Effect of monoamine reuptake inhibiting antidepressants on major histocompatibility complex expression on macrophages in normal rats and rats with experimental allergic neuritis (EAN)

MHC Class I Downregulation in Cancer: Underlying Mechanisms and Potential Targets for Cancer Immunotherapy

In recent years, major advances have been made in cancer immunotherapy. This has led to significant improvement in prognosis of cancer patients, especially in the hematological setting. Nonetheless, translation of these successes to solid tumors was found difficult. One major mechanism through which solid tumors can avoid anti-tumor immunity is the downregulation of major histocompatibility complex class I (MHC-I), which causes reduced recognition by- and cytotoxicity of CD8⁺ T-cells. Downregulation of MHC-I has been described in 40-90% of human tumors, often correlating with worse prognosis. Epigenetic and (post-)transcriptional dysregulations relevant in the stabilization of NFkB, IRFs, and NLRC5 are often responsible for MHC-I downregulation in cancer. The intrinsic reversible nature of these dysregulations provides an opportunity to restore MHC-I expression and facilitate adaptive anti-tumor immunity. In this review, we provide an overview of the mechanisms underlying reversible MHC-I downregulation and describe potential strategies to counteract this reduction in MHC-I antigen presentation in cancer.

The role of macrophages in anti-inflammatory activity of antidepressant drugs

Depression is a common disease influencing patients' quality of life, whose etiology involves complex interactions of environmental, genetic and immunological factors. The latter factors include proinflammatory activation of monocytes and macrophages and increased serum levels of proinflammatory cytokines, altogether formulated as the "macrophage theory of depression". Our current review summarizes the impact of the most commonly used antidepressant drugs on the immune response with special emphasis on the role of macrophages in the clinically observed effects. The anti-inflammatory action of antidepressants mainly results from their direct interaction with immune cells and from changes in the concentration and the relations of neurotransmitters sensed by these cells. The summarized data revealed that Mφs are one of the leading cell populations involved in drug-mediated immune effects that can be observed both in subjects with depression as well as in individuals not suffering from depression. Thus, currently reviewed immunomodulatory effects of the experimental use of different antidepressant drugs suggest the possibility of utilizing them in complex therapeutic strategies dedicated to various inflammatory and immune-mediated diseases. It is worth noting that an excessive inflammatory reaction is also associated with the pathogenesis of various cardiovascular, metabolic and neuro-endocrine diseases. Thus, the inclusion of antidepressants in the complex therapy of these disorders may have beneficial effects through the enhancement of the mood of the patient and alleviation of chronic inflammation. On the other hand, presented data suggest that the influence of chronically used antidepressants on anti-microbial and anti-tumor immunity could also be taken into consideration.

Peripheral Nerve Myelin Modulates the Effect of Antidepressants on Major Histocompatibility Complex Expression on Macrophages in Experimental Allergic Neuritis

The effect of bovine peripheral nerve myelin (BPM) used for induction of experimental allergic neuritis (EAN) in Lewis rats, on antidepressants' modulation of interferon-gamma (IFN-γ)-induced major histocompatibility complex (MHC) class I and II antigen expression on peritoneal macrophages in EAN rats was studied. Antidepressants with different profiles concerning inhibition of the neuronal reuptake of the monoamines serotonin (5-HT) and noradrenalin (NA), respectively, in concentrations of 10−4 to 10−8 M were used. At the concentration of 1.0 U/ml IFN-γ, most antidepressants significantly enhanced both MHC class I and class II expression, except maprotiline, a selective NA reuptake inhibiting antidepressant that suppressed MHC class I expression. Zimeldine, a selective 5-HT reuptake inhibitor did not affect MHC class II expression. BPM in general had an enhancing effect on modulation of both MHC class I and class II expression by antidepressants. By itself BPM enhanced MHC class I expression, but did not affect class II expression at IFN-γ 1.0 U/ml. The modulating effect of BPM on regulation of MHC expression by antidepressants could be the result of contaminating T cells and release of IFN-γ into cultures. The modulatory effect of antidepressants on MHC expression may to some extent be exerted by the action on 5-HT and/or NA regulation, but also by direct effects of antidepressants on macrophages. They probably play a role in zimeldine-induced Guillain-Barré syndrome in some patients and in the suppression of clinical signs of EAN in Lewis rats reported for some antidepressants.

