Neural and humoral pathways of communication from the immune system to the brain: parallel or convergent?

Sensory sentinels: Neuroimmune detection and food allergy

Food allergy is classically characterized by an inappropriate type-2 immune response to allergenic food antigens. However, how allergens are detected and how that detection leads to the initiation of allergic immunity is poorly understood. In addition to the gastrointestinal tract, the barrier epithelium of the skin may also act as a site of food allergen sensitization. These barrier epithelia are densely innervated by sensory neurons, which respond to diverse physical environmental stimuli. Recent findings suggest that sensory neurons can directly detect a broad array of immunogens, including allergens, triggering sensory responses and the release of neuropeptides that influence immune cell function. Reciprocally, immune mediators modulate the activation or responsiveness of sensory neurons, forming neuroimmune feedback loops that may impact allergic immune responses. By utilizing cutaneous allergen exposure as a model, this review explores the pivotal role of sensory neurons in allergen detection and their dynamic bidirectional communication with the immune system, which ultimately orchestrates the type-2 immune response. Furthermore, it sheds light on how peripheral signals are integrated within the central nervous system to coordinate hallmark features of allergic reactions. Drawing from this emerging evidence, we propose that atopy arises from a dysregulated neuroimmune circuit.

Exercise-induced inflammation alters the perception and visual exploration of emotional interactions

Introduction

The study aimed to investigate whether an exercise-induced pro-inflammatory response alters the perception as well as visual exploration of emotional body language in social interactions.

Methods

In a within-subject design, 19 male, healthy adults aged between 19 and 33 years performed a downhill run for 45 min at 70% of their VO2max on a treadmill to induce maximal myokine blood elevations, leading to a pro-inflammatory status. Two control conditions were selected: a control run with no decline and a rest condition without physical exercise. Blood samples were taken before (T0), directly after (T1), 3 h after (T3), and 24 h after (T24) each exercise for analyzing the inflammatory response. 3 h after exercise, participants observed point-light displays (PLDs) of human interactions portraying four emotions (happiness, affection, sadness, and anger). Participants categorized the emotional content, assessed the emotional intensity of the stimuli, and indicated their confidence in their ratings. Eye movements during the entire paradigm and self-reported current mood were also recorded.

Results

The downhill exercise condition resulted in significant elevations of measured cytokines (IL6, CRP, MCP-1) and markers for muscle damage (Myoglobin) compared to the control running condition, indicating a pro-inflammatory state after the downhill run. Emotion recognition rates decreased significantly after the downhill run, whereas no such effect was observed after control running. Participants' sensitivity to emotion-specific cues also declined. However, the downhill run had no effect on the perceived emotional intensity or the subjective confidence in the given ratings. Visual scanning behavior was affected after the downhill run, with participants fixating more on sad stimuli, in contrast to the control conditions, where participants exhibited more fixations while observing happy stimuli.

Conclusion

Our study demonstrates that inflammation, induced through a downhill running model, impairs perception and emotional recognition abilities. Specifically, inflammation leads to decreased recognition rates of emotional content of social interactions, attributable to diminished discrimination capabilities across all emotional categories. Additionally, we observed alterations in visual exploration behavior. This confirms that inflammation significantly affects an individual's responsiveness to social and affective stimuli.

Neuroimmune modulation in liver pathophysiology

The liver, the largest organ in the human body, plays a multifaceted role in digestion, coagulation, synthesis, metabolism, detoxification, and immune defense. Changes in liver function often coincide with disruptions in both the central and peripheral nervous systems. The intricate interplay between the nervous and immune systems is vital for maintaining tissue balance and combating diseases. Signaling molecules and pathways, including cytokines, inflammatory mediators, neuropeptides, neurotransmitters, chemoreceptors, and neural pathways, facilitate this complex communication. They establish feedback loops among diverse immune cell populations and the central, peripheral, sympathetic, parasympathetic, and enteric nervous systems within the liver. In this concise review, we provide an overview of the structural and compositional aspects of the hepatic neural and immune systems. We further explore the molecular mechanisms and pathways that govern neuroimmune communication, highlighting their significance in liver pathology. Finally, we summarize the current clinical implications of therapeutic approaches targeting neuroimmune interactions and present prospects for future research in this area.

Recognizing depression as an inflammatory disease: the search for endotypes

Major depressive disorder (MDD) affects millions of individuals worldwide, leading to considerable social and economic costs. Despite advancements in pharmacological treatments, achieving remission remains a key challenge, with a substantial number of patients showing resistance to existing therapies. This resistance is often associated with elevated levels of proinflammatory cytokines, suggesting a connection between inflammation, MDD pathophysiology, and treatment efficacy. The observation of increased immune activation in about a quarter of patients with MDD resulted in the distinction between inflammatory and noninflammatory endotypes. Although anti-inflammatory treatments show promise in alleviating depression-like symptoms, responses are heterogeneous, thus highlighting the importance of identifying distinct inflammatory endotypes to tailor effective therapeutic strategies. The intestinal microbiome emerges as a crucial modulator of mental health, mediating its effects partially through different immune pathways. Microbiota-derived short-chain fatty acids (SCFAs) significantly impact innate and adaptive immune cells, regulating their differentiation, function, and cellular response. Furthermore, gut-educated immune cells reach the border regions of the central nervous system (CNS), regulating glial cell functions. Although the CNS modulates immune responses via efferent parts of the vagus nerve, afferent tracts concurrently transport information on peripheral inflammation back to the brain. This bidirectional communication is particularly relevant in depression, allowing for therapeutic stimulation of the vagus nerve in the context of inflammatory depression endotypes. In this review, we explore the intricate relationship between inflammation and depression, discuss how inflammatory signals are translated into depressive-like symptoms, and highlight immune-modulating therapeutic avenues.

What is the Vagal-Adrenal Axis?

Some recent publications have used the term "vagal-adrenal axis" to account for mechanisms involved in the regulation of inflammation by electroacupuncture. This concept proposes that efferent parasympathetic nerve fibers in the vagus directly innervate the adrenal glands to influence catecholamine secretion. Here, we discuss evidence for anatomical and functional links between the vagi and adrenal glands that may be relevant in the context of inflammation and its neural control by factors, including acupuncture. First, we find that evidence for any direct vagal parasympathetic efferent innervation of the adrenal glands is weak and likely artifactual. Second, we find good evidence that vagal afferent fibers directly innervate the adrenal gland, although their function is uncertain. Third, we highlight a wealth of evidence for indirect pathways, whereby vagal afferent signals act via the central nervous system to modify adrenal-dependent anti-inflammatory responses. Vagal afferents, not efferents, are thus the likely key to these phenomena.

Neuroimmune modulation by tryptophan derivatives in neurological and inflammatory disorders

The nervous and immune systems are highly developed, and each performs specialized physiological functions. However, they work together, and their dysfunction is associated with various diseases. Specialized molecules, such as neurotransmitters, cytokines, and more general metabolites, are essential for the appropriate regulation of both systems. Tryptophan, an essential amino acid, is converted into functional molecules such as serotonin and kynurenine, both of which play important roles in the nervous and immune systems. The role of kynurenine metabolites in neurodegenerative and psychiatric diseases has recently received particular attention. Recently, we found that hyperactivity of the kynurenine pathway is a critical risk factor for septic shock. In this review, we first outline neuroimmune interactions and tryptophan derivatives and then summarized the changes in tryptophan metabolism in neurological disorders. Finally, we discuss the potential of tryptophan derivatives as therapeutic targets for neuroimmune disorders.

Changes in pain during a depressive episode and relationship to cytokine levels in major depressive disorder

BACKGROUND

Depressed patients have an increased incidence of pain. A pathophysiological connection between depression and pain is still not revealed. Immunological activation has been found in both depression and pain. There are few studies of pain and immune activation in patients with depression, without inflammatory and autoimmune disorders.

METHODS

This is a naturalistic follow-up study of 50 patients with a major depressive disorder (MDD) depressive episode, without any inflammatory or autoimmune conditions. We have previously reported on the relationship between depression and cytokine levels. In this study, we obtained data of depression, pain and cytokine levels before and after 12 weeks of depression treatment. All patients were medication-free at inclusion.

RESULTS

At inclusion three out of four patients experienced pain, and the pain scores correlated with the depression scores. After treatment, as depression was relieved, the pain scores dropped significantly and were no longer correlated to the depression scores. There were no correlations between pain scores and cytokine levels. Pain level at inclusion did not correlate with depression treatment outcome.

CONCLUSION

Our findings indicate that pain is a feature of depression. Pain levels and cytokine values didn't correlate. Pain at inclusion did not predict depression treatment outcome.

