Cellular immunity and the hypothalamic-pituitary axis in major affective disorder: a preliminary study

B cells and the stressed brain: emerging evidence of neuroimmune interactions in the context of psychosocial stress and major depression

The immune system has emerged as a key regulator of central nervous system (CNS) function in health and in disease. Importantly, improved understanding of immune contributions to mood disorders has provided novel opportunities for the treatment of debilitating stress-related mental health conditions such as major depressive disorder (MDD). Yet, the impact to, and involvement of, B lymphocytes in the response to stress is not well-understood, leaving a fundamental gap in our knowledge underlying the immune theory of depression. Several emerging clinical and preclinical findings highlight pronounced consequences for B cells in stress and MDD and may indicate key roles for B cells in modulating mood. This review will describe the clinical and foundational observations implicating B cell-psychological stress interactions, discuss potential mechanisms by which B cells may impact brain function in the context of stress and mood disorders, describe research tools that support the investigation of their neurobiological impacts, and highlight remaining research questions. The goal here is for this discussion to illuminate both the scope and limitations of our current understanding regarding the role of B cells, stress, mood, and depression.

The Role of Inflammation in the Pathophysiology of Depression and Suicidal Behavior: Implications for Treatment

Depression and suicidal behavior are 2 complex psychiatric conditions of significant public health concerns due to their debilitating nature. The need to enhance contemporary treatments and preventative approaches for these illnesses not only calls for distillation of current views on their pathogenesis but also provides an impetus for further elucidation of their novel etiological determinants. In this regard, inflammation has recently been recognized as a potentially important contributor to the development of depression and suicidal behavior. This review highlights key evidence that supports the presence of dysregulated neurometabolic and immunologic signaling and abnormal interaction with microbial species as putative etiological hallmarks of inflammation in depression as well as their contribution to the development of suicidal behavior. Furthermore, therapeutic insights addressing candidate mechanisms of pathological inflammation in these disorders are proposed.

Estrogen, the Peripheral Immune System and Major Depression – A Reproductive Lifespan Perspective

Major depression is a significant medical issue impacting millions of individuals worldwide. Identifying factors contributing to its manifestation has been a subject of intense investigation for decades and several targets have emerged including sex hormones and the immune system. Indeed, an extensive body of literature has demonstrated that sex hormones play a critical role in modulating brain function and impacting mental health, especially among female organisms. Emerging findings also indicate an inflammatory etiology of major depression, revealing new opportunities to supplement, or even supersede, currently available pharmacological interventions in some patient populations. Given the established sex differences in immunity and the profound impact of fluctuations of sex hormone levels on the immune system within the female, interrogating how the endocrine, nervous, and immune systems converge to impact women’s mental health is warranted. Here, we review the impacts of endogenous estrogens as well as exogenously administered estrogen-containing therapies on affect and immunity and discuss these observations in the context of distinct reproductive milestones across the female lifespan. A theoretical framework and important considerations for additional study in regards to mental health and major depression are provided.

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.

Correlation between anxiety-depression symptoms and immune characteristics in inpatients with 2019 novel coronavirus in Wuhan, China

BACKGROUND

Coronavirus disease 2019 (COVID-19) is widely acknowledged as a severe traumatic event, and depression, anxiety, and psychological distress are common in diagnosed patients. However, the correlations of biological indicators with emotion are rarely reported. The primary objective of this study was to explore the dysfunction of immune-inflammatory characteristics in patients with depression-anxiety symptoms.

METHODS

We investigated the mental status of inpatients with COVID-19 in Wuhan and compared the differences in cytokines and lymphocytes between patients with and without depression-anxiety symptoms at admission. After two weeks of treatment, we evaluated the mental conditions and measured the cytokines and lymphocytes of the patients with depression and anxiety symptoms and explored the changes and their associations.

RESULTS

Approximately half of the patients with COVID-19 had depression and anxiety symptoms, and the symptoms were related to the ratio of CD4+/CD8+ and the level of CD4⁺T lymphocytes. When compared with patients without depression-anxiety symptoms, CD4⁺T lymphocytes level was significantly higher in COVID-19 patients with depression-anxiety symptoms.

CONCLUSION

This study provided novel evidence regarding the association between depression and anxiety symptoms and immune characteristics, especially CD4⁺T lymphocyte levels, in COVID-19 patients. We emphasized the importance of paying attention to the dynamic immune process of patients diagnosed with COVID-19 with depression/anxiety.

Depression Induced by CUMS Leads to Bladder Cancer Development and Local Tumor Immunosuppression in Mice

Depression is a common mental disease in bladder cancer patients, leading to a loss of happiness, an increase in the suicide rate, and higher mortality. However, the influence of depression on bladder tumor tissue remains unknown. In this current study, a subcutaneous bladder cancer xenograft model was established on male C57 mice with mouse bladder cell line MB49. Chronic unpredictable mild stress (CUMS) was established to simulate depression in bladder cancer patients. The depression caused by CUMS was confirmed by testing sucrose preference and plasma cortisol and adrenocorticotropic hormone (ACTH) levels. Then, we measured and weighed tumors to demonstrate the promotion of tumor growth by CUMS. Immune-related cells and molecules were examined to reveal the mechanism. There is a significant decrease of CD8+/CD4+T cells ratio, NK cells, IL-2, and IFN-γ and a significant increase of T regs, IL-6, IL-1β, TNF-α, IL-10, and PGE2 in CUMS group, indicating the inhibition of immunity in the tumor microenvironment. Our results supported the perspective that depression exacerbated bladder cancer and revealed a possible mechanism. We suggest attaching importance to the psychological health of bladder cancer patients to prevent a worse prognosis induced by depression.

An Overview of the Heterogeneity of Major Depressive Disorder: Current Knowledge and Future Prospective

Major depressive disorder (MDD) is estimated to impose maximum debilitating effects on the society by 2030, with its critical effects on health, functioning, quality of life and concomitant high levels of morbidity and mortality. Yet, the disease is inadequately understood, diagnosed and treated. Moreover, with the recent drastic rise in the pace of life, stress has materialized as one of the most potent environmental factors for depression. In this scenario, it is important to understand the modern pathogenetic hypotheses and mechanisms, and possibly try to shift from the traditional approaches in depression therapy. These include the elaboration of pathophysiological changes in heterogeneous systems such as genetic, epigenetic, serotonergic, noradrenergic, gamma-aminobutyric acid, glutamatergic and endocannabinoid systems, neurotrophic factors, HPA axis, immune system as well as cellular stress mechanisms. These components interact with each other in a complex matrix and further elucidation of their mechanism and cascade pathways are needed. This might aid in the identification of MDD subtypes as well as the development of sophisticated biomarkers. Further, characterization might also aid in developing multitargeted therapies that hold much promise as compared to the conventional monoamine based treatment. New candidate pharmacons, refined psychotherapeutic modalities, advanced neuro-surgical and imaging techniques as well as the implementation of pharmacokinetic, pharmacogenetic prescribing guidelines constitute the emerging expanses of MDD treatment.

