Involvement of noradrenergic nerves in the activation and clonal deletion of T cells stimulated by superantigen in vivo

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.

Glucocorticoids and sympathetic neurotransmitters modulate the acute immune response to Trypanosoma cruzi

Evidence suggests that natural and adaptive immune responses can trigger neuroendocrine responses. Here, we discuss changes in the activity of the hypothalamus-pituitary-adrenal axis and in autonomic nerves, predominantly of the sympathetic nervous system, in a mouse model of acute infection with Trypanosoma cruzi. The endocrine response includes a marked increased release of glucocorticoid and a decrease of immune-stimulatory hormones, such as dehydroepiandrosterone sulfate, prolactin, and growth hormone during infection. These endocrine changes result in reduced proinflammatory cytokine production, increased regulatory/effector T cell ratio, and thymus atrophy. The sympathetic activity in the spleen of infected mice is also markedly reduced. However, the residual sympathetic activity can modulate the immune response to the parasite, as shown by increased mortality and production of proinflammatory cytokines in sympathetically denervated, infected mice. The outcome of the neuroendocrine response is the moderation of the intensity of the immune response to the parasite, an effect that results in delayed mortality in susceptible mice, and favors the course toward chronicity in more resistant animals.

Inhibition of catecholamine degradation ameliorates while chemical sympathectomy aggravates the severity of acute Friend retrovirus infection in mice

Several lines of evidence indicate that the sympathetic nervous system (SNS) might be involved in the pathogenesis and progression of retroviral infections. However, experimental data are scarce and findings inconsistent. Here, we investigated the role of the SNS during acute infection with Friend virus (FV), a pathogenic murine retrovirus that causes polyclonal proliferation of erythroid precursor cells and splenomegaly in adult mice. Experimental animals were infected with FV complex, and viral load, spleen weight, and splenic noradrenaline (NA) concentration was analyzed until 25 days post infection. Results show that FV infection caused a massive but transient depletion in splenic NA during the acute phase of the disease. At the peak of the virus-induced splenomegaly, splenic NA concentration was reduced by about 90% compared to naïve uninfected mice. Concurrently, expression of the catecholamine degrading enzymes monoamine oxidase A (MAO-A) and catechol-O-methyltransferase (COMT) was significantly upregulated in immune cells of the spleen. Pharmacological inhibition of MAO-A and COMT by the selective inhibitors clorgyline and 3,5-dinitrocatechol, respectively, efficiently blocked NA degradation and significantly reduced viral load and virus-induced splenomegaly. In contrast, chemical sympathectomy prior to FV inoculation aggravated the acute infection and extended the duration of the disease. Together these findings demonstrate that catecholamine availability at the site of viral replication is an important factor affecting the course of retroviral infections.

Effects of acute and repeated administration of Staphylococcal enterotoxin A on Morris water maze learning, corticosterone and hippocampal IL-1β and TNFα

Staphylococcal enterotoxin A (SEA) is a bacterial superantigen that induces pronounced T cell expansion and cytokine production. In addition, SEA activates the HPA axis and forebrain regions relevant to cognitive functions. Since learning-related cognitive changes have not been assessed in response to SEA, spatial learning in the Morris water maze (MWM) was determined in male C57BL/6J mice subjected to acute or repeated injections of 5μg SEA or Saline. Injections were given 2h prior to 4-5days of hidden platform sessions. Animals were then rested for 1month and given retraining without further injections. In addition, splenic IL-1β, IL-2 and TNFα, plasma corticosterone, and hippocampal IL-1β and TNFα were measured after the regimen of treatment used in the behavioral experiments. The results showed no learning impairment following acute or repeated SEA challenge. Moreover, when retested 1month later, and without further injections, the SEA group showed more rapid relearning of the MWM. This suggested that coincidental superantigenic T cell activation and training served to promote long-term improvement in recovery of learning. Furthermore, repeated SEA challenge continued to drive increases in plasma corticosterone, but with a compensatory reduction in hippocampal IL-1β. However, while hippocampal TNFα was reduced after acute and repeated SEA treatment, this was not statistically significant. In view of the importance of modest glucocorticoid elevations and hippocampal IL-1β in promoting contextual learning, the data point to the hypothesis that SEA promotes long-term plasticity by restraining disruptive increases in hippocampal IL-1β, and possibly TNFα, during learning.

