Compromised peripheral immunity of mice injected intrastriatally with six-hydroxydopamine

Zearalenone and deoxynivalenol inhibited IL-4 receptor-mediated Th2 cell differentiation and aggravated bacterial infection in mice

The immunotoxicity of zearalenone (ZEA) and deoxynivalenol (DON), two of the most common environmental mycotoxins, has been well investigated. However, due to the complexity of the immune system, especially during bacterial infection, many types of immune cells are involved in invasion resistance and bacterial clearance. Of these, T helper 2 (Th2) cells, which are members of the helper T cell family, assist B cells to activate and differentiate into antibody-secreting cells, participate in humoral immune response, and, ultimately, eliminate pathogens. Thus, it is important to identify the stage at which these toxins affect the immune function, and to clarity the underlying mechanisms. In this study, mice infected with Listeria monocytogenes (Listeria) were used to study the effects of ZEA, DON, and ZEA + DON on Th2 differentiation, Interleukin-4 Receptor (IL-4R) expression, costimulatory molecules expression and cytokine secretion after Listeria infection. Naive CD4+ T cells, isolated from mice, were used to verify the in vivo effects and the associated mechanisms. In vivo experiments showed that these toxins aggravated spleen damage after Listeria infection and reduced the differentiation of Th2 cells by affecting the synthesis of IL-4R of CD4+ T cells. In addition, the level of the costimulatory molecule CD154 decreased. Consistent with this, in vitro studies showed that these toxins inhibited the differentiation of mouse naive CD4+ T cell into Th2 subtype and decreased IL-4R levels. In addition, the levels of costimulatory molecules CD154, CD278 and the Th2 cells secrete cytokines IL-4, IL-6, and IL-10 decreased. Based on our in vivo and in vitro experiments, we suggest that ZEA, DON, and ZEA + DON inhibit the expression of costimulatory molecules on CD4+ T cell, and inhibit the IL-4R-mediated Th2 cell differentiation. This may indicate that the body cannot normally resist or clear the pathogen after mycotoxin poisoning.

Toward the Existence of a Sympathetic Neuroplasticity Adaptive Mechanism Influencing the Immune Response. A Hypothetical View-Part II

In the preceding work, a hypothesis on the existence of a specific neural plasticity program from sympathetic fibers innervating secondary lymphoid organs was introduced. This proposed adaptive mechanism would involve segmental retraction and degeneration of noradrenergic terminals during the immune system (IS) activation followed by regeneration once the IS returns to the steady-state. Starting from such view, this second part presents clinical and experimental evidence allowing to envision that this sympathetic neural plasticity mechanism is also operative on inflamed non-lymphoid peripheral tissues. Importantly, the sympathetic nervous system regulates most of the physiological bodily functions, ranging from cardiovascular, respiratory and gastro-intestinal functions to endocrine and metabolic ones, among others. Thus, it seems sensible to think that compensatory programs should be put into place during inflammation in non-lymphoid tissues as well, to avoid the possible detrimental consequences of a sympathetic blockade. Nevertheless, in many pathological scenarios like severe sepsis, chronic inflammatory diseases, or maladaptive immune responses, such compensatory programs against noradrenergic transmission impairment would fail to develop. This would lead to a manifest sympathetic dysfunction in the above-mentioned settings, partly accounting for their underlying pathophysiological basis; which is also discussed. The physiological/teleological significance for the whole neural plasticity process is postulated, as well.

Neuro-Immune Mechanisms Regulating Social Behavior: Dopamine as Mediator?

Social interactions are fundamental to survival and overall health. The mechanisms underlying social behavior are complex, but we now know that immune signaling plays a fundamental role in the regulation of social interactions. Prolonged or exaggerated alterations in social behavior often accompany altered immune signaling and function in pathological states. Thus, unraveling the link between social behavior and immune signaling is a fundamental challenge, not only to advance our understanding of human health and development, but for the design of comprehensive therapeutic approaches for neural disorders. In this review, we synthesize literature demonstrating the bidirectional relationship between social behavior and immune signaling and highlight recent work linking social behavior, immune function, and dopaminergic signaling in adolescent neural and behavioral development.

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.

Impaired hepatic function and central dopaminergic denervation in a rodent model of Parkinson's disease: a self-perpetuating crosstalk?

