Staphylococcal enterotoxin B induces fever, brain c-Fos expression, and serum corticosterone in rats

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.

How T-cell-dependent and -independent challenges access the brain: vascular and neural responses to bacterial lipopolysaccharide and staphylococcal enterotoxin B

Bacterial lipopolysaccharide (LPS) is widely used to study immune influences on the CNS, and cerebrovascular prostaglandin (PG) synthesis is implicated in mediating LPS influences on some acute phase responses. Other bacterial products, such as staphylococcal enterotoxin B (SEB), impact target tissues differently in that their effects are T-lymphocyte-dependent, yet both LPS and SEB recruit a partially overlapping set of subcortical central autonomic cell groups. We sought to compare neurovascular responses to the two pathogens, and the mechanisms by which they may access the brain. Rats received iv injections of LPS (2 microg/kg), SEB (1mg/kg) or vehicle and were sacrificed 0.5-3h later. Both challenges engaged vascular cells as early 0.5h, as evidenced by induced expression of the vascular early response gene (Verge), and the immediate-early gene, NGFI-B. Cyclooxygenase-2 (COX-2) expression was detected in both endothelial and perivascular cells (PVCs) in response to LPS, but only in PVCs of SEB-challenged animals. The non-selective COX inhibitor, indomethacin (1mg/kg, iv), blocked LPS-induced activation in a subset of central autonomic structures, but failed to alter SEB-driven responses. Liposome mediated ablation of PVCs modulated the CNS response to LPS, did not affect the SEB-induced activational profile. By contrast, disruptions of interoceptive signaling by area postrema lesions or vagotomy (complete or hepatic) markedly attenuated SEB-, but not LPS-, stimulated central activational responses. Despite partial overlap in their neuronal and vascular response profiles, LPS and SEB appear to use distinct mechanisms to access the brain.

Influence of age on behavioral, immune and endocrine responses to the T-cell superantigen staphylococcal enterotoxin A

Aged subjects are more vulnerable to administration of the endotoxin lipopolysaccharide, but research on age-associated sensitivity to other immune stimulants has been limited. The current study examined the effects of administering the superantigen, staphylococcal enterotoxin A (SEA), to young (4-month-old) and aged (20-month-old) male C57BL/6J mice on consumption of a novel liquid, cytokine production, corticosterone levels, and expression of central mRNA levels of cytokines and corticotropin-releasing hormone. SEA produced exaggerated hypophagia in aged mice, as they showed decreased consumption that persisted for 24 h. SEA increased hypothalamic mRNA levels of interleukin-1beta in the aged, but not the young, mice 2 h after administration. No differences in cytokine expression were observed 24 h after SEA. Both age groups showed increased plasma corticosterone levels 2 h after SEA administration. However, 24 h after SEA exposure the aged, but not the young, mice showed an augmented corticosterone response to the consumption test. Collectively, these data show that aging may exacerbate the behavioral and neuroinflammatory response to superantigen exposure. Further, the present study suggests that immune activation may result in delayed alterations in stress-induced corticosterone production in aged subjects.

Intracellular expression of c-Fos protein in various structures of the hypothalamus in electrical pain stimulation and administration of antigens

Application of different stimuli activated different hypothalamic structures. Immunohistochemical methods demonstrated changes in the numbers of c-Fos-positive cells in various hypothalamic structures after electrical pain stimulation and i.v. administration of antigens (bovine serum albumin (BSA) and lipopolysaccharide (LPS)). Increases in the numbers of c-Fos-positive cells in all the hypothalamic structures studied occurred after electrical pain stimulation and i.v. administration of antigens (BSA and LPS). The highest level of activation in hypothalamic structures was seen in the anterior hypothalamic nucleus (AHN) and posterior hypothalamic area (PH) after electrical pain stimulation and in the paraventricular nucleus (PVN) and lateral hypothalamic area level 28 (LHA-28) after i.v. administration of LPS. Comparative analysis showed that the level of activation of hypothalamic structures after electrical pain stimulation was significantly greater in the AHN, PVN, LHA, and PH than after i.v. administration of antigens (LPS and BSA). Administration of LPS led to more marked activation of cells in hypothalamic structures APH, PVN, LHA-28, dorsomedial hypothalamic nucleus (DMH), and PH (in terms of the numbers of c-Fos-positive cells) than administration of BSA.