Fasting-activated ventrolateral medulla neurons regulate T cell homing and suppress autoimmune disease in mice

Dietary fasting markedly influences the distribution and function of immune cells and exerts potent immunosuppressive effects. However, the mechanisms through which fasting regulates immunity remain obscure. Here we report that catecholaminergic (CA) neurons in the ventrolateral medulla (VLM) are activated during fasting in mice, and we demonstrate that the activity of these CA neurons impacts the distribution of T cells and the development of autoimmune disease in an experimental autoimmune encephalomyelitis (EAE) model. Ablation of VLM CA neurons largely reversed fasting-mediated T cell redistribution. Activation of these neurons drove T cell homing to bone marrow in a CXCR4/CXCL12 axis-dependent manner, which may be mediated by a neural circuit that stimulates corticosterone secretion. Similar to fasting, the continuous activation of VLM CA neurons suppressed T cell activation, proliferation, differentiation and cytokine production in autoimmune mouse models and substantially alleviated disease symptoms. Collectively, our study demonstrates neuronal control of inflammation and T cell distribution, suggesting a neural mechanism underlying fasting-mediated immune regulation.

Impacts of a Simulated Infection on the Locomotor Behavior of Invasive and Noninvasive Species of Congeneric Anurans

AbstractLocomotion is essential for survival, but it requires resources such as energy and metabolites and therefore may conflict with other physiological processes that also demand resources, particularly expensive processes such as immunological responses. This possible trade-off may impose limits on either the magnitude of immune responses or the patterns of activity and performance. Previous studies have shown that invasive species may have a depressed immune response, allowing them to maintain locomotor function and reproduction even when sick. This may contribute to the ecological success of invasive species in colonization and dispersal. In contrast, noninvasive species tend to reduce activity as a response to infection. Here, we studied the impact of a simulated infection on locomotor performance and voluntary movement in the anurans Xenopus laevis (a globally invasive species) and Xenopus allofraseri (a noninvasive congeneric). We found that a simulated infection reduces locomotor performance in both species, with an accentuated effect on X. allofraseri. Voluntary movement was marginally different between species. Our data suggest that a simulated infection leads to behavioral depression and reduced locomotor performance in anurans and show that this effect is limited in the invasive X. laevis. Contrasting responses to an immune challenge have been reported in the few amphibian taxa analyzed to date and suggest relationships between ecology and immunology that deserve further investigation. Specifically, a depressed immune response may underlie a propension to invasion in some species. Whether this is a general trend for invasive species remains to be tested, but our data add to the growing body of work documenting depressed immune systems in invasive species.

Growth differentiation factor-15 is an IFN-γ regulated mediator of infection-induced weight loss and the hepatic FGF21 response

Infections are often accompanied by weight loss caused by alterations in host behavior and metabolism, also known as sickness behaviors. Recent studies have revealed that sickness behaviors can either promote or impede survival during infections depending on factors such as the type of infectious pathogen. Nevertheless, we have an incomplete understanding of the underlying mechanisms of sickness behaviors. Furthermore, although the host immune responses to infections have long been known to contribute to the induction of sickness behaviors, recent studies have identified emerging cytokines that are also key regulators of host metabolism during infection and inflammation, such as growth differentiation factor 15 (GDF-15). GDF-15 is a distant member of the TGF-β superfamily that causes weight loss by suppressing appetite and food consumption and causing emesis. These effects require activation of neurons that express the only known GDF-15 receptor, the GFRAL receptor. GDF-15 also functions in the periphery including the induction of ketogenesis and immunoregulation. Nevertheless, the functions and regulation of GDF-15 during live infections is not yet known. Murine infection with avirulent Toxoplasma gondii is an established model to understand infection-induced weight loss. Past studies have determined that acute T. gondii infection causes weight loss due to diminished food consumption and increased energy expenditure through unknown mechanisms. Additionally, our lab previously demonstrated that T. gondii causes upregulation in serum GDF-15 in an IFN-γ-dependent manner during the post-acute phase of the infection. In this study, we interrogated the in-vivo functions and immune regulation of GDF-15 during Toxoplasma gondii infection. First, we found that in wild-type mice, acute T. gondii infection caused a significant weight loss that is preceded by elevation of serum levels of IFN-γ and GDF-15. To determine whether IFN-γ regulates GDF-15, we neutralized IFN-γ on days 5 and 6 and measured GDF-15 on day 7 and found that serum but not tissue levels of GDF-15 decreased after IFN-γ neutralization. Additionally, exogenous IFN-γ was sufficient to elevate serum GDF-15 in the absence of infection. Next, we compared the outcomes of T. gondii infection between WT and Gdf15-/- mice. We observed that the weight trajectories were declining in WT mice while they were increasing in Gdf15-/-mice during the acute phase of the infection. This difference in trajectories extended throughout the chronic infection resulting to an overall weight loss relative to initial weights in WT mice but not Gdf15-/-mice. Then, we determined that GDF-15 is not essential for survival and immunoregulation during T. gondii infection. We also demonstrated that GDF-15 is required for the induction of FGF21, stress-induced cytokine with prominent roles in regulating host metabolism. Finally, we discovered a cytokine cascade IFN-γ-GDF-15-FGF21 that is likely involved in the regulation of host metabolism. Overall, our study provides evidence that IFN-γ contributes to the regulation of host metabolism during infection by inducing GDF-15 and FGF21. GDF-15 orchestrates changes in host metabolism that supports the host immune response in clearing the infection. These physiological alterations induce FGF21, which in turn, orchestrates the adaptive responses to the effects of GDF-15, which can be detrimental when protracted.

Genetic Overlap Between Global Cortical Brain Structure, C-Reactive Protein, and White Blood Cell Counts

BACKGROUND

For many brain disorders, a subset of patients jointly exhibit alterations in cortical brain structure and elevated levels of circulating immune markers. This may be driven in part by shared genetic architecture. Therefore, we investigated the phenotypic and genetic associations linking global cortical surface area and thickness with blood immune markers (i.e., white blood cell counts and plasma C-reactive protein levels).

METHODS

Linear regression was used to assess phenotypic associations in 30,823 UK Biobank participants. Genome-wide and local genetic correlations were assessed using linkage disequilibrium score regression and local analysis of covariance annotation. The number of shared trait-influencing genetic variants was estimated using MiXeR. Shared genetic architecture was assessed using a conjunctional false discovery rate framework, and mapped genes were included in gene-set enrichment analyses.

RESULTS

Cortical structure and blood immune markers exhibited predominantly inverse phenotypic associations. There were modest genome-wide genetic correlations, the strongest of which were for C-reactive protein levels (rg_surface_area = -0.13, false discovery rate-corrected p = 4.17 × 10-3; rg_thickness = -0.13, false discovery rate-corrected p = 4.00 × 10-2). Meanwhile, local genetic correlations showed a mosaic of positive and negative associations. White blood cells shared on average 46.24% and 38.64% of trait-influencing genetic variants with surface area and thickness, respectively. Additionally, surface area shared 55 unique loci with the blood immune markers while thickness shared 15. Overall, monocyte count exhibited the largest genetic overlap with cortical brain structure. A series of gene enrichment analyses implicated neuronal-, astrocytic-, and schizophrenia-associated genes.

CONCLUSIONS

The findings indicate shared genetic underpinnings for cortical brain structure and blood immune markers, with implications for neurodevelopment and understanding the etiology of brain-related disorders.

Periodontitis and Neuropathic Diseases: A Literature Review

Aim

This narrative review aimed at identifying the existing scientific literature investigating periodontitis and neuropathic diseases.

Materials and Methods

A search of the literature published between 2000 and 2022 was carried out in the electronic databases of Scopus and PubMed. Studies in which the eligible articles were mainly published in English were included. Descriptive correlational studies, case-control studies, comparative studies, and cohort studies were also included. The following main keywords were used: "Neuropathic diseases," "Periodontitis," "Alzheimer's disease," and "Porphyromonas gingivalis."

Results

This narrative review found that cognitively impaired persons with severe periodontitis had a higher prevalence and incidence of periodontal diseases than the rest of the population. A significant positive correlation of salivary interleukin (IL)-1beta and immediate recall scores involved in cognition was also evident. It indicates that the most investigated parameter was whether there is any common link between periodontal disease and neurodegeneration. No randomized controlled clinical studies were found in the current literature review.

Conclusions

Based on the literature reviewed, there is currently no strong scientific evidence to support or discourage the cause-effect relationship of periodontal diseases and neurodegenerative diseases.

