurological disorder. Among the risk factors identified, psychiatric comorbidities, such as depression, seem to play an important role in its onset and clinical course. Patients with migraine are 2.5 times more likely to develop a depressive disorder; this risk becomes even higher in patients suffering from chronic migraine or migraine with aura. This relationship is bidirectional, since depression also predicts an earlier/worse onset of migraine, increasing the risk of migraine chronicity and, consequently, requiring a higher healthcare expenditure compared to migraine alone. All these data suggest that migraine and depression may share overlapping biological mechanisms. Herein, this review explores this topic in further detail: firstly, by introducing the common epidemiological and risk factors for this comorbidity; secondly, by focusing on providing the cumulative evidence of common biological aspects, with a particular emphasis on the serotoninergic system, neuropeptides such as calcitonin-gene-related peptide (CGRP), pituitary adenylate cyclase-activating polypeptide (PACAP), substance P, neuropeptide Y and orexins, sexual hormones, and the immune system; lastly, by remarking on the future challenges required to elucidate the etiopathological mechanisms of migraine and depression and providing updated information regarding new key targets for the pharmacological treatment of these clinical entities.

Zinc Supplementation and an Improved Quality of Life in Patients with Autoimmune Hepatitis

Objecive Patients with autoimmune hepatitis (AIH) reportedly have an impaired quality of life (QOL), mainly due to depression, even during remission. In addition, hypozincaemia has been demonstrated in patients with chronic liver disease, including AIH, and is known to be related to depression. Corticosteroids are known to cause mental instability. We therefore investigated the longitudinal association between zinc supplementation and changes in the mental status among AIH patients treated with corticosteroids. Materials This study enrolled 26 patients with serological remission of AIH routinely treated at our facility after excluding 15 patients who either discontinued polaprezinc (150 mg/day) within 24 months or interrupted treatment. Two questionnaires, the Chronic Liver Disease Questionnaire (CLDQ) and SF-36, were adopted to evaluate the QOL before and after zinc supplementation. Results Serum zinc levels were significantly elevated after zinc supplementation (p<0.0001). The CLDQ worry subscale significantly improved after zinc supplementation (p=0.017), but none of the SF-36 subscales was affected. Multivariate analyses demonstrated that daily prednisolone dosing was inversely related to both the CLDQ worry domain score (p=0.036) and the SF-36 mental health component (p=0.031). There was a significant negative correlation between the changes in the daily steroid dose and the CLDQ worry domain scores before and after zinc supplementation (p=0.006). No serious adverse events occurred during the observation period. Conclusion Zinc supplementation safely and efficiently improved mental impairment, possibly caused by continuous treatment with corticosteroids, in patients with AIH.

Inflammatory markers in persons with clinically-significant depression, anxiety or PTSD: A systematic review and meta-analysis

BACKGROUND

Depression, anxiety and PTSD appear to be risk factors for dementia, but it is unclear whether they are causal or prodromal. The inflammatory-mediated neurodegeneration hypothesis suggests a causal link, proposing that mental illness is associated with an inflammatory response which, in turn, triggers neurodegenerative changes that lead to dementia. Existing meta-analyses have yet to examine inflammatory markers in depression, anxiety or PTSD with the view to exploring the inflammatory-mediated neurodegeneration hypothesis. The current meta-analysis therefore examined whether: a) depression, anxiety and PTSD are individually associated with inflammation, independently of comorbid mental illnesses and physical health problems with known inflammatory responses, and b) there are any similarities in the inflammatory profiles of these disorders in order to provide a basis for exploring inflammation in people with dementia who have a history of clinically-significant anxiety, depression or PTSD.

METHODS

PubMed, EMBASE, PsycINFO and CINAHL searches identified 64 eligible studies.

RESULTS

Depression is associated with an inflammatory response, with tentative evidence to suggest anxiety and PTSD are also associated with inflammation. However, the specific response may differ across these disorders.

LIMITATIONS

The data for anxiety, PTSD and multiple inflammatory markers were limited.

CONCLUSIONS

Depression, anxiety, and PTSD each appear to be associated with an inflammatory response in persons who do not have comorbid mental or physical health problems that are known to be associated with inflammation. Whether this inflammatory response underlies the increased risk of dementia in persons with a history of depression and anxiety, and possibly PTSD, remains to be determined.

