Sympathetic-Immune Interactions during Different Types of Immune Challenge.

BACKGROUND: The neuro-endocrine regulation of immune functions is based on a complex network of interactions. As part of this series of articles, we refer here to immune-sympathetic interactions that are triggered by different types of immune challenge. SUMMARY: We mention the initial hypothesis that led to the proposal that the sympathetic nervous system (SNS) is involved in immunoregulation. We next refer mainly to our initial work performed at a time when most immunologists were concentrated in clarifying aspects of the immune system that are essential for its regulation from within. The first approach was to explore whether immune responses to innocuous antigens and superantigens can elicit changes in the activity of the SNS, and their potential relevance for the regulation of the activity of the immune system. The following step was to explore whether comparable immune-SNS interactions are detected in different models of diseases with immune components, such as parasitic and viral infections and autoimmune pathologies. KEY MESSAGES: We pose some general considerations that may at least partially explain seemly discrepant findings, and remark the importance of interpreting immunoregulatory effects of the SNS together with other neuro-endocrine inputs that simultaneously occur when the activity of the immune system changes. Finally, we provide some arguments to re-consider the use of the expression "reflex" in immunology.

To protect or to kill: A persisting Darwinian immune dilemma.

The immune system, which evolved as a protective system, can paradoxically mediate lethal effects when it is over-activated. These effects can be traced back to infected insects and are mainly mediated by phylogenetically old cytokines that have been found already in starfishes and sponges. We hypothesize that these anti-homeostatic effects are important for restricting the cumulative risk of transmission of highly mutating environmental pathogens that may endanger species, particularly when they start to originate and expand. Considering the Darwinian view that evolution is a permanent process, this anti-homeostatic program is preserved and expressed even when there is no risk for the species. Here, we review these aspects and discuss how evolutionary-imposed anti-homeostatic immune programs are expressed during acute and chronic human diseases, which can be further aggravated in the absence of medical interventions. The relevance of early identification of ancestral biomarkers that predict a shift from protective to deleterious immune outcomes is emphasized.

Nose-to-Brain Delivery of Dexamethasone: Biodistribution Studies in Mice.

Neuroinflammation (NI) is an important physiologic process which promotes the tissue repair and homeostatic maintenance in the central nervous system after different types of insults. However, when it is exacerbated and sustained in time, NI plays a critical role in the pathogenesis of different neurologic diseases. The high systemic doses required for brain-specific targeting lead to severe undesirable effects. The intranasal (IN) route has been proposed as an alternative drug administration route for a better NI control. Herein, the brain biodistribution of intranasally administered dexamethasone versus intravenously administered one is reported. A higher amount of dexamethasone was found in every analyzed region of those brains of intranasally administered mice. HPLC analysis also revealed that IN administration allows Dex to arrive faster and in a greater concentration to the brain in comparison with intravenous administration, data confirmed by immunofluorescence and HPLC analysis. These data support the proposal of the IN administration of Dex as an alternative for a more efficient control of NI. SIGNIFICANCE STATEMENT: This work highlights the biodistribution of dexamethasone after its intranasal administration. Intranasal administration allows for a faster arrival, better distribution, and a higher concentration of the drug within the brain compared to its intravenous administration. These results explain some of the evidence shown in a previous work in which dexamethasone controls neuroinflammation in a murine stroke model and can be used to propose alternative treatments for neuroinflammatory diseases.

Treatment-Resistant Human Extraparenchymal Neurocysticercosis: An Immune-Inflammatory Approach to Cysticidal Treatment Outcome.

OBJECTIVE: The aim of this study is to analyze the immune-endocrine profile in neurocysticercosis (NC) patients resistant to cysticidal treatment. METHODS: The inflammatory and regulatory responses of 8 resistant NC patients with extraparenchymal parasites and 5 healthy controls were evaluated through flow cytometry. Serum interleukin levels were measured by ELISA and catecholamines levels by high performance liquid chromatography. RESULTS: Higher percentages of Tr1, CD4+CD25+FOXP3+CD127- and CD4+CD45RO+FOXP3HI were found in NC patients compared with healthy controls, but no difference was found in catecholamine levels. Antigen-specific proliferative immune response was observed in NC patients. Neither anti-inflammatory nor pro-inflammatory cytokines showed differences between patients and controls, but IL-6 levels were lower in treatment-resistant NC patients. In addition, TGFß showed a significant negative correlation with dopamine. CONCLUSIONS: Altogether, these results may point to a modulation of the neuroinflammation in these patients that could indirectly favor cysticercal survival in CNS microenvironment.