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.

Altered B Cell Homeostasis in Patients with Major Depressive Disorder and Normalization of CD5 Surface Expression on Regulatory B Cells in Treatment Responders

Pro-inflammatory activity and cell-mediated immune responses have been widely observed in patients with major depressive disorder (MDD). Besides their well-known function as antibody-producers, B cells play a key role in inflammatory responses by secreting pro- and anti-inflammatory factors. However, homeostasis of specific B cell subsets has not been comprehensively investigated in MDD. In this study, we characterized circulating B cells of distinct developmental steps including transitional, naïve-mature, antigen-experienced switched, and non-switched memory cells, plasmablasts and regulatory B cells by multi-parameter flow cytometry. In a 6-weeks follow-up, circulating B cells were monitored in a small group of therapy responders and non-responders. Frequencies of naïve lgD⁺CD27^- B cells, but not lgD⁺CD27⁺ memory B cells, were reduced in severely depressed patients as compared to healthy donors (HD) or mildly to moderately depressed patients. Specifically, B cells with immune-regulatory capacities such as CD1d⁺CD5⁺ B cells and CD24⁺CD38^hi transitional B cells were reduced in MDD. Also Bm1-Bm5 classification in MDD revealed reduced Bm2' cells comprising germinal center founder cells as well as transitional B cells. We further found that reduced CD5 surface expression on transitional B cells was associated with severe depression and normalized exclusively in clinical responders. This study demonstrates a compromised peripheral B cell compartment in MDD with a reduction in B cells exhibiting a regulatory phenotype. Recovery of CD5 surface expression on transitional B cells in clinical response, a molecule involved in activation and down-regulation of B cell responses, further points towards a B cell-dependent process in the pathogenesis of MDD.

Innate and adaptive immunity in the development of depression: An update on current knowledge and technological advances

The inflammation theory of depression, proposed over 20years ago, was influenced by early studies on T cell responses and since then has been a stimulus for numerous research projects aimed at understanding the relationship between immune function and depression. Observational studies have shown that indicators of immunity, especially C reactive protein and proinflammatory cytokines, such as interleukin 6, are associated with an increased risk of depressive disorders, although the evidence from randomized trials remains limited and only few studies have assessed the interplay between innate and adaptive immunity in depression. In this paper, we review current knowledge on the interactions between central and peripheral innate and adaptive immune molecules and the potential role of immune-related activation of microglia, inflammasomes and indoleamine-2,3-dioxygenase in the development of depressive symptoms. We highlight how combining basic immune methods with more advanced 'omics' technologies would help us to make progress in unravelling the complex associations between altered immune function and depressive disorders, in the identification of depression-specific biomarkers and in developing immunotherapeutic treatment strategies that take individual variability into account.

An Act of Balance Between Adaptive and Maladaptive Immunity in Depression: a Role for T Lymphocytes

Historically the monoaminergic neurotransmitter system, in particular the serotonergic system, was seen as being responsible for the pathophysiology of major depressive disorder (MDD). With the advent of psychoneuroimmunology an important role of the immune system in the interface between the central nervous systems (CNS) and peripheral organ systems has emerged. In addition to the well-characterised neurobiological activities of cytokines, T cell function in the context of depression has been neglected so far. In this review we will investigate the biological roles of T cells in depression. Originally it was thought that the adaptive immune arm including T lymphocytes was excluded from the CNS. It is now clear that peripheral naïve T cells not only carry out continuous surveillance within the brain but also maintain neural plasticity. Furthermore animal studies demonstrate that regulatory T lymphocytes can provide protection against maladaptive behavioural responses associated with depression. Psychogenic stress as a major inducer of depression can lead to transient trafficking of T lymphocytes into the brain stimulating the secretion of certain neurotrophic factors and cytokines. The separate and combined mechanism of CD4 and CD8 T cell activation is likely to determine the response pattern of CNS specific neurokines and neurotrophins. Under chronic stress-induced neuroinflammatory conditions associated with depression, T cell responses may become maladaptive and can be involved in neurodegeneration. Additionally, intracellular adhesion and MHC molecule expression as well as glucocorticoid receptor expression within the brain may play a role in determining T lymphocyte functionality in depression. Taken together, T lymphocyte mechanisms, which confer susceptibility or resilience to MDD, are not yet fully understood. Further insight into the cellular and molecular mechanisms which balance the adaptive and maladaptive roles of T lymphocytes may provide a better understanding of both the neuro- degenerative and -regenerative repair functions as present within the neuroimmune network during depression. Furthermore T cells may be important players in restoration of normal behaviour and immune cell homeostasis in depression.

NK cell immunesenescence is increased by psychological but not physical stress in older adults associated with raised cortisol and reduced perforin expression

NK cell cytotoxicity (NKCC) reduces with age and this has been associated previously with increased mortality. The immune response is also modulated by stress, and here, we assessed the effect of the physical stress of hip fracture and the psychological stress of depression on NKCC in an aged immune system. NKCC was assessed in 101 hip fracture patients (81 female) 6 weeks and 6 months after injury and in 50 healthy age-matched controls (28 female). Thirty-eight patients were depressed at 6 weeks post-injury, and NKCC was reduced in patients who developed depression compared with non-depressed hip fracture patients (p = 0.004) or controls (p < 0.02). NKCC remained lower in the depressed patients compared to those without depression 6 months post-fracture (p = 0.017). We found reduced expression of perforin in NK cells of depressed hip fracture patients compared with controls at 6 weeks (p = 0.001) post-fracture. Serum cortisol levels were also elevated in patients with depression compared to non-depressed patients at 6 weeks (p = 0.01) and 6 months (p = 0.05). NK cells treated with dexamethasone showed a concentration-dependent reduction in NKCC and perforin expression. We propose that depression is the major factor affecting NK cell immunity after hip fracture.

Bipolar affective disorder and thrombocytopenia

This report describes the case of a 62 year old man with late onset bipolar affective disorder whose mood swings were associated with episodes of thrombocytopenia. The inter-relationships between affective symptoms, the immune system and the hypothalamic pituitary axis are discussed.

Immune-endocrine host response to endotoxin in major depression

OBJECTIVE

An impaired hypothalamic-pituitary-adrenocortical (HPA) function is a well-established finding in major depression (MD), but it is still unclear how this dysfunction affects immune responses in this disorder.

METHOD

To further examine the relationship between immune and endocrine responses in MD, 0.4ng/kg body weight endotoxin [LPS] or 100mug hCRH were sequentially applied to 12 patients with MD and to 12 age- and gender-matched healthy controls after pre-treatment with 1.5mg dexamethasone (DEX). Immune (TNF-alpha, IL-6, rectal temperature) and endocrine (ACTH, cortisol) parameters were examined as area under the curve (AUC) levels.

