Effect of 6-hydroxydopamine on host resistance against Listeria monocytogenes infection

Skin neuropathy and immunomodulation in diseases

Skin is a vital barrier tissue of the body. Immune responses in the skin must be precisely controlled, which would otherwise cause severe disease conditions such as psoriasis, atopic dermatitis, or pathogenic infection. Research evidence has increasingly demonstrated the essential roles of neural innervations, i.e., sensory and sympathetic signals, in modulating skin immunity. Notably, neuropathic changes of such neural structures have been observed in skin disease conditions, implicating their direct involvement in various pathological processes. An in-depth understanding of the mechanism underlying skin neuropathy and its immunomodulatory effects could help reveal novel entry points for therapeutic interventions. Here, we summarize the neuroimmune interactions between neuropathic events and skin immunity, highlighting the current knowledge and future perspectives of this emerging research frontier.

The Sympathetic Nervous System Is Necessary for Development of CD4+ T-Cell Memory Following Staphylococcus aureus Infection

Lymph nodes and spleens are innervated by sympathetic nerve fibers that enter alongside arteries. Despite discovery of these nerve fibers nearly 40 years ago, the role of these nerves during response to infection remains poorly defined. We have found that chemical depletion of sympathetic nerve fibers compromises the ability of mice to develop protective immune memory to a Staphylococcus aureus infection. Innate control of the primary infection was not impacted by sympathectomy. Germinal center formation is also compromised in nerve-depleted animals; however, protective antibody responses are still generated. Interestingly, protective CD4+ T-cell memory fails to form in the absence of sympathetic nerves after S aureus infection.

Autonomic Regulation of Nociceptive and Immunologic Changes in a Mouse Model of Complex Regional Pain Syndrome

Chronic pain frequently develops after limb injuries, and its pathogenesis is poorly understood. We explored the hypothesis that the autonomic nervous system regulates adaptive immune system activation and nociceptive sensitization in a mouse model of chronic post-traumatic pain with features of complex regional pain syndrome (CRPS). In studies sympathetic signaling was reduced using 6-hydroxydopamine (6-OHDA) or lofexidine, while parasympathetic signaling was augmented by nicotine administration. Hindpaw allodynia, unweighting, skin temperature, and edema were measured at 3 and 7 weeks after fracture. Hypertrophy of regional lymph nodes and IgM deposition in the skin of injured limbs were followed as indices of adaptive immune system activation. Passive transfer of serum from fracture mice to recipient B cell deficient (muMT) mice was used to assess the formation of pain-related autoantibodies. We observed that 6-OHDA or lofexidine reduced fracture-induced hindpaw nociceptive sensitization and unweighting. Nicotine had similar effects. These treatments also prevented IgM deposition, hypertrophy of popliteal lymph nodes, and the development of pronociceptive serum transfer effects. We conclude that inhibiting sympathetic or augmenting parasympathetic signaling inhibits pro-nociceptive immunological changes accompanying limb fracture. These translational results support the use of similar approaches in trials potentially alleviating persistent post-traumatic pain and, possibly, CRPS. PERSPECTIVE: Selective treatments aimed at autonomic nervous system modulation reduce fracture-related nociceptive and functional sequelae. The same treatment strategies limit pain-supporting immune system activation and the production of pro-nociceptive antibodies. Thus, the therapeutic regulation of autonomic activity after limb injury may reduce the incidence of chronic pain.

Efficient roles of miR-146a in cellular and molecular mechanisms of neuroinflammatory disorders: An effectual review in neuroimmunology

Known as one of the most sophisticated systems of the human body, the nervous system consists of neural cells and controls all parts of the body. It is closely related to the immune system. The effects of inflammation and immune reactions have been observed in the pathogenesis of some neurological disorders. Defined as the gene expression regulators, miRNAs participate in cellular processes. miR-146a is a mediator in the neuroimmune system, leaving substantial effects on the homeostasis of immune and brain cells, neuronal identities acquisition, and immune responses regulation in the nervous system. Its positive efficiency has been proven in modulating inflammatory reactions, hemorrhagic complications, and pain. Moreover, the miR-146a targets play a key role in the pathogenesis of these illnesses. Based on the performance of its targets, miR-146a can have various effects on the disease progress. The abnormal expression/function of miR-146a has been reported in neuroinflammatory disorders. There is research evidence that this molecule qualifies as a desirable biomarker for some disorders and can even be a therapeutic target. This study aims to provide a meticulous review regarding the roles of miR-146a in the pathogenesis and progression of several neuroinflammatory disorders such as multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer's disease, temporal lobe epilepsy, ischemic stroke, etc. The study also considers its eligibility for use as an ideal biomarker and therapeutic target in these diseases. The awareness of these mechanisms can facilitate the disease management/treatment, lead to patients' amelioration, improve the quality of life, and mitigate the risk of death.