The sympathetic nervous system affects the susceptibility and course of Trypanosoma cruzi infection.

Trypanosoma cruzi (T. cruzi) is an intracellular parasite that causes Chagas' disease, a major health problem in Latin America. Using a murine model of infection with this parasite, we have previously shown that corticosterone blood levels are markedly elevated during the course of the disease in C57Bl/6 male mice and that this increase is protective for the host by restricting the production of pro-inflammatory cytokines. Since the hypothalamus-pituitary-adrenal (HPA) axis usually operates in a concerted way with the sympathetic nervous system (SNS), we have now studied whether noradrenergic nerves can affect the course of T. cruzi infection and the sexual dimorphism observed in the disease. We found a decreased splenic noradrenaline concentration and content, paralleled by a reduction in noradrenergic nerve fibers in the spleen of infected mice, and increased HPA axis activity. These alterations were more marked in males than in females. When the spontaneous loss of noradrenergic nerve fibers was advanced by chemical sympathectomy prior to infection, males died earlier and mortality significantly increased in females. Chemical denervation did not significantly affect the concentration of specific IgM and IgG2a antibodies to T. cruzi, and did not worsen myocarditis, but resulted in increased parasitemia and IL-6 and IFN-γ blood levels. The results obtained in this model of parasitic disease provide further indications of the relevance of interactions between the immune system and the SNS for host defense.

Helminth infection alters mood and short-term memory as well as levels of neurotransmitters and cytokines in the mouse hippocampus.

UNLABELLED: Helminthic infections are important causes of morbidity and mortality in many developing countries, where children bear the greatest health burden. The ability of parasites to cause behavioral changes in the host has been observed in a variety of host-parasite systems, including the Taenia crassiceps-mouse model. In murine cysticercosis, mice exhibit a disruption in the sexual, aggressive and avoidance predator behaviors. OBJECTIVE: The present study was conducted to characterize short-term memory and depression-like behavior, as well as levels of neurotransmitters and cytokines in the hippocampus of cysticercotic male and female mice. METHODS: Cytokines were detected by RT-PCR and neurotransmitters were quantified by HPLC. RESULTS: Chronic cysticercosis infection induced a decrease in short-term memory in both male and female mice, having a more pronounced effect in females. Infected females showed a significant increase in forced swimming tests with a decrease in immobility. In contrast, male mice showed an increment in total activity and ambulation tests. Serotonin levels decreased by 30% in the hippocampus of infected females whereas noradrenaline levels significantly increased in infected males. The hippocampal expression of IL-4 increased in infected female mice, but decreased in infected male mice. CONCLUSION: Our study suggests that intraperitoneal chronic infection with cysticerci in mice leads to persistent deficits in tasks dependent on the animal's hippocampal function. Our findings are a first approach to elucidating the role of the neuroimmune network in controlling short-term memory and mood in T. crassiceps-infected mice.

Adverse neuro-immune-endocrine interactions in patients with active tuberculosis.

