Emerging tendency towards autoimmune process in major depressive patients: a novel insight from Th17 cells

The impact of stress on immune systems and its relevance to mental illness

Stress due to adverse and demanding conditions alters immune functions. How innate and adaptive immune systems respond to stress and affect neural processes remains unclear. Rodent studies have demonstrated crucial roles of stress-induced immune responses for depressive- and anxiety-like behaviors. In the periphery, stress evokes the mobilization of neutrophils and monocytes to the circulation via sympathetic nerves and glucocorticoids. These myeloid cells are thought to promote depressive- and anxiety-like behaviors by infiltrating the brain's perivascular space, releasing cytokines, and affecting vascular endothelial functions. In the brain, stress activates microglia via innate immune receptors TLR2/4. The activated microglia in the medial prefrontal cortex secrete cytokines and alter neuronal morphology and activity in their vicinity. In subcortical brain areas, prostaglandin (PG) E₂ released from the activated microglia attenuates the dopaminergic projection to the medial prefrontal cortex via PGE receptor EP1. These multiple actions of microglia promote depressive-like behavior in concert. These rodent findings may be translatable to depression that clinical studies have associated with brain and peripheral inflammations. Understanding causal relationships between immune and neural alterations under stress might be exploitable to develop inflammation-targeting therapeutics for mental illness.

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.

Highlighting Immune System and Stress in Major Depressive Disorder, Parkinson's, and Alzheimer's Diseases, with a Connection with Serotonin

There is recognition that both stress and immune responses are important factors in a variety of neurological disorders. Moreover, there is an important role of several neurotransmitters that connect these factors to several neurological diseases, with a special focus in this paper on serotonin. Accordingly, it is known that imbalances in stressors can promote a variety of neuropsychiatric or neurodegenerative pathologies. Here, we discuss some facts that link major depressive disorder, Alzheimer’s, and Parkinson’s to the stress and immune responses, as well as the connection between these responses and serotonergic signaling. These are important topics of investigation which may lead to new or better treatments, improving the life quality of patients that suffer from these conditions.

Depression and Obesity in Patients With Psoriasis and Psoriatic Arthritis: Is IL-17-Mediated Immune Dysregulation the Connecting Link?

Patients with psoriasis are frequently obese and experience anxiety or suffer from depressive disorders. The immunopathogenesis of psoriasis and indeed psoriatic arthritis is largely based on the pivotal role of IL-17/IL-23 axis, to an extent that currently monoclonal antibodies selectively inhibiting IL-17 or IL-23 are routinely used for the treatment of psoriatic diseases. Emerging data, demonstrating a decisive role for IL-17 and IL-17 producing cell subsets, such as Th17 in the induction and progression of obesity and depression has led authors to suggest that psoriatic disease, obesity and anxiety/depression may indeed be interconnected manifestation of a state of immunedysregulation, the linked being IL-17 and its related cells. We discuss this hypothetical link in depth taking into account the beneficial effects anti-IL17 and anti-IL-17 receptor inhibitors in treating psoriatic disease and the on-going debate as to whether these biologics may exert a direct or indirect effect in ameliorating concomitant obesity and depressive disorders, which are frequently noted in the same patient.

Psychologic Morbidity Among Psoriatic Arthritis Patients in Remission or With Low Disease Activity: A Comparison Between Biologic and Conventional Synthetic Disease-Modifying Antirheumatic Drugs

OBJECTIVE

The aim of this study was to compare the effect of biologic agents and conventional synthetic disease-modifying antirheumatic drugs (csDMARDs) on the psychologic status of patients with psoriatic arthritis (PsA) in remission or with low disease activity.

METHODS

This is a case-control study of PsA patients in remission or with low disease activity treated at a single-center combined rheumatologic-dermatologic clinic between 2015 and 2017. Patients were assigned to 2 comparison groups according to their treatment (1) biologic drugs and (2) csDMARDs therapy. Psoriatic arthritis disease activity was evaluated by disease activity score-28. Anxiety, somatization, and depression were evaluated by patient health questionnaires (PHQ): generalized anxiety disorder-7, PHQ-15, and PHQ-9, respectively. Disability was assessed by the health assessment questionnaire disability index (HAQ-DI).

RESULTS

Thirty PsA patients on biologic treatment (BT) and 14 PsA patients in csDMARDs were enrolled. No significant differences in disease duration and treatment duration between the 2 groups were found. Disease activity score-28 was significantly better in the BT group compared with the csDMARDs group (1.8 ± 0.4 vs 2.1 ± 0.4, respectively, p = 0.028). A nonsignificant tendency toward higher scores in psychologic questionnaires was seen among the non-BT group. Moderate to high correlations between all mental questionnaires and HAQ-DI were found in both groups (0.567 ≤ r ≤ 0.850, p < 0.05). Patients with mental disturbance (generalized anxiety disorder-7/PHQ-15/PHQ-9 ≥ 5) showed significant poorer performance in their HAQ-DI in comparison with patient without physiological comorbidities in both groups.

CONCLUSIONS

Tight disease control in PsA patients, achieved with BT, may offer an improvement in psychological outcomes in addition to relieving clinical symptoms.

[Correlation between Anxiety, Depression and Changes in Th17/Treg and Inflammatory Levels in Patients with Pulmonary Nodules]

BACKGROUND

The incidence of lung cancer is increasing annually. Clinicians pay special attention to lung tests during physical examinations. Due to the popularity of low-dose computed tomography, not only can lung cancer be diagnosed early, but physical examinations often reveal the presence of pulmonary nodules, an important health issue that cannot be ignored. Patients with pulmonary nodules are prone to adverse emotions such as anxiety and depression. Many studies have shown that patients with emotional disorders have immune system dysfunction and changes in inflammation levels. This study aimed to investigate the changes in anxiety, depression, the ratios of T helper cells 17 (Th17) and regulatory T cells (Tregs), and inflammation levels in patients with pulmonary nodules.

METHODS

A total of 143 subjects from The First Affiliated Hospital of Anhui Medical University were included from April 2019 to July 2019. All of the subjects were assessed with the Beck Anxiety Inventory (BAI) and the Beck Depression Inventory-II (BDI-II). Overall, 40 cases were healthy controls (HC) and 103 cases were patients with pulmonary nodules. The patients were divided into two groups according to the scale scores: 62 cases in a non-anxiety and non-depression (NAD) group and 41 cases in an anxiety and/or depression (AD) group. The percentage of Th17 and Tregs in the peripheral blood and inflammatory factors in the serum were detected. The absolute Th17 cell counts were calculated and the differences between the groups and correlations between these indicators were analyzed.

RESULTS

There were statistically significant differences in the percentage of Th17 cells, the absolute counts of Th17 and Th17/Treg cells, and the levels of interleukin-2 (IL-2), IL-6, and tumor necrosis factor-α (TNF-α) among three groups (all P<0.001). The AD group was higher than the HC and NAD groups (all P<0.05). There was no statistically significant difference between the HC and NAD groups (all P>0.05). The previously described indicators had no significant correlation with the severity of anxiety and depression (P>0.05). There were no significant differences in the percentage of Tregs or levels of IL-4 and IL-10 between the groups (all P>0.05). The proportion of anxiety and/or depression in female patients with pulmonary nodules was higher than that in males (P<0.05).

CONCLUSIONS

Patients with pulmonary nodules are prone to varying degrees of anxiety and depression, which leads to immune dysfunction and low-grade inflammation.