RESULTS

After pre-treatment with DEX, LPS evoked an immune response in all participants of the study with most immune parameters significantly related to the endotoxin challenge. However, only a marked immune response resulted in an additional endocrine reaction. Subsequently, the quantitative extent of the endocrine reaction was related to the extent of the immune response after DEX/LPS challenge. Pre-LPS AUC levels of cortisol, ACTH and post-LPS levels of IL-6 as well as the post-CRH AUC levels of cortisol and ACTH were related to the depressive symptomatology as measured by the Beck depression inventory (BDI). In depressive patients who showed increased cortisol plasma levels before LPS, the later increase in IL-6 was reduced.

CONCLUSIONS

The challenge with DEX/LPS did not reveal major impairments of evoked immune functions in MD. Only the endocrine parameters and the IL-6 response were related to the depressive symptomatology, suggesting a limited interaction between immune and endocrine dysfunctions in MD.

Serotonin, 5-HT1A serotonin receptors and proliferation of lymphocytes in major depression patients

Serotonin receptors are present in lymphocytes and might be related to the functionality of these cells in health and in pathology. The serotonergic system is affected in the brain and in peripheral immune cells of depressed patients. The objectives of this work were to evaluate the basal proliferation of lymphocytes, the response to the mitogen concanavalin A, and the role of serotonin 5-HT(1A) receptors. Twenty-nine patients, 19-52 years old, were diagnosed for a major depression episode with the Statistical and Diagnostic Manual-IV of the American Psychiatric Association, approved by ethic committees and gave written consent. The Hamilton depression score was 30.60 +/- 2.65. An apparently healthy group without a family history of psychiatric illness was included. Blood peripheral lymphocytes were isolated by density gradients with Ficoll/Hypaque and differential adhesion to plastic, cultured in 96-well plaques with RPMI-1640 medium with or without 4 mug/ml of concanavalin A. 8-Hydroxy-2-(di-n-propylamino)tetralin (5-40 nM) and WAY-100,478 (0.1-100 microM), agonist and antagonist of 5-HT(1A) receptors, serotonin (12.5-100 nM) or imipramine (0.1-100 microM) were also added. Proliferation was evaluated at 72 h with 3-[4,5-dimethythiazol-2-yl]-2,5-diphenyltetrazolium bromide, and the optical density was 570 nm. Basal proliferation was three times higher in depressed patients than in controls, whereas no response to mitogen was obtained, and 5-HT(1A) receptors significantly reacted to the agonist, with increases of about 31-54% at 10, 20 and 40 nM of the specific agonist, indicating initial activation probably in relation to autoimmunity and overreactivity of these receptors in depression. The antagonist reduced proliferation in mitogen-stimulated lymphocytes, 50% in controls and 70% in depressed patients, with a differential concentration dependency; probably, these receptors are more sensitive in depression due to increased 5-HT(1A) receptor transduction. The antagonist also reduced the stimulation produced by the 5-HT(1A) agonist. Imipramine caused biphasic effects according to concentrations, showing a possible dual role for serotonin, although all values were significantly higher in depressed subjects. The described alterations might be of relevance in the pathophysiology of depression.

Lymphocyte subset differences in patients with chronic fatigue syndrome, multiple sclerosis and major depression

Chronic fatigue syndrome (CFS) is a heterogeneous disorder of unknown aetiology characterized by debilitating fatigue, along with other symptoms, for at least 6 months. Many studies demonstrate probable involvement of the central and autonomic nervous system, as well as a state of generalized immune activation and selective immune dysfunction in patients with CFS. The aim of this study was to compare the lymphocyte subsets of patients with chronic fatigue syndrome to those of patients with major depression and multiple sclerosis as well as those of healthy control subjects. No differences were found in total numbers of T cells, B cells or natural killer (NK) cells. However, differences were found in T, B and NK cell subsets. Patients with major depression had significantly fewer resting T (CD3(+)/CD25(-)) cells than the other groups. Patients with major depression also had significantly more CD20(+)/CD5(+) B cells, a subset associated with the production of autoantibodies. Compared to patients with multiple sclerosis, patients with CFS had greater numbers of CD16(+)/CD3(-) NK cells. Further study will be required to determine whether these alterations in lymphocyte subsets are directly involved in the pathophysiology of these disorders, or are secondary effects of the causal agent(s).

Immune parameters in patients with anxiety or depression during psychotherapy

BACKGROUND

Numerous studies have described distinctive immunological findings in patients with depression. In contrast, only very little is known about the possible influence of anxiety disorders on the immune system. It is also unknown whether treatment with psychotherapy alone has any influence on immunological variations in patients with psychiatric disorders.

METHODS

We measured immunological and psychological parameters in patients with minor depression (N=10) or anxiety disorder (N=13) over an 8-week course of inpatient psychotherapy. Data for patients and a group of healthy controls (N=11) were recorded three times in 4-week intervals. A FACS analysis revealed the composition of lymphocyte subpopulations. The production of reactive oxygen species (ROS) by phagocytes was analyzed using lucigenin-enhanced chemiluminescence.

RESULTS

On admission, patients with anxiety disorder showed a markedly elevated ratio of CD4(+) (T helper) versus CD8(+) (T suppressor/cytotoxic) lymphocytes compared to healthy controls (P<0.001) and minor depressives (P<0.01). The increased ratio in patients with anxiety disorder could mainly be attributed to a reduced count in CD8(+) T cells compared to healthy controls (P<0.01) and depressives (P<0.05). There were no differences between patients with depression and healthy controls with respect to the CD4(+)/CD8(+) ratio. We did not observe any differences in the production of ROS by phagocytes in patients compared to healthy controls. The CD4(+)/CD8(+) ratio remained elevated in patients with anxiety disorders during the following 8 weeks. There were no significant changes in this parameter over the course of the inpatient treatment.

LIMITATIONS

As a pilot study on the immune status in patients with anxiety disorders, the study's main limitation is the relatively low number of patients observed.

CONCLUSIONS

In this study we demonstrated for the first time marked immunological changes in patients with anxiety disorders. In addition, our results provide preliminary evidence that these immunological variations are not reversible by an 8-week course of inpatient psychotherapy alone.

High numbers of circulating activated T cells and raised levels of serum IL-2 receptor in bipolar disorder

BACKGROUND

Previously, we found an increased prevalence of thyroid autoantibodies in patients with bipolar disorder. In the present study, we investigated other signs of immune activation in bipolar patients, in particular an activation of the T cell system.

METHODS

Fluorescence activated cell scanning (FACS) analysis was performed on lymphocytes of 64 outpatients with DSM-IV bipolar disorder using the T cell marker CD3 in combination with the activation markers MHC-class II, CD25, CD69 or CD71. In 34 patients, these assays were repeated after an interval of 2 years. In addition, T cell activation was determined by measuring serum soluble IL-2 receptor (sIL-2R) in 172 bipolar outpatients. Outcomes were compared with a healthy control group.