Electrical activity in rat cortico-limbic structures after single or repeated administration of lipopolysaccharide or staphylococcal enterotoxin B

Immune-to-brain communication is essential for an individual to aptly respond to challenging internal and external environments. However, the specificity by which the central nervous system detects or 'senses' peripheral immune challenges is still poorly understood. In contrast to post-mortem c-Fos mapping, we recorded neural activity in vivo in two specific cortico-limbic regions relevant for processing visceral inputs and associating it with other sensory signalling, the amygdala (Am) and the insular cortex (IC). Adult rats were implanted with deep-brain monopolar electrodes and electrical activity was monitored unilaterally before and after administration of two different immunogens, the T-cell-independent antigen lipopolysaccharide (LPS) or the T-cell-dependent antigen staphylococcal enterotoxin B (SEB). In addition, the neural activity of the same individuals was analysed after single as well as repeated antigen administration, the latter inducing attenuation of the immune response. Body temperature and circulating cytokine levels confirmed the biological activity of the antigens and the success of immunization and desensitization protocols. More importantly, the present data demonstrate that neural activity of the Am and IC is not only specific for the type of immune challenge (LPS versus SEB) but seems to be also sensitive to the different immune state (naive versus desensitization). This indicates that the forebrain expresses specific patterns of electrical activity related to the type of peripheral immune activation as well as to the intensity of the stimulation, substantiating associative learning paradigms employing antigens as unconditioned stimuli. Overall, our data support the view of an intensive immune-to-brain communication, which may have evolved to achieve the complex energetic balance necessary for mounting effective immunity and improved individual adaptability by cognitive functions.

Neuroimunomodulação: sobre o diálogo entre os sistemas nervoso e imune

OBJETIVO: Trabalhos de pesquisa provenientes do campo da neuroimunomodulação vêm tornando explícitas as intrincadas relações existentes entre o sistema nervoso central e o sistema imune. Uma revisão bibliográfica foi realizada com o objetivo de descrever as bases de estudo da neuroimunomodulação. MODELOS EXPERIMENTAIS: Sabe-se, hoje, que estados emocionais como ansiedade e depressão são capazes de modificar a atividade do sistema imune como também o fazem o estresse e fármacos com ação no sistema nervoso central. COMPORTAMENTO DOENTIO: Os comportamentos apresentados por um organismo doente devem ser encarados como decorrência de estratégias homeostáticas de cada indivíduo. POSSÍVEIS MECANISMOS DE SINALIZAÇÃO DO SISTEMA IMUNE PARA O SISTEMA NERVOSO CENTRAL: Grande destaque tem sido atribuído para a participação do eixo hipotálamo-pituitária-adrenal, do sistema nervoso autônomo simpático e das citocinas nas sinalizações entre o sistema nervoso central e o sistema imune. CONCLUSÃO: O presente artigo pretende mostrar a relevância dos fenômenos de neuroimunomodulação; ele faz uma análise crítica das influências do sistema nervoso central sobre o sistema imune e vice-versa.

Physiology of psychoneuroimmunology: a personal view

This article offers a personal view on how the concept of the existence of a network of immune-neuro-endocrine interactions has evolved in the last 30 years. The main topic addressed is the relevance of the exchange of signals between the immune, endocrine and nervous systems for immunoregulation and brain functions. Particular emphasis is given to circuits involving immune cell products, the hypothalamus-pituitary-adrenal axis and the sympathetic nervous system. The operation of these circuits can affect immune functions and the course of inflammatory, autoimmune and infectious diseases. We also discuss increasing evidence that brain-born cytokines play an important role in brain physiology and in the integration of the immune-neuro-endocrine network.