Dendritic Cells: Neglected Modulators of Peripheral Immune Responses and Neuroinflammation in Mood Disorders?

Affective disorders (AD) including major depressive disorder (MDD) and bipolar disorder (BD) are common mood disorders associated with increased disability and poor health outcomes. Altered immune responses characterized by increased serum levels of pro-inflammatory cytokines and neuroinflammation are common findings in patients with AD and in corresponding animal models. Dendritic cells (DCs) represent a heterogeneous population of myeloid cells that orchestrate innate and adaptive immune responses and self-tolerance. Upon sensing exogenous and endogenous danger signals, mature DCs secrete proinflammatory factors, acquire migratory and antigen presenting capacities and thus contribute to neuroinflammation in trauma, autoimmunity, and neurodegenerative diseases. However, little is known about the involvement of DCs in the pathogenesis of AD. In this review, we summarize the current knowledge on DCs in peripheral immune responses and neuroinflammation in MDD and BD. In addition, we consider the impact of DCs on neuroinflammation and behavior in animal models of AD. Finally, we will discuss therapeutic perspectives targeting DCs and their effector molecules in mood disorders.

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.

Brain-immune crosstalk in the treatment of major depressive disorder

A growing number of studies are pointing out the need for a conceptual shift from a brain-centered to a body-inclusive approach in mental health research. In this perspective, the link between the immune and the nervous system, which are deeply interconnected and continuously interacting, is one of the most important novel theoretical framework to investigate the biological bases of major depressive disorder and, more in general, mental illness. Indeed, depressed patients show high levels of inflammatory markers, administration of pro-inflammatory drugs triggers a depressive symptomatology and antidepressant efficacy is reduced by excessive immune system activation. A number of molecular and cellular mechanisms have been hypothesized to act as a link between the immune and brain function, thus representing potential pharmacologically targetable processes for the development of novel and effective therapeutic strategies. These include the modulation of the kynurenine pathway, the crosstalk between metabolic and inflammatory processes, the imbalance in acquired immune responses, in particular T cell responses, and the interplay between neural plasticity and immune system activation. In the personalized medicine approach, the assessment and regulation of these processes have the potential to lead, respectively, to novel diagnostic approaches for the prediction of treatment outcome according to the patient's immunological profile, and to improved efficacy of antidepressant compounds through immune modulation.

Analysis of cytokine levels, T regulatory cells and serotonin content in patients with depression

Alterations in peripheral serotonin concentrations and an imbalanced immune system have been reported in patients with depression. Cytokines and T regulatory (Treg) cells may play an important role in the development of depression. This study investigates the levels of cytokines and Treg cells, as well as the concentration of serotonin (5-HT) in the blood of 89 patients suffering from depression and 89 healthy participants between two acquisitions. We investigated the state of health before (T1) and after (T2) psychological and pharmacological therapy. Both cytokine (IL-6, IL-10, TNF-α, and INF-γ) and 5-HT levels in the blood were measured by enzyme-linked immunosorbent assays. The levels of CD4⁺ CD25⁺ Treg cells were determined by flow cytometric analysis. Patients with depression showed significantly higher serum levels of IL-6 and INF-γ, no altered serum levels of IL-10 and TNF-α, and decreased platelet and serum 5-HT levels compared with healthy participants at the first acquisition. In addition, the symptoms of depression and anxiety, the TNF-α level, and the amount of CD4⁺ CD25⁺ cells in the blood were decreased from the first to the second acquisition. Further, a correlation between IL-6 and platelet 5-HT has been observed in patients. An imbalance of the immune system in patients with depression and an association of the serotonergic system and cytokines were observed. These results indicate that the development of depression might be related to several interacting proteins, including cytokines and 5-HT, and the treatment affects imbalances of these factors.

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.

The Role of Hypothalamic Inflammation in Diet-Induced Obesity and Its Association with Cognitive and Mood Disorders

Obesity is often associated with cognitive and mood disorders. Recent evidence suggests that obesity may cause hypothalamic inflammation. Our aim was to investigate the hypothesis that there is a causal link between obesity-induced hypothalamic inflammation and cognitive and mood disorders. Inflammation may influence hypothalamic inter-connections with regions important for cognition and mood, while it may cause dysregulation of the Hypothalamic-Pituitary-Adrenal (HPA) axis and influence monoaminergic systems. Exercise, healthy diet, and glucagon-like peptide receptor agonists, which can reduce hypothalamic inflammation in obese models, could improve the deleterious effects on cognition and mood.

Dysregulation of the gut-brain-skin axis and key overlapping inflammatory and immune mechanisms of psoriasis and depression

The occurrence, progression and recurrence of psoriasis are thought to be related to mood and psychological disorders such as depression. Psoriasis can lead to depression, and depression, in turn, exacerbates psoriasis. No specific mechanism can explain the association between psoriasis and depression. The gut-brain-skin axis has been used to explain correlations among the gut microbiota, emotional states and systemic and skin inflammation, and this axis may be associated with overlapping mechanisms between psoriasis and depression. Therefore, in the context of the gut-brain-skin axis, we systematically summarized and comparatively analysed the inflammatory and immune mechanisms of psoriasis and depression and illustrated the dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and the gut microbiota. This review provides a theoretical basis and new targets for the treatment of psoriasis and depression.

Inflammatory versus Anti-inflammatory Profiles in Major Depressive Disorders-The Role of IL-17, IL-21, IL-23, IL-35 and Foxp3

Background: The authors of this research study intended to verify whether there are any changes in gene expression in depressed patients without coexisting inflammatory diseases for selected immune-inflammatory factors that are particularly important in autoimmune disease pathogenesis (IL-17, IL-21, IL-23, IL-35, Foxp3). Methods: The study was carried out on a group of 190 patients with depression and 100 healthy volunteers. The severity of depressive symptoms was assessed using the Hamilton Depression Scale. RT-PCR was used to evaluate mRNA expression and ELISA was used to measure protein expression of these genes. Results: The level of gene expression for IL-17, IL-21, IL-23, and IL-35 was substantially higher in the group of patients with depression compared to the control group. The mean mRNA expression of Foxp3 was considerably reduced in patients suffering from depressive disorders. There was a statistically significant correlation between the number of hospitalizations and the expression of specific inflammatory factors. Conclusions: Expression of specific inflammatory genes may be a factor in the etiopathogenesis of depressive disorders. The duration of the disease seems to be more important for the expression of the genes in question than the severity of depression. These cytokines may affect the metabolism of neurotransmitters and neuroendocrine functions in the brain as well as be a marker and a new potential therapeutic target for recurrent depressive disorders.

Interleukin-17 induced by cumulative mild stress promoted depression-like behaviors in young adult mice

The number of young adult patients with major depression, one of the most common mental disorders, is gradually increasing in modern society. Stressful experiences in early life are considered one of the risk factors for chronic depressive symptoms, along with an abnormal inflammatory response in later life. Although increased inflammatory activity has been identified in patients with depression, the cause of long-lasting depressive states is still unclear. To identify the effects of cumulative mild stress in brain development periods, we generated a young adult depression mouse model exposed to cumulative mild stress (CPMS; cumulative mild prenatal stress, mild maternal separation, and mild social defeat) to mimic early life adversities. CPMS mice exhibited more long-lasting anxiety and depression-like behaviors than groups exposed to single or double combinations of mild stress in young adult age. Using the molecular works, we found that inflammatory cytokines, especially interleukin (IL)-17, upregulated microglial activation in the hippocampus, amygdala, and prefrontal cortex of CPMS mice. In the brains of CPMS mice, we also identified changes in the T helper (Th)-17 cell population as well as differentiation. Finally, anti-IL-17 treatment rescued anxiety and depression-like behavior in CPMS mice. In conclusion, we found that cumulative mild stress promoted long-lasting depressive symptoms in CPMS mice through the upregulation of IL-17. We suggest that the CPMS model may be useful to study young adult depression and expect that IL-17 may be an important therapeutic target for depression in young adults.