Th17 Cells, Glucocorticoid Resistance, and Depression

Depression is a severe mental disorder that disrupts mood and social behavior and is one of the most common neuropsychological symptoms of other somatic diseases. During the study of the disease, a number of theories were put forward (monoamine, inflammatory, vascular theories, etc.), but none of those theories fully explain the pathogenesis of the disease. Steroid resistance is a characteristic feature of depression and can affect not only brain cells but also immune cells. T-helper cells 17 type (Th17) are known for their resistance to the inhibitory effects of glucocorticoids. Unlike the inhibitory effect on other subpopulations of T-helper cells, glucocorticoids can enhance the differentiation of Th17 lymphocytes, their migration to the inflammation, and the production of IL-17A, IL-21, and IL-23 in GC-resistant disease. According to the latest data, in depression, especially the treatment-resistant type, the number of Th17 cells in the blood and the production of IL-17A is increased, which correlates with the severity of the disease. However, there is still a significant gap in knowledge regarding the exact mechanisms by which Th17 cells can influence neuroinflammation in depression. In this review, we discuss the mutual effect of glucocorticoid resistance and Th17 lymphocytes on the pathogenesis of depression.

Treg cell: Critical role of regulatory T-cells in depression

Depression is a highly prevalent disorder of the central nervous system. The neuropsychiatric symptoms of clinical depression are persistent and include fatigue, anorexia, weight loss, altered sleep patterns, hyperalgesia, melancholia, anxiety, and impaired social behaviours. Mounting evidences suggest that neuroinflammation triggers dysregulated cellular immunity and increases susceptibility to psychiatric diseases. Neuroimmune responses have transformed the clinical approach to depression because of their roles in its pathophysiology and their therapeutic potential. In particular, activated regulatory T (Treg) cells play an increasingly evident role in the inflammatory immune response. In this review, we summarized the available data and discussed in depth the fundamental roles of Tregs in the pathogenesis of depression, as well as the clinical therapeutic potential of Tregs. We aimed to provide recent information regarding the potential of Tregs as immune-modulating biologics for the treatment and prevention of long-term neuropsychiatric symptoms of depression.

Inflammation in the pathogenesis of depression: a disorder of neuroimmune origin

There are several hypotheses concerning the underlying pathophysiological mechanisms of major depression, which centre largely around adaptive changes in neuronal transmission and plasticity, neurogenesis, and circuit and regional connectivity. The immune and endocrine systems are commonly implicated in driving these changes. An intricate interaction of stress hormones, innate immune cells and the actions of soluble mediators of immunity within the nervous system is described as being associated with the symptoms of depression. Bridging endocrine and immune processes to neurotransmission and signalling within key cortical and limbic brain circuits are critical to understanding depression as a disorder of neuroimmune origins. Emergent areas of research include a growing recognition of the adaptive immune system, advances in neuroimaging techniques and mechanistic insights gained from transgenic animals. Elucidation of glial-neuronal interactions is providing additional avenues into promising areas of research, the development of clinically relevant disease models and the discovery of novel therapies. This narrative review focuses on molecular and cellular mechanisms that are influenced by inflammation and stress. The aim of this review is to provide an overview of our current understanding of depression as a disorder of neuroimmune origin, focusing on neuroendocrine and neuroimmune dysregulation in depression pathophysiology. Advances in current understanding lie in pursuit of relevant biomarkers, as the potential of biomarker signatures to improve clinical outcomes is yet to be fully realised. Further investigations to expand biomarker panels including integration with neuroimaging, utilising individual symptoms to stratify patients into more homogenous subpopulations and targeting the immune system for new treatment approaches will help to address current unmet clinical need.