An overview of the role of sympathetic regulation of immune responses in infectious disease and autoimmunity

Stress in patients and pre-clinical research animals plays a critical role in disease progression Activation of the sympathetic nervous system (SNS) by stress results in secretion of the catecholamines epinephrine (Epi) and norepinephrine (NE) from the adrenal gland and sympathetic nerve endings. Adrenergic receptors for catecholamines are present on immune cells and their activity is affected by stress and the accompanying changes in levels of these neurotransmitters. In this short review, we discuss how this adrenergic stress impacts two categories of immune responses, infections and autoimmune diseases. Catecholamines signal primarily through the β2-adrenergic receptors present on innate and adaptive immune cells which are critical in responding to infections caused by pathogens. In general, this adrenergic input, particularly chronic stimulation, suppresses lymphocytes and allows infections to progress. On the other hand, insufficient adrenergic control of immune responses allows progression of several autoimmune diseases.

The role of autonomic efferents and uncoupling protein 1 in the glucose-lowering effect of leptin therapy

Objective

Leptin reverses hyperglycemia in rodent models of type 1 diabetes (T1D). Direct application of leptin to the brain can lower blood glucose in diabetic rodents, and can activate autonomic efferents and non-shivering thermogenesis in brown adipose tissue (BAT). We investigated whether leptin reverses hyperglycemia through a mechanism that requires autonomic innervation, or uncoupling protein 1 (UCP1)-mediated thermogenesis.

Methods

To examine the role of parasympathetic and sympathetic efferents in the glucose-lowering action of leptin, mice with a subdiaphragmatic vagotomy or 6-hydroxydopamine induced chemical sympathectomy were injected with streptozotocin (STZ) to induce hyperglycemia, and subsequently leptin treated. To test whether the glucose-lowering action of leptin requires activation of UCP1-mediated thermogenesis in BAT, we administered leptin in STZ-diabetic Ucp1 knockout (Ucp1^−/−) mice and wildtype controls.

Results

Leptin ameliorated STZ-induced hyperglycemia in both intact and vagotomised mice. Similarly, mice with a partial chemical sympathectomy did not have an attenuated response to leptin-mediated glucose lowering relative to sham controls, and showed intact leptin-induced Ucp1 expression in BAT. Although leptin activated BAT thermogenesis in STZ-diabetic mice, the anti-diabetic effect of leptin was not blunted in Ucp1^−/− mice.

Conclusions

These results suggest that leptin lowers blood glucose in insulin-deficient diabetes through a manner that does not require parasympathetic or sympathetic innervation, and thus imply that leptin lowers blood glucose through an alternative CNS-mediated mechanism or redundant target tissues. Furthermore, we conclude that the glucose lowering action of leptin is independent of UCP1-dependent thermogenesis.

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Leptin does not require vagal innervation to reverse hyperglycemia.

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Leptin therapy reverses hyperglycemia in mice with a partial chemical sympathectomy.

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Leptin reverses hyperglycemia independent of uncoupling protein 1.

Catecholamines and acetylcholine are key regulators of the interaction between microbes and the immune system

Recent studies suggest that catecholamines (CAs) and acetylcholine (ACh) play essential roles in the crosstalk between microbes and the immune system. Host cholinergic afferent fibers sense pathogen-associated molecular patterns and trigger efferent cholinergic and catecholaminergic pathways that alter immune cell proliferation, differentiation, and cytokine production. On the other hand, microbes have the ability to produce and degrade ACh and also regulate autogenous functions in response to CAs. Understanding the role played by these neurotransmitters in host-microbe interactions may provide valuable information for the development of novel therapies.