Interleukin-1 Beta in Peripheral Blood Mononuclear Cell Lysates as a Longitudinal Biomarker of Response to Antidepressants: A Pilot Study

Interleukin-1 beta (IL1β) is primarily produced by monocytes in the periphery and the brain. Yet, IL1β protein levels have to date been investigated in major depressive disorder (MDD) and antidepressant response using either plasma or serum assays although with contradictory results, while mononuclear cell assays are lacking despite their extensive use in other contexts. In this pilot study, we comparatively assessed IL1β in mononuclear lysates and plasma in depressed MDD patients over treatment and healthy controls (HC). We recruited 31 consecutive adult MDD inpatients and 25 HC matched on age, sex, and BMI. Twenty-six patients completed an 8-week follow-up under treatment. IL1β was measured in both lysates and plasma in patients at baseline (T0) and at study end (T1) as well as in HC. We calculated ΔIL1β(%) for both lysates and plasma as IL1β percent changes from T0 to T1. Seventeen patients (65.4% of completers) were responders at T1 and had lower baseline BMI than non-responders (p = 0.029). Baseline IL1β from either plasma or lysates could not efficiently discriminate between depressed patients and HC, or between responders and non-responders. However, the two response groups displayed contrasting IL1β trajectories in lysates but not in plasma assays (response group by time interactions, p = 0.005 and 0.96, respectively). ΔIL1β(%) in lysates predicted response (p = 0.025, AUC = 0.81; accuracy = 84.6%) outperforming ΔIL1β(%) in plasma (p = 0.77, AUC=0.52) and was robust to adjusting for BMI. In conclusion, ΔIL1β(%) in mononuclear lysates may be a longitudinal biomarker of antidepressant response, potentially helpful in avoiding untimely switching of antidepressants, thereby warranting further investigation.

Neuroinflammation in Mood Disorders: Role of Regulatory Immune Cells

Mood disorders are associated with chronic low-grade systemic (sterile) inflammation, with increased plasma levels of pro-inflammatory mediators targeting all tissues including the brain. Importantly, pro-inflammatory cytokines (ex., tumor-necrosis factor alpha [TNF-α], interleukin [IL]-6) regulate mood behavior and cognition by influencing neurotransmitter levels, activating stress-responsive endocrine axes, among other effects. However, the mechanisms underlying this enhanced inflammation are not well understood. There is increasing evidence indicating that impaired immunoregulatory mechanisms may play a role in this context. Patients with mood disorders (major depression [MDD] and bipolar disorder [BD]) have reduced numbers of major regulatory cells of both innate (natural killer regulatory cells and myeloid-derived suppressor cells [MDSCs]) and adaptive immune responses (CD4+CD25+FoxP3+, B regulatory cells). Dysfunctional regulatory immune cells might contribute to systemic and neuroinflammation observed in mood disorders via different mechanisms, such as: (i) failure to develop adequate stress-related responses, (ii) indirectly through microglial activation, (iii) lack of trophic support and pro-cognitive functions of T cells in the brain, and (iv) dysbiosis. In conclusion, maladaptive immunoregulatory mechanisms seem to be involved with both onset and progression of mood disorders. A deeper understanding of these mechanisms may lead to the development of new therapeutic strategies.

Is Interleukin 17 (IL-17) Expression A Common Point in the Pathogenesis of Depression and Obesity?

(1) Background: Activated immune-inflammatory pathways play an important role in the pathogenesis of depression and pathological obesity. Obesity might promote production of cytokine interleukin 17, which plays a significant role in neuro-immune reactions. The study aimed at assessing the relationship between Body Mass Index (BMI) and IL-17 expression, taking into account the clinical psychiatric variables in patients with depression. (2) Methods: A total of 125 participants took part in the study (95 depressed patients, 30 healthy controls). Data concerning the course of depressive disorders and BMI were collected. The severity of depressive symptoms was assessed using the Hamilton Depression Rating Scale (HDRS). Reverse transcription polymerase chain reaction (RT-PCR) was used to assess IL-17 gene expression at the mRNA levels, while enzyme-linked immunosorbent assay (ELISA) was used to assess IL-17 expression at the protein level. (3) Results: Patients with more hospitalizations showed significantly higher IL-17 mRNA expression levels and higher BMI. However, no correlation between BMI and IL-17 expression was found in depressed patients. (4) Conclusions: Our study revealed that BMI does not affect IL-17 expression in patients with depression. However, further studies should be conducted to evaluate the effects of IL-17 inhibition on adipose tissue and vice versa.

Good, better, best: clinical scenarios for the use of L-methylfolate in patients with MDD

Depression is among the most prevalent mental disorders worldwide, and a substantial proportion of patients do not respond adequately to standard antidepressants. Our understanding of the pathophysiology of depression is no longer limited to the chemical imbalance of neurotransmitters, but also involves the interplay of proinflammatory modulators in the central nervous system, as well as folate metabolism. Additional factors such as stress and metabolic disorders also may contribute. Multiple inflammatory, metabolic, and genetic markers have been identified and may provide critical information to help clinicians individualize treatments for patients to achieve optimal outcomes. Recent advancements in research have clarified underlying causes of depression and have led to possible new avenues for adjunctive treatment. Among these is L-methylfolate, a medical food that is thought to enhance synthesis of monoamines (serotonin, norepinephrine, and dopamine), suppress inflammation, and promote neural health. Clinical studies that assessed supplemental use of L-methylfolate in patients with usual care-resistant depression found that it resulted in improved outcomes. Patients with selective serotonin reuptake inhibitor-resistant depression, and particularly subgroups with biomarkers of inflammation or metabolic disorders or folate metabolism-related genetic polymorphisms (or ≥2 of these factors), had the best responses. Considering this, the goals of this review are to 1) highlight recent advances in the pathophysiology of major depressive disorder as it pertains to folate and associated biomarkers and 2) establish the profiles of patients with depression who could benefit most from supplemental use of L-methylfolate.

Pregnancy associated epigenetic markers of inflammation predict depression and anxiety symptoms in response to discrimination

Latina mothers, who have one of the highest fertility rates among ethnic groups in the United States (US), often experience discrimination. Psychosocial influences during pregnancy, such as discrimination stress, promotes inflammation. However, the role of epigenetic markers of inflammation as a mediator between, and predictor of, maternal discrimination stress and neuropsychiatric outcomes has not been extensively studied. The current study investigates the role of DNA methylation at FOXP3 Treg-cell-specific demethylated region (TSDR), as a marker of regulatory T (Treg) cells that are important negative regulators of inflammation, and the promoter of tumour necrosis factor-alpha (TNF-α) gene, an important pro-inflammatory cytokine, in relation to discrimination stress during pregnancy and depression and anxiety symptomatology.