Immune mechanisms of depression in rheumatoid arthritis

Depression is a common and disabling comorbidity in rheumatoid arthritis that not only decreases the likelihood of remission and treatment adherence but also increases the risk of disability and mortality in patients with rheumatoid arthritis. Compelling data that link immune mechanisms to major depressive disorder indicate possible common mechanisms that drive the pathology of the two conditions. Preclinical evidence suggests that pro-inflammatory cytokines, which are prevalent in rheumatoid arthritis, have various effects on monoaminergic neurotransmission, neurotrophic factors and measures of synaptic plasticity. Neuroimaging studies provide insight into the consequences of inflammation on the brain (for example, on neural connectivity), and clinical trial data highlight the beneficial effects of immune modulation on comorbid depression. Major depressive disorder occurs more frequently in patients with rheumatoid arthritis than in the general population, and major depressive disorder also increases the risk of a future diagnosis of rheumatoid arthritis, further highlighting the link between rheumatoid arthritis and major depressive disorder. This Review focuses on interactions between peripheral and central immunobiological mechanisms in the context of both rheumatoid arthritis and major depressive disorder. Understanding these mechanisms will provide a basis for future therapeutic development, not least in depression.

Regional neuroinflammation induced by peripheral infection contributes to fatigue-like symptoms: a [18F]DPA-714 positron emission tomography study in rats

Introduction

A series of symptoms, including fever, widespread pain, fatigue, and even ageusia, have frequently been reported in the context of various infections, such as COVID-19. Although the pathogenic mechanisms underlying an infection causing fever and pain have been well established, the mechanisms of fatigue induced by infection in specific brain regions remain unclear.

Methods

To elucidate whether and how the peripheral infection cause fatigue via regional neuroinflammation, we performed a brain-wide investigation of neuroinflammation in a peripheral pseudoinfection rat model using [18F]DPA-714 positron emission tomography (PET) imaging analysis, in which the polyriboinosinic: polyribocytidylic acid (poly I:C) was intraperitoneally injected.

Results

Transient fever lasting for several hours and subsequent suppression of spontaneous activity lasting a few days were induced by poly I:C treatment. Significant increase in plasma interleukin (IL)-1β, IL-6 and tumour necrosis factor (TNF)-α were observed at 2 and 4 h following poly I:C treatment. PET imaging analysis revealed that the brain uptake of [18F]DPA-714 was significantly increased in several brain regions one day after poly I:C treatment, such as the dorsal raphe (DR), parvicellular part of red nucleus (RPC), A5 and A7 noradrenergic nucleus, compared with the control group. The accumulation of [18F]DPA-714 in the DR, RPC and A5 was positively correlated with subsequent fatigue-like behavior, and that in the A7 tended to positively correlate with fever.

Discussion

These findings suggest that peripheral infection may trigger regional neuroinflammation, which may cause specific symptoms such as fatigue. A similar mechanism might be involved in COVID-19.

Role of SIRT1 in sepsis-induced encephalopathy: Molecular targets for future therapies

Sepsis induces neuroinflammation, BBB disruption, cerebral hypoxia, neuronal mitochondrial dysfunction, and cell death causing sepsis-associated encephalopathy (SAE). These pathological consequences lead to short- and long-term neurobehavioural deficits. Till now there is no specific treatment that directly improves SAE and its associated behavioural impairments. In this review, we discuss the underlying mechanisms of sepsis-induced brain injury with a focus on the latest progress regarding neuroprotective effects of SIRT1 (silent mating type information regulation-2 homologue-1). SIRT1 is an NAD+ -dependent class III protein deacetylase. It is able to modulate multiple downstream signals (including NF-κB, HMGB, AMPK, PGC1α and FoxO), which are involved in the development of SAE by its deacetylation activity. There are multiple recent studies showing the neuroprotective effects of SIRT1 in neuroinflammation related diseases. The proposed neuroprotective action of SIRT1 is meant to bring a promising therapeutic strategy for managing SAE and ameliorating its related behavioural deficits.

Impact of alternating amino acid sequences on beta-amyloid-induced neurotoxicity and neuroinflammation in Alzheimer's disease

Alzheimer's disease (AD) is a chronic neurodegenerative disease and the common cause of dementia. The aggregation of beta-amyloid (Aβ peptide) leading to excessive neuroinflammation is considered to be the neuropathological hallmark of AD, although the precise mechanisms remain unclear. Oligomerization of these peptides may be associated with their 42 amino acid residue arrangement. However, the process of amyloid plaque formation is still not well known. The protein folding-shape code (PFSC) method is a powerful tool to analyze protein confirmation which could exhibit the local structural folding features in detail. In our study, we utilized the PFSC to analyze Aβ peptide in humans and mice and found that mouse Aβ42 is less likely to polymerize than human's. Subsequently, we used the PFSC method to analyze the 42 amino acids of Aβ, transformed some species in human Aβ42 and obtained 7 mutants. We showed that it was not easy to aggregate Aβ in mutants. Herein, inflammatory responses were decreased, as indicated by the expression of cytokines. We confirmed that the neurotoxicity of mutant human Aβ was decreased by preventing peptide aggregation. This may represent a new therapeutic approach for treating AD.

Preemptive transcranial direct current stimulation induces analgesia, prevents chronic inflammation and fibrosis, and promotes tissue repair in a rat model of postoperative pain

This study evaluated the effects of previous exposure to Transcranial Direct Current Stimulation (tDCS) on nociceptive, neuroinflammatory, and neurochemical parameters, in rats subjected to an incisional pain model. Forty adult male Wistar rats (60 days old; weighing ∼ 250 g) were divided into five groups: 1. control (C); 2. drugs (D); 3. surgery (S); 4. surgery + sham-tDCS (SsT) and 5. surgery + tDCS (ST). Bimodal tDCS (0.5 mA) was applied for 20 min/day/8 days before the incisional model. Mechanical allodynia (von Frey) was evaluated at different time points after surgery. Cytokines and BDNF levels were evaluated in the cerebral cortex, hippocampus, brainstem, and spinal cord. Histology and activity of myeloperoxidase (MPO) and N-acetyl-β-D-glucosaminidase (NAGase) were evaluated in the surgical lesion sites in the right hind paw. The results demonstrate that the surgery procedure increased BDNF and IL-6 levels in the spinal cord levels in the hippocampus, and decreased IL-1β and IL-6 levels in the cerebral cortex, IL-6 levels in the hippocampus, and IL-10 levels in the brainstem and hippocampus. In addition, preemptive tDCS was effective in controlling postoperative pain, increasing BDNF, IL-6, and IL-10 levels in the spinal cord and brainstem, increasing IL-1β in the spinal cord, and decreasing IL-6 levels in the cerebral cortex and hippocampus, IL-1β and IL-10 levels in the hippocampus. Preemptive tDCS also contributes to tissue repair, preventing chronic inflammation, and consequent fibrosis. Thus, these findings imply that preemptive methods for postoperative pain management should be considered an interesting pain management strategy, and may contribute to the development of clinical applications for tDCS in surgical situations.

Selective breeding of rats for high (HAB) and low (LAB) anxiety-related behaviour: A unique model for comorbid depression and social dysfunctions

Animal models of selective breeding for extremes in emotionality are a strong experimental approach to model psychopathologies. They became indispensable in order to increase our understanding of neurobiological, genetic, epigenetic, hormonal, and environmental mechanisms contributing to anxiety disorders and their association with depressive symptoms or social deficits. In the present review, we extensively discuss Wistar rats selectively bred for high (HAB) and low (LAB) anxiety-related behaviour on the elevated plus-maze. After 30 years of breeding, we can confirm the prominent differences between HAB and LAB rats in trait anxiety, which are accompanied by consistent differences in depressive-like, social and cognitive behaviours. We can further confirm a single nucleotide polymorphism in the vasopressin promotor of HAB rats causative for neuropeptide overexpression, and show that low (or high) anxiety and fear levels are unlikely due to visual dysfunctions. Thus, HAB and LAB rats continue to exist as a reliable tool to study the multiple facets underlying the pathology of high trait anxiety and its comorbidity with depression-like behaviour and social dysfunctions.

Estimation of antibody levels after COVID-19 vaccinations: Preliminary evidence for immune interoception

To date, 72 % of the world's population has received at least one COVID-19 vaccination. The number of antibodies produced by some individuals is exponentially higher than in others, for various mostly unknown reasons. This variation causes great diversity in the future susceptibility to infection by the original or variants of the SARS-CoV-2 virus. The following study investigated whether individuals were able to estimate the strength of their antibody response after their COVID-19 vaccinations. 166 recently vaccinated participants provided a blood sample for determination of antibody titers. Participants were asked to estimate how many antibodies they thought they had produced, and were further asked how protected they felt from COVID-19 due to vaccination. Both self-rated antibody levels, and feelings of protection against COVID-19 were significantly related to their actual IgG spike antibody titers, after controlling for age, days since vaccination, BMI and cross vaccination. These results suggest that individuals may have a form of "immune interoception" which relates to their response to their COVID-19 vaccination.