β-Adrenergic blockade protects BALB/c mice against infection with a small inoculum of Leishmania mexicana mexicana (LV4)

In order to test the influence of the sympathetic nervous system on Leishmania mexicana infection, groups of female BALB/c mice were treated (i.p.) with the non-selective β-adrenergic receptor (β-AR) antagonist (S)-propranolol (5mg/kg thrice a day), the β2-AR agonist clenbuterol (1mg/kg once a day) or the α2-AR antagonist yohimbine (2mg/kg twice a day) during 5days. During the second day of treatments, mice were inoculated in the footpad with 1×10(6) or 1×10(3) metacyclic promastigotes of L. mexicana mexicana (LV4). The lesion size was measured weekly, and parasite burden on week 12. In mice treated with (S)-propranolol, the percentage of splenic T lymphocytes producing IFN-γ after antigen challenge was determined by flow cytometry. In mice infected with 1×10(6) parasites, only (S)-propranolol caused a reduction of footpad swelling (p<0.05, weeks 11-12), without effects on parasite burden, or in the percentage of IFN-γ-immunopositive CD4(+) or CD8(+) T lymphocytes. In mice infected with 1×10(3) parasites, the effects of treatments vs. control group were as follows: (a) inhibition of footpad swelling by (S)-propranolol (p<0.01, weeks 3-12), clenbuterol (p<0.05, weeks 7-10), and yohimbine (p<0.01, week 7); (b) a decrease of the parasite burden by (S)-propranolol (p<0.01) and yohimbine (p<0.05); (c) in control mice the percentage of CD4(+) T-cells producing IFN-γ was 6.2±0.5%, while in those treated with (S)-propranolol it increased to 8.7±0.6% (p<0.01); (d) in control mice the percentage of CD8(+) T-cells producing IFN-γ was 3.1±0.4%, while in those treated with (S)-propranolol it increased to 10.4±0.2% (p<0.01). These results indicate that the blockade of β-ARs during infection of BALB/c mice with an inoculum of L. mexicana mexicana similar to that delivered by the bite of a sand fly produces a Th1 bias in the immune response, favoring an increment of T lymphocytes secreting IFN-γ, which correlated with a reduced parasite burden (p<0.05, Spearman's test). We suggest that β-AR antagonists could be of therapeutic value, either as treatment or as adjuvant of vaccines for L. mexicana.

[Host responses to bacterial infections]

Pathogenic bacteria and host defense system have been evolved by their offense and defense. In vivo research is crucial for elucidation of interactions between them. I have investigated their offence and defense by various standpoints using mouse models of Listeria monocytogenes and Staphylococcus aureus infections. Herein, the results of my research including the roles of endogenous cytokines in host defense, the attenuation of host defense mechanism in obesity and diabetes, the development of vaccines against S. aureus infection by staphylococcal enterotoxin (SE) family molecules, and the emesis-inducing mechanism of SEA are described.

Neural control of the immune system

Neural reflexes support homeostasis by modulating the function of organ systems. Recent advances in neuroscience and immunology have revealed that neural reflexes also regulate the immune system. Activation of the vagus nerve modulates leukocyte cytokine production and alleviates experimental shock and autoimmune disease, and recent data have suggested that vagus nerve stimulation can improve symptoms in human rheumatoid arthritis. These discoveries have generated an increased interest in bioelectronic medicine, i.e., therapeutic delivery of electrical impulses that activate nerves to regulate immune system function. Here, we discuss the physiology and potential therapeutic implications of neural immune control.

Spinal cord injury, immunodepression, and antigenic challenge

The inability to effectively control microbial infection is a leading cause of morbidity and mortality in individuals affected by spinal cord injury (SCI). Available evidence from clinical studies as well as animal models of SCI demonstrate that increased susceptibility to infection is derived from disruption of central nervous system (CNS) communication with the host immune system that ultimately leads to immunodepression. Understanding the molecular and cellular mechanisms governing muted cellular and humoral responses that occur post-injury resulting in impaired host defense following infection is critical for improving the overall quality of life of individuals with SCI. This review focuses on studies performed using preclinical animal models of SCI to evaluate how injury impacts T and B lymphocyte responses following either viral infection or antigenic challenge.

The dopaminergic system in autoimmune diseases

Bidirectional interactions between the immune and the nervous systems are of considerable interest both for deciphering their functioning and for designing novel therapeutic strategies. The past decade has brought a burst of insights into the molecular mechanisms involved in neuroimmune communications mediated by dopamine. Studies of dendritic cells (DCs) revealed that they express the whole machinery to synthesize and store dopamine, which may act in an autocrine manner to stimulate dopamine receptors (DARs). Depending on specific DARs stimulated on DCs and T cells, dopamine may differentially favor CD4⁺ T cell differentiation into Th1 or Th17 inflammatory cells. Regulatory T cells can also release high amounts of dopamine that acts in an autocrine DAR-mediated manner to inhibit their suppressive activity. These dopaminergic regulations could represent a driving force during autoimmunity. Indeed, dopamine levels are altered in the brain of mouse models of multiple sclerosis (MS) and lupus, and in inflamed tissues of patients with inflammatory bowel diseases or rheumatoid arthritis (RA). The distorted expression of DARs in peripheral lymphocytes of lupus and MS patients also supports the importance of dopaminergic regulations in autoimmunity. Moreover, dopamine analogs had beneficial therapeutic effects in animal models, and in patients with lupus or RA. We propose models that may underlie key roles of dopamine and its receptors in autoimmune diseases.