RESULTS

Significantly higher numbers of circulating activated T cells and raised sIL-2R levels were found in euthymic, manic, and depressed bipolar patients when compared with healthy controls. In general, these abnormalities were stable over time. Manic patients showed significantly higher levels of sIL-2R in comparison with depressed patients.

CONCLUSION

The T cell system was found to be activated in both symptomatic and euthymic patients with bipolar disorder. The pathophysiological significance of these findings remains to be explored.

The relationship of depression and stressors to immunological assays: a meta-analytic review

This is a broad meta-analysis of the relations of both depression and stressors to immunological assays. The number of study samples (greater than 180) and measures (greater than 40) is much more extensive than any so far. Analyses are done by both fixed and random effects. By a fixed-effects analysis, both major depression and naturally occurring acute stressors are associated with (1) an overall leukocytosis, (2) mild reductions in absolute NK-cell counts and relative T-cell proportions, (3) marginal increases in CD4/CD8 ratios, and (4) moderate decreases in T- and NK-cell function. However, the degree of heterogeneity of the studies' results raises questions about their robustness. Therefore, we also did the first random effects analysis to estimate what is likely to appear in future studies. For depression, the analysis showed the immunological correlates included (1) an overall leukocytosis, manifesting as a relative neutrophilia and lymphoenia; (2) increased CD4/CD8 ratios; (3) increased circulating haptoglobin, PGE(2), and IL-6 levels; (4) reduced NK-cell cytotoxicity; and (5) reduced lymphocyte proliferative response to mitogen. For stressors, the random effects analysis showed that future studies are likely to find the following effects: (1) an overall leukocytosis, manifesting as an absolute lymphocytosis; (2) alterations in cytotoxic lymphocyte levels, CD4/CD8 ratios, and natural killer cell cytotoxicity with the direction of change depending on the chronicity of the stressor; (3) a relative reduction of T-cell levels; (3) increased EBV antibody titers; (4) reduced lymphocyte proliferative response and proportion of IL-2r bearing cells following mitogenic stimulation; and (5) increased leukocyte adhesiveness. The random-effects analysis revealed that for both major depression and naturally occurring stressors the following effects are shared: leukocytosis, increased CD4/CD8 ratios, reduced proliferative response to mitogen, and reduced NK cell cytotoxicity. The implications for these findings for disease susceptibility and the pathophysiology of these conditions is discussed.

A unifying hypothesis of Alzheimer's disease. III. Risk factors

Normal ageing and Alzheimer's disease (AD) have many features in common and, in many respects, both conditions only differ by quantitative criteria. A variety of genetic, medical and environmental factors modulate the ageing-related processes leading the brain into the devastation of AD. In accordance with the concept that AD is a metabolic disease, these risk factors deteriorate the homeostasis of the Ca(2+)-energy-redox triangle and disrupt the cerebral reserve capacity under metabolic stress. The major genetic risk factors (APP and presenilin mutations, Down's syndrome, apolipoprotein E4) are associated with a compromise of the homeostatic triangle. The pathophysiological processes leading to this vulnerability remain elusive at present, while mitochondrial mutations can be plausibly integrated into the metabolic scenario. The metabolic leitmotif is particularly evident with medical risk factors which are associated with an impaired cerebral perfusion, such as cerebrovascular diseases including stroke, cardiovascular diseases, hypo- and hypertension. Traumatic brain injury represents another example due to the persistent metabolic stress following the acute event. Thyroid diseases have detrimental sequela for cerebral metabolism as well. Furthermore, major depression and presumably chronic stress endanger susceptible brain areas mediated by a host of hormonal imbalances, particularly the HPA-axis dysregulation. Sociocultural and lifestyle factors like education, physical activity, diet and smoking may also modulate the individual risk affecting both reserve capacity and vulnerability. The pathophysiological relevance of trace metals, including aluminum and iron, is highly controversial; at any rate, they may adversely affect cellular defences, antioxidant competence in particular. The relative contribution of these factors, however, is as individual as the pattern of the factors. In familial AD, the genetic factors clearly drive the sequence of events. A strong interaction of fat metabolism and apoE polymorphism is suggested by intercultural epidemiological findings. In cultures, less plagued by the 'blessings' of the 'cafeteria diet-sedentary' Western lifestyle, apoE4 appears to be not a risk factor for AD. This intriguing evidence suggests that, analogous to cardiovascular diseases, apoE4 requires a hyperlipidaemic lifestyle to manifest as AD risk factor. Overall, the etiology of AD is a key paradigm for a gene-environment interaction. Copyright 2000 John Wiley & Sons, Ltd.

Plasma levels of cytokines and soluble cytokine receptors in psychiatric patients upon hospital admission: effects of confounding factors and diagnosis

It has been hypothesized that the immune system plays a pathogenetic role in psychiatric disorders, in particular in major depression and schizophrenia. This hypothesis is supported by a number of reports on altered circulating levels and in vitro production of cytokines in these disorders. However, the respective evidence is not consistent. This may be in part due to an incomplete control for numerous confounding influences in earlier studies. We investigated the plasma levels of cytokines and soluble cytokine receptors in psychiatric patients (N = 361) upon hospital admission and compared the results to those obtained in healthy controls (N = 64). By multiple regression analysis we found that circulating levels of interleukin-1 receptor antagonist (IL-1Ra), soluble IL-2 receptor (sIL-2R), tumor necrosis factor-alpha (TNF-alpha), soluble TNF receptors (sTNF-R p55, sTNF-R p75) and IL-6 were significantly affected by age, the body mass index (BMI), gender, smoking habits, ongoing or recent infectious diseases, or prior medication. Cytokine or cytokine receptor levels were significantly increased in patients treated with clozapine (sIL-2R, sTNF-R p75), lithium (TNF-alpha, sTNF-R p75, IL-6) or benzodiazepines (TNF-alpha, sTNF-R p75). Taking all these confounding factors into account, we found no evidence for disease-related alterations in the levels of IL-1Ra, sIL-2R, sTNF-R p75 and IL-6, whereas levels of TNF-alpha and sTNF-R p55 in major depression and sTNF-R p55 in schizophrenia were slightly decreased compared to healthy controls. We conclude that, if confounding factors are carefully taken into account, plasma levels of the above mentioned cytokines and cytokine receptors yield little, if any, evidence for immunopathology in schizophrenia or major depression.

Circulating lymphocyte subsets in major depression and dysthymia with typical or atypical features

OBJECTIVE

Inconsistent results have been reported concerning circulating lymphocyte subsets in depression. To establish whether the immune alterations in depression could be related to neurovegetative symptoms, lymphocyte subsets were assessed in major depressive and dysthymic patients who exhibited either typical or atypical features (ie, the latter characterized by mood reactivity and reversed neurovegetative features).

METHOD

Blood was collected from major depressive, atypical depressive, typical dysthymic, or atypical dysthymic patients and from nondepressed control subjects. Circulating lymphocyte subsets (CD3, CD4, CD8, CD19, CD16/CD56) were determined by flow cytometry. In a subset of patients, lymphocyte subsets were also determined after a 12-week course of antidepressant medication.