In Parkinson's disease (PD), aside from the central lesion, involvement of visceral organs has been proposed as part of the complex clinical picture of the disease. The issue is still poorly understood and relatively unexplored. In this study we used a classic rodent model of nigrostriatal degeneration, induced by the intrastriatal injection of 6-hydroxydopamine (6-OHDA), to investigate whether and how a PD-like central dopaminergic denervation may influence hepatic functions. Rats received an intrastriatal injection of 6-OHDA or saline (sham), and blood, cerebrospinal fluid, liver and brain samples were obtained for up to 8 weeks after surgery. Specimens were analyzed for changes in cytokine and thyroid hormone levels, as well as liver mitochondrial alterations. Hepatic mitochondria isolated from animals bearing extended nigrostriatal lesion displayed increased ROS production, while membrane potential (ΔΨ) and ATP production were significantly decreased. Reduced ATP production correlated with nigral neuronal loss. Thyroid hormone levels were significantly increased in serum of PD rats compared to sham animals while steady expression of selected cytokines was detected in all groups. Hepatic enzyme functions were comparable in all animals. Our study indicates for the first time that in a rodent model of PD, hepatic mitochondria dysfunctions arise as a consequence of nigrostriatal degeneration, and that thyroid hormone represents a key interface in this CNS-liver interaction. Liver plays a fundamental detoxifying function and a better understanding of PD-related hepatic mitochondrial alterations, which might further promote neurodegeneration, may represent an important step for the development of novel therapeutic strategies.

Dopaminergic neurotoxicant 6-OHDA induces oxidative damage through proteolytic activation of PKCδ in cell culture and animal models of Parkinson's disease

The neurotoxicant 6-hydroxydopamine (6-OHDA) is used to investigate the cellular and molecular mechanisms underlying selective degeneration of dopaminergic neurons in Parkinson's disease (PD). Oxidative stress and caspase activation contribute to the 6-OHDA-induced apoptotic cell death of dopaminergic neurons. In the present study, we sought to systematically characterize the key downstream signaling molecule involved in 6-OHDA-induced dopaminergic degeneration in cell culture and animal models of PD. Treatment of mesencephalic dopaminergic neuronal N27 cells with 6-OHDA (100 μM) for 24h significantly reduced mitochondrial activity and increased cytosolic cytochrome c, followed by sequential activation of caspase-9 and caspase-3. Co-treatment with the free radical scavenger MnTBAP (10 μM) significantly attenuated 6-OHDA-induced caspase activities. Interestingly, 6-OHDA induced proteolytic cleavage and activation of protein kinase C delta (PKCδ) was completely suppressed by treatment with a caspase-3-specific inhibitor, Z-DEVD-FMK (50 μM). Furthermore, expression of caspase-3 cleavage site-resistant mutant PKCδ(D327A) and kinase dead PKCδ(K376R) or siRNA-mediated knockdown of PKCδ protected against 6-OHDA-induced neuronal cell death, suggesting that caspase-3-dependent PKCδ promotes oxidative stress-induced dopaminergic degeneration. Suppression of PKCδ expression by siRNA also effectively protected N27 cells from 6-OHDA-induced apoptotic cell death. PKCδ cleavage was also observed in the substantia nigra of 6-OHDA-injected C57 black mice but not in control animals. Viral-mediated delivery of PKCδ(D327A) protein protected against 6-OHDA-induced PKCδ activation in mouse substantia nigra. Collectively, these results strongly suggest that proteolytic activation of PKCδ is a key downstream event in dopaminergic degeneration, and these results may have important translational value for development of novel treatment strategies for PD.

Differential contribution of beta-adrenergic receptors expressed on radiosensitive versus radioresistant cells to protection against inflammation and mortality in murine endotoxemia

The sympathetic nervous system modulates immune responses via the secretion of catecholamines and subsequent activation of adrenergic receptors (ARs), and systemic catecholamine levels increase markedly in the setting of endotoxemia and sepsis. Previous studies have demonstrated that stimulation of beta-ARs by pharmacological agonists attenuates the inflammatory response to LPS observed in vitro and can increase survival in animal models of endotoxemia and sepsis. However, the consequences of beta-AR activation by endogenous catecholamines have not been explored in these settings. Furthermore, the relative contribution of beta-ARs expressed on immune versus nonimmune cells to LPS-mediated inflammation and mortality is not known. Our first goal was therefore to determine the impact of beta-AR stimulation by endogenous catecholamines released during endotoxemia on LPS-mediated inflammation and mortality in vivo. To address this question, we examined the LPS response of mice lacking all three known betaAR subtypes, beta1-, beta2-, and beta3-AR, and demonstrated that these beta-less mice exhibited a net increase in inflammation (increased TNF-alpha levels and decreased IL-10 levels in serum) and a 50% decrease in survival relative to wild-type animals. The second goal of our study was to determine the relative contribution of beta-ARs expressed on radiosensitive immune versus radioresistant cells to the protective action of beta-ARs in the setting of endotoxemia. We therefore examined the LPS response of bone marrow chimeras generated between beta-less and wild-type mice, and concluded that beta-ARs expressed on radioresistant cells play the dominant role in protecting against LPS-mediated mortality and attenuating systemic TNF-alpha responses. Finally, we determined that beta3-AR subtype does not play a significant role in regulating LPS-mediated mortality and inflammation by evaluating mice lacking the beta1- and beta2-AR subtypes only.