Orphanin FQ/nociceptin interactions with the immune system in vivo: gene expression changes in lymphoid organs and regulation of the cytokine response to staphylococcal enterotoxin A

Orphanin FQ/nociceptin (OFQ/N) is a neuropeptide implicated in immunomodulation. Here, we show that endogenous and exogenous OFQ/N modulated the cytokine response to the bacterial superantigen staphylococcal enterotoxin A (SEA). Specifically, OFQ/N enhanced TNFalpha and IFNgamma transcripts in the spleen when injected prior to SEA challenge. Moreover, mice lacking the OFQ/N precursor gene showed diminished TNFalpha and IFNgamma mRNA induction in the spleen following SEA challenge. In addition, mRNA levels of ppOFQ/N and the OFQ/N receptor, NOP, were altered in thymus and spleen after SEA challenge. Overall, this suggests that the OFQ/N system can influence immune function and is itself influenced by immune stimuli.

The Role of Noradrenergic Nerves in the Development of the Lymphoproliferative Disease in Fas-Deficient, lpr/lpr Mice

Lpr/lpr mice develop a lymphoproliferative, autoimmune, lupus-like disease. These mice lack functional Fas (CD95) expression and are resistant to Fas ligand (CD178)-mediated apoptosis, a critical mechanism for the maintenance of peripheral tolerance. In this study, we show that noradrenaline (NA), the main sympathetic neurotransmitter, can induce apoptosis of lymphoid cells independently of functional Fas. Based on this finding, we used lpr/lpr mice as model to study the role of noradrenergic nerves in the expression of a lymphoproliferative disease. Early in ontogeny, the concentration of NA was significantly increased in the spleen of lpr/lpr mice, compared with normal littermates. However, splenic sympathetic innervation gradually declined as the disease progressed, and IgM blood levels and splenic NA concentration inversely correlated when the disease was overtly manifested. When the loss of noradrenergic fibers that occurred naturally during adult life in lpr/lpr mice was experimentally advanced by neonatal sympathectomy, the concentration of IgM and IgG2a in blood was markedly higher than that of control lpr/lpr mice, and the appearance of lymphadenopathy was accelerated. Furthermore, although neonatal denervation did not affect the life span of normal animals, it shortened significantly the survival time of lpr/lpr mice. These data show that, in addition to defects in the Fas pathway, an altered sympathetic innervation in lpr/lpr mice also contributes to the pathogenesis of the autoimmune disease, and strongly support the hypothesis that the sympathetic nervous system can modulate the expression of lymphoproliferative diseases.

CNS activational responses to staphylococcal enterotoxin B: T-lymphocyte-dependent immune challenge effects on stress-related circuitry

Staphylococcal enterotoxin B (SEB) is a bacterial superantigen that engages the immune system in a T-lymphocyte-dependent manner and induces a cytokine profile distinct from that elicited by the better-studied bacterial pathogen analog, lipopolysaccharide (LPS). Because of reports of SEB recruiting central nervous system (CNS) host defense mechanisms via pathways in common with LPS, we sought to further characterize central systems impacted by this agent. Rats were treated with SEB at doses of 50-5,000 mug/kg, and killed 0.5-6 hours thereafter. SEB injection produced a discrete pattern of Fos induction in brain that peaked at 2-3 hours postinjection and whose strength was dose-related. Induced Fos expression was predominantly subcortical and focused in a set of interconnected central autonomic structures, including aspects of the bed n. of the stria terminalis, central amygdala and lateral parabrachial nuclei; functionally related (and LPS-responsive) cell groups in the n. solitary tract, ventrolateral medulla, and paraventricular hypothalamic n. (PVH) were, by contrast, weakly responsive. SEB also activated cell groups in the limbic forebrain (lateral septal n, medial prefrontal cortex) and hypothalamic GABAergic neurons, which could account for its failure to elicit reliable increases in Fos-ir or corticotropin-releasing factor (CRF) mRNA in the PVH. SEB nevertheless did provoke reliable pituitary-adrenal secretory responses. The identification of subsets of central autonomic and limbic forebrain structures that are sensitive to SEB provides a basis for a systems-level understanding of the physiological and behavioral effects attributed to the superantigen. Core SEB-responsive cell groups exclude a medullary-PVH circuit implicated in pituitary-adrenal responses to LPS.