A sample of 148 Latina women residing in the US (mean age 27.6 years) were assessed prenatally at 24–32 weeks’ gestation and 4–6 weeks postnatally for perceived discrimination exposure (Everyday Discrimination Scale, EDS), emotional distress (depression, anxiety, perinatal-specific depression), acculturation, and acculturative stress. DNA methylation levels at the FOXP3 and TNFα promoter regions from blood samples collected at the prenatal stage were assessed by bisulphite pyrosequencing.

Regression analyses showed that prenatal EDS associated with postnatal emotional distress, depression and anxiety symptoms only in those individuals with higher than mean levels of FOXP3 TSDR and TNFα promoter methylation; no such significant associations were found in those with lower than mean levels of methylation for either. We further found that these relationships were mediated by TNFα only in those with high FOXP3 TSDR methylation, implying that immunosuppression via TNFα promoter methylation buffers the impact of discrimination stress on postpartum symptomatology. These results indicate that epigenetic markers of immunosuppression and inflammation play an important role in resilience or sensitivity, respectively, to prenatal stress.

Identification of a Signaling Mechanism by Which the Microbiome Regulates Th17 Cell-Mediated Depressive-Like Behaviors in Mice

OBJECTIVE

Microbiota dysbiosis has been linked to major depressive disorder, but the mechanisms whereby the microbiota modulates mood remain poorly understood. The authors tested whether specific changes in the microbiome modulate depressive-like behaviors.

METHODS

Stools from learned helpless, non-learned helpless, and non-shocked mice were analyzed by V4 16S RNA sequencing to identify gut bacteria associated with learned helplessness and to quantify the level of the quorum-sensing molecule autoinducer-2 (AI-2). T cells were analyzed by flow cytometry, and serum amyloid proteins (SAA) were analyzed by quantitative real-time polymerase chain reaction. Fecal transfer approach and administration of oleic acid and AI-2 were used to determine the effects of the microbiome and quorum-sensing molecules on depressive-like behaviors.

RESULTS

Mice deficient in segmented filamentous bacteria (SFB) were resilient to the induction of depressive-like behavior, and were resensitized when SFB was reintroduced in the gut. SFB produces the quorum-sensing AI-2 and promotes the production of SAA1 and SAA2 by the host, which increases T helper 17 (Th17) cell production. Th17 cells were required to promote depressive-like behaviors by AI-2, as AI-2 administration did not promote susceptibility to depressive-like behaviors or SAA1 and SAA2 production in Th17-deficient mice after stress. Oleic acid, an AI-2 inhibitor, exhibited antidepressant properties, reducing depressive-like behavior, intestinal SAA1 and SAA2 production, and hippocampal Th17 cell accumulation. Stool samples from 10 people with current depressive symptoms and 10 matched healthy control subjects were analyzed as well. Patients with current major depressive disorder exhibited increased fecal interleukin 17A, SAA, and SFB levels.

CONCLUSIONS

The study results reveal a novel mechanism by which bacteria alter mood.

The Risk of Systemic Diseases in Those with Psoriasis and Psoriatic Arthritis: From Mechanisms to Clinic

Psoriasis and psoriatic arthritis (PsA) have been recently considered as chronic systemic inflammatory disorders. Over the past decades, enormous evidence indicates that patients with psoriasis and PsA have a higher risk of developing various comorbidities including cardiovascular disease, metabolic disease, cancers, infections, autoimmune disease, and psychiatric diseases. However, reported risks of some comorbidities in those with psoriasis and PsA are somewhat different according to the research design. Moreover, pathomechanisms underlying comorbidities of those with psoriasis and PsA remain poorly elucidated. The purpose of this review is to provide the most updated comprehensive view of the risk of systemic comorbidities in those with psoriasis and PsA. Molecular mechanisms associated with the development of various comorbidities in those with psoriasis and PsA are also reviewed based on recent laboratory and clinical investigations. Identifying the risk of systemic comorbidities and its associated pathomechanisms in those with psoriasis and PsA could provide a sufficient basis to use a multi-disciplinary approach for treating patients with psoriasis and PsA.

Diminished functional properties of T regulatory cells in major depressive disorder: The influence of selective serotonin reuptake inhibitor

The properties of CD4⁺CD25^hi T regulatory cells (Tregs), and interleukin (IL)-2 pathway were investigated in major depressive disorder (MDD) patients treated with or without selective serotonin reuptake inhibitor (SSRI). The frequencies of FOXP3 and pSTAT5 in peripheral Tregs were found to be diminished in untreated patients (SSRI^-) versus HCs (p < .001 for both), while their percentages were increased in treated patients (SSRI⁺) versus untreated patients (p < .001 and p = .04). The proliferation of CD4⁺ T cells was higher in SSRI^-MDD patients versus HCs (p = .03). The SSRI^-MDD patients showed a lower concentration of supernatant TGF-β than HCs (p = .001), while the production of TGF-β was enhanced in SSRI⁺MDD versus SSRI^-MDD patients (p = .003). The number of CD45RA-expressing Tregs, the expression of JAK1 and JAK3, and the levels of IL-2 and IL-10 were similar between the patients and HCs. The study results showed that untreated patients have an impaired IL-2 signaling pathway and defective Tregs, and SSRI treatment may improve the Tregs function.

Depression and suicidality: A link to premature T helper cell aging and increased Th17 cells

BACKGROUND

Previous research has demonstrated a strong link between immune system abnormalities and Major Depressive Disorder (MDD). High suicide risk is a major complication of MDD and has recently been linked to strong (neuro-)immune alterations, but little is known on the link between circulating immune cell composition and suicidal risk status.

METHODS

Here, we assessed percentages of circulating peripheral blood mononuclear cells with focus on T helper cell subsets (memory T helper cells, Th1, Th2, Th17 and T regulatory cells) in a large and well-matched cohort of 153 patients diagnosed with MDD and 153 age and sex matched controls. We explored the association of these cell populations with suicide risk while accounting for age, sex, BMI, depression severity and childhood trauma.

RESULTS

Patients with MDD had reduced percentages of NK cells, and higher percentages of B and T cells in line with current literature. Further exploration of T-cells revealed a robustly elevated number of memory T helper cells, regardless of age group. Patients at high risk for suicide had the highest memory T helper cells and additionally showed a robust increase of Th17 cells compared to other suicide risk groups.

CONCLUSIONS

The higher abundance of memory T helper cells points towards premature aging of the immune system in MDD patients, even during young adulthood. Patients at high risk for suicide show the clearest immune abnormalities and may represent a clinically relevant subtype of depression.

The Bidirectional Relationship of Depression and Inflammation: Double Trouble

Depression represents the number one cause of disability worldwide and is often fatal. Inflammatory processes have been implicated in the pathophysiology of depression. It is now well established that dysregulation of both the innate and adaptive immune systems occur in depressed patients and hinder favorable prognosis, including antidepressant responses. In this review, we describe how the immune system regulates mood and the potential causes of the dysregulated inflammatory responses in depressed patients. However, the proportion of never-treated major depressive disorder (MDD) patients who exhibit inflammation remains to be clarified, as the heterogeneity in inflammation findings may stem in part from examining MDD patients with varied interventions. Inflammation is likely a critical disease modifier, promoting susceptibility to depression. Controlling inflammation might provide an overall therapeutic benefit, regardless of whether it is secondary to early life trauma, a more acute stress response, microbiome alterations, a genetic diathesis, or a combination of these and other factors.