β2-Adrenoreceptor agonist inhibits antigen cross-presentation by dendritic cells

Despite widespread usage of β-adrenergic receptor (AR) agonists and antagonists in current clinical practice, our understanding of their interactions with the immune system is surprisingly sparse. Among the AR expressed by dendritic cells (DC), β2-AR can modify in vitro cytokine release upon stimulation. Because DC play a pivotal role in CD8(+) T cell immune responses, we examined the effects of β2-AR stimulation on MHC class I exogenous peptide presentation and cross-presentation capacities. We demonstrate that β2-AR agonist-exposed mature DC display a reduced ability to cross-present protein Ags while retaining their exogenous peptide presentation capability. This effect is mediated through the nonclassical inhibitory G (Gαi/0) protein. Moreover, inhibition of cross-presentation is neither due to reduced costimulatory molecule expression nor Ag uptake, but rather to impaired phagosomal Ag degradation. We observed a crosstalk between the TLR4 and β2-AR transduction pathways at the NF-κB level. In vivo, β2-AR agonist treatment of mice inhibits Ag protein cross-presentation to CD8(+) T cells but preserves their exogenous MHC class I peptide presentation capability. These findings may explain some side effects on the immune system associated with stress or β-agonist treatment and pave the way for the development of new immunomodulatory strategies.

Chemical sympathectomy increases susceptibility to ocular herpes simplex virus type 1 infection

The cornea is one of the most highly innervated tissues in the mammalian host. We hypothesized changes to cornea innervation through chemical sympathectomy would significantly alter the host response to the neurotropic viral pathogen, herpes simplex virus type 1 (HSV-1) following ocular infection. Mice treated with 6-hydroxydopamine hydrobromide displayed reduced tyrosine hydroxylase-positive fibers residing in the cornea. Sympathectomized mice were also found to show a transient rise in virus recovered in infected tissues and succumbed to infection in greater numbers. Whereas there were no differences in infiltrating leukocyte populations including HSV-1-specific cytotoxic T lymphocytes in the infected tissue, an increase in substance P and a decrease in IFN-gamma levels in the trigeminal ganglion but not brain stem of sympathectomized mice were noted. Sympathectomized mice treated with the neurokinin-1 receptor antagonist L703,606 had delayed mortality implicating the involvement of substance P in HSV-1-mediated death.

Sympathetic modulation of immunity: relevance to disease

Optimal host defense against pathogens requires cross-talk between the nervous and immune systems. This paper reviews sympathetic-immune interaction, one major communication pathway, and its importance for health and disease. Sympathetic innervation of primary and secondary immune organs is described, as well as evidence for neurotransmission with cells of the immune system as targets. Most research thus far has focused on neural-immune modulation in secondary lymphoid organs, has revealed complex sympathetic modulation resulting in both potentiation and inhibition of immune functions. SNS-immune interaction may enhance immune readiness during disease- or injury-induced 'fight' responses. Research also indicate that dysregulation of the SNS can significantly affect the progression of immune-mediated diseases. However, a better understanding of neural-immune interactions is needed to develop strategies for treatment of immune-mediated diseases that are designed to return homeostasis and restore normal functioning neural-immune networks.

Catecholamines and sympathomimetic drugs decrease early Salmonella Typhimurium uptake into porcine Peyer's patches

Peyer's patches of the small intestine serve as inductive sites for mucosal immunity as well as targets for invasive enteropathogens, including Salmonella. Because they are innervated by catecholamine-containing enteric nerves, the hypothesis that the endogenous catecholamines dopamine and norepinephrine or sympathomimetic drugs alter Salmonella Typhimurium uptake into Peyer's patches was tested. Porcine jejunal Peyer's patch explants were mounted in Ussing chambers and inoculated with a porcine field isolate of Salmonella Typhimurium DT104. Salmonella recovery from gentamicin-treated tissues increased significantly between 30 and 90 min of bacterial exposure to the mucosal surface. Addition of the neuronal conduction blocker saxitoxin (0.1 micromol L(-1)) or dopamine (30 micromol L(-1)) to the contraluminal aspect of explants decreased bacterial recovery after 60 min of Salmonella exposure. The effects of dopamine were mimicked by cocaine and methamphetamine (30 micromol L(-1)), which act on catecholaminergic nerve terminals to increase synaptic neurotransmitter concentrations. These results suggest that enteric catecholaminergic nerves modulate Salmonella colonization of Peyer's patches at the earliest stages of infection, in part by altering epithelial uptake of bacteria.