Neuronal, endocrine, and anorexic responses to the T-cell superantigen staphylococcal enterotoxin A: dependence on tumor necrosis factor-alpha

Staphylococcal enterotoxin A (SEA) is a microbial superantigen that activates T-lymphocytes and induces production of various cytokines, including tumor necrosis factor-alpha (TNFalpha). Previously, it was shown that SEA activates the hypothalamic-pituitary-adrenal axis and augments gustatory neophobic behaviors. In the present study, it was hypothesized that these effects involve neuronal activation in forebrain regions mediating fear and/or anxiety and are dependent on the production of TNFalpha. Male C57BL/6J mice were given intraperitoneal injections of 10 microg of SEA and 5 microg of lipopolysaccharide (LPS) or saline and perfused 2 h later for histochemical determination of brain c-Fos immunoreactivity (IR). The results showed increased c-Fos IR in the paraventricular nucleus, arcuate nucleus, central nucleus of the amygdala, bed nucleus of the stria terminalis, and lateral septum. Challenge of TNF-/- mice with SEA did not produce a significant increase in brain c-Fos IR, although c-Fos was increased after exposure to a psychogenic stressor (i.e., open field). In additional experiments, the elevated corticosterone response to SEA was abrogated in TNF-/- mice and was shown to be corticotropin-releasing hormone dependent. Finally, the augmented reduction in novel food intake after SEA challenge was attenuated in TNF-/- mice as well as in wild-type mice administered antibody to TNFalpha. In conclusion, challenge with SEA recruits brain regions mediating stress and anxiety responses, an effect that requires endogenous TNFalpha. Whether this is indicative of all T-cell superantigens remains to be determined, although it stands in contrast to other models of neuroimmunomodulation (e.g., LPS) that involve multiple cytokine influences.

Hypothalamic integration of immune function and metabolism

The immune and neuroendocrine systems are closely involved in the regulation of metabolism at peripheral and central hypothalamic levels. In both physiological (meals) and pathological (infections, traumas and tumors) conditions immune cells are activated responding with the release of cytokines and other immune mediators (afferent signals). In the hypothalamus (central integration), cytokines influence metabolism by acting on nucleus involved in feeding and homeostasis regulation leading to the acute phase response (efferent signals) aimed to maintain the body integrity. Peripheral administration of cytokines, inoculation of tumor and induction of infection alter, by means of cytokine action, the normal pattern of food intake affecting meal size and meal number suggesting that cytokines acted differentially on specific hypothalamic neurons. The effect of cytokines-related cancer anorexia is also exerted peripherally. Increase plasma concentrations of insulin and free tryptophan and decrease gastric emptying and d-xylose absorption. In addition, in obesity an increase in interleukin (IL)-1 and IL-6 occurs in mesenteric fat tissue, which together with an increase in corticosterone, is associated with hyperglycemia, dyslipidemias and insulin resistance of obesity-related metabolic syndrome. These changes in circulating nutrients and hormones are sensed by hypothalamic neurons that influence food intake and metabolism. In anorectic tumor-bearing rats, we detected upregulation of IL-1beta and IL-1 receptor mRNA levels in the hypothalamus, a negative correlation between IL-1 concentration in cerebro-spinal fluid and food intake and high levels of hypothalamic serotonin, and these differences disappeared after tumor removal. Moreover, there is an interaction between serotonin and IL-1 in the development of cancer anorexia as well as an increase in hypothalamic dopamine and serotonin production. Immunohistochemical studies have shown a decrease in neuropeptide Y (NPY) and dopamine (DA) and an increase in serotonin concentration in tumor-bearing rats, in first- and second-order hypothalamic nuclei, while tumor resection reverted these changes and normalized food intake, suggesting negative regulation of NPY and DA systems by cytokines during anorexia, probably mediated by serotonin that appears to play a pivotal role in the regulation of food intake in cancer. Among the different forms of therapy, nutritional manipulation of diet in tumor-bearing state has been investigated. Supplementation of tumor bearing rats with omega-3 fatty acid vs. control diet delayed the appearance of tumor, reduced tumor-growth rate and volume, negated onset of anorexia, increased body weight, decreased cytokines production and increased expression of NPY and decreased alpha-melanocyte-stimulating hormone (alpha-MSH) in hypothalamic nuclei. These data suggest that omega-3 fatty acid suppressed pro-inflammatory cytokines production and improved food intake by normalizing hypothalamic food intake-related peptides and point to the possibility of a therapeutic use of these fatty acids. The sum of these data support the concept that immune cell-derived cytokines are closely related with the regulation of metabolism and have both central and peripheral actions, inducing anorexia via hypothalamic anorectic factors, including serotonin and dopamine, and inhibiting NPY leading to a reduction in food intake and body weight, emphasizing the interconnection of the immune and neuroendocrine systems in regulating metabolism during infectious process, cachexia and obesity.