Chronic stress, neuroinflammation, and depression: an overview of pathophysiological mechanisms and emerging anti-inflammatories

In a subset of patients, chronic exposure to stress is an etiological risk factor for neuroinflammation and depression. Neuroinflammation affects up to 27% of patients with MDD and is associated with a more severe, chronic, and treatment-resistant trajectory. Inflammation is not unique to depression and has transdiagnostic effects suggesting a shared etiological risk factor underlying psychopathologies and metabolic disorders. Research supports an association but not necessarily a causation with depression. Putative mechanisms link chronic stress to dysregulation of the HPA axis and immune cell glucocorticoid resistance resulting in hyperactivation of the peripheral immune system. The chronic extracellular release of DAMPs and immune cell DAMP-PRR signaling creates a feed forward loop that accelerates peripheral and central inflammation. Higher plasma levels of inflammatory cytokines, most consistently interleukin IL-1β, IL-6, and TNF-α, are correlated with greater depressive symptomatology. Cytokines sensitize the HPA axis, disrupt the negative feedback loop, and further propagate inflammatory reactions. Peripheral inflammation exacerbates central inflammation (neuroinflammation) through several mechanisms including disruption of the blood-brain barrier, immune cellular trafficking, and activation of glial cells. Activated glial cells release cytokines, chemokines, and reactive oxygen and nitrogen species into the extra-synaptic space dysregulating neurotransmitter systems, imbalancing the excitatory to inhibitory ratio, and disrupting neural circuitry plasticity and adaptation. In particular, microglial activation and toxicity plays a central role in the pathophysiology of neuroinflammation. Magnetic resonance imaging (MRI) studies most consistently show reduced hippocampal volumes. Neural circuitry dysfunction such as hypoactivation between the ventral striatum and the ventromedial prefrontal cortex underlies the melancholic phenotype of depression. Chronic administration of monoamine-based antidepressants counters the inflammatory response, but with a delayed therapeutic onset. Therapeutics targeting cell mediated immunity, generalized and specific inflammatory signaling pathways, and nitro-oxidative stress have enormous potential to advance the treatment landscape. Future clinical trials will need to include immune system perturbations as biomarker outcome measures to facilitate novel antidepressant development. In this overview, we explore the inflammatory correlates of depression and elucidate pathomechanisms to facilitate the development of novel biomarkers and therapeutics.

Peripheral blood cellular immunophenotype in depression: a systematic review and meta-analysis

INTRODUCTION

Meta-analyses implicate immune dysfunction in depression confirming increased levels of circulating immune proteins (e.g., cytokines) in depression cases compared to controls. White blood cells (WBC) both produce and are influenced by cytokines, and play key roles in orchestrating innate and adaptive immune responses, but their role in depression remains unclear. Therefore, a systematic review of studies of various WBC subsets in depression is required for a greater understanding of the nature of immune dysfunction in this illness.

METHODS

We searched PubMed and PsycINFO databases (inception to 5th April 2022) and conducted a systematic review and meta-analysis of identified studies comparing absolute count and/or relative percentage of flow cytometry-derived WBC subsets between depression cases and controls. Selected studies were quality assessed. Random-effect meta-analysis was performed.

RESULTS

Thirty-three studies were included and 27 studies (n = 2277) were meta-analysed. We report an increase in mean absolute counts of WBC (seven studies; standardised mean difference [SMD] = 1.07; 95% CI, 0.61-1.53; P < 0.01; I2 = 64%), granulocytes (two studies; SMD = 2.07; 95% CI, 1.45-2.68; P < 0.01; I2 = 0%), neutrophils (four studies; SMD = 0.91; 95% CI, 0.23-1.58; P < 0.01; I2 = 82%), monocytes (seven studies; SMD = 0.60; 95% CI, 0.19-1.01; P < 0.01; I2 = 66%), CD4+ helper T cells (11 studies; SMD = 0.30; 95% CI, 0.15-0.45; P < 0.01; I2 = 0%), natural killer cells (11 studies; SMD = 1.23; 95% CI, 0.38-2.08; P < 0.01; I2 = 95%), B cells (10 studies; SMD = 0.30; 95% CI, 0.03-0.57; P = 0.03; I2 = 56%), and activated T cells (eight studies; SMD = 0.45; 95% CI, 0.24-0.66; P < 0.01; I2 = 0%) in depression, compared to controls. Fewer studies reported relative percentage, indicating increased neutrophils and decreased total lymphocytes, Th1, and Th2 cells in depression.

CONCLUSIONS

Depression is characterised by widespread alterations in circulating myeloid and lymphoid cells, consistent with dysfunction in both innate and adaptive immunity. Immune cells could be useful biomarkers for illness subtyping and patient stratification in future immunotherapy trials of depression, along with cytokines, other biomarkers, and clinical measures.