Impairment of the host's antibacterial resistance by norepinephrine activated neutrophils

The susceptibility of mice to infectious complications is dramatically increased in an accompaniment with systemic inflammatory response syndrome (SIRS). Polymorphonuclear neutrophils with immunosuppressive ability (PMN-II) that appear in response to SIRS have been classified as one of the cells responsible for the increased susceptibility of mice with SIRS (SIRS mice) to sepsis induced by cecal-ligation and puncture (CLP). Since a high level of norepinephrine (NE) is demonstrated in the plasma of SIRS mice, in the present study, the role of NE on the appearance of PMN-II in SIRS mice was studied. Similar to SIRS mice, normal mice became susceptible to CLP-induced infectious complications after inoculation with NE-treated PMN. CCL2 and IL-10 (biomarkers for PMN-II) were equally produced by PMN-II prepared from SIRS mice and NE-treated PMN. However, CCL3 and IL-12 (biomarkers for immunostimulatory PMN, PMN-I) were not detected in culture fluids from either PMN preparation. These results indicate that NE mass-produced in association with SIRS development plays a role on the generation of PMN-II and the appearing PMN-II are responsible, in part, for increased susceptibility of SIRS mice to CLP-induced infectious complications.

Beta1-adrenergic receptors on immune cells impair innate defenses against Listeria

Cold restraint (CR) for 1 h elicits a psychological and physiological stress that inhibits host defenses against Listeria monocytogenes (LM). Previous analyses indicated that this inhibition is not due to depletion of B or T cells but is instead dependent on signaling through beta-adrenoceptors (betaARs). We now show that impaired host resistance by CR cannot be accounted for by a decrease in LM-specific (listeriolysin O(91-99) tetramer(+)) effector CD8(+) T cells; this result is consistent with previous observations that CR-induced effects are mainly limited to early anti-LM responses. beta2-Adrenoceptor (beta2AR)(-/-) FVB/NJ and wild-type FVB/NJ mice had equivalent anti-LM defenses, whereas beta1-adrenoceptor (beta1AR)(-/-) FVB/NJ mice had lower levels of LM even when subjected to CR treatment. Additionally, host-resistance competency of beta1AR(-/-) mice could be transferred to irradiated wild-type mice reconstituted with beta1AR(-/-) bone marrow progenitors and spleen cells, indicating that beta1AR signaling on immune cells reduces anti-LM responses. beta1AR(-/-) mice had improved cellular (delayed-type hypersensitivity) responses while beta2AR(-/-) mice had improved humoral responses (IgG1, IgG2, and IgM), a result that further explains the strain differences in LM defenses. CR-induced expression of beta1AR and beta2AR mRNA was assessed by real-time PCR. CR treatment significantly increased betaAR mRNAs in Ficoll-purified and F4/80(+)-enhanced liver but not splenic homogenates, demonstrating an organ-specific effect of stress that alters host defenses. Finally, CR treatment induced early increases in perforin expression that may enhance immune cell apoptosis and interfere with LM clearance. In conclusion, beta1AR signaling has immunomodulatory effects on early cell-mediated immune responses; a lack of beta1AR signaling improves antilisterial defenses and cell-mediated immunity, in general.

Role of sympathetic nerves on early embryonic development and immune modulation of uterus in pregnant mice

To determine the role of sympathetic nerves in the early embryonic development and the immune modulation of maternal uterus during pregnancy, a model of chemical sympathectomy in mice was established by intraperitoneal injection of 6-hydroxydopamine (6-OHDA). The embryonic development and the distribution of maternal uterine immunocytes were investigated during early pregnancy (E1-E9) with methods of histology, immunohistochemistry and ELISA. Our data showed that in the 6-OHDA-treated group, the number of implanted embryos was only 64.4% of that in the control group at E7, and the development of uterine glands and vessels was poor in pregnant mice. In addition, in uterine tissues of 6-OHDA-treated mice, the number of CD8+ T cells increased ten-fold and the concentration of IL-2 increased 3.6-fold at E5. However, no obvious changes to the number of CD4+ T cells and IL-4 were observed. Thus, the CD4+/CD8+ T cells ratio significantly decreased, while the IL-2/IL-4 ratio significantly increased. These findings indicated that the activation of sympathetic nerves might be favorable to fetal survival and development during early pregnancy through influencing on immune function and decidua formation of uterus.