Effect of endogenous catecholamines in lymphocytes on lymphocyte function

Our previous work has showed that lymphocytes can synthesize catecholamines (CAs). However, role and mechanism of the endogenous CAs in lymphocytes in modulation of immune function are less known. In the present study, we used alpha-methyl-p-tyrosine (alpha-MT), an inhibitor of tyrosine hydroxylase (TH), and pargyline, an inhibitor of monoamine oxydase, to block the synthesis and degradation of CAs in lymphocytes and then observed changes of lymphocyte proliferation induced by concanavalin A (Con A). Phentolamine and propranolol, antagonists respectively to alpha- and beta-adrenoreceptors, were employed to investigate the receptor mechanism. We found that TH mRNA in the Con A-activated lymphocytes was 2.4 times higher in relative density than that in the resting lymphocytes. Similarly, the intracellular and supernatant CAs, including DA, NE and E, of the Con A-stimulated lymphocytes were significantly raised relative to those of the resting cells. alpha-MT (10(-11), 10(-10) and 10(-9) M) facilitated the Con A-induced lymphocyte proliferation, but pargyline (10(-11), 10(-10) and 10(-9) M) attenuated the cell proliferation. Meanwhile, alpha-MT and pargyline respectively led to decrease and increase in the intracellular and supernatant CAs (DA, NE and E) of the Con A-stimulated lymphocytes. Propranolol completely blocked, but phentolamine partly reversed, the suppressive effect of pargyline on the Con A-induced lymphocyte proliferation. Content of cAMP was remarkably increased in the lymphocytes treated with pargyline alone, but it dropped to control level after these cells were treated with propranolol plus pargyline. These results on the one hand further demonstrate the ability of lymphocytes to synthesize CAs and the enhancive ability of the activated lymphocytes to synthesize CAs, and on the other hand reveal an important role of the endogenous CAs in regulation of function of lymphocytes themselves. Besides, our present findings suggest that CAs synthesized by lymphocytes can secrete out of the lymphocytes via paracrine or autocrine pathway and affect lymphocyte function by beta-adrenoreceptor and cAMP mediating mechanism. Thus, it can be implied that CAs in lymphocytes are also involved in the cross-talk in the neuro-endocrine-immune networks.

Changes in the density and distribution of sympathetic nerves in spleens from Lewis rats with adjuvant-induced arthritis suggest that an injury and sprouting response occurs