[Curcumin as an ajuvant treatment of depression: mechanisms of action and application prospects]

Curcumin, a natural compound found in the rhizomes of turmeric, has a pronounced anti-inflammatory activity. Rodent models of depression show that this activity is similar to the effect of antidepressants (AD). Experimental data indicate that this activity may be related to the effect of curcumin on the monoamine cycle, oxidative and nitrosative stress, neurogenesis, hypothalamic-pituitary-adrenal, and immune systems. A number of meta-analyzes indicate the effectiveness of the combined use of curcumin with antidepressants in the treatment of depression. The mechanism of action of curcumin, as well as the prospects for its further use are considered.

Blunted Expansion of Regulatory T Lymphocytes Is Associated With Increased Bacterial Translocation in Patients With Major Depressive Disorder

Background: Major Depressive Disorder (MDD) is associated with both proinflammatory and adaptive immune response abnormalities. Regulatory T lymphocytes (Tregs), a subtype of CD4+ T cells, are relevant for maintaining immune-inflammatory system homeostasis and control of inflammation such as the kind potentially induced by the interactions between the intestinal microbiome and gut mucosa. We investigated the Treg population and its distribution along their stages of differentiation/activation, as well as its function in MDD patients without concomitant diseases. We also studied the potential association between Treg alterations, intestinal barrier damage, and bacterial translocation. Methods: 30 MDD patients and 20 healthy controls were studied. The levels of circulating CD25FoxP3⁺ Tregs and their distribution on the naïve (T_N), effector (T_E), central (T_CM), and effector memory(T_EM) differentiation/activation stages were analyzed using polychromatic flow cytometry. Chemokine receptors (CCR) 2, 5, and 6, and the intracytoplasmic IL-10 expression by the Tregs were also analyzed. The serum IL-10 was measured using Luminex. The serum levels of zonulin and the intestinal fatty acid-binding protein (I-FABP), both markers of gut barrier function, and the LPS-binding protein (LBP), a marker of bacterial translocation, were measured using an enzyme-linked immunosorbent assay. Results: MDD patients had increased number of circulating Tregs cells with enhanced number of Tregs at the T_N, T_E, T_CM, and T_EM stages. The percentage of Tregs cells at T_N stage was significantly higher in MDD patients. The percentage of Tregs that expressed CCR2 and CCR6 was increased as well as those expressing IL-10. MDD patients had significantly increased levels of circulating I-FABP and LBP. MDD patients with high LBP levels had a significant reduction in the number of circulating Tregs compared to normal-LBP MDD patients. Conclusions: MDD patients showed an expansion of circulating Tregs and their CD25^highFoxP3⁺ and CD25^lowFoxP3⁺ subsets throughout the different stages of CD4+ T lymphocyte differentiation/activation. Tregs also showed an increased frequency of cells expressing CCR6 and CCR2. IL-10 Treg production was also enhanced in MDD patients that concurrently had increased serum IL-10 levels. However, this Treg expansion was blunted in MDD patients with gut barrier damage and increased bacterial translocation.

Interleukin-6 signaling pathway involved in major depressive disorder: selective serotonin reuptake inhibitor regulates IL-6 pathway

Background

Evidence indicates that pro-inflammatory Th17 and Th1 cells are involved in major depressive disorder (MDD) pathogenesis. Development of Th17 and Th1 are regulated by IL-6 and IFN-γ, respectively. In this study, the levels of IL-6 and IFN-γ, and mRNA expression of related signaling components and, Th17/Th1 transcription factors were investigated in MDD patients with/without selective serotonin reuptake inhibitor (SSRI) medication.

Materials and methods

Forty-six patients and 38 healthy controls (HCs) were recruited. Twenty patients were received the SSRI (sertraline 50–200 mg/day) for at least 1 year, and 26 patients were not received medication. Expression of IL-6R, IFN-γR, JAK1, JAK2, TYK2, STAT1, STAT3, T-bet and RORγt were assessed with Real-Time-PCR. Serum and supernatant levels of IL-6 and IFN-γ were determined using ELISA.

Results and discussion

The serum and supernatant levels of IL-6 were increased in patients without (SSRI−) compared with HCs, while its levels was reduced in SSRI+. Elevated expressions of IL-6R, STAT3 and RORγt were observed in SSRI− compared with HCs. Expressions of IL-6R, STAT3, RORγt and IFN-γR, were decreased in SSRI+ compared to SSRI− patients.

Conclusion

Increased IL-6 involved in MDD, and SSRI regulates IL-6 pathway and IL-6 production. MDD patients may benefit from IL-6/IL-6R targeted therapeutic intervention.

Alterations in the Levels of Growth Factors in Adolescents with Major Depressive Disorder: A Longitudinal Study during the Treatment with Fluoxetine

Major depressive disorder (MDD) has a prevalence of 5% in adolescents. Several studies have described the association between the inflammatory response and MDD, but little is known about the relationship between MDD and growth factors, such as IL-7, IL-9, IL-17A, VEGF, basic FGF, G-CSF, and GM-CSF. It must be appointed that there are scarce reports on growth factors in adolescents with MDD and even fewer with a clinical follow-up. In this work, we evaluated the levels of growth factors (IL-7, IL-9, IL-17A, VEGF, basic FGF, G-CSF, and GM-CSF) in MDD adolescents and the clinical follow-up during eight weeks of treatment with fluoxetine. Methods. All patients were diagnosed according to the DSM-IV-TR, and the severity of the symptoms was evaluated using the Hamilton Depression Rating Scale (HDRS). Growth factors IL-7, IL-9, IL-17A, VEGF, basic FGF, G-CSF, and GM-CSF were quantified by cytometric bead array using serum samples from 22 adolescents with MDD and 18 healthy volunteers. Results. All patients showed clinical improvement since the fourth week of pharmacological treatment according to the HDRS. Considerably higher levels of IL-7, IL-9, IL-17A, VEGF, basic FGF, G-CSF, and GM-CSF were detected in MDD adolescents as compared to healthy volunteers. A significant but temporal decrease was detected in basic FGF, G-CSF, and GM-CSF at week four of fluoxetine administration. Conclusions. To the best of our knowledge, this is the first report to show alterations in the levels of growth factors, such as IL-7, IL-9, IL-17A, VEGF, basic FGF, G-CSF, and GM-CSF in MDD adolescents during eight weeks of clinical follow-up. These disturbances might be involved in the physiopathology of MDD since such growth factors have been proven to participate in the neural development and correct functioning of the CNS; therefore, subtle alterations in it may contribute to MDD.

Systemic Inhibition of Soluble Tumor Necrosis Factor with XPro1595 Exacerbates a Post-Spinal Cord Injury Depressive Phenotype in Female Rats

Spinal cord injury (SCI) is associated with a three-fold risk of major depressive disorder compared with the general population. Current antidepressant therapy is often not as effective in this patient population, suggesting the need for a more efficacious therapeutic target. The goal of this study was to elucidate the role of inflammatory cytokine tumor necrosis factor (TNF) in the dorsal raphe nucleus (DRN, the principle source of serotonin to the brain) in the development and possible treatment of depression after SCI. A depressive phenotype following moderate T9 contusion was identified in adult female rats using a battery of behavioral tests (forced swim test, sucrose preference test, novel object recognition test, open field locomotion, and social exploration). Data revealed two clusters of injured rats (58%) that exhibit increased immobility in the forced swim test, indicating depressive phenotype or a melancholic-depressive phenotype with concomitant decrease in sucrose preference. ElevatedTNF levels in the DRN of these two clusters correlated with increased immobility in the forced swim test. We then tested the efficacy of soluble TNF inhibition with XPro1595 treatment to prevent the depressive phenotype after SCI. Subcutaneous (s.c.) delivery of XPro1595 caused an exacerbation of depressive phenotype, with all treated clusters exhibiting increased forced swim immobility compared with saline-treated non-depressed rats. Intracerebroventricular (i.c.v.) administration of the drug did not prevent or enhance the development of depression after injury. These results suggest a complex role for TNF-based neuroinflammation in SCI-induced depression that needs to be further explored, perhaps in conjunction with a broader targeting of additional post-SCI inflammatory cytokines.