Sympathetic nervous system influence on the innate immune response

Our studies focused on the sympathetic nervous system (SNS) influence on dendritic cells (DCs), which play a crucial role in the innate immune response. We found that DCs express a variety of adrenergic receptors (ARs) with alpha1-ARs playing a stimulatory and beta2-ARs an inhibitory effect on DCs migration. beta2-ARs in skin and bone marrow-derived DCs when stimulated by bacterial toll-like receptors (TLRs) agonists respond to norepinephrine (NE) by decreased interleukin-12 (IL-12) and increased IL-10 production which in turn downregulates inflammatory cytokine production and CCR7 expression and thus their migration ability leading to reduced T helper-1 (Th1) priming. We also found that contact sensitizers that may induce a predominant Th1 response, do so by inhibiting the local NE turnover in the skin. The SNS seems therefore to contribute in shaping the information conveyed by DCs to T cells and thus in inducing the appropriate adaptive immune response. In this sense, the SNS physiological influence may allow Th2 priming to fight infections sustained by extracellular pathogens and limit the risk for organ-specific autoimmune reactions associated with excessive Th1 priming and inhibition of T regulatory cell functions. More recently, we found that preconditioning of the skin by beta-adrenergic antagonist and the TLR2 agonist S. Aureus peptidoglycan (PGN) may instruct a Th1 adaptive response to a soluble protein antigen. On the contrary, when the TLR4 agonist E. Coli lipopolysaccharide was used, the presence of the beta-adrenergic antagonist was not effective. These effects were consonant with the pattern of TLRs expression shown by epidermal keratinocytes (EKs) but not by skin DCs. As beta-ARs signaling defects together with S. Aureus infections are thought to serve as initiation and/or persistence factors for numerous Th1-sustained autoimmune inflammatory skin diseases, we might have disclosed at least part of the relevant pathogenetic mechanism.

The role of macrophage migration inhibitory factor in lethal Listeria monocytogenes infection in mice

Macrophage migration inhibitory factor (MIF) has been characterized as a proinflammatory cytokine. Previous studies have indicated that MIF may play a beneficial role or a detrimental role in microbial infections, depending on pathogens. In this study, we investigated the role of MIF in Listeria monocytogenes infection. The MIF titers increased 6h after lethal L. monocytogenes infection but not in the sublethal infection. The elimination of bacteria from the spleens and livers was not affected by anti-MIF antibody (Ab) injection in the sublethal infection, whereas anti-MIF Ab treatment rescued mice from the lethal infection, suggesting that MIF plays a deteriorating role in lethal L. monocytogenes infection. Anti-MIF Ab treatment significantly augmented interleukin (IL)-10 production in the spleens and livers 24h after infection, suggesting that MIF might down-regulate IL-10 production. Although the administration of anti-IL-10 monoclonal Ab showed no significant effect on the bacterial growth in the organs, the bacterial infection was deteriorated by the combined administration of Abs against MIF and IL-10. On the other hand, anti-MIF Ab treatment also increased in the serum cortisol titer 6h after infection compared with the control immunoglobulin G-injected group. Depletion of endogenous IL-10 decreased serum cortisol titers. These results suggested that IL-10 and cortisol might be involved in the deteriorating effect of MIF on lethal L. monocytogenes infection.

Urocortin 2 suppresses host resistance to Listeria monocytogenes infection via up-regulation of interleukin-10

Previous studies have showed that corticotropin-releasing factor (CRF) modulates immune response during inflammation. We investigated the effect of CRF family peptides on host resistance to Listeria monocytogenes infection in mice. When mice were administered ip with CRF, urocortin (Ucn), or Ucn2 30 min prior a sublethal infection with L. monocytogenes, the numbers of bacteria in the organs of Ucn2-treated mice were dramatically increased, and most of these mice succumbed. However, host resistance to the infection was retained in CRF- or Ucn-treated mice. The suppressive effect of Ucn2 was dependent on CRF receptor type 2 because an antagonist to the receptor canceled the effect of Ucn2. IL-10 production was significantly increased, and interferon-gamma and TNFalpha production was decreased in the spleens of Ucn2-treated mice, compared with those in Ucn2-untreated control mice. The effect of Ucn2 was canceled by treatment with anti-IL-10 monoclonal antibody and in IL-10-deficient mice. The expression and activation of signal transducers and activators of transcription (STAT) 3 were up-regulated, and the expression and activation of STAT1 were down-regulated in the spleens from Ucn2-treated mice, compared with vehicle-treated mice. Moreover, suppression of TNFalpha production and augmentation of IL-10 production and expression and activation of STAT3 by Ucn2 treatment were observed in heat-killed L. monocytogenes-stimulated macrophages. These results suggested that Ucn2 suppresses host resistance to L. monocytogenes infection via up-regulation of IL-10 production.