Time-dependent alterations of peripheral immune parameters after nigrostriatal dopamine depletion in a rat model of Parkinson's disease

Dysfunction of the central dopaminergic system is associated with neurodegenerative disorders and mental illnesses such as Parkinson's disease and schizophrenia. Patients suffering from these diseases were reported to exhibit altered immune functions compared to healthy subjects and imbalance of the central dopaminergic system has been suggested as one causative factor for the immune disturbances. However, it is unclear whether the observed immune changes are primary or secondary to the disease. Here we demonstrate that central dopamine (DA) depletion in a rat model of Parkinson's disease induced transient changes in blood leukocyte distribution and cytokine production that were apparent until four weeks after bilateral intrastriatal administration of the neurotoxin 6-hydroxydopamine (6-OHDA). Eight weeks after treatment, no differences in blood immune parameters were anymore evident between neurotoxin-treated and control animals. Nevertheless, animals with a widespread damage of dopaminergic neurons in the nigrostriatal system showed an exacerbated pro-inflammatory response following in vivo challenge with bacterial lipopolysaccharide. Our data indicate that peripheral immune perturbations in the early phase after intrastriatal 6-OHDA administration might have been related to the neurodegenerative process itself whereas the increased sensitivity to the inflammatory stimulus seems to have resulted from an impaired dopaminergic control of prolactin (PRL) and corticosterone (CORT) secretion. The findings demonstrate that the brain dopaminergic system is involved in peripheral immune regulation and suggest that central dopaminergic hypoactivity bears the risk of excessive inflammation, e.g., during infection or tissue injury.

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.

Host resistance model to an intracellular pathogen

This unit describes a model for the determination of host resistance in mice using a Gram-positive intracellular bacterium, Listeria monocytogenes (LM), and discusses its broad use in immunotoxicological studies. The provides detailed procedures for LM infection and sample analysis, including preparation and infection of mice with LM, recording of sickness behaviors in infected mice, and determination of viable LM numbers in the tissues from infected animals. The protocol also describes use of serum and tissue homogenates for assessment of cytokines. Additionally, background information on LM and LM infection is provided for better understanding and utilization of this model. The LM infection model is useful for the initial screening of possible modulation of immune responses, particularly innate immunity and type-1 cell-mediated immunity (CMI), by environmental factors, as well as for further investigation of the underlying mechanisms of environmental factor-induced changes in immunity.

Splenic norepinephrine depletion following acute stress suppresses in vivo antibody response

Exposure to an intense acute stressor immediately following immunization leads to a reduction in anti-KLH IgM, IgG, and IgG2a, but not IgG1. Stress also depletes splenic norepinephrine (NE) content. Immunization during pharmacological (alpha-methyl-p-tyrosine) or stress-induced splenic NE depletion results in antibody suppression similar to that found in rats immunized prior to stressor exposure. Prevention of splenic NE depletion during stress by tyrosine, but not pharmacological elevation (mirtazapine) of NE, resulted in normal antibody responses. These data support the hypothesis that splenic NE depletion is necessary and sufficient for stress-induced suppression of antibody to a T-cell dependent antigen.

Influence of polychlorinated biphenyls and turning preference on striatal dopamine metabolism

Male BALB/c mice, assessed for spontaneous nocturnal rotation that has been linked with functional differences in striatal dopamine (DA) content, were divided into right (R), left (L), and no turning preference (NP) groups. Both total turning activity and turning in the preferred direction were greatest in the R mice. To determine whether turning preference influences the response to exposure to an environmental toxicant known to reduce striatal DA function, striatal tissues from R, L, or NP mice were exposed to polychlorinated biphenyls (PCBs). In vitro exposure of striata from these mice to varying concentrations of PCBs for 4 h concentration-dependently decreased tissue DA content and increased the concentrations of DA and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in the media, a phenomenon already observed, although of smaller magnitude, with rat tissues. These effects were independent of the turning preference of the mice. Although the DA content initially did not differ among the striatal tissue from R, L, and NP mice, following 4 h of incubation in control medium (without PCBs), there was significantly greater DA content in striata from R mice in comparison to that from either L or NP mice. This difference was also apparent after 6 h of incubation, and it was not due to differences in DA turnover or cytotoxicity. Rather, the greater DA content in the striata of R mice was due to increased DA synthesis, since tyrosine hydroxylase (TH) activity was greater in striata from R mice than in striata from either L or NP mice. These differences in striatal DA synthesis, if present in vivo, may explain the observed greater nocturnal turning activity of the R mice. Additionally, the in vitro analyses suggest that striata from R mice have differential responses to stress compared with striata from L or NP mice. With regard to the effects of PCBs, however, it appears that (1) striata derived from mice with different turning preference are equally sensitive to this dopaminergic toxicant and (2) mice appear more sensitive to PCBs than rats.