Inflammation in depression: is adiposity a cause?

Mounting evidence indicates that inflammation may play a significant role in the development of depression. Patients with depression exhibit increased inflammatory markers, and administration of cytokines and other inflammatory stimuli can induce depressive symptoms. Mechanisms by which cytokines access the brain and influence neurotransmitter systems relevant to depression have also been described, as have preliminary findings indicating that antagonizing inflammatory pathways may improve depressive symptoms. One primary source of inflammation in depression appears to be adiposity. Adipose tissue is a rich source of inflammatory factors including adipokines, chemokines, and cytokines, and a bidirectional relationship between adiposity and depression has been revealed. Adiposity is associated with the development of depression, and depression is associated with adiposity, reflecting a potentional vicious cycle between these two conditions which appears to center around inflammation. Treatments targeting this vicious cycle may be especially relevant for the treatment and prevention of depression as well as its multiple comorbid disorders such as cardiovascular disease, diabetes, and cancer, all of which have also been associated with both depression and inflammation.

Eating ourselves to death (and despair): the contribution of adiposity and inflammation to depression

Obesity and related metabolic conditions are of epidemic proportions in most of the world, affecting both adults and children. The accumulation of lipids in the body in the form of white adipose tissue in the abdomen is now known to activate innate immune mechanisms. Lipid accumulation causes adipocytes to directly secrete the cytokines interleukin (IL) 6 and tumor necrosis factor alpha (TNFalpha), but also monocyte chemoattractant protein 1 (MCP-1), which results in the accumulation of leukocytes in fat tissue. This sets up a chronic inflammatory state which is known to mediate the association between obesity and conditions such as cardiovascular disease, type 2 diabetes, and cancer. There is also a substantial literature linking inflammation with risk for depression. This includes the observations that: (1) people with inflammatory diseases such as multiple sclerosis, cardiovascular disease, and psoriasis have elevated rates of depression; (2) many people administered inflammatory cytokines such as interferon alpha develop depression that is indistinguishable from depression in non-medically ill populations; (3) a significant proportion of depressed persons show upregulation of inflammatory factors such as IL-6, C-reactive protein, and TNFalpha; (4) inflammatory cytokines can interact with virtually every pathophysiologic domain relevant to depression, including neurotransmitter metabolism, neuroendocrine function, and synaptic plasticity. While many factors may contribute to the association between inflammatory mediators and depression, we hypothesize that increased adiposity may be one causal pathway. Mediational analysis suggests a bi-directional association between adiposity and depression, with inflammation possibly playing an intermediary role.

The impact of neuroimmune dysregulation on neuroprotection and neurotoxicity in psychiatric disorders--relation to drug treatment

An inflammatory pathogenesis has been postulated for schizophrenia and major depression (MD). In schizophrenia and depression, opposing patterns oftype-1 vs type-2 immune response seem to be associated with differences in the activation of the enzyme indoleamine 2,3-dioxygenase and in the tryptophan-kynurenine metabolism, resulting in increased production of kynurenic acid in schizophrenia and decreased production of kynurenic acid in depression. These differences are associated with an imbalance in the glutamatergic neurotransmission, which may contribute to an excessive agonist action of N-methyl-D-aspartate (NMDA) in depression and of NMDA antagonism in schizophrenia. Regarding the neuroprotective function of kynurenic acid and the neurotoxic effects of quinolinic acid (QUIN), different patterns of immune activation may also lead to an imbalance between the neuroprotective and the neurotoxic effects of the tryptophanlkynurenine metabolism. The differential activation of microglia cells and astrocytes may be an additional mechanism contributing to this imbalance. The immunological imbalance results in an inflammatory state combined with increased prostaglandin E2 production and increased cyclo-oxygenase-2 (COX-2) expression. The immunological effects of many existing antipsychotics and antidepressants, however, partly correct the immune imbalance and the excess production of the neurotoxic QUIN, COX-2 inhibitors have been tested in animal models of depression and in preliminary clinical trials, pointing to favorable effects in schizophrenia and in MD.