The effect of chronic stress on behaviors, inflammation and lymphocyte subtypes in male and female rats

Excessively released proinflammatory mediators from activated macrophages and lymphocytes may contribute to the etiology of depression. However, the relationship between lymphocytes and depression is not fully understood. Although women have higher depression risk than men, sex/gender differences in psychoneuroimmunological mechanisms are still unclear. To explore these two questions, chronic unpredictable mild stress (CUMS) was used to evaluate the changes in behaviors, inflammation and lymphocyte subtypes in adult male and female Wistar rats. Results show that CUMS increased anhedonia and anxiety-like behaviors, along with increased serum corticosterone, hippocampal pro-inflammatory factors, CD11b, IFN-γ, IL-6 and IL-17, but decreased CD4, CD25, CD4/CD8 ratio, GFAP, 5-hydroxytryptamine (5-HT) and NE concentrations, regardless of sex. There was no positive correlation between sucrose preference and blood CD4/CD8 ratio, but a positive correlation between sucrose preference and spleen CD25, sucrose preference and neurotransmitters (NE and 5-HT), spleen CD25 and serum TGF-β1/IL-6 ratio were found, regardless of sex. Females presented higher basal locomotion, blood CD4, CD4/CD8 ratio, serum corticosteroid and IL-6 concentrations, but lower hippocampal norepinephrine (NE) than males. Although CUMS didn't induce significant sex differences, females presented more changes in CD4 and CD8 lymphocytes than male rats. CUMS caused abnormalities in corticosteroid, lymphocytes, cytokines and neurotransmitters, which might be the precursors for inducing depression-like behaviors in both sexes.

Regulatory T Cell Proportion and Phenotype Are Altered in Women Using Oral Contraception

Regulatory T (Treg) cells are a specialized CD4+ T cell subpopulation that are essential for immune homeostasis, immune tolerance, and protection against autoimmunity. There is evidence that sex-steroid hormones estrogen and progesterone modulate Treg cell abundance and phenotype in women. Since natural oscillations in these hormones are modified by hormonal contraceptives, we examined whether oral contraception (OC) use impacts Treg cells and related T cell populations. T cells were analyzed by multiparameter flow cytometry in peripheral blood collected across the menstrual cycle from healthy women either using OC or without hormonal contraception and from age-matched men. Compared to naturally cycling women, women using OC had fewer Treg cells and an altered Treg cell phenotype. Notably, Treg cells exhibiting a strongly suppressive phenotype, defined by high FOXP3, CD25, Helios, HLADR, CTLA4, and Ki67, comprised a lower proportion of total Treg cells, particularly in the early- and mid-cycle phases. The changes were moderate compared to more substantial differences in Treg cells between women and men, wherein women had fewer Treg cells-especially of the effector memory Treg cell subset-associated with more T helper type 1 (Th1) cells and CD8+ T cells and lower Treg:Th1 cell and Treg:CD8+ T cell ratios than men. These findings imply that OC can modulate the number and phenotype of peripheral blood Treg cells and raise the possibility that Treg cells contribute to the physiological changes and altered disease susceptibility linked with OC use.

Blood T-helper 17 cells and interleukin-17A correlate with the elevated risk of postpartum depression and anxiety

Background

T‐helper (Th) cells regulate inflammation and immunity, which is implicated in psychological disorders. The current study aimed to explore the clinical role of blood Th1, Th2, and Th17 cells and their main secreted cytokines in postpartum depression (PPD) and postpartum anxiety (PPA).

Methods

A total of 226 postpartum women were included. At 6 weeks postpartum, Edinburgh Postnatal Depression Scale (EPDS) and State Trait Anxiety Inventory 6 item version (STAI6) scores were assessed; meanwhile, blood Th1, Th2, and Th17 cells were detected by flow cytometry, serum interferon‐gamma (IFN‐γ), interleukin‐4 (IL‐4), and IL‐17A were detected by enzyme‐linked immunosorbent assay.

Results

The incidence of PPD and PPA were 24.3% and 27.9%, respectively. Th17 cells and IL‐17A were positively correlated with EPDS score and STAI6 score (all p < 0.001). Besides, Th17 cells (p < 0.001) and IL‐17A (p = 0.002) were increased in PPD cases vs. non‐PPD cases, and they were also elevated in PPA cases vs. non‐PPA cases (both p < 0.05). However, Th1 cells, Th2 cells, IFN‐γ, and IL‐4 were not linked with EPDS score or STAI6 score (all p > 0.05); besides, they did not vary in PPD cases vs. non‐PPD cases or in PPA cases vs. non‐PPA cases (all p > 0.05). Multivariate logistic regression model analysis showed that Th17 cells were independently associated with an elevated risk of PPD (odds ratio [OR] = 1.600, p = 0.001) and PPA (OR = 1.371, p = 0.022).