Relationship of varying patterns of cytokine production to the anorexic and neuroendocrine effects of repeated Staphylococcal enterotoxin A exposure

Staphylococcal enterotoxin A (SEA) is a superantigen that stimulates T cells and induces the production of multiple cytokines. Previous studies have shown that SEA augments gustatory neophobia and activates the hypothalamic-pituitary-adrenal (HPA) axis. This study aimed to determine if the cytokine response, behavioral effects, and HPA axis activation persisted after repeated SEA treatment. Male C57BL/6J mice were given 1-4 intraperitoneal injections of 5 microg SEA, after which food intake, corticosterone, or peripheral cytokines were measured. In a series of experiments, it was found that secondary exposure to SEA two or three days after priming increased corticosterone, but attenuated splenic TNFalpha, while augmenting IL-1beta, IL-2, and IFNgamma. The anorexic response was intact after secondary exposure, but absent after a third injection, which was still able to elevate corticosterone. It is unlikely that IL-1 mediated the persistent effects on corticosterone, since this was increased in groups lacking corticosterone elevations. Similarly, TNFalpha was only modestly elevated under repeated SEA conditions that elevated plasma corticosterone. This attenuation appeared to be inversely related to the levels of IL-10, the production of which incrementally rose with each successive injection. In conclusion, repeated exposure to SEA activates the HPA axis and alters behavior. However, there may be dissociation between the behavioral and endocrine effects of SEA with increased SEA exposure. Furthermore, it is possible that while TNFalpha was previously shown to be important in response to acute SEA-induced HPA axis activation, further exposure to SEA elicits other cytokines that may exert neuromodulatory effects through sensitization and/or synergistic mechanisms.

Immunological and central nervous system changes in mice suffering from Staphyloccocus aureus and treated with Saccharomyces cerevisiae var. vini living cells

The influence of Saccharomyces cerevisiae var. vini viable cells on the Staphylococcus aureus-suffering mice was ascertained: (1) effect of S. aureus living cells on antibacterial and antitoxic antibodies, (2) effect of S. aureus on the number of neurons and macroglial cells in different areas of mouse hippocampus, (3) effect of S. cerevisiae var. vini viable cells on the above-mentioned changes of immune and nervous system. Treatment with S. cerevisiae var. vini provokes immune stimulation and change of the total number of macroglial elements in the CA1 field of hippocampus.

c-Fos immunoreactivity in selected brain regions of rats after heat exposure and pyrogen administration

We determined c-Fos immunoreactivity (Fos-IR) in selected hypothalamic nuclei, the organum vasculosum of the laminae terminals (OVLT) and somatosensory cortex of rats after hyperthermia induced by exogenous heat exposure, Gram-negative or Gram-positive pyrogen administration. The magnitude of Fos-IR was similar in thermoregulatory hypothalamic nuclei of rats after heat exposure or lipopolysaccharide (LPS) injection, despite the different origins of the hyperthermias. Heat-induced hyperthermia was associated with increased Fos-IR in the somatosensory cortex. LPS, but not heat exposure or injection of killed Staphylococcus aureus cells activated OVLT neurons. The OVLT may thus not be a port of entry for humoral mediators of Gram-positive bacterial fevers.

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.