A psychoneuroimmunological perspective to Emil Kraepelins dichotomy: schizophrenia and major depression as inflammatory CNS disorders

The Kraepelinian classification of psychiatric disorders, in particular the dichotomy of dementia praecox and manic-depressive psychosis is under discussion since a long time. In recent years, not only new research in the fields of psychopathology and clinical outcome, but also findings of biological markers in the areas of neurophysiology, neuroendocrinology, psychoneuroimmunology, genetics, or psychopharmacology show a big overlap between both groups of disorders. This overlap of symptoms and markers of both disorders intensified the discussion and the proposals for new criteria for the classification of psychiatric disorders. By means of findings from the field of psychoneuroimmunology and inflammation it will be shown that different pathological mechanisms in depression and schizophrenia may lead to the same final common pathway of inflammation. These mechanisms include the immunological balance between type-1 and type-2 immune activation which influences the tryptophan-degradating enzyme indoleamine 2,3-dioxygenase (IDO) in the CNS in opposite ways, leading to an altered availability of tryptophan and serotonin, and a disturbance of the kynurenine metabolism with an imbalance in favor of the production of the NMDA-receptor agonist quinolinic acid in depression and of the NMDA-receptor antagonist kynurenic acid in schizophrenia. In both disorders, however, an increased production of prostaglandin E2 and increased expression of cyclo-oxygenase-2 reflect a slight inflammatory process taking place probably in different regions of the CNS. Albeit this common inflammatory pathway--inflammation is a general pathway of the body as answer to a lot of different noxae and pathogens--the Kraepelinian dichotomy is important with respect to pathological mechanisms and therapeutic approaches, not only for further research in understanding the exact pathological mechanisms but also for the development of preventive strategies in high risk individuals and in patients. Opposite pathways regarding the immune activation, the neurotoxic versus neuroprotective kynurenine metabolites and the agonistic versus antagonistic effects on the NMDA receptor and the glutamatergic neurotransmission show despite a possible therapeutic advantage of anti-inflammatory therapy in both disorders that the Kraepelinian dichotomy still has a significant value from a biologic-psychiatric point of view.

The immune-mediated alteration of serotonin and glutamate: towards an integrated view of depression

Beside the well-known deficiency in serotonergic neurotransmission as pathophysiological correlate of major depression (MD), recent evidence points to a pivotal role of increased glutamate receptor activation as well. However, cause and interaction of these neurotransmitter alterations are not understood. In this review, we present a hypothesis integrating current concepts of neurotransmission and hypothalamus-pituitary-adrenal (HPA) axis dysregulation with findings on immunological alterations and alterations in brain morphology in MD. An immune activation including increased production of proinflammatory cytokines has repeatedly been described in MD. Proinflammatory cytokines such as interleukin-2, interferon-gamma, or tumor necrosis factor-alpha activate the tryptophan- and serotonin-degrading enzyme indoleamine 2,3-dioxygenase (IDO). Depressive states during inflammatory somatic disorders are also associated with increased proinflammatory cytokines and increased consumption of tryptophan via activation of IDO. An enhanced consumption of serotonin and its precursor tryptophan through IDO activation could well explain the reduced availability of serotonergic neurotransmission in MD. An increased activation of IDO and its subsequent enzyme kynurenine monooxygenase by proinflammatory cytokines, moreover, leads to an enhanced production of quinolinic acid, a strong agonist of the glutamatergic N-methyl-D-aspartate receptor. In inflammatory states of the central nervous system, IDO is mainly activated in microglial cells, which preferentially metabolize tryptophan to the NMDA receptor agonist quinolinic acid, whereas astrocytes - counteracting this metabolism due to the lack of an enzyme of this metabolism - have been observed to be reduced in MD. Therefore the type 1/type 2 immune response imbalance, associated with an astrocyte/microglia imbalance, leads to serotonergic deficiency and glutamatergic overproduction. Astrocytes are further strongly involved in re-uptake and metabolic conversion of glutamate. The reduced number of astrocytes could contribute to both, a diminished counterregulation of IDO activity in microglia and an altered glutamatergic neurotransmission. Further search for antidepressant agents should take into account anti-inflammatory drugs, for example, cyclooxygenase-2 inhibitors, might exert antidepressant effects by acting on serotonergic deficiency, glutamatergic hyperfunction and antagonizing neurotoxic effects of quinolinic acid.