Conclusion

Blood Th17 cells and IL‐17A are positively linked with the risk of PPD and PPA, indicating which may be involved in the development of PPD and PPA.

Targeting the Adaptive Immune System in Depression: Focus on T Helper 17 Cells

There is a vital need to understand mechanisms contributing to susceptibility to depression to improve treatments for the 11% of Americans who currently suffer from this debilitating disease. The adaptive immune system, comprising T and B cells, has emerged as a potential contributor to depression, as demonstrated in the context of lymphopenic mice. Overall, patients with depression have reduced circulating T and regulatory B cells, "immunosuppressed" T cells, and alterations in the relative abundance of T cell subtypes. T helper (Th) cells have the capacity to differentiate to various lineages depending on the cytokine environment, antigen stimulation, and costimulation. Regulatory T cells are decreased, and the Th1/Th2 ratio and the Th17 cells are increased in patients with depression. Evidence for changes in each Th lineage has been reported to some extent in patients with depression. However, the evidence is strongest for the association of depression with changes in Th17 cells. Th17 cells produce the inflammatory cytokine interleukin (IL)-17A, and the discovery of Th17 cell involvement in depression evolved from the well established link that IL-6, which is required for Th17 cell differentiation, contributes to the onset, and possibly maintenance, of depression. One intriguing action of Th17 cells is their participation in the gut-brain axis to mediate stress responses. Although the mechanisms of action of Th17 cells in depression remain unclear, neutralization of IL-17A by anti-IL-17A antibodies, blocking stress-induced production, or release of gut Th17 cells represent feasible therapeutic approaches and might provide a new avenue to improve depression symptoms. SIGNIFICANCE STATEMENT: Th17 cells appear as a promising therapeutic target for depression, for which efficacious therapeutic options are limited. The use of neutralizing antibodies targeting Th17 cells has provided encouraging results in depressed patients with comorbid autoimmune diseases.

T cell responses in depressed mice induced by chronic unpredictable mild stress

BACKGROUND

The relationship between depression and adaptive immunity has gradually attracted increasing attentions. However, no consistent conclusions have been drawn about alterations in adaptive immunity in depression.

METHODS

Eight-week-old weight-matched male C57BL/6 mice were randomly divided into a chronic unpredictable mild stress (CUMS) model group and a control group, with twelve mice in each group. After 8-week CUMS modeling duration and depressive behavioral tests, T cell responses were evaluated at the cell, cytokine, and cell-specific transcription factor levels. Lymphocytes in the spleen were detected by flow cytometry; serum cytokines were assessed by enzyme-linked immunosorbent assays; expression levels of cytokines and cell-specific transcription factors in the hippocampus were determined by quantitative PCR.

RESULTS

CUMS exposure induced depression-like behaviors with decreased sucrose preference and longer immobility time in the tail suspension test and forced swim test. The CUMS group had a lower proportion of CD4+T cells than the control group. A decreased number of T helper 17 (Th17) cells in the spleen and down regulated serum interleukin (IL)-17 and hippocampal retinoid-related orphan receptor-γt levels were detected in the CUMS group. Depressed mice in the CUMS group showed increases in serum IL-1β and IL-6 and hippocampal IL-6 and IL-4 levels.

LIMITATION

The study was based on a mouse model. Further studies are needed to determine whether the results are applicable to patients with depression.

CONCLUSION

CUMS exposure can induce depression-like behaviors and decrease Th17 cell counts.