The role of peripheral inflammatory insults in Alzheimer's disease: a review and research roadmap

Peripheral inflammation, defined as inflammation that occurs outside the central nervous system, is an age-related phenomenon that has been identified as a risk factor for Alzheimer's disease. While the role of chronic peripheral inflammation has been well characterized in the context of dementia and other age-related conditions, less is known about the neurologic contribution of acute inflammatory insults that take place outside the central nervous system. Herein, we define acute inflammatory insults as an immune challenge in the form of pathogen exposure (e.g., viral infection) or tissue damage (e.g., surgery) that causes a large, yet time-limited, inflammatory response. We provide an overview of the clinical and translational research that has examined the connection between acute inflammatory insults and Alzheimer's disease, focusing on three categories of peripheral inflammatory insults that have received considerable attention in recent years: acute infection, critical illness, and surgery. Additionally, we review immune and neurobiological mechanisms which facilitate the neural response to acute inflammation and discuss the potential role of the blood-brain barrier and other components of the neuro-immune axis in Alzheimer's disease. After highlighting the knowledge gaps in this area of research, we propose a roadmap to address methodological challenges, suboptimal study design, and paucity of transdisciplinary research efforts that have thus far limited our understanding of how pathogen- and damage-mediated inflammatory insults may contribute to Alzheimer's disease. Finally, we discuss how therapeutic approaches designed to promote the resolution of inflammation may be used following acute inflammatory insults to preserve brain health and limit progression of neurodegenerative pathology.

A review of cytokine-based pathophysiology of Long COVID symptoms

The Long COVID/Post Acute Sequelae of COVID-19 (PASC) group includes patients with initial mild-to-moderate symptoms during the acute phase of the illness, in whom recovery is prolonged, or new symptoms are developed over months. Here, we propose a description of the pathophysiology of the Long COVID presentation based on inflammatory cytokine cascades and the p38 MAP kinase signaling pathways that regulate cytokine production. In this model, the SARS-CoV-2 viral infection is hypothesized to trigger a dysregulated peripheral immune system activation with subsequent cytokine release. Chronic low-grade inflammation leads to dysregulated brain microglia with an exaggerated release of central cytokines, producing neuroinflammation. Immunothrombosis linked to chronic inflammation with microclot formation leads to decreased tissue perfusion and ischemia. Intermittent fatigue, Post Exertional Malaise (PEM), CNS symptoms with "brain fog," arthralgias, paresthesias, dysautonomia, and GI and ophthalmic problems can consequently arise as result of the elevated peripheral and central cytokines. There are abundant similarities between symptoms in Long COVID and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). DNA polymorphisms and viral-induced epigenetic changes to cytokine gene expression may lead to chronic inflammation in Long COVID patients, predisposing some to develop autoimmunity, which may be the gateway to ME/CFS.

Inflammation-Related Functional and Structural Dysconnectivity as a Pathway to Psychopathology

Findings from numerous laboratories and across neuroimaging modalities have consistently shown that exogenous administration of cytokines or inflammatory stimuli that induce cytokines disrupts circuits and networks involved in motivation and motor activity, threat detection, anxiety, and interoceptive and emotional processing. While inflammatory effects on neural circuits and relevant behaviors may represent adaptive responses promoting conservation of energy and heightened vigilance during immune activation, chronically elevated inflammation may contribute to symptoms of psychiatric illnesses. Indeed, biomarkers of inflammation such as cytokines and acute phase reactants are reliably elevated in a subset of patients with unipolar or bipolar depression, anxiety-related disorders, and schizophrenia and have been associated with differential treatment responses and poor clinical outcomes. A growing body of literature also describes higher levels of endogenous inflammatory markers and altered, typically lower functional or structural connectivity within these circuits in association with transdiagnostic symptoms such as anhedonia and anxiety in psychiatric and at-risk populations. This review presents recent evidence that inflammation and its effects on the brain may serve as one molecular and cellular mechanism of dysconnectivity within anatomically and/or functionally connected cortical and subcortical regions in association with transdiagnostic symptoms. We also discuss the need to establish reproducible methods to assess inflammation-associated dysconnectivity in relation to behavior for use in translational studies or biomarker-driven clinical trials for novel pharmacological or behavioral interventions targeting inflammation or its effects on the brain.

Effect of selective cyclooxygenase inhibitors on animal behaviour and monoaminergic systems of the rat brain

The long-term effects of cyclooxygenase 1 and 2 (COX-1/2) inhibitors are usually tested in terms of the periphery of the organism. Therefore, we studied the effects of SC560 (selective COX-1 inhibitor) and celecoxib (selective COX-2 inhibitor) on the activity of brain monoaminergic systems and animal behaviour. Additionally, we tested the effect of these inhibitors during inflammation. We have observed that long-term administration of celecoxib reduces the activity of the noradrenergic system, increases the activity of dopaminergic and serotonergic systems, increases locomotor activity, and enhances the exploratory behaviour of rats. Administration of SC560 also increases the activity of dopaminergic and serotonergic systems but reduces locomotor activity and impairs the exploratory behaviour of rats. The mechanism responsible for decreased activity of the noradrenergic system may be related to the weakening of activity of the positive feedback loop between the paraventricular nucleus and coeruleus locus. We suggest that the effect of used inhibitors on the dopaminergic system is associated with a possible increase in anandamide concentration and its effect on dopamine reuptake in synaptic clefts. It also appears that cyclooxygenase peroxidase activity may play a role in this process. In turn, changes in the activity of the serotonergic system may be related to the activity of indoleamine-2,3-dioxygenase, which decreases because of the decreased concentration of pro-inflammatory compounds. We believe that behavioural changes induced by COX inhibitors are the result of the modified activity of monoaminergic CNS systems in the brainstem, hypothalamus, and medial prefrontal cortex.

β-patchoulene alleviates cognitive dysfunction in a mouse model of sepsis associated encephalopathy by inhibition of microglia activation through Sirt1/Nrf2 signaling pathway

BACKGROUND

Sepsis associated encephalopathy (SAE) is a common but poorly understood complication during sepsis. Currently, there are no preventive or therapeutic agents available for this neurological disorder. The present study was designed to determine the potential protective effects of β-patchoulene (β-PAE) in a mouse model of SAE and explore the putative mechanisms underpinning the beneficial effects.

MATERIALS AND METHODS

SAE was induced in C57BL/6 mice by cecal ligation and puncture(CLP). Mice were administrated with β-PAE or saline by intra-cerebral ventricle(i.c.v) injection immediately after CLP surgery. The inhibitory avoidance tests and open field tests were performed at 24h, 48h and 7days after procedures. Cytokines expression, oxidative parameters, microglia polarization and apoptosis in the brain tissue were assessed. Sirt1, Nrf2, HO-1and cleaved-caspase3 expression in hippocampus was determined by western-blotting. Further, serum cytokines expression and spleen lymphocytes apoptosis were evaluated, and survival study was performed.

RESULTS

Septic mice suffered severe cognitive decline following CLP as evidenced by decreased memory latency time and lower frequency of line crossing in the behavioral tests. A high dose of β-PAE(1mg/kg) improved the cognitive impairment in SAE mice, which was accompanied by reduced cytokines expression and oxidative stress. Immunofluorescence assay showed that β-PAE inhibited the expression of Iba-1 and iNOS in microglia. The mechanistic study indicated that β-PAE could promote the nuclear expression of Sirt1/Nrf2 and enhance cytoplasmic HO-1 expression. Furthermore, i.c.v administration of β-PAE decreased the expression of serum cytokines and apoptosis in the spleen, thus leading to an improved 7-day survival of septic mice. Finally, blockade of Nrf2 activation with ML385 largely mitigated the protective effects of β-PAE on the cognitive function, neuroinflammation and survival in SAE mice.

CONCLUSION

In this study, we found that β-PAE significantly altered sepsis induced neuroinflammation and microglia activation, thus reversed the cognitive decline and improved the peripheral immune function. The neuroprotective effects were possibly mediated by the activation of Sirt1/Nrf2/HO-1 pathway. β-PAE might serve as a promising therapeutic agent for SAE prevention and treatment.