The nervous, endocrine and immune systems play a crucial role in maintaining homeostasis and interact with each other for a successful defensive strategy against injurious agents. However, the situation is different in long-term diseases with marked inflammation, in which defensive mechanisms become altered. In the case of tuberculosis (TB), this is highlighted by several facts: an imbalance of plasma immune and endocrine mediators, that results in an adverse environment for mounting an adequate response against mycobacteria and controlling inflammation; the demonstration that dehidroepiandrosterone (DHEA) secretion by a human adrenal cell line can be inhibited by culture supernatants from Mycobacterium tuberculosis-stimulated peripheral blood mononuclear cells - PBMC - of TB patients, with this effect being partly reverted when neutralizing transforming growth factor-ß in such supernantants; the in vitro effects of adrenal steroids on the specific immune response of PBMC from TB patients, that is a cortisol inhibition of mycobacterial antigen-driven lymphoproliferation and interferon-γ production as well as a suppression of TGF-ß production in DHEA-treated PBMC; and lastly the demonstration that immune and endocrine compounds participating in the regulation of energy sources and immune activity correlated with the consumption state of TB patients. Collectively, immune-endocrine disturbances of TB patients are involved in critical components of disease pathology with implications in the impaired clinical status and unfavorable disease outcome. This article is part of a Special Issue entitled 'Neuroinflammation in neurodegeneration and neurodysfunction'.

Intranasal Versus Intravenous Dexamethasone to Treat Hospitalized COVID-19 Patients: A Randomized Multicenter Clinical Trial.

BACKGROUND: SARS-CoV2 induces flu-like symptoms that can rapidly progress to severe acute lung injury and even death. The virus also invades the central nervous system (CNS), causing neuroinflammation and death from central failure. Intravenous (IV) or oral dexamethasone (DXM) reduced 28 d mortality in patients who required supplemental oxygen compared to those who received conventional care alone. Through these routes, DMX fails to reach therapeutic levels in the CNS. In contrast, the intranasal (IN) route produces therapeutic levels of DXM in the CNS, even at low doses, with similar systemic bioavailability. AIMS: To compare IN vs. IV DXM treatment in hospitalized patients with COVID-19. METHODS: A controlled, multicenter, open-label trial. Patients with COVID-19 (69) were randomly assigned to receive IN-DXM (0.12 mg/kg for three days, followed by 0.6 mg/kg for up to seven days) or IV-DXM (6 mg/d for 10 d). The primary outcome was clinical improvement, as defined by the National Early Warning Score (NEWS) ordinal scale. The secondary outcome was death at 28 d between IV and IN patients. Effects of both treatments on biochemical and immunoinflammatory profiles were also recorded. RESULTS: Initially, no significant differences in clinical severity, biometrics, and immunoinflammatory parameters were found between both groups. The NEWS-2 score was reduced, in 23 IN-DXM treated patients, with no significant variations in the 46 IV-DXM treated ones. Ten IV-DXM-treated patients and only one IN-DXM patient died. CONCLUSIONS: IN-DMX reduced NEWS-2 and mortality more efficiently than IV-DXM, suggesting that IN is a more efficient route of DXM administration.

A cytokine network involving brain-borne IL-1ß, IL-1ra, IL-18, IL-6, and TNFα operates during long-term potentiation and learning.

We have previously shown that long-term potentiation (LTP) induces hippocampal IL-1ß and IL-6 over-expression, and interfering their signalling either inhibits or supports, respectively, LTP maintenance. Consistently, blockade of endogenous IL-1 or IL-6 restricts or favours hippocampal-dependent memory, effects that were confirmed in genetically manipulated mice. Since cytokines are known for their high degree of mutual crosstalk, here we studied whether a network of cytokines with known neuromodulatory actions is activated during LTP and learning. We found that, besides IL-1ß and IL-6, also IL-1 receptor antagonist (IL-1ra) and IL-18, but not TNFα are over-expressed during LTP maintenance in freely moving rats. The increased expression of these cytokines is causally related to an increase in synaptic strength since it was abrogated when LTP was interfered by blockade of NMDA-glutamate receptors. Likewise, IL-1 and IL-6 were found to be over-expressed in defined regions of the hippocampus during learning a hippocampus-dependent task. However, during learning, changes in IL-18 were restricted to the dorsal hippocampus, and no differences in TNFα and IL1-ra expression were noticed in the hippocampus. Noticeably, IL-1ra transcripts were significantly reduced in the prefrontal cortex. The relation between cytokine expression and learning was causal because such changes were not observed in animals from a pseudo-trained group that was subject to the same manipulation but could not learn the task. Taken together with previous studies, we conclude that activation of a cytokine network in the brain is a physiologic relevant phenomenon not only for LTP maintenance but also for certain types of learning.