Social Defeat Modulates T Helper Cell Percentages in Stress Susceptible and Resilient Mice

Altered adaptive immunity involving T lymphocytes has been found in depressed patients and in stress-induced depression-like behavior in animal models. Peripheral T cells play important roles in homeostasis and function of the central nervous system and thus modulate behavior. However, the T cell phenotype and function associated with susceptibility and resilience to depression remain largely unknown. Here, we characterized splenic T cells in susceptible and resilient mice after 10 days of social defeat stress (SDS). We found equally decreased T cell frequencies and comparably altered expression levels of genes associated with T helper (Th) cell function in resilient and susceptible mice. Interleukin (IL)-17 producing CD4⁺ and CD8⁺ T cell numbers in the spleen were significantly increased in susceptible mice. These animals further exhibited significantly reduced numbers of regulatory T cells (T_reg) and decreased gene expression levels of TGF-β. Mice with enhanced Th17 differentiation induced by conditional deletion of PPARγ in CD4⁺ cells (CD4-PPARγ^KO), an inhibitor of Th17 development, were equally susceptible to SDS when compared to CD4-PPARγ^WT controls. These data indicate that enhanced Th17 differentiation alone does not alter stress vulnerability. Thus, SDS promotes Th17 cell and suppresses T_reg cell differentiation predominantly in susceptible mice with yet unknown effects in immune responses after stress exposure.

Neuroimmune nexus of depression and dementia: Shared mechanisms and therapeutic targets

Dysfunctional immune activity is a physiological component of both Alzheimer's disease (AD) and major depressive disorder (MDD). The extent to which altered immune activity influences the development of their respective cognitive symptoms and neuropathologies remains under investigation. It is evident, however, that immune activity affects neuronal function and circuit integrity. In both disorders, alterations are present in similar immune networks and neuroendocrine signalling pathways, immune responses persist in overlapping neuroanatomical locations, and morphological and structural irregularities are noted in similar domains. Epidemiological studies have also linked the two disorders, and their genetic and environmental risk factors intersect along immune-activating pathways and can be synonymous with one another. While each of these disorders individually contains a large degree of heterogeneity, their shared immunological components may link distinct phenotypes within each disorder. This review will therefore highlight the shared immune pathways of AD and MDD, their overlapping neuroanatomical features, and previously applied, as well as novel, approaches to pharmacologically manipulate immune pathways, in each neurological condition. LINKED ARTICLES: This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc.

The role of Th17 cells in the pathophysiology of pregnancy and perinatal mood and anxiety disorders

T cells play a key role in adaptive immune responses, and shifts among T cell classes occur in normal pregnancy. There is evidence for the role of T_H17 cells and dysregulation of the T_H17/T_reg cell balance in morbidities and autoimmune diseases during pregnancy. Because T_H17 responses may play a role in depression and anxiety outside of pregnancy, we hypothesize that T_H17 responses and the balance of T_H17/T_reg activity may also contribute to the development of depression and anxiety during pregnancy. To explore this hypothesis, this review has three main aims: 1) to evaluate systematically the role of T_H17 cells and cytokines during pregnancy; 2) to compare changes in the ratio of T_H17/T_reg cells during pregnancy morbidities with the changes that occur in depression and anxiety outside of pregnancy; and 3) to provide a basis for further research on T_H17 cells in perinatal mood and anxiety disorders, with an eye toward the development of novel therapeutics. We also review the limited literature concerning perinatal mood and anxiety disorders, and hypothesize about the potential role of T_H17 cells in these illnesses. Understanding the pathophysiology of perinatal mood and anxiety disorders will aid development of novel therapeutics that address immunological mechanisms, in addition to the serotonin system, which are targetable molecules in treating depression and anxiety during pregnancy.

Psoriasis and suicidality: A review of the literature

Psoriasis is a chronic systemic inflammatory skin disease, which has been associated with an increased risk of numerous medical and psychiatric comorbidities, including suicidality. Suicidality, which can be divided into the categories of suicidal ideation, suicide attempt, and completed suicide, is highly prevalent in the psoriasis population, and multiple studies have been published on the subject of psoriasis and suicidal ideation and behavior (SIB), including two recent meta-analyses. However, the available literature is limited and inconsistent, and the association between the two remains incompletely understood. The present review aims to cohesively synthesize and summarize the available evidence, while making a clinically relevant distinction between the sub-categories of suicidality, by examining not only the epidemiology of the association but also the plausible molecular mechanisms and the potential influence of biologic therapies. Additionally, this review aims to critically examine and understand the potential contribution of depression in the psoriasis and suicidality relationship. This will allow us to better understand the complex and multi-faceted relationship between psoriasis and suicidality, to identify those who may be most at risk for SIB, to make evidence-based clinical decisions regarding treatment and management, and to more completely address the needs of psoriasis patients.

Elevated Levels of Serum IL-17A in Community-Dwelling Women with Higher Depressive Symptoms

Recent studies indicate that patients with depression have increased concentrations of serum pro-inflammatory cytokines. However, studies of IL-17 and studies on community-dwellers are few. The purpose of this study was to investigate serum cytokine levels, especially IL-17A, among subjects with high and low depressive symptoms of a general population. The participants comprised 20 female community-dwellers aged 40 years or older who contributed to a Shika study in Ishikawa, Japan. Ten participants who showed higher and ten who showed lower depressive symptoms among 208 females assessed by the Japanese version of the Centre for Epidemiologic Studies Depression Scale (CES-D) were selected for this study. Serum samples were analyzed for TNF-alpha, IL-6, IL-10, IL-12, and IL-17A using a multiplex Luminex analysis. For the comparison between the high and low depressive groups statistically, linear regression analyses were applied. The serum level of IL-17A was significantly higher among the high depressive participants (p < 0.05) even after controlling possible confounders, whereas there were no differences in TNF-alpha, IL-6, IL-10, or IL-12 between the high and low depressive groups. Our findings supported an association between serum IL-17A levels and depressive symptoms. Peripheral IL-17A immune response may be a preventive and treatment target for depression.