RESULTS

Although T and B cell populations did not differ between the depressive subtypes and control subjects, circulating natural killer (NK) cells were elevated in depressive illness, and varied as a function of depressive subtype and sex. Among male patients, NK cells were elevated to a greater extent in typical than in atypical depression, and more so in major depressive than in dysthymic patients. Among female patients, circulating NK cells were lower than in male patients, and only among the typical major depressive patients did NK cells exceed those of controls. Normalization of NK cells occurred with successful pharmacotherapy.

CONCLUSIONS

Depression may be associated with elevated levels of circulating NK cells. Although the neurovegetative features associated with depression, particularly altered eating, may have contributed to the elevated NK cells, depressive affect itself also contributed in this respect. However, the relative contributions of these factors varied between male and female patients.

T-lymphocyte subsets in patients with abnormal body weight: longitudinal studies. in anorexia nervosa and obesity

OBJECTIVE

In contrast to other types of starvation which are characterized by low CD4+ counts and increased susceptibility to infection, anorexia nervosa is not associated with an increase in infectious complications. To determine why infection risk of anorectics differs from that of other starving populations, we studied T-lymphocytes, including CD4+ and CD8+ phenotypes, in patients with anorexia nervosa, and for comparison, in dieting obese subjects.

METHODS

T-lymphocyte phenotypes were determined by flow cytometric analysis of monoclonal antibody-labeled cells obtained from patients with anorexia nervosa before and after successful therapy and weight gain, and in obese subjects before and after weight loss on a very-low-calorie diet.

RESULTS

Weight loss in anorectics and obese dieters was associated with normal CD4+ counts. Unexpectedly, CD8+ counts were low in anorectics, both before and after weight gain, and in obese subjects after (but not before) dieting.

DISCUSSION

Normal CD4+ counts in anorectics and obese dieters, despite marked weight loss, may explain the lack of increased infection risk in these eating-disordered patients, in contrast to other starving populations. The observation that CD8+ counts are low in anorectics with low and restored body weight and in obese patients after dieting has not been previously reported. The persistence of low CD8+ counts in anorectics even after weight gain suggests that some factors other than weight loss per se may be involved, possibly including effects due to stress, comorbid psychiatric conditions, or unidentified aspects of dysregulated pathophysiology secondary to disordered eating.

Variations of lymphocyte subsets associated with stress in depressive populations

Major depression and dysthymia have been associated with increased perception of day-to-day stressors, greater reliance on emotion-focused coping efforts, and reduced perception of uplifting events. Moreover, it has been observed that levels of circulating natural killer (NK) cells were elevated in depressed patients. Given that mild stressors may increase circulating NK cells, it is conceivable that the elevated NK cells in depression may be secondary to the increased stress perception associated with the illness. In the present investigation a laboratory stressor, comprising a mathematical challenge, increased circulating NK cells; however, the extent of the increase was comparable in depressive, dysthymic and control subjects. Moreover, the increased NK cells induced by the stressor procedure appeared to be independent of variations of plasma cortisol, ACTH or norepinephrine. Interestingly, although the NK changes were not differentially influenced by stressors in the subject populations, in the major depressive patients correspondence existed between NK cell levels and emotion-focused coping styles. Likewise, the response to a laboratory stressor was directly related to the severity of depression and to the use of coping styles involving cognitive restructuring or problem solving.

Tricyclic antidepressants inhibit IL-6, IL-1 beta and TNF-alpha release in human blood monocytes and IL-2 and interferon-gamma in T cells

Tricyclic antidepressants (TCAs) are widely used in treating depressive disorders. It has been demonstrated that, for instance, IL-1 beta and IL-6 inhibit the HPA axis, which plays a role in the development of depressions. Therefore. we were interested in investigating how TCAs influence cytokine release by T lymphocytes and monocytes respectively. Cells were incubated with either 5 microM clomipramine, 15 microM imipramine or 20 microM citalopram. IL-2 release was suppressed to 60% of the control values by clomipramine and imipramine (p = 0.001; p = 0.000), but citalopram was found to cause a much weaker inhibition (only 18%) (p = 0.16). INF-gamma release was affected to a lower degree than IL-2 release, and imipramine (34%) (p = 0.054) was more potent than clomipramine (24%) (p = 0.16) and citalopram (12%) (p = 0.059) in this case. Monocytes incubated with TCA for 4 h exhibited only limited inhibition of IL-1 beta and IL-6 release, i.e., 6-25% for all three compounds. The corresponding value for TNF-alpha release was 20-45% inhibition, with citalopram being the weakest inhibitor. After 10 h of monocytes to LPS exposure, all three compounds exerted a strong inhibition of IL-1 beta and TNF-alpha release, i.e., 60-70% with p-values below 0.012 for all of them. However the inhibition of IL-6 release was less than 35%. Citalopram was equality as potent as imipramine and clomipramine in inhibiting IL-6 release after long-term exposure of monocytes to LPS. All three TCAs elevated intracellular cAMP concentrations significantly in T lymphocytes and monocytes (p < 0.001).

Lymphocyte subsets associated with major depression and dysthymia: modification by antidepressant treatment

Major depression and dysthymia (chronic, low grade depression) were associated with an increase in the number of CD16/56 (natural killer; NK) cells in blood, whereas other lymphocyte subsets (CD3, CD4, CD8, CD19, and the CD4/CD8 ratio) did not differ from control subjects. After treatment with a specific serotonin reuptake inhibitor, the symptoms of depression were alleviated in both the major depressive and dysthymic patients. Likewise, NK cell numbers declined to control values in these treated groups. Among the major depressive patients, the NK cell number reached control values within 4 weeks, whereas 6 months of treatment was required for such an effect to be achieved in the dysthymic patients. Although plasma levels of epinephrine, norepinephrine, cortisol, and ACTH were not different between groups, among the major depressive patients ACTH was inversely correlated with total lymphocytes, CD3, and CD19, and epinephrine was directly related to the CD4 and CD4/CD8 ratio. Among dysthymics, ACTH was unrelated to any of the lymphocyte subsets, but norepinephrine was directly related to total lymphocytes, CD3, CD4, and NK cells. The data are interpreted in terms of stress perception among major depressive and dysthymic patients and the potential impact of stressor experiences on immune processes.

Effects of chronic mild stress on serum complement activity, saccharin preference, and corticosterone levels in Flinders lines of rats

Complement proteins and fragments participate in the induction and modulation of specific and nonspecific immune reactions. We have examined the effect of 4 weeks of chronic mild stress (CMS) on complement sheep red blood cell hemolytic activity measured in CH50 units in two selectively bred lines of rats, the Flinders resistant line (FRL) and the Flinders sensitive line (FSL), that differ in cholinergic sensitivity and behavioral characteristics. Additionally, CMS-induced hedonic deficit (decreased preference for 0.02% saccharin over water) and serum corticosterone levels were compared in FRL and FSL rats. CMS caused a significantly (p < 0.01) greater decline in CH50 responses in FSL (-15%) than in FRL (-7%) rats. This was accompanied by a significant (p < 0.01) suppression of saccharin preference over a 24 h period in both FRL and FSL rats. Both lines showed a similar, more than 2-fold (p < 0.01) increase in corticosterone levels following CMS. These results further confirm that CMS induces a depressive-like state in rats as well as the validity of the FSL rat as a genetic model of depression. They also indicate that the effect of stress on the immune system can be monitored by measuring the complement CH50 response.