Intranasal dexamethasone: a new clinical trial for the control of inflammation and neuroinflammation in COVID-19 patients.

BACKGROUND: By end December of 2021, COVID-19 has infected around 276 million individuals and caused over 5 million deaths worldwide. Infection results in dysregulated systemic inflammation, multi-organ dysfunction, and critical illness. Cells of the central nervous system are also affected, triggering an uncontrolled neuroinflammatory response. Low doses of glucocorticoids, administered orally or intravenously, reduce mortality among moderate and severe COVID-19 patients. However, low doses administered by these routes do not reach therapeutic levels in the CNS. In contrast, intranasally administered dexamethasone can result in therapeutic doses in the CNS even at low doses. METHODS: This is an approved open-label, multicenter, randomized controlled trial to compare the effectiveness of intranasal versus intravenous dexamethasone administered in low doses to moderate and severe COVID-19 adult patients. The protocol is conducted in five health institutions in Mexico City. A total of 120 patients will be randomized into two groups (intravenous vs. intranasal) at a 1:1 ratio. Both groups will be treated with the corresponding dexamethasone scheme for 10 days. The primary outcome of the study will be clinical improvement, defined as a statistically significant reduction in the NEWS-2 score of patients with intranasal versus intravenous dexamethasone administration. The secondary outcome will be the reduction in mortality during hospitalization. CONCLUSIONS: This protocol is currently in progress to improve the efficacy of the standard therapeutic dexamethasone regimen for moderate and severe COVID-19 patients. TRIAL REGISTRATION: ClinicalTrials.gov NCT04513184 . Registered November 12, 2020. Approved by La Comisión Federal para la Protección contra Riesgos Sanitarios (COFEPRIS) with identification number DI/20/407/04/36. People are currently being recruited.

Central and peripheral cytokines mediate immune-brain connectivity.

The immune system is a homeostatic system that contributes to maintain the constancy of the molecular and cellular components of the organism. Immune cells can detect the intrusion of foreign antigens or alteration of self-components and send information to the central nervous system (CNS) about this kind of perturbations, acting as a receptor sensorial organ. The brain can respond to such signals by emitting neuro/endocrine signals capable of affecting immune reactivity. Thus, the immune system, as other physiologic systems, is under brain control. Under disease conditions, when priorities for survival change, the immune system can, within defined limits, reset brain-integrated neuro-endocrine mechanisms in order to favour immune processes at the expenses of other physiologic systems. In addition, some cytokines initially conceived as immune products, such as IL-1 and IL-6, are also produced in the "healthy" brain by glial cells and even by some neurons. These and other cytokines have the capacity to affect synaptic plasticity acting as mediators of interactions between astrocytes and pre- and post-synaptic neurons that constitute what is actually defined as a tripartite synapse. Since the production of cytokines in the brain is affected by peripheral immune and central neural signals, it is conceivable that tripartite synapses can, in turn, serve as a relay system in immune-CNS communication.

The role of the sympathetic nervous system in the thymus in health and disease.

The existence of a network of immunoneuroendocrine interactions that results in the reciprocal modulation of the classical functions of each system is well established at present. Most of the evidence derives from studies on secondary lymphoid organs, such as the spleen and lymph nodes. In this article, several aspects relevant to understand the role of the sympathetic nervous system in the establishment of these interactions in the thymus are discussed. At present, the sympathetic innervation of the thymus, the expression of adrenergic receptors in thymic cells, particularly of ß-adrenergic receptors, and the effect of sympathetic neurotransmitters, although mainly derived from in vitro or pharmacological studies, seem to be relatively well studied. However, other aspects, such as the relevance that immune-sympathetic interactions at the thymic level may have for certain diseases, specially autoimmune or other diseases that primarily involve the activation of the immune system, as well as how the integration of sympathetic and hormonal signals at local levels may affect thymic functions, certainly deserve further investigation.

New insights into cytokine gene expression in the rat hypothalamus following endotoxin challenge.