Evolutionary Aspects of Infections: Inflammation and Sickness Behaviors

Sickness behavior was conceptualized initially as the behavioral counterpart of the fever response to infectious pathogens. It helps to raise body temperature to its higher setpoint and to maintain it at this new level and it has the additional benefit of enabling a weakened organism to protect itself from other dangers. The discovery of the behavioral effects of proinflammatory cytokines produced by activated immune cells provided a cellular and molecular basis to this phenomenon. The administration of cytokines or cytokine inducers like lipopolysaccharide to healthy rodents allowed to reveal the similarities and differences between inflammation-induced sickness behavior and the fever response. It also led to the understanding of how the inflammatory response that is triggered at the periphery can propagate into the brain and induce the behavioral manifestations of sickness. At the behavioral level, the demonstration that sickness behavior is the expression of a motivational state that reorganizes perception and action in face of a microbial pathogen just like fear in face of a predator appeared at first glance to strengthen the adaptive value of this behavior. However, all aspects of sickness behavior are not always favorable for the organism. This is the case for anorexia that is beneficial in the context of bacterial infection but detrimental in the context of viral infection. In addition, studies of sickness behavior in natural conditions revealed that like any other defensive behavior, sickness behavior requires trade-offs between its survival benefits for the sick individual and the costs incurred especially in the context of gregarious groups. Thanks to these studies, evidence is emerging that sickness behavior is much more variable in its expression than initially thought, and that part of this variability depends not only on the pathogen and the social context in which the infection develops but also on individual factors including species, sex, age, nutrition, and physiological status.

The Heart Is at Risk: Understanding Stroke-Heart-Brain Interactions with Focus on Neurogenic Stress Cardiomyopathy-A Review

In recent years, it has been convincingly demonstrated that acute brain injury may cause severe cardiac complications-such as neurogenic stress cardiomyopathy (NSC), a specific form of takotsubo cardiomyopathy. The pathophysiology of these brain-heart interactions is complex and involves sympathetic hyperactivity, activation of the hypothalamic-pituitary-adrenal axis, as well as immune and inflammatory pathways. There have been great strides in our understanding of the axis from the brain to the heart in patients with isolated acute brain injury and more specifically in patients with stroke. On the other hand, in patients with NSC, research has mainly focused on hemodynamic dysfunction due to arrhythmias, regional wall motion abnormality, or left ventricular hypokinesia that leads to impaired cerebral perfusion pressure. Comparatively little is known about the underlying secondary and delayed cerebral complications. The aim of the present review is to describe the stroke-heart-brain axis and highlight the main pathophysiological mechanisms leading to secondary and delayed cerebral injury in patients with concurrent hemorrhagic or ischemic stroke and NSC as well as to identify further areas of research that could potentially improve outcomes in this specific patient population.

The Role of Gut Dysbiosis in the Pathophysiology of Neuropsychiatric Disorders

Mounting evidence shows that the complex gut microbial ecosystem in the human gastrointestinal (GI) tract regulates the physiology of the central nervous system (CNS) via microbiota and the gut-brain (MGB) axis. The GI microbial ecosystem communicates with the brain through the neuroendocrine, immune, and autonomic nervous systems. Recent studies have bolstered the involvement of dysfunctional MGB axis signaling in the pathophysiology of several neurodegenerative, neurodevelopmental, and neuropsychiatric disorders (NPDs). Several investigations on the dynamic microbial system and genetic-environmental interactions with the gut microbiota (GM) have shown that changes in the composition, diversity and/or functions of gut microbes (termed "gut dysbiosis" (GD)) affect neuropsychiatric health by inducing alterations in the signaling pathways of the MGB axis. Interestingly, both preclinical and clinical evidence shows a positive correlation between GD and the pathogenesis and progression of NPDs. Long-term GD leads to overstimulation of hypothalamic-pituitary-adrenal (HPA) axis and the neuroimmune system, along with altered neurotransmitter levels, resulting in dysfunctional signal transduction, inflammation, increased oxidative stress (OS), mitochondrial dysfunction, and neuronal death. Further studies on the MGB axis have highlighted the significance of GM in the development of brain regions specific to stress-related behaviors, including depression and anxiety, and the immune system in the early life. GD-mediated deregulation of the MGB axis imbalances host homeostasis significantly by disrupting the integrity of the intestinal and blood-brain barrier (BBB), mucus secretion, and gut immune and brain immune functions. This review collates evidence on the potential interaction between GD and NPDs from preclinical and clinical data. Additionally, we summarize the use of non-therapeutic modulators such as pro-, pre-, syn- and post-biotics, and specific diets or fecal microbiota transplantation (FMT), which are promising targets for the management of NPDs.

Interactions between gut microbiota and Parkinson's disease: The role of microbiota-derived amino acid metabolism

Non-motor symptoms (NMS) of Parkinson's disease (PD), such as constipation, sleep disorders, and olfactory deficits, may emerge up to 20 years earlier than motor symptoms. A series of evidence indicates that the pathology of PD may occur from the gastrointestinal tract to the brain. Numerous studies support that the gut microbiota communicates with the brain through the immune system, special amino acid metabolism, and the nervous system in PD. Recently, there is growing recognition that the gut microbiota plays a vital role in the modulation of multiple neurochemical pathways via the “gut microbiota-brain axis” (GMBA). Many gut microbiota metabolites, such as fatty acids, amino acids, and bile acids, convey signaling functions as they mediate the crosstalk between gut microbiota and host physiology. Amino acids' abundance and species alteration, including glutamate and tryptophan, may disturb the signaling transmission between nerve cells and disrupt the normal basal ganglia function in PD. Specific amino acids and their receptors are considered new potential targets for ameliorating PD. The present study aimed to systematically summarize all available evidence on the gut microbiota-derived amino acid metabolism alterations associated with PD.

Environmental Stressors and the PINE Network: Can Physical Environmental Stressors Drive Long-Term Physical and Mental Health Risks?

Both psychosocial and physical environmental stressors have been linked to chronic mental health and chronic medical conditions. The psycho-immune-neuroendocrine (PINE) network details metabolomic pathways which are responsive to varied stressors and link chronic medical conditions with mental disorders, such as major depressive disorder via a network of pathophysiological pathways. The primary objective of this review is to explore evidence of relationships between airborne particulate matter (PM, as a concrete example of a physical environmental stressor), the PINE network and chronic non-communicable diseases (NCDs), including mental health sequelae, with a view to supporting the assertion that physical environmental stressors (not only psychosocial stressors) disrupt the PINE network, leading to NCDs. Biological links have been established between PM exposure, key sub-networks of the PINE model and mental health sequelae, suggesting that in theory, long-term mental health impacts of PM exposure may exist, driven by the disruption of these biological networks. This disruption could trans-generationally influence health; however, long-term studies and information on chronic outcomes following acute exposure event are still lacking, limiting what is currently known beyond the acute exposure and all-cause mortality. More empirical evidence is needed, especially to link long-term mental health sequelae to PM exposure, arising from PINE pathophysiology. Relationships between physical and psychosocial stressors, and especially the concept of such stressors acting together to impact on PINE network function, leading to linked NCDs, evokes the concept of syndemics, and these are discussed in the context of the PINE network.

Integrating biobehavioral information to predict mood disorder suicide risk

The will to live and the ability to maintain one's well-being are crucial for survival. Yet, almost a million people die by suicide globally each year (Aleman and Denys, 2014), making premature deaths due to suicide a significant public health problem (Saxena et al., 2013). The expression of suicidal behaviors is a complex phenotype with documented biological, psychological, clinical, and sociocultural risk factors (Turecki et al., 2019). From a brain disease perspective, suicide is associated with neuroanatomical, neurophysiological, and neurochemical dysregulations of brain networks involved in integrating and contextualizing cognitive and emotional regulatory behaviors. From a symptom perspective, diagnostic measures of dysregulated mood states like major depressive symptoms are associated with over sixty percent of suicide deaths worldwide (Saxena et al., 2013). This paper reviews the neurobiological and clinical phenotypic correlates for mood dysregulations and suicidal phenotypes. We further propose machine learning approaches to integrate neurobiological measures with dysregulated mood symptoms to elucidate the role of inflammatory processes as neurobiological risk factors for suicide.

Earlier age of onset is associated with a pro-inflammatory state in major depressive disorder

Major depressive disorder (MDD) is a common condition that affects the general population over a wide range of ages, regardless of gender and social background. Early-onset of MDD in adulthood, between ages of 18 and 30 years, is associated with worse outcomes and increased years of disability. Stress load and physical health have been associated with age of onset in MDD. We aim to investigate whether early onset MDD might be associated with changes in systemic inflammatory markers. We examined levels of following cytokines: IL-1β, IL-6, IL-10 and TNFα in 234 patients with MDD. Higher serum levels of TNFα and IL-1β are associated with the early onset of the disorder in patients with MDD. IL-6 levels were also higher in the early onset group and IL-10 levels were higher in the late onset group, but with no significant difference. Changes in the anti-inflammatory/pro-inflammatory balance have been described in mood disorders and may be implicated in its severity and pattern of progression. Our findings reinforce that higher serum levels of IL-1β and TNFα may be associated with the earlier onset subgroup of MDD patients. Future research that target inflammatory markers of immune modulation may be, key in the search for novel preventative therapeutics.