Chemical sympathectomy inhibits periodontal disease in Fischer 344 rats

OBJECTIVE

The responsiveness of the sympathetic nervous system (SNS) and the hypothalamic--pituitary--adrenal (HPA) axis plays a major role in immune regulation and for the outcome of infections and inflammatory disorders. This study was designed to investigate whether chemical SNS denervation with the noradrenaline-selective neurotoxic drug 6-hydroxydopamine (6-OHDA), which destroys peripheral noradrenaline terminals, would influence immune responses to Gram-negative bacterial lipopolysaccharide (LPS) stimulation, and the progression of ligature-induced periodontal disease in Fischer 344 rats.

MATERIAL AND METHODS

6-OHDA (40--60 microg/kg) or vehicle was injected intraperitoneally (i.p.) on days 1, 3 and 5, 10 days before application of the ligatures, and thereafter weekly in doses of 80 microg/kg. Periodontal disease was assessed when the ligatures had been in place for 49 days. At 24 and 2 h before decapitation, all rats received LPS (150 microg/kg i.p.) to induce a robust immune and HPA axis response.

RESULTS

The 6-OHDA-treated rats showed significantly reduced bone loss as measured by digital X-rays (p< 0.01), and enhanced levels of the cytokines transforming growth factor-beta (p=0.05) and interleukin-6 (p=0.05), as well as the HPA axis derived hormone corticosterone (p=0.01), induced by LPS stimulation.

CONCLUSIONS

6-OHDA-induced chemical sympathectomy inhibits ligature-induced periodontal disease in this model. This effect may be attributable to the well-documented ability of the SNS to regulate immune system function primarily via the adrenergic neurotransmitter noradrenaline released at sympathetic nerve terminals. The enhanced HPA axis activation may be a compensatory response that reduces the T helper (Th)2 to Th1 skewing effect of treatment with 6-OHDA.

Effects of space flight conditions on the function of the immune system and catecholamine production simulated in a rodent model of hindlimb unloading

The rodent model of hindlimb unloading has been successfully used to simulate some of the effects of space flight conditions. Previous studies have indicated that mice exposed to hindlimb-unloading conditions have decreased resistance to infections compared to restrained and normally housed control mice.

OBJECTIVE

The purpose of this study was to clarify the mechanisms involved in resistance to infection in this model by examining the effects of hindlimb unloading on the function of the immune system and its impact on the production of catecholamines.

METHODS

Female Swiss Webster mice were hindlimb-unloaded during 48 h and the function of the immune system was assessed in spleen and peritoneal cells immediately after this period. In addition, the kinetics of catecholamine production was measured throughout the hindlimb-unloading period.

RESULTS

The function of the immune system was significantly suppressed in the hindlimb-unloaded group compared to restrained and normally housed control mice. Levels of catecholamines were increased in the hindlimb-unloaded group and peaked at 12 h following the commencement of unloading.

CONCLUSION

These results suggest that physiological responses of mice are altered early after hindlimb unloading and that catecholamines may play a critical role in the modulation of the immune system. These changes may affect the ability of mice to resist infections.

Increased norepinephrine production associated with burn injuries results in CCL2 production and type 2 T cell generation

The susceptibility of thermally injured mice (TI-mice) to various infections is markedly influenced by burn-associated type 2 T cell responses, which are common with severe thermal injuries. Previously, we have reported that CC chemokine ligand 2/monocyte chemoattractant protein-I (CCL2) is produced in mice within 1 day of thermal injury, and the subsequent development of burn-associated type 2 T cell responses are triggered by this chemokine produced early after thermal injury. In this study, influence of norepinephrine (NE) on CCL2 production in mice early after thermal injury (TI) was investigated. Peripheral blood mononuclear cells (PBMC) and peritoneal macrophages (PMphi) from TI-mice produced CCL2, but the same cell preparations from normal mice did not. This chemokine was not produced by PBMC and PMphi from TI-mice previously treated with 6-hydroxydopamine (6-OHDA), which destroys sympathetic nerve termini. NE production was increased in circulation of TI-mice, and treatment of TI-mice with 6-OHDA resulted in the inhibition of NE secretion. When PBMC from normal mice were treated with NE, they acquired the ability to produce CCL2. Splenic T cells from TI-mice produced IL-4 into their culture fluids, while the cytokine was not produced by splenic T cells from TI-mice previously treated with 6-OHDA. These results indicate that NE may have an important role on early CCL2 production and the subsequent development of burn-associated type 2 T cell responses.