Distinct characteristics of hippocampal pathogenic TH17 cells in a mouse model of depression

Increasing evidence indicates that multiple actions of the immune system are closely intertwined with the development of depression and subsequent recovery processes. One of these interactions is substantial evidence that the TH17 subtype of CD4+ T cells promotes susceptibility to depression-like behaviors in mice. Comparing subtypes of CD4+ T cells, we found that administration of TH17 cells, but not TH1 cells or TREGS, promoted susceptibility to learned-helplessness depressive-like behavior and accumulated in the hippocampus of learned helpless mice. Adoptively transferred TH17 cells into Rag2-/- mice that are devoid of endogenous T cells increased susceptibility to learned helplessness, demonstrating that increased peripheral TH17 cells are capable of modulating depression-like behavior. Moreover, in wild-type mice, adoptively transferred TH17 cells accumulated in the hippocampus of learned-helpless mice and induced endogenous TH17 cell differentiation. Hippocampal TH17 cells from learned-helpless mice expressed markers of pathogenic TH17 cells (CCR6, IL-23R) and of follicular cells (CXCR5, PD-1), indicating that the hippocampal cells are TFH-17-like cells. Knockout of CCR6 blocked TH17 cells from promoting learned helplessness, which was associated with increased expression of PD-1 in CCR6-deficient TH17 cells. In summary, these results reinforce the conclusion that depression-like behaviors are selectively facilitated by TH17 cells, and revealed that these cells in the hippocampus of learned helpless mice display characteristics of TFH17-like cells, which may contribute to their pathogenic actions in promoting depression.

Involvement of Innate and Adaptive Immune Systems Alterations in the Pathophysiology and Treatment of Depression

Major depressive disorder (MDD) is a prevalent and debilitating disorder, often fatal. Treatment options are few and often do not provide immediate relief to the patients. The increasing involvement of inflammation in the pathology of MDD has provided new potential therapeutic avenues. Cytokine levels are elevated in the blood and cerebrospinal fluid of MDD patients whereas immune cells often exhibit an immunosuppressed phenotype in MDD patients. Blocking cytokine actions in patients exhibiting MDD show some antidepressant efficacy. However, the role of cytokines, and the immune response in MDD patients remain to be determined. We reviewed here the roles of the innate and adaptive immune systems in MDD, as well as potential mechanisms whereby the immune response might be regulated in MDD.

Elevated interleukin-17 and reduced testosterone in bipolar disorder. Relation with suicidal behaviour

Hormonal imbalance and inflammation are associated with bipolar disorder and suicidal behavior. The present study was designed to assess the levels of testosterone and interleukin-17 and their association with suicidal behavior in patients with bipolar disorder in remission. 41 bipolar disorder cases in remission and 41 age matched controls were enrolled in the study. Testosterone and interleukin-17 levels were assessed in both the groups. Interleukin-17 was significantly increased and testosterone was significantly reduced in bipolar disorder when compared with controls. IL-17 was negatively correlated with testosterone (r = -0.368, p = 0.018) and positively correlated with duration of disease (r = 0.382, p = 0.014) in bipolar disorder patients. Both didn't show any association with suicidal behavior. We conclude that testosterone is increased and interleukin-17 is reduced in bipolar disorder in remission and these were not associated with suicidal behavior in these patients.

Alterations of the Innate Immune System in Susceptibility and Resilience After Social Defeat Stress

Dysregulation of innate immune responses has frequently been reported in stress-associated psychiatric disorders such as major depression. In mice, enhanced circulating cytokine levels as well as altered innate immune cell numbers have been found after stress exposure. In addition, stress-induced recruitment of peripheral monocytes to the brain has been shown to promote anxiety-like behavior. However, it is yet unclear whether specific differences in the innate immune system are associated with stress susceptibility or resilience in mice. Utilizing chronic social defeat, a model of depression and stress vulnerability, we characterized peripheral and brain-invading myeloid cells in stress-susceptible and resilient animals. In all defeated animals, we found reduced percentages of CD11c⁺ dendritic cells (DCs) by flow cytometry in the spleen when compared to non-defeated controls. Exclusively in susceptible mice conventional DCs of the spleen showed up-regulated expression of MHC class II and co-stimulatory CD80 molecules pointing toward an enhanced maturation phenotype of these cells. Susceptible, but not resilient animals further exhibited an increase in inflammatory Ly6C^hi monocytes and higher numbers of spleen-derived CD11b⁺ cells that produced the proinflammatory cytokine tumor necrosis factor (TNF) upon lipopolysaccharide (LPS) stimulation. Increased percentages of peripheral CD45^hi CD11b⁺ cells immigrated into the brain of defeated mice, regardless of resilience or susceptibility. However, cellular infiltrates in the brain of susceptible mice contained higher percentages of CC chemokine receptor 2 (CCR2⁺) Ly6C^hi monocytes representing an inflammatory phenotype. Thus, we defined specific stress-related immune signatures involving conventional DCs and inflammatory Ly6C^hi monocytes in susceptible and resilient mice. Together, our findings suggest an impact of the innate immune system in vulnerability to stress-related disorders such as major depression.

T helper 17 cell/regulatory T-cell imbalance in hidradenitis suppurativa/acne inversa: the link to hair follicle dissection, obesity, smoking and autoimmune comorbidities

BACKGROUND

Disintegration of the infundibula of terminal hair follicles (HFs) in intertriginous skin areas exhibits the histological hallmark of hidradenitis suppurativa (HS)/acne inversa, featuring a dissecting terminal hair folliculitis. Elevated serum levels of interleukin (IL)-17 and local increase in the ratio of proinflammatory T helper (Th)17 cells and anti-inflammatory regulatory T cells (Tregs) have been reported. Perifollicular Tregs play a key role in HF stem cell homeostasis and infundibular integrity.

OBJECTIVES

In this review, we evaluate the Th17/Treg ratio in HS, its aggravating conditions and associated comorbidities. Furthermore, we intended to clarify whether drugs with reported beneficial effects in the treatment of HS readjust the deviated Th17/Treg axis.

METHODS

PubMed-listed, peer-reviewed original research articles characterizing Th17/Treg regulation in HS/acne inversa and associated comorbidities were selected for this review.

RESULTS

This review presents HS as a disease that exhibits an increased Th17/Treg ratio. Perifollicular deficiencies in Treg numbers or function may disturb HF stem cell homeostasis, initiating infundibular dissection of terminal HFs and perifollicular inflammation. The Th17/Treg imbalance is aggravated by obesity, smoking and decreased Notch signalling. In addition, HS-associated autoimmune diseases exhibit a disturbed Th17/Treg axis resulting in a Th17-dominant state. All drugs that have beneficial effects in the treatment of HS normalize the Th17/Treg ratio.

CONCLUSIONS

HS immunopathogenesis is closely related to deviations of the Th17/Treg balance, which may negatively affect Treg-controlled HF stem cell homeostasis and infundibular integrity. Pharmacological intervention should not only attenuate Th17/IL-17 signalling, but should also improve Treg function in order to stabilize HF stem cell homeostasis and infundibular integrity.

"Immune Gate" of Psychopathology-The Role of Gut Derived Immune Activation in Major Psychiatric Disorders

Interaction between the gastrointestinal tract (GI) and brain functions has recently become a topic of growing interest in psychiatric research. These multidirectional interactions take place in the so-called gut-brain axis or more precisely, the microbiota-gut-brain axis. The GI tract is the largest immune organ in the human body and is also the largest surface of contact with the external environment. Its functions and permeability are highly influenced by psychological stress, which are often a precipitating factor in the first episode, reoccurrence and/or deterioration of symptoms of psychiatric disorders. In recent literature there is growing evidence that increased intestinal permeability with subsequent immune activation has a major role in the pathophysiology of various psychiatric disorders. Numerous parameters measured in this context seem to be aftermaths of those mechanisms, yet at the same time they may be contributing factors for immune mediated psychopathology. For example, immune activation related to gut-derived bacterial lipopolysaccharides (LPS) or various food antigens and exorphins were reported in major depression, schizophrenia, bipolar disorder, alcoholism and autism. In this review the authors will summarize the evidence and roles of such parameters and their assessment in major psychiatric disorders.