Previously we demonstrated reduced norepinephrine concentrations in spleens from Lewis rats with adjuvant-induced arthritis (AA), an animal model of rheumatoid arthritis. This study extends these findings, examining the anatomical localization and density of sympathetic nerves in the spleen with disease development. Noradrenergic (NA) innervation in spleens of Lewis rats was examined 28 days following adjuvant treatment to induce arthritis or vehicle for the adjuvant by using fluorescence histochemistry for catecholamines, with morphometric analysis and immunocytochemistry for tyrosine hydroxylase. In AA rats, sympathetic nerve density in the hilar regions, where NA nerves enter the spleen, was increased twofold over that observed in vehicle-treated rats. In contrast, there was a striking twofold decline in the density of NA nerves in splenic regions distal to the hilus in arthritic rats compared with nonarthritic rats. In both treatment groups, NA nerves distributed to central arterioles, white pulp regions, trabeculae, and capsule. However, NA nerve density was reduced in the white pulp but was increased in the red pulp in AA rats compared with non-AA rats. These findings indicate an injury/sprouting response with disease development whereby NA nerves die back in distal regions and undergo a compensatory sprouting response in the hilus. The redistribution of NA nerves from white pulp to red pulp suggests that these nerves signal activated immune cells localized in the red pulp in AA. Although the mechanisms of this redistribution of NA nerves into the red pulp are not known, it may be due to migration from white pulp to red pulp of target immune cells that provide trophic support for these nerves. The redistribution of NA nerves into the red pulp may be critical in modulating immune functions that contribute to the chronic inflammatory stages of arthritis.

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.

Choroid plexus selectively accumulates T-lymphocytes in normal controls and after peripheral immune activation

We determined T-lymphocyte migration into brain and choroid plexus (CPx) after enterotoxin-induced systemic immune activation. CPx T-lymphocytes/mm2 in control mice were > 3 logs more numerous than brain and increased by as much as 150-fold by post-enterotoxin Day 3 (p < 0.01). Flow cytometry of pooled CPx confirmed post-enterotoxin increases. Brain T-lymphocytes increased up to 17-fold after SEB and accumulated in subependymal and periventricular brain. T cell apoptosis was absent. These results show preferential T-lymphocyte migration to CPx over brain and suggest that brain T cells may be derived from the CPx by direct migration or by cerebrospinal fluid dissemination.

Effect of lesions of cerebellar fastigial nuclei on lymphocyte functions of rats

The cerebellum, probably owing to its traditional concept limited to motor control, is less well studied in immunoregulation. To obtain more comprehension and knowledge on cerebellar functions, we investigated effect of cerebellar fastigial nucleus (FN), an output nucleus of the spinocerebellum, on lymphocyte functions, and explored central and peripheral pathways involved in the effect. Kainic acid (KA) was microinjected into bilateral FN of rats (0.4 microg KA in 0.4 microl saline for each side) to destroy neurons of the nuclei. On days 8, 16 and 32 following the FN lesions, methyl-thiazole-tetrazolium (MTT) assay and flow cytometry were used to measure proliferation of concanavalin A (Con A)-induced lymphocytes and cytotoxicity of natural killer (NK) cells against YAC-1 cells, respectively. Meanwhile, glutamate and monoamine neurotransmitters, including norepinephrine (NE), dopamine (DA) and 5-hydroxytryptamine (5-HT), in the hypothalamus and the spleen were determined by means of high-performance liquid chromatography (HPLC) assay. Adrenocorticotropic hormone (ACTH) and cortisol in the plasma were also detected respectively by radioimmunoassay and chemiluminescent immunoassay after the FN lesions. We found that the Con A-induced lymphocyte proliferation and the NK cell cytotoxicity were both significantly enhanced on days 8, 16 and 32 following the effective lesions of the bilateral FN in comparison with those of matching control rats microinjected with saline in their FN. Contents of glutamate and NE, not DA and 5-HT, in the hypothalamus, and concentration of NE, not DA, in the spleen were all remarkably reduced on the 16th day following the FN lesions, when both the T lymphocyte proliferation and the NK cell cytotoxicity were dramatically increased. However, levels of ACTH and cortisol in the plasma had no notable differences between FN lesion rats and FN saline ones when the enhanced T and NK cell functions occurred. These findings reveal that the cerebellar FN participates in the modulation of lymphocyte functions and that the hypothalamus and sympathetic nerves innervating lymphoid organs are involved in this neuroimmunomodulation. Thus, a possible central and peripheral pathway for the spinocerebellum to regulate lymphocyte functions is suggested, i.e. cerebellum-hypothalamus-sympathetic nerves-lymphocytes, while the functional axis of hypothalamus-pituitary-adrenal gland may not contribute to mediation of the spinocerebellar immunomodulation.