Peripheral injection of the endotoxin LPS in rats 3 weeks prior to a second injection of LPS derived from another bacterial strain results in elevated corticosterone and decreased pro-inflammatory cytokines in the blood. We further investigated this model by measuring cytokine expression in the hypothalamus and spleen. In LPS-pretreated rats, hypothalamic expression of a range of cytokines was attenuated in response to the second injection of LPS while splenic expression was elevated. This is the first demonstration that prior exposure to an endotoxin can differentially affect cytokine expression in the brain and peripheral tissues when a host is confronted with a second, acute, pro-inflammatory stimulus. Changes in hypothalamic cytokine expression in endotoxin pretreated rats may provide new evidence for the involvement of central cytokine pathways in modulating peripheral inflammation and mediating psychopathological alterations associated with inflammatory diseases.

Interleukin-1 resets glucose homeostasis at central and peripheral levels: relevance for immunoregulation.

We briefly discuss here evidence showing that the capacity of IL-1beta to mediate adjustments of glucose homeostasis can be added to the already well-known pleiotropic effects of this cytokine. Such adjustments, which are necessary for satisfying the high energetic demands of immune/inflammatory responses, can be mediated by effects of endogenous IL-1 exerted at peripheral and brain levels in a concerted action with other cytokines and neuroendocrine mechanisms.

When immune-neuro-endocrine interactions are disrupted: experimentally induced arthritis as an example.

We studied whether, in parallel to the activity of the hypothalamus-pituitary-adrenal axis and the sympathetic nervous system, hypothalamic cytokine expression and monoaminergic neurotransmitter concentrations are affected during the development and chronification of arthritis induced by immunization of rats with type II collagen. Corticosterone levels were increased only transiently, and were even below the normal range as the disease progressed. Increased adrenaline blood levels and hypothalamic IL-1beta and IL-6 overexpression were observed only during the induction phase of the disease. The increase in hypothalamic noradrenaline content during the symptomatic phase was paralleled by a gradual loss of sympathetic fibers in the joints. Depletion of hypothalamic noradrenergic neurons at this time did not affect the symptomatology. Contrary to observations in healthy animals, no correlation between hypothalamic IL-1beta expression and noradrenaline content was observed in rats with arthritis. The dissociation between hypothalamic cytokine gene expression and noradrenergic neuronal activity, the lack of sustained stimulation of the stress axes, and the loss of sympathetic signals in the joints indicate that the communication between afferent immune messages to the central nervous system and two main efferent anti-inflammatory pathways under control of the brain are disrupted during experimental arthritis.

A clinical correlate of the dysregulated immunoendocrine response in human tuberculosis.

Wasting is a prominent feature in tuberculosis (TB), but its underlying mechanisms are incompletely understood. Immunoendocrine disturbances may be linked to the consumption state of TB patients, since hormones and cytokines can affect energy expenditure and metabolism. To approach this possibility, we have determined leptin, IL-18, and adrenal steroid plasma levels and body mass index (BMI) in newly diagnosed patients with mild, moderate and severe pulmonary TB, household contacts (HHC), and healthy controls (HCO). HHC displayed higher levels of leptin than HCO and TB patients. TB patients showed a gradual decrease in BMI and leptin concentrations with increasing disease severity, whereas a positive correlation between this hormone and BMI was found in the HCO group. Cortisol concentrations tended to be higher in TB patients. DHEA levels were decreased in TB patients and to a lesser extent in HHC, whereas IL-18 concentration was significantly increased in patients with severe disease. Since HHC are known to cause a latent subclinical infection, it seems clear that controlled tuberculous infection and manifested TB disease are accompanied by a dissimilar profile of immunoendocrine markers.

Intranasal Dexamethasone Reduces Mortality and Brain Damage in a Mouse Experimental Ischemic Stroke Model.