Evidence for an immune response in major depression: a review and hypothesis

1. This paper reviews recent findings on cellular and humoral immunity and inflammatory markers in depression. 2. It is shown that major depression may be accompanied by systemic immune activation or an inflammatory response with involvement of phagocytic (monocytes, neutrophils) cells, T cell activation, B cell proliferation, an "acute" phase response with increased plasma levels of positive and decreased levels of negative acute phase proteins, higher autoantibody (antinuclear, antiphospholipid) titers, increased prostaglandin secretion, disorders in exopeptidase enzymes, such as dipeptidyl peptidase IV, and increased production of interleukin (IL)-1 beta and IL-6 by peripheral blood mononuclear cells. 3. It is hypothesized that increased monocytic production of interleukins (Il-1 beta and Il-6) in severe depression may constitute key phenomena underlying the various aspects of the immune and "acute" phase response, while contributing to hypothalamic-pituitary-adrenal-axis hyperactivity, disorders in serotonin metabolism, and to the vegetative symptoms (i.e. the sickness behavior) of severe depression.

Natural killer cell activity in major depression: relation to circulating natural killer cells, cellular indices of the immune response, and depressive phenomenology

1. Recently, blunted natural killer cell activity (NKCA) has been found in major depression. The present study investigates the relationships between ex vivo blunted NKCA in major depression, number or percentage of NKC, in vivo indices of systemic immune activation and depressive phenomenology. 2. Toward this end, NKCA, absolute number of leukocytes and number or percentage of lymphocytes, monocytes, neutrophils, activated T lymphocytes (HLA-DR+, CD25+) and NKC (CD3-CD56+) were determined in 13 normal controls and 36 depressed inpatients. 3. NKCA was significantly and positively related to number and percentage of NKC in the peripheral blood. The major depression-related reduction in NKCA was not related to alterations in peripheral NKC. There were significant negative correlations between NKCA and number or percentage of leukocytes, monocytes, neutrophils and HLA-DR+ T cells. Up to 50% of the variance in NKCA could be explained by the regression on the number of monocytes, percentage of HLA-DR+ T and NKC cells, and diagnostic classification. Up to 43% of the variance in NKCA was explained by depressed mood, somatic anxiety and less diurnal variation. 4. The results show that blunted NKCA in major depression is not related to alterations in peripheral NKC, but reflects in part the systemic immune activation in that illness.

Relationships between increased haptoglobin plasma levels and activation of cell-mediated immunity in depression

Recently, it was found that major depression is accompanied by an acute phase (AP) response with increased haptoglobin (Hp) plasma levels and various indices of systemic immune stimulation. The present study has been carried out in order to determine the relationships between hyperhaptoglobinemia and indices of systemic immune activation in severe depression. Toward this end, the authors investigated the relationships between Hp levels and number of leukocytes, monocytes, neutrophils, lymphocytes, and activated T lymphocytes (CD25+, HLA-DR+), in depression. Hp plasma levels were significantly higher in major depressed subjects as compared to healthy controls and minor depressives. There was a significant positive correlation between Hp levels and severity of illness. Hp plasma levels showed significant and positive relationships with the absolute number of leukocytes, neutrophils, monocytes, CD25+ and HLA-DR+ T cells. Up to 35% of the variance in Hp levels could be explained by the regression on the number of neutrophils and HLA-DR+ T cells. The results show that hyperhaptoglobinemia in major depression is significantly related to activation of cell-mediated immunity.

A review on the acute phase response in major depression

There is some evidence that major depression is characterized by systemic immune activation with involvement of phagocytic cells, T cell activation, B cell proliferation and increased autoantibody production. This paper reviews that major depression may be accompanied by higher concentrations of positive and lower concentrations of negative acute phase proteins (APPs). The most prominent abnormalities of APPs in major depression are increased haptoglobin (Hp) plasma levels. The latter are significantly and positively correlated with interleukin (IL)-6 production, various indices of systemic immune activation (e.g. monocytosis, neutrophilia, T cell activation) and with the vegetative symptoms of depression (e.g. anorexia, weight loss, psychomotor retardation, sleep disorders, anergy). Major depression is characterized by an altered distribution of Hp phenotypes and genes suggesting that genetic variation on chromosome 16 may be associated with this illness. It is concluded that increased production of IL-6 and IL-1 in major depression may underlie both immune activation and the "acute" phase response in that illness, and that disorders in Hp may be related to the pathophysiology and pathogenesis of major depression.

Relationships between interleukin-6 activity, acute phase proteins, and function of the hypothalamic-pituitary-adrenal axis in severe depression

Recent studies from this laboratory have provided some evidence that major depression, in particular melancholia, may be accompanied by an immune response. The present study was designed to investigate whether severe depression is characterized by increased interleukin-6 (Il-6) activity and whether Il-6 production is related to altered levels of acute phase reactants and to abnormal function of the hypothalamic-pituitary-adrenal (HPA) axis. Measurements were made in 8 healthy control subjects and 24 depressed inpatients of Il-6 production in culture supernatants of mitogen-stimulated peripheral leukocytes and plasma levels of haptoglobin (Hp), transferrin (Tf), and postdexamethasone cortisol. Il-6 activity was significantly higher in melancholic subjects than in healthy control subjects and in patients with minor depression or nonmelancholic major depression. Il-6 production was significantly correlated with Hp (positively) and Tf (negatively) plasma levels. There were significant and positive correlations between Il-6 activity and postdexamethasone cortisol values. The findings may suggest that increased Il-6 activity in severe depression is related to hypotransferrinemia, hyperhaptoglobinemia, and hyperactivity of the HPA axis.

Psychomotor retardation, anorexia, weight loss, sleep disturbances, and loss of energy: psychopathological correlates of hyperhaptoglobinemia during major depression

Recently, we have established that major depression is characterized by hyperhaptoglobinemia, which may be regarded as an index of an "acute" phase response in that illness. The present study investigates the psychopathological correlates of increased plasma concentrations of haptoglobin (Hp) in major depression. To this end, the authors studied the Hp levels in relation to depressive items of the Structured Clinical Interview for DSM-III (SCID) and the Hamilton Rating Scale for Depression (HRSD) in 90 depressed subjects. There was a significant positive relationship between the SCID symptoms anorexia/weight loss, sleep, and psychomotor disorders and Hp plasma concentrations. Hp plasma levels were significantly and positively correlated with overall severity of illness (HRSD). The HRSD symptom correlates of higher Hp levels were loss of interest, middle insomnia, and psychomotor retardation. Up to 31.4% of the variance in Hp plasma values could be explained by psychomotor disorders, anorexia, weight loss, middle insomnia, and less diurnal variation of mood. It is suggested that hyperhaptoglobinemia, as an index of an "acute" phase response in major depression, is related to the somatic dimension of depressive illness.