Splenic norepinephrine and serum corticosterone level fluctuations associated with bacteria-induced stress

Corticosterone (CORT) and norepinephrine (NE), two effector molecules of the hypothalamic-pituitary-adrenal (HPA) and the sympathetic-lymphoid (SL) axes, respectively, differentially influence murine host resistance to Listeria monocytogenes (LM). Serum CORT and splenic NE levels early (< or =24 h) after infection correlated positively with host resistance, as long as the LM burden did not exceed approximately 10(6) cfu LM per spleen. As previously reported, mice with right-circling preference (R-mice) have significantly greater host resistance to LM than those with left-circling preference (L-mice) and early after infection, R-mice had significantly higher serum CORT levels than L-mice. However, rapid pathogenesis with a high bacterial burden induced high activation of the HPA and SL axes, which prevented observable differences in the defense against LM, especially later in infection. With the high bacterial inoculum (10(5) LM), the splenic NE levels significantly increased, but no differences among R- and L-mice were discernible. We suggest that endogenous asymmetry of neuroimmune circuits contributes to differential host resistance, but the level of stress (bacterial inoculum) is critical. With regard to the neuroendocrine factors assessed, CORT, but not NE, levels significantly correlated with the enhanced defenses of R-mice in comparison to L-mice. The differential host resistance based on brain laterality seems to be more a function of the HPA axis and possibly other CNS effects on peripheral immunity than neurotransmitter release by the sympathetic innervation of the spleen.

Effects of dopaminergic drugs on the mast cell degranulation and nitric oxide generation in RAW 264.7 cells

Effects of dopaminergic drugs on the degranulation of mast cells (RBL-2H3 cells) and the nitric oxide production from macrophage cells (RAW 264.7) were studied. Among the dopaminergic agonists and antagonists tested, bromocriptine, 7-OH-DPAT, haloperidol, and clozapine showed potent inhibitions of mast cell degranualtion (IC50 value, 5 microM). However, these dopaminergic agents did not affect the tyrosine phosphorylations of the signaling components of the high affinity IgE receptor (FcepsilonRI), such as Syk, PLCgamma1, and PLCgamma2.; This suggested that these signaling components were not involved in the inhibition of the mast cell degranulation by these compounds. On the other hand, dopamine, bromocriptine, 7-OH-DAPT, and haloperidol markedly inhibited the nitric oxide production from RAW 264.7 cells (IC50 values, 10-20 microM). Bromocriptine, a dopamine agonist that is routinely used for the treatment of Parkinsons disease, inhibited the expression of the inducible nitric oxide synthase at an early stage of the LPS-induced protein expression in a dose-dependent manner. The results suggested that these dopaminergic agents, when used for the treatment of dopamine receptors-related diseases, such as Schizophrenia or Parkinsons disease, might have additional beneficial effects.

Central catecholamine depletion inhibits peripheral lymphocyte responsiveness in spleen and blood

Experimental and clinical evidence has demonstrated extensive communication between the CNS and the immune system. To analyse the role of central catecholamines in modulating peripheral immune functions, we injected the neurotoxin 6-hydroxydopamine (6-OHDA) i.c.v. in rats. This treatment significantly reduced brain catecholamine content 2, 4 and 7 days after injection, and in the periphery splenic catecholamine levels were reduced 4 days after treatment. Central catecholamine depletion induced an inhibition of splenic and blood lymphocyte proliferation and splenic cytokine production and expression (interleukin-2 and interferon-gamma) 7 days after injection. In addition, central treatment with 6-OHDA reduced the percentage of spleen and peripheral blood natural killer (CD161 +) cells, and T-cytotoxic (CD8 +) cells in peripheral blood. The reduction in splenocyte proliferation was not associated with a glucocorticoid alteration but was completely abolished by prior peripheral sympathectomy. These data demonstrate a crucial role of central and peripheral catecholamines in modulating immune function.