Neuroinflammation triggered by the expression of damaged-associated molecular patterns released from dying cells plays a critical role in the pathogenesis of ischemic stroke. However, the benefits from the control of neuroinflammation in the clinical outcome have not been established. In this study, the effectiveness of intranasal, a highly efficient route to reach the central nervous system, and intraperitoneal dexamethasone administration in the treatment of neuroinflammation was evaluated in a 60-min middle cerebral artery occlusion (MCAO) model in C57BL/6 male mice. We performed a side-by-side comparison using intranasal versus intraperitoneal dexamethasone, a timecourse including immediate (0 h) or 4 or 12 h poststroke intranasal administration, as well as 4 intranasal doses of dexamethasone beginning 12 h after the MCAO versus a single dose at 12 h to identify the most effective conditions to treat neuroinflammation in MCAO mice. The best results were obtained 12 h after MCAO and when mice received a single dose of dexamethasone (0.25 mg/kg) intranasally. This treatment significantly reduced mortality, neurological deficits, infarct volume size, blood-brain barrier permeability in the somatosensory cortex, inflammatory cell infiltration, and glial activation. Our results demonstrate that a single low dose of intranasal dexamethasone has neuroprotective therapeutic effects in the MCAO model, showing a better clinical outcome than the intraperitoneal administration. Based on these results, we propose a new therapeutic approach for the treatment of the damage process that accompanies ischemic stroke.

Intranasal Methylprednisolone Effectively Reduces Neuroinflammation in Mice With Experimental Autoimmune Encephalitis.

Relapsing-remitting multiple sclerosis, the most common form, is characterized by acute neuroinflammatory episodes. In addition to continuous disease-modifying therapy, these relapses require treatment to prevent lesion accumulation and progression of disability. Intravenous methylprednisolone (1-2 g for 3-5 days) is the standard treatment for relapses. However, this treatment is invasive, requires hospitalization, leads to substantial systemic exposure of glucocorticoids, and can only reach modest concentrations in the central nervous system (CNS). Intranasal delivery may represent an alternative to deliver relapse treatment directly to the CNS with higher concentrations and reducing side effects. Histopathological analysis revealed that intranasal administration of methylprednisolone to mice with experimental autoimmune encephalomyelitis (EAE) suppressed the neuroinflammatory peak, and reduced immune cell infiltration and demyelination in the CNS similarly to intravenous administration. Treatment also downregulated Iba1 and GFAP expression. A similar significant reduction of IL-1ß, IL-6, IL-17, IFN-γ, and TNF-α levels in the spinal cord was attained in both intranasal and intravenously treated mice. No damage in the nasal cavity was found after intranasal administration. This study demonstrates that intranasal delivery of methylprednisolone is as efficient as the intravenous route to treat neuroinflammation in EAE.

Re-exposure to endotoxin induces differential cytokine gene expression in the rat hypothalamus and spleen.

This study was designed to investigate whether the pattern of hypothalamic and splenic cytokine expression induced by peripheral administration of a bacterial lipopolysaccharide (LPS) is affected by prior exposure to LPS derived from another bacterial strain. Injection of LPS from Salmonella enteritidis (LPS(2)) alone resulted in increased hypothalamic gene expression of IL-1beta, IL-6, TNFalpha, IL-1ra and IL-10. However, pre-exposure to LPS derived from Escherichia coli (LPS(1)) 3 weeks before, significantly attenuated hypothalamic IL-1ra, IL-6 and IL-10 expression. IL-1beta expression also tended to be lower. This pattern contrasted with the robust cytokine expression in the spleen of LPS(2)-treated rats previously exposed to LPS(1), since pre-treatment with endotoxin resulted in a significantly greater response of IL-1beta and IL-1ra to LPS(2). Expression of TNFalpha and IL-10 also tended to be higher. Pre-treatment with LPS(1) did not significantly affect the marked increase in corticosterone and adrenaline blood levels induced by LPS(2). Thus, while endotoxin pre-exposure seemed not to induce a "tolerant" state in the periphery as judged by the immune and endocrine parameters evaluated upon re-stimulation, expression of four of the six cytokines measured was decreased in the hypothalamus. This is the first demonstration that endotoxin priming can differentially affect cytokine expression in the central nervous system and peripheral tissues when a host is confronted with a second, acute, pro-inflammatory stimulus. These results may provide new evidence for the involvement of cytokine pathways in the central nervous system in modulating peripheral inflammation and mediating cognitive and behavioural alterations during inflammatory diseases.