Heart rate variability as a predictor of disease exacerbation in pediatric inflammatory bowel disease

OBJECTIVES

Heart rate variability (HRV), a marker of the parasympathetic vagal activity, was reportedly significantly lower in patients with inflammatory bowel disease (IBD) compared to healthy controls. The aim of this study was to evaluate HRV as a predictor of clinical outcomes in pediatric IBD.

METHODS

This was a prospective study. Children (12-18 years of age) with IBD were prospectively recruited. Each patient underwent two 10-min HRV measurements by means of a photoplethysmograph finger sensor. The square root of the mean squared differences of successive R-R pulse intervals (RMSSD), an indirect index of vagal activity, was calculated. Clinical data, including demographic variables, disease activity and course, medications, and laboratory results were collected during a follow-up of 12 months. The relation between RMSSD and clinical outcomes was examined, adjusting for confounders.

RESULTS

A total of 34 children with IBD were included. Patients in clinical remission had a significantly higher RMSSD compared to patients with active disease (67.72 ± 27.81 versus 45.76 ± 22.04, respectively, P = 0.022). A multivariate analysis revealed that a higher RMSSD was a significant and independent predictor of lower risk of IBD exacerbation (odds ratio = 0.941, 95% confidence interval 0.887-0.998, p = 0.044).

CONCLUSION

HRV correlates with IBD activity and may also serve as an independent predictor of disease exacerbation in pediatric IBD.

Neuroimmunological complications arising from chemotherapy-induced gut toxicity and opioid exposure in female dark agouti rats

Cancer patients may experience symptom clusters, including chemotherapy-induced (CI) gut toxicity (CIGT) and cognitive impairment. Analgesic selection for pain associated with CIGT is difficult as opioids induce glial reactivity and unwanted side effects. This study quantified central glial reactivity and proinflammatory effects in rats with CIGT using three mechanistically different analgesics. Regional adaptations were indicative of immune-to-brain signaling routes. Utilizing a 5-fluorouracil-induced GT (5IGT) rat model and analgesic intervention (carprofen (CAR), buprenorphine (BUP), and tramadol (TRAM)), spinal and brain neuroimmune modulation was examined via microglial, astrocyte, and proinflammatory (cluster of differentiation molecule 11b; CD11b, glial fibrillary associated protein; GFAP, and interleukin-1 beta; IL1β) reactivity marker expression changes by western blot analysis. 5IGT significantly increased thoracic GFAP (p < 0.05) and IL-1β (p < 0.0001) expression, CAR and BUP ameliorated these effects. BUP and TRAM with 5-FU synergistically increased hippocampal GFAP expression. CAR administered with 5IGT significantly elevated hippocampal and thoracic CD11b expression levels (p < 0.05). The neuroimmune responses observed in this study suggest activation of peripheral-to-central immune signaling pathways. We speculate that the opioid-induced hippocampal changes inferred a humorally mediated mechanism, whereas thoracic neuroimmune modifications indicated activation of an indirect neural route. Although TRAM ameliorated 5IGT-intestinal inflammation, this opioid presents complications relating to bodyweight and regional glial dysregulation (neuroinflammation) and may not be optimal in the management of pain associated with 5IGT. The chemotherapy-induced gut-derived neuroimmune consequences observed suggest a potential mechanistic contribution to central components of the cancer symptom cluster experience, while the opioid-related glial changes have implications for optimal pain management in this setting warranting further investigation.

Functional roles of the microbiota-gut-brain axis in Alzheimer’s disease: Implications of gut microbiota-targeted therapy

Increasing scientific evidence demonstrates that the gut microbiota influences normal physiological homeostasis and contributes to pathogenesis, ranging from obesity to neurodegenerative diseases, such as Alzheimer’s disease (AD). Gut microbiota can interact with the central nervous system (CNS) through the microbiota-gut-brain axis. The interaction is mediated by microbial secretions, metabolic interventions, and neural stimulation. Here, we review and summarize the regulatory pathways (immune, neural, neuroendocrine, or metabolic systems) in the microbiota-gut-brain axis in AD pathogenesis. Besides, we highlight the significant roles of the intestinal epithelial barrier and blood–brain barrier (BBB) in the microbiota-gut-brain axis. During the progression of AD, there is a gradual shift in the gut microbiota and host co-metabolic relationship, leading to gut dysbiosis, and the imbalance of microbial secretions and metabolites, such as lipopolysaccharides (LPS) and short-chain fatty acids (SCFAs). These products may affect the CNS metabolic state and immune balance through the microbiota-gut-brain axis. Further, we summarize the potential microbiota-gut-brain axis-targeted therapy including carbohydrates, probiotics, dietary measures, and propose new strategies toward the development of anti-AD drugs. Taken together, the data in this review suggest that remodeling the gut microbiota may present a tractable strategy in the management and development of new therapeutics against AD and other neurodegenerative diseases.

Brain injury, endothelial injury and inflammatory markers are elevated and express sex-specific alterations after COVID-19

Objective

Although COVID-19 is a respiratory disease, all organs can be affected including the brain. To date, specific investigations of brain injury markers (BIM) and endothelial injury markers (EIM) have been limited. Additionally, a male bias in disease severity and mortality after COVID-19 is evident globally. Sex differences in the immune response to COVID-19 may mediate this disparity. We investigated BIM, EIM and inflammatory cytokine/chemokine (CC) levels after COVID-19 and in across sexes.

Methods

Plasma samples from 57 subjects at < 48 h of COVID-19 hospitalization, and 20 matched controls were interrogated for the levels of six BIMs—including GFAP, S100B, Syndecan-1, UCHLI, MAP2 and NSE, two EIMs—including sICAM1 and sVCAM1. Additionally, several cytokines/chemokines were analyzed by multiplex. Statistical and bioinformatics methods were used to measure differences in the marker profiles across (a) COVID-19 vs. controls and (b) men vs. women.

Results

Three BIMs: MAP2, NSE and S100B, two EIMs: sICAM1 and sVCAM1 and seven CCs: GRO IL10, sCD40L, IP10, IL1Ra, MCP1 and TNFα were significantly (p < 0.05) elevated in the COVID-19 cohort compared to controls. Bioinformatics analysis reveal a stronger positive association between BIM/CC/EIMs in the COVID-19 cohort. Analysis across sex revealed that several BIMs and CCs including NSE, IL10, IL15 and IL8 were significantly (p < 0.05) higher in men compared to women. Men also expressed a more robust BIM/ EIM/CC association profile compared to women.

Conclusion

The acute elevation of BIMs, CCs, and EIMs and the robust associations among them at COVID-19 hospitalization are suggestive of brain and endothelial injury. Higher BIM and inflammatory markers in men additionally suggest that men are more susceptible to the risk compared to women.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02323-8.

Peripheral and central immune system crosstalk in Alzheimer disease - a research prospectus

Dysregulation of the immune system is a cardinal feature of Alzheimer disease (AD), and a considerable body of evidence indicates pathological alterations in central and peripheral immune responses that change over time. Considering AD as a systemic immune process raises important questions about how communication between the peripheral and central compartments occurs and whether this crosstalk represents a therapeutic target. We established a whitepaper workgroup to delineate the current status of the field and to outline a research prospectus for advancing our understanding of peripheral-central immune crosstalk in AD. To guide the prospectus, we begin with an overview of seminal clinical observations that suggest a role for peripheral immune dysregulation and peripheral-central immune communication in AD, followed by formative animal data that provide insights into possible mechanisms for these clinical findings. We then present a roadmap that defines important next steps needed to overcome conceptual and methodological challenges, opportunities for future interdisciplinary research, and suggestions for translating promising mechanistic studies into therapeutic interventions.

Vancomycin-Induced Changes in Host Immunity and Behavior: Comparative Genomic and Metagenomic Analysis in C57BL/6 and BALB/c Mice

BACKGROUND

The consequence of treatment with antibiotics on the gut microbiota can be destructive. The antibiotics, however, can be utilized to understand the role of gut microbiota on the host physiology.