Regulatory T Cells As Supporters of Psychoimmune Resilience: Toward Immunotherapy of Major Depressive Disorder

There is growing evidence that inflammation plays a role in major depressive disorder (MDD). As the main role of regulatory T cells (Tregs) is to control inflammation, this might denote a Treg insufficiency in MDD. However, neither a qualitative nor a quantitative defect of Tregs has been ascertained and no causality direction between inflammation and depression has been established. Here, after reviewing the evidence supporting a relation between Treg insufficiency and MDD, we conclude that a novel therapeutic approach based on Treg stimulation could be valuable in at least the subset of patients with inflammatory MDD. Low-dose interleukin-2 appears to be a good candidate as it is not only a safe stimulator of Tregs in humans but also an inhibitor of pro-inflammatory Th17 lymphocytes. Here, we discuss that a thorough immune investigation as well as immunotherapy will be heuristic for deciphering the pathophysiology of MDD.

TNFα disrupts blood brain barrier integrity to maintain prolonged depressive-like behavior in mice

Recovery from major depressive disorder is difficult, particularly in patients who are refractory to antidepressant treatments. To examine factors that regulate recovery, we developed a prolonged learned helplessness depression model in mice. After the induction of learned helplessness, mice were separated into groups that recovered or did not recover within 4 weeks. Comparisons were made between groups in hippocampal proteins, inflammatory cytokines, and blood brain barrier (BBB) permeability. Compared with mice that recovered and control mice, non-recovered mice displaying prolonged learned helplessness had greater hippocampal activation of glycogen synthase kinase-3 (GSK3), higher levels of tumor necrosis factor-α (TNFα), interleukin-17A, and interleukin-23, increased permeability of the blood brain barrier (BBB), and lower levels of the BBB tight junction proteins occludin, ZO1, and claudin-5. Treatment with the GSK3 inhibitor TDZD-8 reduced inflammatory cytokine levels, increased tight junction protein levels, and reversed impaired recovery from learned helplessness, demonstrating that prolonged learned helplessness is reversible and is maintained by abnormally active GSK3. In non-recovered mice with prolonged learned helpless, stimulation of sphingosine 1-phosphate receptors by Fingolimod or administration of the TNFα inhibitor etanercept repaired the BBB and reversed impaired recovery from prolonged learned helplessness. Thus, disrupted BBB integrity mediated in part by TNFα contributes to blocking recovery from prolonged learned helplessness depression-like behavior. Overall, this report describes a new model of prolonged depression-like behavior and demonstrates that stress-induced GSK3 activation contributes to disruption of BBB integrity mediated by inflammation, particularly TNFα, which contributes to impaired recovery from prolonged learned helplessness.

Th17 cells in depression

T helper 17 (Th17) cells have recently been implicated in depression, which adds to the list of several other diseases of the central nervous system (CNS) that are already known to involve Th17 cells. In CNS diseases, it is thought that the signature cytokine produced by Th17 cells, interleukin-17A (IL-17A), mediates the detrimental effects of Th17 cells. In depression, although Th17 cells increase, the lack of a consistent correlation between depression severity and blood IL-17A levels suggests that Th17 cells promote depressive symptoms, which may not be entirely dependent on IL-17. However, little is known about the mechanism of action of Th17 cells or the source of CNS Th17 cells in depression. It is likely that Th17 cells promote neuroinflammation and activation of microglia and astrocytes, actions that may contribute to neuronal damage. A source of Th17 cells is the small intestine where they are regulated by the composition of the microbiome. It remains to be determined through what mechanisms of action Th17 cells affect depression and if Th17 cells can be considered a novel therapeutic target in depression.

Chronic social stress induces peripheral and central immune activation, blunted mesolimbic dopamine function, and reduced reward-directed behaviour in mice

Psychosocial stress is a major risk factor for depression, stress leads to peripheral and central immune activation, immune activation is associated with blunted dopamine (DA) neural function, DA function underlies reward interest, and reduced reward interest is a core symptom of depression. These states might be inter-independent in a complex causal pathway. Whilst animal-model evidence exists for some specific steps in the pathway, there is currently no animal model in which it has been demonstrated that social stress leads to each of these immune, neural and behavioural states. Such a model would provide important existential evidence for the complex pathway and would enable the study of causality and mediating mechanisms at specific steps in the pathway. Therefore, in the present mouse study we investigated for effects of 15-day resident-intruder chronic social stress (CSS) on each of these states. Relative to controls, CSS mice exhibited higher spleen levels of granulocytes, inflammatory monocytes and T helper 17 cells; plasma levels of inducible nitric oxide synthase; and liver expression of genes encoding kynurenine pathway enzymes. CSS led in the ventral tegmental area to higher levels of kynurenine and the microglia markers Iba1 and Cd11b and higher binding activity of DA D1 receptor; and in the nucleus accumbens (NAcc) to higher kynurenine, lower DA turnover and lower c-fos expression. Pharmacological challenge with DA reuptake inhibitor identified attenuation of DA stimulatory effects on locomotor activity and NAcc c-fos expression in CSS mice. In behavioural tests of operant responding for sucrose reward validated as sensitive assays for NAcc DA function, CSS mice exhibited less reward-directed behaviour. Therefore, this mouse study demonstrates that a chronic social stressor leads to changes in each of the immune, neural and behavioural states proposed to mediate between stress and disruption of DA-dependent reward processing. The model can now be applied to investigate causality and, if demonstrated, underlying mechanisms in specific steps of this immune-neural-behavioural pathway, and thereby to identify potential therapeutic targets.

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Mouse chronic social stress (CSS) leads to spleen and liver immune activation.

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Mouse CSS leads to mesolimbic immune activation and blunted dopamine function.

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Mouse CSS leads to reduced reward-directed behaviour in operant tests.

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This constitutes an important model for the study of pathophysiological mechanisms.

Personalized Antidepressant Selection and Pathway to Novel Treatments: Clinical Utility of Targeting Inflammation

Major depressive disorder (MDD) is a chronic condition that affects one in six adults in the US during their lifetime. The current practice of antidepressant medication prescription is a trial-and-error process. Additionally, over a third of patients with MDD fail to respond to two or more antidepressant treatments. There are no valid clinical markers to personalize currently available antidepressant medications, all of which have similar mechanisms targeting monoamine neurotransmission. The goal of this review is to summarize the recent findings of immune dysfunction in patients with MDD, the utility of inflammatory markers to personalize treatment selection, and the potential of targeting inflammation to develop novel antidepressant treatments. To personalize antidepressant prescription, a c-reactive protein (CRP)-matched treatment assignment can be rapidly implemented in clinical practice with point-of-care fingerstick tests. With this approach, 4.5 patients need to be treated for 1 additional remission as compared to a CRP-mismatched treatment assignment. Anti-cytokine treatments may be effective as novel antidepressants. Monoclonal antibodies against proinflammatory cytokines, such as interleukin 6, interleukin 17, and tumor necrosis factor α, have demonstrated antidepressant effects in patients with chronic inflammatory conditions who report significant depressive symptoms. Additional novel antidepressant strategies targeting inflammation include pharmaceutical agents that block the effect of systemic inflammation on the central nervous system. In conclusion, inflammatory markers offer the potential not only to personalize antidepressant prescription but also to guide the development of novel mechanistically-guided antidepressant treatments.