Langerhans cells beta 2-adrenoceptors: role in migration, cytokine production, Th priming and contact hypersensitivity

We showed that norepinephrine (NE) hampers IL-12 and stimulates IL-10 production via adrenoceptors (ARs) in bone marrow-derived dendritic cells (BMDC) influencing their Th priming ability. Others have shown that Langerhans cells (LC) express mRNA for beta1-, beta2- and alpha1(A)-(ARs) and that catecholamines may inhibit the antigen-presenting capability via beta2-ARs. Here, we show that also BMDC express mRNA for beta1-, beta2-, alpha2(A)- and alpha2(C)-ARs. Inhibition of IL-12 is mediated by both beta2- and alpha2(A)-ARs, while stimulation of IL-10 by beta2-ARs only. In addition, LC migration, the contact hypersensitivity response (CHS) and production of IFN-gamma and IL-2 in draining lymph node cells is increased in mice treated topically with the beta2-AR antagonist ICI 118,551 during FITC sensitization. Activation of beta2-ARs in BMDC before adoptive transfer could reduce both migration and CHS response to FITC. Finally, preincubation of BMDC with LPS in presence of the specific beta2-AR agonist salbutamol impaired their chemotactic response to CCL19 and CCL21 and this effect was neutralized by anti-IL-10 mAb. We suggest that the physiological activation of beta2-ARs in DC (LC) results in stimulation of IL-10 which in turn restrains DC (LC) migration influencing antigen presentation and the consequent CHS response.

Acute cold/restraint stress inhibits host resistance to Listeria monocytogenes via beta1-adrenergic receptors

We previously reported that acute cold/restraint stress (ACRS) significantly inhibits host resistance to Listeria monocytogenes (LM) in BALB/c mice and that the sympathetic nervous system plays a major role in this inhibition. Here, we have further investigated the involvement of adrenergic receptor (ADR) subtypes. beta-ADR antagonist propranolol, but not alpha-ADR antagonist phentolamine significantly enhanced host resistance of ACRS mice. Pro-inflammatory cytokine (IL-6, IL-1beta, and TNFalpha) and IFNgamma levels positively correlated with the LM levels in all groups of mice. Furthermore, beta1-ADR antagonist atenolol but not beta2-ADR antagonist ICI118,551 significantly decreased LM burden in ACRS mice. In addition, SCID mice on the same genetic background (BALB/c), which have no adaptive immune potential, were used to assess the immune responses targeted by ACRS. ACRS-induced suppression of host resistance was not observed in SCID mice, and propranolol pretreatment provided no further improvement of host resistance, indicating that ACRS mainly affects adaptive immunity, which is less critical in mice with greater innate than adaptive immunity. In summary, the data suggest that ACRS inhibition of host resistance to LM is mediated through beta1-ADR stimulation, which appears to directly or indirectly modify activation of T cells or subsequent T cell functions involved in adaptive immunity, thus inhibiting overall host resistance. Interestingly, with heightened innate immunity and the absence of adaptive immunity, as observed in the SCID mice, ACRS does not affect host resistance, which emphasizes the importance of innate immunity in defense against bacterial infection.

Short exposure of maturing, bone marrow-derived dendritic cells to norepinephrine: impact on kinetics of cytokine production and Th development

The information gathered by dendritic cells (DC) during the innate immune response to a pathogen is determinant for the type of adaptive response. Here we show that short-term (3 h) exposure of bone marrow-derived DC to norepinephrine (NE), at the beginning of lipopolysaccharide (LPS) or keyhole limpet hemocyanin (KLH) stimulation hampers IL-12 production and increases IL-10 release. The NE effect was mediated by both beta- and alpha2-adrenergic receptors. The capacity of NE-exposed DC to produce IL-12 upon CD40 cross-linking as well as to stimulate allogeneic T-helper (Th) lymphocytes was reduced. Adoptive transfer of NE-exposed DC induced a Th2 slanted response in vivo. Thus, a brief NE exposure of antigen-stimulated DC seems to limit their Th1 polarizing properties. Noteworthy, the ganglionic blocker pentolinium administered in mice before skin sensitization with fluoroscein isothiocyanate (FITC) could increase the Th1-type response in the draining lymph nodes. Our results suggest that the extent of Th differentiation in the response to an antigen might be influenced by the local sympathetic nervous activity in the early phase of dendritic cell stimulation.