Neuroimmune-endocrine crosstalk in schizophrenia and mood disorders

This review focuses on possible causes and the impact of different immune states in schizophrenia and major depression. It discusses the fact that, in schizophrenia, an over-activation of the type 2 immune response may dominate, while the type 1 and the pro-inflammatory immune responses are over-activated in major depression. The consequence of these diverse immune states is the activation and, respectively, inhibition of different enzymes in tryptophan/kynurenine metabolism, which may lead to an overemphasis of N-methyl-D-aspartate (NMDA) receptor antagonism in schizophrenia and of NMDA-receptor agonism in depression, resulting in glutamatergic hypofunction in schizophrenia and glutamatergic hyperfunction in major depression. In addition, the activation of the type 1 and the pro-inflammatory immune responses in major depression result in increased serotonin degradation and a serotonergic deficit. While antipsychotics and antidepressants today mainly act on the dopaminergic-glutamatergic and the noradrenergic-serotonergic neurotransmission, anti-inflammatory and immune-modulating therapies might act more basically at the pathophysiological mechanism. The limitations of this concept, however, are critically discussed.

Anti-cytokine autoantibodies in experimental autoimmune neuritis in Lewis rats

Experimental autoimmune neuritis (EAN) is a CD4+ T-cell-mediated, inflammatory demyelinating disease of the peripheral nervous system (PNS) that serves as a model for Guillain-Barre syndrome (GBS) in humans. Cytokine production has been suggested to act a pathogenic role for EAN. To study the potential role of cytokines in context with cytokine autoantibodies (Aabs) in EAN, we used in situ hybridization to detect mRNA expression of interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, IL-4, IL-10, and transforming growth factor (TGF)-beta in lymph node mononuclear cell (MNC) and in sciatic nerve sections, as well as ELISA for detection of their autoantibodies in sera and cerebrospinal fluid (CSF) over the course of EAN. Increased mRNA expression for IFN-gamma and TNF-alpha was registered correlating with the peak of clinical signs of EAN, and high levels of mRNA expression for IL-4, IL-10, and TGF-beta were associated with EAN recovery. The levels of cytokine mRNAs were generally inversely correlated to their autoantibodies in serum and CSF, whereby the CSF levels were equal to or lower than the serum levels. Autoantibodies to IFN-gamma dose-dependently inhibited IFN-gamma-induced MHC expression by peritoneal macrophages proving a neutralizing biological effect of these autoantibodies. Our data demonstrate the existence of the anti-cytokine autoantibodies in the sera and CSF of rats with EAN; however, the role of anti-cytokine autoantibodies in the disease process of EAN remains to be resolved.

Clomipramine and imipramine suppress clinical signs and T and B cell response to myelin proteins in experimental autoimmune neuritis in Lewis rats

5-Hydroxytryptamine (5-HT) reuptake inhibitors of the zimeldine-type have induced polyneuropathies similar to Guillain-Barré syndrome (GBS) in patients with endogenous depression. Some monoamine neurotransmitters have been shown to affect immune reactions in vivo and in vitro in a concentration-dependent manner. We therefore studied the effect of the monoamine reuptake inhibitory anti-depressants, clomipramine and imipramine on specific immune response and the clinical course of experimental autoimmune neuritis (EAN), the animal model of GBS in humans. Clomipramine and imipramine both suppressed clinical signs of EAN induced by immunization with bovine peripheral nerve myelin (BPM), when given at a dose of 20 mg/kg/day intraperitoneally, via osmotic pumps. Clomipramine and imipramine reduced the numbers of Th1 cells secreting IFN-gamma in response to the neuritogenic myelin proteins BPM, P0 and P2 among lymph node mononuclear cells (MNC) from rats with EAN. The levels of cells secreting IgG antibodies to BPM, P2 and GM1 in lymph nodes were reduced at the height of EAN in clomipramine and imipramine treated animals. The action of clomipramine and imipramine on induced IFN-gamma and anti-myelin antibodies suggests that the mechanism for the suppressive effect of those substances on EAN symptoms may be due to an action on myelin T and B cell autoreactivity. Considering that the main common pharmacological principle of clomipramine and imipramine is to increase the functional activity of the nor-adrenaline (NA) and serotonin (5-HT) of the monoamines, it seems justified to postulate that the actions of clomipramine and imipramine demonstrated in this study to some extent involve NA and/or 5-HT. The immunomodulatory effects of clomipramine and imipramine call for further research on the potential role of drugs acting on the monoamine system in the treatment of autoimmune diseases, and for further studies of immunological mechanisms in the pathogenesis of depressive disorders.