Translational evidence for the Inflammatory Response System (IRS)/Compensatory Immune Response System (CIRS) and neuroprogression theory of major depression

Major depressive disorder (MDD) is a common, severe and disabling neuropsychiatric disorder with a heterogenous etiology. Among the most widely recognized etiological models, immunopathogenesis is a predominant one. Numerous studies have demonstrated aberrant levels of inflammatory markers in the peripheral blood, cerebrospinal fluid (CSF) and brain of patients with MDD. Multiple studies including meta-analyses have reported increased peripheral levels of acute phase proteins, and pro-inflammatory cytokines, particularly IL-1β, TNF-α, and IL-6 in MDD. Postmortem brain studies similarly demonstrated upregulated expressions of these pro-inflammatory cytokines. This along with evidence of monocytic, lymphocytic and microglial activation, suggest an activated inflammatory response system (IRS) in MDD. A few studies show increased levels of anti-inflammatory cytokines or defective inflammatory pathways and a deficit in T cell maturation and responses in MDD patients. This suggests the presence of a Compensatory Immune Response System (CIRS), which can counterbalance the effects of IRS in major depression. More recently, simultaneously increased levels of both the pro-and anti-inflammatory cytokines are reported in the brain of MDD patients; this indicates activity of both the IRS and CIRS in MDD. The IRS and CIRS are the evolutionarily conserved and integral elements of an overarching system. The relevance of a dysregulated IRS-CIRS system in the neurobiological construct of MDD is just beginning to be understood. Speculation is rife that the disrupted IRS-CIRS elements might determine the onset, episodes, neuroprogressive processes, treatment response as well as recovery of patients with MDD. Notably, the signatures of an activated IRS-CIRS might emerge as potential biomarkers of MDD. Herein, an attempt has been made to highlight the biology and pathobiological relevance of IRS-CIRS activation in MDD and provide an insight into the role of these components in pharmacological therapy.

T helper cells in depression: central role of Th17 cells

Depression is one of the most common neuropsychiatric disorders in the world. While conventional pharmaceutical therapy targets monoaminergic pathway dysfunction, it has not been totally successful in terms of positive outcomes, remission, and preventing relapses. There is an increasing amount of evidence that neuroinflammation may play a significant part in the pathophysiology of depression. Among the key components of the neuroinflammatory pathways already known to be active are the T helper (Th) cells, especially Th17 cells. While various preclinical and clinical studies have reported increased levels of Th17 cells in both serum and brain tissue of laboratory model animals, contradictory results have argued against a pertinent role of Th17 cells in depression. Recent studies have also revealed a role for more pathogenic and inflammatory subsets of Th17 in depression, as well as IL-17A and Th17 cells in non-responsiveness to conventional antidepressant therapy. Despite recent advances, there is still a significant knowledge gap concerning the exact mechanism by which Th17 cells influence neuroinflammation in depression. This review first provides a short introduction to the major findings that led to the discovery of the role of Th cells in depression. The major subsets of Th cells known to be involved in neuroimmunology of depression, such as Th1, Th17, and T regulatory cells, are subsequently described, with an in-depth discussion on current knowledge about Th17 cells in depression.

Glycogen Synthase Kinase-3: A Focal Point for Advancing Pathogenic Inflammation in Depression

Increasing evidence indicates that the host immune response has a monumental role in the etiology of major depressive disorder (MDD), motivating the development of the inflammatory hypothesis of depression. Central to the involvement of chronic inflammation in MDD is a wide range of signaling deficits induced by the excessive secretion of pro-inflammatory cytokines and imbalanced T cell differentiation. Such signaling deficits include the glutamatergic, cholinergic, insulin, and neurotrophin systems, which work in concert to initiate and advance the neuropathology. Fundamental to the communication between such systems is the protein kinase glycogen synthase kinase-3 (GSK-3), a multifaceted protein critically linked to the etiology of MDD and an emerging target to treat pathogenic inflammation. Here, a consolidated overview of the widespread multi-system involvement of GSK-3 in contributing to the neuropathology of MDD will be discussed, with the feed-forward mechanistic links between all major neuronal signaling pathways highlighted.