Glucocorticoids modulate soluble interleukin-2 receptor levels in vivo depending on the state of immune activation and the duration of glucocorticoid exposure

We have studied the modulation of circulating soluble interleukin-2 receptor (sIL-2R) levels by glucocorticoids in subjects with different states of immune activation. In contrast to normal subjects, 40 mg methylprednisolone administration over 6 days resulted in a significant fall of elevated circulating sIL-2R levels (p < 0.05) in patients with active atopic dermatitis, most pronounced in those patients showing the highest pre-treatment levels of sIL-2R and scores of disease activity. Following administration of 1 mg dexamethasone, sIL-2R levels remained unchanged both in normal subjects and patients with atopic dermatitis. Circulating sIL-2R levels were significantly decreased in patients with long-term hypercortisolism due to Cushing's disease (p < 0.05) and significantly elevated (p < 0.05) in hypocortisolemic patients. Blockade of adrenal cortisol secretion by 1.5 g metyrapone did not change sIL-2R levels in normal subjects and sIL-2R levels were not affected in depressive patients, either before or after clinical remission or following 1.5 g metyrapone administration. These data suggest that the effect of glucocorticoid administration on circulating sIL-2R levels depends on the state of immune activation and the duration of glucocorticoid exposure. The circulating sIL-2R levels show significant changes in patients with chronic alterations of endogenous glucocorticoid secretion and in response to prolonged glucocorticoid therapy in disorders with immune activation.

Significantly increased expression of T-cell activation markers (interleukin-2 and HLA-DR) in depression: further evidence for an inflammatory process during that illness

1. Recently, the authors have reported that severe depression may be accompanied by a systemic immune activation with an increase in the number of T cells expressing activation receptors. 2. The present large-scale study examines specific T (CD2+HLADR+ and CD7+CD25+) and B (CD7-CD25+) cell activation markers in depressed inpatients and normal volunteers together with the number of leukocytes and monocytes. 3. The authors have established that depression is characterized by a significantly increased expression of T cell activation receptors (CD7+CD25+) and by the appearance of previously unexpressed T cell surface markers (CD2+HLADR+). There was a significant and positive correlation between the number of CD7+CD25+ cells and monocytes, with the expression of the HLADR and CD25 T cell activation markers being significantly and positively correlated. Up to 64% of all depressed subjects exhibit an increased expression of these activation markers with a specificity of 91%. 4. The normal control group and the depressive sample constitute two discrete classes (i.e., qualitatively distinct groups) with respect to the expression of these activation markers and leukocytosis. 5. It is concluded that our results are compatible with the presence of T-cell activation in a considerable number of depressed patients.

Immune disorders in depression: higher T helper/T suppressor-cytotoxic cell ratio

This study investigated the leukocyte T helper and T suppressor-cytotoxic cell (sub)set profile of minor, simple major and melancholic depressives versus normal controls. Using both monoclonal antibody staining and flow cytometry, we determined the absolute numbers and percentages of the following T cell immune subsets: T helper (CD4+), T virgin (CD4+CD45+), T memory (CD4+CD45-), T suppressor/cytotoxic (CD8+), CD8+ T suppressor (CD8+CD57-) and CD8+ T cytotoxic (CD8+CD57+) cells. After computing the CD4+/CD8+ ratio, we detected a significantly increased ratio in depressed patients as compared with healthy controls. Depression per se is characterized by a higher percentage of CD4+ and a lower percentage of CD8+CD57- cells. Melancholic depressed subjects exhibit a significantly increased number of CD4+ and CD4+CD45- cells. The combined use of various percentages of CD4+ and CD8+ (sub)sets yields a high degree of marker positivity for melancholia: through cumulative evaluation of those percentages, the marker positivity increases to 68% (sensitivity) and the specificity is 95%. These results together with our previous reports may refer to a depression-related state of T cell activation.

Plasma beta-endorphin and natural killer cell activity in major depression: a preliminary study

Low concentrations of beta-endorphin have been found to enhance human natural killer (NK) cell activity in vitro. Both beta-endorphin and NK activity are changed by clinical depression. To evaluate whether circulating concentrations of beta-endorphin have a role in the in vivo modulation of cellular immunity in humans, we measured plasma beta-endorphin and NK cell activity in 14 depressed patients and 14 age-matched control subjects. In the depressed patients, both plasma beta-endorphin and NK cell activity were reduced to 76% and 57%, respectively, of the mean levels in the control subjects. In addition, beta-endorphin showed a significant positive correlation with lytic units of NK cell activity in the combined group of all subjects and in the patient group (p = 0.04), but not in the control group. The study supports the hypothesis that circulating endorphin is correlated with NK cell activity in vivo. This correlation may be higher in the depressed patient group.

Hemispheric asymmetry in the effects of substantia nigra lesioning on lymphocyte reactivity in mice

Asymmetry in brain modulation of the immune system has previously been demonstrated at the neocortex level. In these experiments, the possibility of subcortical immunomodulation was investigated. In mice the substantia nigra was lesioned using the neurotoxin 6-hydroxydopamine. Four and six weeks after left or right lesions of the substantia nigra, spleen lymphocyte mitogenesis was slightly depressed or enhanced respectively as compared to sham operated controls. Differences appeared when comparing left and right lesioned groups. However, natural killer cell activity was unaffected by unilateral lesions of the substantia nigra. These results show that asymmetrical brain modulation may occur at the sub-cortical level and suggest that central dopamine is involved in neuroimmunomodulation.

Evidence for a systemic immune activation during depression: results of leukocyte enumeration by flow cytometry in conjunction with monoclonal antibody staining

Several studies have reported a suppressed immune function (e.g. blast transformation) during depression. In an attempt to define the cellular basis of the reported immune disorders, the present study investigates the leukocyte cell subset profile of minor, simple major, and melancholic depressives, versus normal controls. We have counted the number of white blood cells (WBC) lymphocytes, monocytes, and granulocytes, while the number of lymphocyte (sub)populations has been identified by phenotype, using monoclonal antibody staining in conjunction with flow cytometry. The following cell surface antigens were determined: CD3+ (pan T), CD19+ (pan B), CD4+ (T helper/inducer), CD8+ (T suppressor/cytotoxic), CD4+CD45RA (T-memory cells), CD4+CD45RA+ (T-virgin cells), surface Ig, class II MHC HLA-DR, and CD25+ (IL-2 receptor). By means of pattern recognition methods, we established distinct immunological changes in minor and simple major depressed and in melancholic patients, setting them apart from the reference population. Depression, per se, is characterized by a higher number of WBC, monocytes, class II MHC HLA-DR, and memory T cells. Minor and simple major depressives exhibited an increased T helper/suppressor ratio. Increased numbers of IL-2 receptor bearing cells are a hallmark for major depression. Melancholics showed an increased number of pan T, pan B and T suppressor/cytotoxic cells. It was concluded that the established immune cell profile of depressed patients may point towards the existence of a systemic immune activation during that illness.