Increased prevalence of semaphorin 3C, a repellent of sympathetic nerve fibers, in the synovial tissue of patients with rheumatoid arthritis

OBJECTIVE

The presence of selective sympathetic nerve repellents, i.e., semaphorins, may be responsible for the observed reduction of sympathetic innervation in the synovial tissue of patients with rheumatoid arthritis (RA). This study was undertaken to investigate the presence of different semaphorins in synovial tissue of patients with RA, patients with osteoarthritis (OA), and control subjects without inflammation.

METHODS

In situ hybridizations with digoxigenin-labeled RNA probes directed against different semaphorins were performed. The presence of semaphorin 3C (S3C) in the synovial tissue of 10 RA, 10 OA, and 5 control subjects was investigated using a polyclonal antiserum directed against S3C.

RESULTS

All in situ hybridizations revealed the presence of S3C messenger RNA, but no other investigated semaphorin (i.e., against primary afferent sensory nerve fibers), in the synovial tissue of RA and OA patients. Immunohistologic double staining demonstrated that macrophages and fibroblasts were positive for S3C protein. Quantitative analysis of S3C protein staining showed an increased density of S3C-positive cells in the synovial tissue of RA patients (mean +/- SEM 339 +/- 65 cells/mm(2)) in comparison with OA patients (168 +/- 27/mm(2); P = 0.031 versus RA) and controls (126 +/- 26/mm(2); P = 0.027 versus RA). Studies of the relationship between sympathetic nerve fiber density and S3C-positive cell density in the tissue of all patients showed that RA patients generally had lower densities of sympathetic nerve fibers and higher densities of S3C-positive cells than OA patients and control subjects.

CONCLUSION

These findings suggest that S3C from macrophages and fibroblasts, which is selectively directed against sympathetic nerve fibers, could be one element responsible for reduced sympathetic innervation in RA tissue. The inability of sympathetic nerve fibers to reinnervate synovial tissue could contribute to the chronic nature of RA.

Expression of tyrosine hydroxylase in lymphocytes and effect of endogenous catecholamines on lymphocyte function

OBJECTIVES

To comprehend the changes and significance of the endogenous catecholamines in the immune system, we explored the synthesis of catecholamines by lymphocytes in various lymphoid organs and in different activated states, and the effect of the endogenous catecholamines synthesized by lymphocytes on the function of the lymphocytes themselves.

METHODS

Immunohistochemistry for lymphoid organs (mesenteric lymph nodes, spleen and thymus) and lymphocytes was used to observe their expression of tyrosine hydroxylase (TH), an initial rate-limiting enzyme of the catecholamine synthesis. The contents of catecholamines, including norepinephrine (NE), dopamine (DA) and epinephrine (E), in lymphocytes were tested by means of high-performance liquid chromatography with electrochemical detection. Western blot was used to examine the character and relative quantity of TH-stained protein in lymphocytes, lymph nodes and adrenal medullary tissue. The effect of alpha-methyl-P-tyrosine (alpha-MT), an inhibitor of TH activity, on concanavalin A (Con A)-induced interleukin-2 (IL-2) production was determined by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay.

RESULTS

TH-positive cells were found in the three examined lymphoid organs, but the lymph nodes had the highest and the thymus had the lowest density. Both TH expression and the contents of NE, DA and E in the Con A-activated lymphocytes were markedly increased in comparison with those in the nonactivated lymphocytes. A band with TH immunoreactivity was seen in the extracts from either Con A-activated lymphocytes or nonactivated cells and the molecular weight of the protein was 59.4 +/- 0.3 kD. However, the relative quantity of the protein was notably higher in the activated lymphocytes than in the nonactivated cells. As a positive control, a similar band of TH immunoreactivity in the adrenal medullary tissue was also obtained. Alpha-MT at the doses of 10(-11), 10(-10) and 10(-9) M was found to significantly facilitate the Con A-induced IL-2 production.

CONCLUSIONS

These results suggest that lymphocytes can synthesize catecholamines and their synthesis levels may increase in the activated state, and that endogenous catecholamines synthesized by the lymphocytes can regulate the function of the lymphocytes themselves.