Psychoneuroimmunology and the cytokine action in the CNS: implications for psychiatric disorders

1. Parallel to the current rapid development of new immunological methods, immune mechanisms are gaining more importance for our understanding of psychiatric disorders. The purpose of this article is to review basic and clinical investigations that elucidate the relationship between the CNS and the immune system. 2. The topical literature dealing with the interactions of immune system, neurotransmitters, psychological processes, and psychiatric disorders, especially in relation to cytokines, is reviewed. 3. An activation of the immune system in schizophrenia and depressive disorders has repeatedly been described. Cytokines, actively transported into the CNS, play a key role in this immune activation. It was recently observed that cytokines activate astrocytes and microglia cells, which in turn produce cytokines by a feedback mechanism. Moreover, they strongly influence the dopaminergic, noradrenergic, and serotonergic neurotransmission. 4. There are indications that the cascade of cytokines can be activated by neuronal processes. These findings close a theoretical gap between stress and its influence on immunity. Psychomotor, sickness behavior and sleep are related to IL-1; disturbances of memory and cognitive impairment are to IL-2, in part also to TNF-alpha. The hypersecretion of IL-2 is assumed to have a prominent influence on schizophrenia, and IL-6, on depressive disorders. 5. Although single cytokines most likely do not have a specificity for certain psychiatric disorders, a characteristic pattern of cytokine actions in the CNS, including influences of the cytokines on the blood-brain barrier, seems to play a role in psychiatric disorders. This may have therapeutic implications for the future.

Potential role of autoantibodies in the regulation of cytokine responses during bacterial infections

An immunoregulatory mechanism involving release of neutralizing autoantibodies (Aabs) to self cytokines during bacterial infections is presented herein. Intraperitoneal inoculation of Haemophilus influenzae type b into Sprague-Dawley rats resulted in a self-limiting meningitis. High levels of cells expressing mRNA for gamma interferon (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) were detected 12 to 48 h postinoculation (p.i.) in splenocytes, and large numbers of IFN-gamma-secreting cells were present in the spleen on day 3 p.i. These levels were undetectable at days 9 and 14 p.i. Increased titers of Aabs of immunoglobulin G (IgG) isotypes to both cytokines were observed, with a peak at day 7 p.i. and with very low levels at day 30. Upon reinoculation with H. influenzae type b at day 30, regeneration of Aabs was recorded 7 days later (i.e., at day 37). To elucidate their regulatory importance, Aabs dose-dependently inhibited IFN-gamma production by splenocytes, IFN-gamma-induced major histocompatibility complex expression by peritoneal macrophages, and TNF-alpha-induced thymocyte proliferation. To control the specificity of these Aabs, Fab fragments of purified serum Igs from day p.i. exhibited binding and neutralizing effects. Furthermore, preincubation of the sera with a cytokine inhibited the binding and neutralization effects of that particular cytokine, but not those of any other cytokine. Aab-producing B cells were cloned, and their supernatants had similar effects. Our data suggest a role for autoimmunity in cytokine regulation and suggest that a maintained balance of this mechanism may protect from sequelae.

Influence of ion channel modulation on in vitro interferon-gamma induced MHC class I and II expression on macrophages

The in vitro effect of K+ channel blockers quinidine and verapamil, anion channel blocker SITS and K+ channel openers diazoxide, pinacidil, and BRL 38227 on interferon-gamma (IFN-gamma) induced MHC class I and II expression of Lewis rat peritoneal macrophages was investigated by cell ELISA assay. MHC class I expression was significantly enhanced by diazoxide at concentrations of 10(-5)M to 10(-6)M and by pinacidil and BRL 38227 at the concentration of 10(-6)M. MHC class II expression was enhanced by pinacidil and BRL 38227 at concentrations of 10(-5)M to 10(-6)M. The enhancing effect of pinacidil could be blocked by inhibitors of the protein kinases PKA and PKC suggesting that activation of both is required for optimum induction of MHC molecule expression. K+ and anion channel blockers were less active in modulation of MHC molecule expression. Verapamil had no influence, quinidine suppressed MHC class I expression at concentrations of 10(-4)M to 10(-5)M, and SITS suppressed MHC class I expression at the concentration of 10(-3)M. Since MHC class II expression is essential for efficient antigen presentation to T helper cells and MHC class I expression is required for target cell lysis by cytotoxic T cells, ion channel modulating drugs may be potential candidates for immunopharmacological intervention in inflammatory diseases.