AIM

Earlier, we reported the efficacy of vancomycin in gut microbiota perturbation. We continued to understand the effect of restoration kinetics of perturbed gut microbiota on the immunity and behavior of Th1 (C57BL/6)- and Th2 (BALB/c)-biased mice.

METHODS

We studied restoration kinetics of the gut microbiota for two months following the withdrawal of vancomycin treatment in both mice strains. We analyzed cecal microbiome composition, different behavioral assays, and expression of select genes associated with stress and barrier function in gut and brain.

RESULTS

Metagenomic analysis of gut microbiota revealed that the treatment with vancomycin caused a significant decrease in the relative abundance of Firmicutes and Bacteroidetes phyla with a time-dependent increase in Proteobacteria and Verrucomicrobia phyla. Maximum restoration (> 70%) of gut microbiota happened by the 15th day of withdrawal of vancomycin. BALB/c mice showed a more efficient restoration of gut microbiota compared to C57BL/6 mice. We established the correlation patterns of gut microbiota alteration and its effect on (a) the behavior of mice, (b) expression of key brain molecules, and (c) immunity-related genes.

CONCLUSIONS

The results revealed that the gut microbiome profiling, behavior, and immune responses varied significantly between Th1- and Th2-biased mice. By withdrawing the treatment with vancomycin of major gut microbes, important physiological and behavioral changes of both mice strains returned to the normal (untreated control) level.

The Association of Periodontitis and Alzheimer's Disease: How to Hit Two Birds with One Stone

Alzheimer's disease (AD) is the leading cause of cognitive impairment in the elderly. Recent evidence suggests that preventive interventional trials could significantly reduce the risk for development of dementia. Periodontitis is the most common dental disease characterized by chronic inflammation and loss of alveolar bone and perialveolar attachment of teeth. Growing number of studies propose a potential link between periodontitis and neurodegeneration. In the first part of the paper, we overview case-control studies analyzing the prevalence of periodontitis among AD patients and healthy controls. Second, we survey observational libraries and cross-sectional studies investigating the risk of cognitive decline in patients with periodontitis. Next, we describe the current view on the mechanism of periodontitis linked neural damage, highlighting bacterial invasion of neural tissue from dental plaques, and periodontitis induced systemic inflammation resulting in a neuroinflammatory process. Later, we summarize reports connecting the four most common periodontal pathogens to AD pathology. Finally, we provide a practical guide for further prevalence and interventional studies on the management of cognitively high-risk patients with and without periodontitis. In this section, we highlight strategies for risk control, patient information, dental evaluation, reporting protocol and dental procedures in the clinical management of patients with a risk for periodontitis and with diagnosed periodontitis. In conclusion, our review summarizes the current view on the association between AD and periodontitis and provides a research and intervention strategy for harmonized interventional trials and for further case-control or cross-sectional studies.

White Matter Alterations Associated with Pro-inflammatory Cytokines in Patients with Major Depressive Disorder

Objective

Regarding the neuroinflammatory theory of major depressive disorder (MDD), little is known about the effect of pro-inflammatory cytokines on white matter (WM) changes in MDD. We aimed to investigate the relationship between pro-inflammatory cytokines and WM alterations in patients with MDD.

Methods

Twenty-two patients with MDD and 22 healthy controls (HC) were evaluated for brain imaging and pro-inflammatory cytokines including interleukin (IL)-1β, IL-6, IL-8, interferon-γ and tumor necrosis factor (TNF)-α. Tract-based spatial statistics and FreeSurfer were used for brain image analysis.

Results

The levels of TNF-α and IL-8 were significantly higher in the MDD group than in HC. Compared to HC, lower fractional anisotropy (FA), and higher median diffusivity (MD) and radial diffusivity (RD) values were found in the MDD group for several WM regions. Voxel-wise correlation analysis showed that the level of TNF-α was negatively correlated with FA, and positively correlated with MD and RD in the left body and genu of the corpus callosum, left anterior corona radiata, and left superior corona radiata.

Conclusion

Our findings suggest that TNF-α may play an important role in the WM alterations in depression, possibly through demyelination.

Pathophysiology of Fever and Application of Infrared Thermography (IRT) in the Detection of Sick Domestic Animals: Recent Advances

Body-temperature elevations are multifactorial in origin and classified as hyperthermia as a rise in temperature due to alterations in the thermoregulation mechanism; the body loses the ability to control or regulate body temperature. In contrast, fever is a controlled state, since the body adjusts its stable temperature range to increase body temperature without losing the thermoregulation capacity. Fever refers to an acute phase response that confers a survival benefit on the body, raising core body temperature during infection or systemic inflammation processes to reduce the survival and proliferation of infectious pathogens by altering temperature, restriction of essential nutrients, and the activation of an immune reaction. However, once the infection resolves, the febrile response must be tightly regulated to avoid excessive tissue damage. During fever, neurological, endocrine, immunological, and metabolic changes occur that cause an increase in the stable temperature range, which allows the core body temperature to be considerably increased to stop the invasion of the offending agent and restrict the damage to the organism. There are different metabolic mechanisms of thermoregulation in the febrile response at the central and peripheral levels and cellular events. In response to cold or heat, the brain triggers thermoregulatory responses to coping with changes in body temperature, including autonomic effectors, such as thermogenesis, vasodilation, sweating, and behavioral mechanisms, that trigger flexible, goal-oriented actions, such as seeking heat or cold, nest building, and postural extension. Infrared thermography (IRT) has proven to be a reliable method for the early detection of pathologies affecting animal health and welfare that represent economic losses for farmers. However, the standardization of protocols for IRT use is still needed. Together with the complete understanding of the physiological and behavioral responses involved in the febrile process, it is possible to have timely solutions to serious problem situations. For this reason, the present review aims to analyze the new findings in pathophysiological mechanisms of the febrile process, the heat-loss mechanisms in an animal with fever, thermoregulation, the adverse effects of fever, and recent scientific findings related to different pathologies in farm animals through the use of IRT.

Gut Microbiota and Alzheimer's Disease: Pathophysiology and Therapeutic Perspectives

Alzheimer's disease (AD) is the most common cause of dementia in the elderly and is characterized by a progressive decline in cognitive function. Amyloid-β protein accumulation is believed to be the key pathological hallmark of AD. Increasing evidence has shown that the gut microbiota has a role in brain function and host behaviors. The gut microbiota regulates the bidirectional interactions between the gut and brain through neural, endocrine, and immune pathways. With increasing age, the gut microbiota diversity decreases, and the dominant bacteria change, which is closely related to systemic inflammation and health status. Dysbiosis of the gut microbiota is related to cognitive impairment and neurodegenerative diseases. The purpose of this review is to discuss the impacts of the gut microbiota on brain function and the development of AD. It is a feasible target for therapeutic invention. Modulating the composition of the gut microbiota through diet, physical activity or probiotic/prebiotic supplements can provide new prevention and treatment options for AD.

Neuromodulation by the immune system: a focus on cytokines

Interactions between the immune system and the nervous system have been described mostly in the context of diseases. More recent studies have begun to reveal how certain immune cell-derived soluble effectors, the cytokines, can influence host behaviour even in the absence of infection. In this Review, we contemplate how the immune system shapes nervous system function and how it controls the manifestation of host behaviour. Interactions between these two highly complex systems are discussed here also in the context of evolution, as both may have evolved to maximize an organism's ability to respond to environmental threats in order to survive. We describe how the immune system relays information to the nervous system and how cytokine signalling occurs in neurons. We also speculate on how the brain may be hardwired to receive and process information from the immune system. Finally, we propose a unified theory depicting a co-evolution of the immune system and host behaviour in response to the evolutionary pressure of pathogens.

Systemic inflammation is associated with differential neural reactivity and connectivity to affective images

Systemic inflammation is increasingly appreciated as a predictor of health and well-being. Further, inflammation has been shown to influence and be influenced by affective experiences. Although prior work has substantiated associations between inflammatory and affective processes, fewer studies have investigated the neurobiological correlates that underlie links between systemic, low-grade inflammation and affective reactivity. Thus, the current study examined whether markers of systemic inflammation (i.e. interleukin-6, C-reactive protein) are associated with differential patterns of neural activation and connectivity in corticolimbic regions in response to affective images. We investigated this question in a sample of 66 adults (44 women, M age = 54.98 years, range = 35–76) from the Midlife in the United States study. Higher levels of inflammation were associated with lower activity in limbic regions (i.e. amygdala, hippocampus, anterior insula, temporal pole) when viewing positive (vs neutral) images. Higher levels of inflammation were also associated with greater connectivity between the hippocampus and the medial prefrontal cortex in response to positive images. Inflammatory markers were not associated with significant differences in activation or connectivity to negative images. These findings highlight the utility of health neuroscience approaches in demonstrating that physiological processes such as inflammation are related to how our brains respond to affective information.