A study on the blunted natural killer cell activity in severely depressed patients

Recently, some investigators have established a blunted natural killer cell activity (NKCA) in severely depressed patients. In order to replicate these findings NKC cytotoxicity assays--on fresh cell suspensions in human plasma and fetal calf serum--were performed in healthy controls and depressed inpatients. Instead of the commonly used 51Cr-release assay we have used a fluorescent NKC cytotoxicity assay, which allows a greater sensitivity. We observed a significantly blunted NKCA in melancholic patients as compared with healthy controls and minor depressives, whilst simple major depressives exhibited an intermediate position. NKC cytotoxicity assays in fetal calf serum were significantly and negatively correlated with the severity of illness. We were unable to establish any relationship between NKCA and measures of hypothalamic-pituitary-adrenal-axis function, such as baseline, postdexamethasone plasma cortisol and 24 hr urinary cortisol secretion. In addition, we did not find any effects of dexamethasone administration (1 mg orally) on NKCA.

Reduced natural killer cell cytotoxicity in depression but not in schizophrenia

A reduction of natural killer (NK) cell activity has been found in hospitalized patients with major depressive disorder. To examine whether a reduction of NK activity is found in other psychiatric patients or related to the nonspecific effects of hospitalization, NK cell cytotoxicity was compared in hospitalized depressed patients, schizophrenic inpatients, and two groups of controls separately age matched to each patient group. NK activity was significantly (p less than 0.01) lower in depressed inpatients than control subjects. However, in the hospitalized schizophrenic patients values of natural cytotoxicity did not differ from controls. These findings suggest that reduced NK cytotoxicity in depression is independent of the effects of hospitalization.

Depression, natural killer cell activity, and cortisol secretion

Natural killer (NK) cell activity was evaluated in 34 ambulatory patients with Major Depressive Disorder (MDD) and 21 healthy controls. No mean differences between the groups were found. However, female depressives (n = 19) exhibited higher NK activity than female controls (n = 14). The relationship between cortisol secretion and NK activity was examined using an integrated cortisol value derived from multiple blood samples taken between 1:00 and 4:00 PM. This comprehensive assessment of cortisol secretion circumvents spurious "single stick" cortisol values and provides a more accurate determination of hypercortisolemia than the dexamethasone suppression test. NK activity in depressives with cortisol hypersecretion (greater than 11 micrograms/dl) (n = 7) was no different than NK activity in depressives and controls with normal cortisol secretion. Furthermore, there was no correlation between cortisol secretion and NK activity in any of the groups. These results indicate that decreased NK activity is not a consistent finding in MDD and cannot be predicted by the presence of hypercortisolemia in these patients.

A further exploration of the relationships between immune parameters and the HPA-axis activity in depressed patients

In order to investigate the relationship between the immune apparatus and the hypothalamic-pituitary-adrenal (HPA)-axis activity in depressed patients, we measured in vitro lymphocyte responses to the mitogens Phytohaemagglutinin (PHA), Pokeweed (PWM) and Concanavalin A (Con A) and 8 a.m. baseline cortisol values in plasma, free cortisol excretion in 24 h urine (UFC), basal and post-dexamethasone beta-endorphin values. Major depressed patients with melancholia/psychotic features exhibited a significantly lower mitogen-induced blast transformation as compared to minor and simple major depressed patients. The lymphocyte responses to the three mitogens were significantly inversely related to baseline cortisol values and postdexamethasone beta-endorphin values. The proliferative capacity of lymphocytes to stimulation with PHA and PWM was significantly and positively related to UFC excretion. Up to 45% of the variance in the immune-responses to the mitogens was explained by the baseline cortisol, post-dexamethasone beta-endorphin and UFC values.

Biological measures and cellular immunological function in depressed psychiatric inpatients

Thirty depressed psychiatric inpatients, including 18 with a diagnosis of major depression, and 25 hospital staff controls were compared with respect to cellular immune function--that is, mitogen responsiveness to concanavalin A (con A), phytohemagglutinin (PHA), and pokeweed mitogen (PWM); natural killer cell (NK) activity; and T cell subsets, including helper/inducer T cells (CD4) and suppressor/cytotoxic cells (CD8). Only physically healthy subjects, who had not used psychoactive medications (except for low dose benzodiazepines) or other medications known to affect the immune system for at least 14 days, were included. Paired comparisons of the immune measures of patients with a DSM-III diagnosis of major depression (n = 18) with their controls demonstrated a statistically significant reduction of the patients' con A response. In addition, the patients with major depression had significantly lower con A and PHA responses than the combined patients with other forms of depression (atypical, dysthymic, or atypical bipolar). There was no indication that severity of depression, dexamethasone suppression test status, benzodiazepine use, or age accounted for the differences in immune function. A possibly important, unexpected finding was that antihistamine use was associated with lower immune function.

Antiphospholipid, antinuclear, Epstein-Barr and cytomegalovirus antibodies, and soluble interleukin-2 receptors in depressive patients

To determine whether depression might be associated with serologic indices of autoimmune processes or active virus infections, we measured the following parameters in healthy controls, minor, simple major and melancholic patients: antiphospholipid (anticardiolipin, antiphosphatidylserine), antinuclear, and Epstein-Barr (EBV) and cytomegalovirus (CMV) antibodies. In addition, the soluble interleukin-2 receptor (sIL-2R) circulating levels in serum were measured and used as a marker of T cell activation. The anticardiolipin antibody titers were higher in melancholics than in healthy controls and minor depressives. Antinuclear antibodies were present significantly more frequently in depressed patients than in normal volunteers. The anticardiolipin and antinuclear antibody titers were significantly and positively intercorrelated. Depression is characterized by increased serum circulating levels of sIL-2Rs compared to the healthy state. Antinuclear-positive subjects exhibited significantly higher sIL-2Rs than those without detectable antinuclear titers. There was a positive correlation between anticardiolipin activity and sIL-2Rs. We found no evidence that depression is linked to EBV or CMV infection.

Measurement of cortisol and lymphocyte subpopulations in depressed and conduct-disordered adolescents

Lymphocyte subpopulations were analyzed in 11 adolescents with major depressive disorder, 11 with conduct disorder, and eight normal age-matched subjects. No significant differences were noted on any T or B cell measure between the groups. Further, no significant correlations were found between any cortisol measure (baseline cortisol, post-dexamethasone cortisol, urinary free cortisol) and any lymphocyte measure in either depressed or conduct-disordered adolescents. The negative findings in this small sample contrast with those reported in adult patients and suggest that an aging effect may be associated with the immunological changes reported in older depressed patients.