The Architecture of Circulating Immune Cells Is Dysregulated in People Living With HIV on Long Term Antiretroviral Treatment and Relates With Markers of the HIV-1 Reservoir, Cytomegalovirus, and Microbial Translocation

Long-term changes in the immune system of successfully treated people living with HIV (PLHIV) remain incompletely understood. In this study, we assessed 108 white blood cell (WBC) populations in a cohort of 211 PLHIV on stable antiretroviral therapy and in 56 HIV-uninfected controls using flow cytometry. We show that marked differences exist in T cell maturation and differentiation between PLHIV and HIV-uninfected controls: PLHIV had reduced percentages of CD4+ T cells and naïve T cells and increased percentages of CD8+ T cells, effector T cells, and T helper 17 (Th17) cells, together with increased Th17/regulatory T cell (Treg) ratios. PLHIV also exhibited altered B cell maturation with reduced percentages of memory B cells and increased numbers of plasmablasts. Determinants of the T and B cell composition in PLHIV included host factors (age, sex, and smoking), markers of the HIV reservoir, and CMV serostatus. Moreover, higher circulating Th17 percentages were associated with higher plasma concentrations of interleukin (IL) 6, soluble CD14, the gut homing chemokine CCL20, and intestinal fatty acid binding protein (IFABP). The changes in circulating lymphocytes translated into functional changes with reduced interferon (IFN)- γ responses of peripheral blood mononuclear cells to stimulation with Candida albicans and Mycobacterium tuberculosis. In conclusion, this comprehensive analysis confirms the importance of persistent abnormalities in the number and function of circulating immune cells in PLHIV on stable treatment.

Th17 Cells in Depression: Are They Crucial for the Antidepressant Effect of Ketamine?

Background: Major depressive disorder is associated with inflammation and immune processes. Depressive symptoms correlate with inflammatory markers and alterations in the immune system including cytokine levels and immune cell function. Th17 cells are a T cell subset which exerts proinflammatory effects. Th17 cell accumulation and Th17/Treg imbalances have been reported to be critical in the pathophysiology of major depressive disorder and depressive-like behaviors in animal models. Th17 cells are thought to interfere with glutamate signaling, dopamine production, and other immune processes. Ketamine is a newly characterized antidepressant medication which has proved to be effective in rapidly reducing depressive symptoms. However, the mechanisms behind these antidepressant effects have not been fully elucidated.

Method: Literature about Th17 cells and their role in depression and the antidepressant effect of ketamine are reviewed, with the possible interaction networks discussed.

Result: The immune-modulating role of Th17 cells may participate in the antidepressant effect of ketamine.

Conclusion: As Th17 cells play multiple roles in depression, it is important to explore the mechanisms of action of ketamine on Th17 cells and Th17/Treg cell balance. This provides new perspectives for strengthening the antidepressant effect of ketamine while reducing its side effects and adverse reactions.

Expansion of CD4 T Lymphocytes Expressing Interleukin 17 and Tumor Necrosis Factor in Patients with Major Depressive Disorder

BACKGROUND

We have investigated the distribution of the Th1, Th2 and Th17 subsets in circulating CD4⁺ T lymphocytes and their naïve (T_N), effector (T_E), central (T_CM) and effector memory (T_EM) activation/differentiation stages in patients with major depressive disorder (MDD).

METHODS

Thirty MDD patients and 30 healthy controls were studied. The counts of circulating CD4⁺ T lymphocytes and their distribution on the T_N, T_E, T_CM and T_EM activation/differentiation stages were analyzed by polychromatic flow cytometry. The intracytoplasmic interferon gamma (IFNγ), interleukin (IL)-4, IL-17A and tumor necrosis factor alpha (TNF-alpha) and membrane CD28 expression were also measured. The serum IFNγ, IL-4, Il-17A and TNF-alpha were measured by Luminex, respectively.

RESULTS

MDD patients had normal counts of CD4⁺ T lymphocytes and of their T_N, T_CM and T_EM subsets but increased number and percentage of T_E CD4⁺ subset. CD4⁺ T lymphocytes had significantly enhanced percentage of cells that express IL-17 and TNF-alpha explained by the expansions found in the T_N, T_CM and, T_EM and T_CM, T_EM and T_E activation/differentiation stages, respectively. A selective increase in the percentages of T_CM and T_EM expressing IFNγ was also observed. We found a significant correlation between the percentages of CD4⁺ T lymphocytes expressing IFNγ and TNF-alpha in these patients. MDD patients showed increased serum levels of IL-17 and TNF-alpha, but normal IFNγ and IL-4 concentration.

LIMITATIONS

the cross-sectional nature of the study could be considered a limitation.

CONCLUSIONS

MDD patients have abnormal circulating CD4⁺ T lymphocytes with expansion of the IL-17 and TNF-alpha expressing cells as well as increased levels of circulating IL-17 and TNF-alpha.