GFAP and desmin expression in lymphatic tissues leads to difficulties in distinguishing between glial and stromal cells

Recently, we found many immune cells including antigen presenting cells neurally hard wired in the T-cell zone of most lymphoid organs like amongst others, lymph nodes in rats, mice and humans. Single immune cells were reached by single neurites and enclosed with a dense neural meshwork. As it is well known that axons are always accompanied by glial cells, we were able to identify Schwann cells in the hilum, medullary and capsule region, like expected. Unexpected was the result, that we found oligodendrocyte-like cells in these regions, myelinating more than one axon. Likewise important was the finding, that one of the standard glial markers used, a polyclonal GFAP antibody equally bound to desmin and therefore marked nearly all stromal cells in cortical, paracortical and medullary cord regions. More detailed analysis showed that these results also appeared in many other non-lymphoid organs. Therefore, polyclonal GFAP antibodies are only conditionally usable for immunohistochemical analysis in peripheral tissues outside the central nervous system. It remains to be elucidated, if the binding of the GFAP antibody to desmin has its reason in a special desmin variant that can give stromal cells glial character.

Gut Microbiota: Critical Controller and Intervention Target in Brain Aging and Cognitive Impairment

The current trend for the rapid growth of the global aging population poses substantial challenges for society. The human aging process has been demonstrated to be closely associated with changes in gut microbiota composition, diversity, and functional features. During the first 2 years of life, the gut microbiota undergoes dramatic changes in composition and metabolic functions as it colonizes and develops in the body. Although the gut microbiota is nearly established by the age of three, it continues to mature until adulthood, when it comprises more stable and diverse microbial species. Meanwhile, as the physiological functions of the human body deteriorated with age, which may be a result of immunosenescence and "inflammaging," the guts of elderly people are generally characterized by an enrichment of pro-inflammatory microbes and a reduced abundance of beneficial species. The gut microbiota affects the development of the brain through a bidirectional communication system, called the brain-gut-microbiota (BGM) axis, and dysregulation of this communication is pivotal in aging-related cognitive impairment. Microbiota-targeted dietary interventions and the intake of probiotics/prebiotics can increase the abundance of beneficial species, boost host immunity, and prevent gut-related diseases. This review summarizes the age-related changes in the human gut microbiota based on recent research developments. Understanding these changes will likely facilitate the design of novel therapeutic strategies to achieve healthy aging.

Impact of the Gut Microbiota Balance on the Health-Disease Relationship: The Importance of Consuming Probiotics and Prebiotics

Gut microbiota is a group of microorganisms that are deposited throughout the entire gastrointestinal tract. Currently, thanks to genomic tools, studies of gut microbiota have pointed towards the understanding of the metabolism of important bacteria that are not cultivable and their relationship with human homeostasis. Alterations in the composition of gut microbiota could explain, at least in part, some epidemics, such as diabetes and obesity. Likewise, dysbiosis has been associated with gastrointestinal disorders, neurodegenerative diseases, and even cancer. That is why several studies have recently been focused on the direct relationship that these types of conditions have with the specific composition of gut microbiota, as in the case of the microbiota-intestine-brain axis. In the same way, the control of microbiota is related to the diet. Therefore, this review highlights the importance of gut microbiota, from its composition to its relationship with the human health-disease condition, as well as emphasizes the effect of probiotic and prebiotic consumption on the balance of its composition.

A Review of Inflammatory Bowel Disease: A Model of Microbial, Immune and Neuropsychological Integration

Objective: Inflammatory bowel diseases (IBDs) are complex chronic inflammatory disorders of the gastro-intestinal (GI) tract with uncertain etiology. IBDs comprise two idiopathic disorders: Crohn's disease (CD) and ulcerative colitis (UC). The aetiology, severity and progression of such disorders are still poorly understood but thought to be influenced by multiple factors (including genetic, environmental, immunological, physiological, psychological factors and gut microbiome) and their interactions. The overarching aim of this review is to evaluate the extent and nature of the interrelationship between these factors with the disease course. A broader conceptual and longitudinal framework of possible neuro-visceral integration, core microbiome analysis and immune modulation assessment may be useful in accurately documenting and characterizing the nature and temporal continuity of crosstalk between these factors and the role of their interaction (s) in IBD disease activity. Characterization of these interactions holds the promise of identifying novel diagnostic, interventions, and therapeutic strategies. Material and Methods: A search of published literature was conducted by exploring PubMed, EMBASE, MEDLINE, Medline Plus, CDSR library databases. Following search terms relating to key question were set for the search included: "Inflammatory bowel diseases," "gut microbiota," "psychological distress and IBD," "autonomic reactivity and IBD," "immune modulation," "chronic inflammation," "gut inflammation," "enteric nervous system," "gut nervous system," "Crohn's disease," "Ulcerative colitis", "depression and IBD", "anxiety and IBD", "quality of life in IBD patients," "relapse in IBDs," "remission in IBDs," "IBD disease activity," "brain-gut-axis," "microbial signature in IBD," "validated questionnaires in IBD," "IBD activity indices," "IBD aetiology," "IBDs and stress," "epidemiology of IBDs", "autonomic nervous system and gut inflammation", "IBD and environment," "genetics of IBDs," "pathways of immune response in IBDs," "sleep disturbances in IBD," "hypothalamic-pituitary-adrenal axis (HPA)," "sympatho-adrenal axis," "CNS and its control of gut function" "mucosal immune response," "commensal and pathogenic bacteria in the gut," "innate and adaptive immunity." Studies evaluating any possible associations between gut microbiome, psychological state, immune modulation, and autonomic function with IBDs were identified. Commonly cited published literatures with high quality research methodology/results and additional articles from bibliographies of recovered papers were examined and included where relevant. Results: Although there is a substantial literature identifying major contributing factors with IBD, there has been little attempt to integrate some factors over time and assess their interplay and relationship with IBD disease activity. Such contributing factors include genetic and environmental factors, gut microbiota composition and function, physiological factors, psychological state and gut immune response. Interdependences are evident across psychological and biological factors and IBD disease activity. Although from the available evidence, it is implausible that a single explanatory model could elucidate the interplay between such factors and the disease course as well as the sequence of the effect during the pathophysiology of IBD. Conclusion: Longitudinal monitoring of IBD patients and integrating data related to the contributing/risk factors including psychological state, physiological conditions, inflammatory/immune modulations, and microbiome composition/function, could help to explain how major factors associate and interrelate leading to exacerbation of symptoms and disease activity. Identifying the temporal trajectory of biological and psychosocial disturbances may also help to assess their effects and interdependence on individuals' disease status. Moreover, this allows greater insight into understanding the temporal progressions of subclinical events as potential ground for disease severity in IBD. Furthermore, understanding the interaction between these risk factors may help better interventions in controlling the disease, reducing the costs related to disease management, further implications for clinical practice and research approaches in addition to improving patients' mental health and quality of life.

Comorbid anxiety-like behavior in a rat model of colitis is mediated by an upregulation of corticolimbic fatty acid amide hydrolase

Peripheral inflammatory conditions, including those localized to the gastrointestinal tract, are highly comorbid with psychiatric disorders such as anxiety and depression. These behavioral symptoms are poorly managed by conventional treatments for inflammatory diseases and contribute to quality of life impairments. Peripheral inflammation is associated with sustained elevations in circulating glucocorticoid hormones, which can modulate central processes, including those involved in the regulation of emotional behavior. The endocannabinoid (eCB) system is exquisitely sensitive to these hormonal changes and is a significant regulator of emotional behavior. The impact of peripheral inflammation on central eCB function, and whether this is related to the development of these behavioral comorbidities remains to be determined. To examine this, we employed the trinitrobenzene sulfonic acid-induced model of colonic inflammation (colitis) in adult, male, Sprague Dawley rats to produce sustained peripheral inflammation. Colitis produced increases in behavioral measures of anxiety and elevations in circulating corticosterone. These alterations were accompanied by elevated hydrolytic activity of the enzyme fatty acid amide hydrolase (FAAH), which hydrolyzes the eCB anandamide (AEA), throughout multiple corticolimbic brain regions. This elevation of FAAH activity was associated with broad reductions in the content of AEA, whose decline was driven by central corticotropin releasing factor type 1 receptor signaling. Colitis-induced anxiety was reversed following acute central inhibition of FAAH, suggesting that the reductions in AEA produced by colitis contributed to the generation of anxiety. These data provide a novel perspective for the pharmacological management of psychiatric comorbidities of chronic inflammatory conditions through modulation of eCB signaling.