Behavioural endocrine immune-conditioned response is induced by taste and superantigen pairing

Administration of bacterial superantigen, such as staphylococcal enterotoxin B (SEB), induces in vivo stimulation of T cell proliferation and cytokine production such as interleukin-2 (IL-2). It has been previously reported that SEB administration induces fever, c-Fos expression in the brain, and hypothalamus-pituitary-adrenal axis activation, demonstrating that the brain is able to sense and respond to SEB. Previously it had been shown that immune functions can be behaviourally conditioned pairing a novel gustatory stimulus together with an immunomodulatory drug or an antigen. We designed an experimental protocol using Dark Agouti rats in which saccharin taste, as conditioned stimulus, was paired with an i.p. injection of SEB (2 mg/kg), as unconditioned stimulus. Six days later, when conditioned animals were re-exposed to the conditioned stimulus they displayed strong conditioned taste avoidance to the saccharin. More importantly, re-exposure to the conditioned stimulus significantly increased IL-2, interferon-gamma and corticosterone plasma levels, in comparison with conditioned animals which had not been re-exposed to saccharin taste. These results demonstrate a behavioural-immune-endocrine conditioned response using a superantigen as unconditioned stimulus. In addition, they illustrate the brain abilities to mimic the unconditioned effects of a superantigen by yet unknown mechanisms.

Integrated evolutionary, immunological, and neuroendocrine framework for the pathogenesis of chronic disabling inflammatory diseases

The pathogenesis of chronic disabling inflammatory diseases (CDIDs) is poorly understood. Current concepts that focus on abnormalities of the immune system are, in our view, incomplete. Here we propose that chronic disruption of homeostasis through abnormal neuronal and endocrine host responses to transient inflammatory reactions contributes to the appearance of CDIDs. Coordinated reactions of the supersystems (immune, nervous, endocrine, and reproductive) that maintain homeostasis have been evolutionarily conserved to respond to and eliminate foreign agents over a period of days to a few weeks. If the responses of these supersystems fail to return to normal after elimination of the pathogen, a continuous aggressive immune response is created; this situation can trigger development of CDIDs. Maladaptation of the supersystems during CDIDs has not been evolutionarily conserved but is nevertheless still prevalent because a large proportion of these diseases tend to appear after the reproductive phase. We propose that this integrated systems hypothesis may permit better identification of a patient at risk or in the early stages of developing a CDID such as rheumatoid arthritis and enable more coordinated intervention than is presently attempted.

Sympathetic abnormalities during autoimmune processes: potential relevance of noradrenaline-induced apoptosis

The sympathetic nervous system is one of the major pathways involved in immune-neuroendocrine interactions. Disturbances in these interactions are likely to have consequences during lymphoproliferative diseases. Work derived from our group as well as from several others led us to the hypothesis that the overstimulation of the immune system that characterizes this type of pathology results in decreased sympathetic nerve activity in lymphoid organs. To explore this possibility, we used as a model lpr/lpr mice, which develop a genetically determined autoimmune, lupus-like lymphoproliferative disease. We show that 18-week-old female C57Bl/6J lpr/lpr mice, which do not show overt symptoms of the disease but already have increased IgM and IgG2a levels in the blood, have decreased noradrenaline (NA) concentration and content in the spleen, but not in the kidney, as compared to normal C57Bl/6J littermates. Lpr/lpr mice do not express normal Fas, and therefore apoptosis cannot be triggered through this receptor. The defects in sympathetic innervation in the spleen of lpr/lpr mice prompted us to evaluate whether NA could influence lymphoid cell mass by inducing apoptosis. We found that NA can directly induce apoptosis in normal lymphoid cells via beta-adrenergic receptors. From the reported results we propose that reduction in sympathetic nerve function in lpr/lpr mice contributes to aggravation of the disease and suggest that in addition to the incapacity to mount Fas-mediated apoptosis, a second proapoptotic mechanism, namely, that triggered by NA, is defective in these animals because of reduced availability of the neurotransmitter.