Human leukocyte antigen-DQ8 transgenic mice: a model to examine the toxicity of aerosolized staphylococcal enterotoxin B

Staphylococcal enterotoxins (SEs) belong to a large group of bacterial exotoxins that cause severe immunopathologies, especially when delivered as an aerosol. SEs elicit the release of lethal amounts of cytokines by binding to major histocompatibility complex (MHC) class II and cross-linking susceptible T-cell receptors. Efforts to develop effective therapeutic strategies to protect against SEs delivered as an aerosol have been hampered by the lack of small animal models that consistently emulate human responses to these toxins. Here, we report that human leukocyte antigen-DQ8 (HLA-DQ8) transgenic (Tg) mice, but not littermate controls, succumbed to lethal shock induced by SEB aerosols without potentiation. Substantial amounts of perivascular edema and inflammatory infiltrates were noted in the lungs of Tg mice, similar to the pathology observed in nonhuman primates exposed by aerosol to SEB. Furthermore, the observed pathologies and lethal shock correlated with an upsurge in proinflammatory cytokine mRNA gene expression in the lungs and spleens, as well as with marked increases in the levels of proinflammatory circulating cytokines in the Tg mice. Unlike the case for littermate controls, telemetric evaluation showed significant hypothermia in Tg mice exposed to lethal doses of SEB. Taken together, these results show that this murine model will allow for the examination of therapeutics and vaccines developed specifically against SEB aerosol exposure and possibly other bacterial superantigens in the context of human MHC class II receptors.

Neuroimmunological activation of the afferent laryngeal neural circuit in experimentally induced laryngeal inflammation

CONCLUSIONS

These results show that laryngeal inflammatory reactions may induce the expression of proinflammatory cytokines along the afferent laryngeal circuit and in nuclei associated with the HPA axis. Local laryngeal inflammation may induce functional and physiologic alterations in the laryngeal neural system via neuroimmunologic reactions.

OBJECTIVE

Idiopathic laryngeal disorders associated with various neurologic conditions such as spasmodic dysphonia, idiopathic vocal fold paralysis and sudden infant death syndrome are causally related to upper respiratory tract infections, and it can be speculated that these disorders result in neurophysiologic alterations. The goal of this study was to identify the neurophysiologic effect on the central nervous system of local inflammatory alterations in the larynx.

MATERIAL AND METHODS

The expression of c-fos and IL-1beta was identified after injecting saline solution, 10 microg of lipopolysaccharide or 100 microg of lipopolysaccharide into the larynx of 12 rats.

RESULTS

The inflammatory cytokine IL-1beta was mainly expressed in the inferior olivary nucleus and raphe nucleus, which are associated with the hypothalamic-pituitary-adrenal (HPA) axis. IL-1beta expression was also found in the nuclei of afferent nervous pathways of the superior laryngeal nerve, such as the nucleus tractus solitarius, nucleus ambiguus, lateral reticular nucleus, magnocellular reticular nucleus and paragigantocellular reticular nucleus.

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.

Effects of bacterial superantigens on behavior of mice in the elevated plus maze and light-dark box

Bacterial superantigens, such as staphylococcal enteroxins A and B (SEA/SEB) stimulate T cells to produce high levels of cytokines in blood. Previously it had been shown that these toxins were capable of stimulating increased neuroendocrine activity and enhanced behavioral reactivity to novel gustatory and non-gustatory stimuli. Therefore, it was suggested that these superantigens may promote anxiety-like behavior. In the current set of experiments, BALB/cByJ and C57BL/6J male mice were challenged with either SEB (50 microg) or SEA (5 or 10 microg) and tested for behavior in the elevated plus maze (EPM). Results suggested an absence of increased anxiety-like behavior, with exploration of the open arms being enhanced by SEA or SEB treatment. In another test of anxiety, the light-dark box, SEB challenge of BALB/cByJ mice 90 min prior to testing, did not alter exit latency, activity nor time spent in the dark. However, in a second experiment, it was found that if animals were first tested for consumption, followed by testing in the light-dark box, SEB challenged animals displayed increased exit latency and reduced exploration. These studies suggest that in standard tests of rodent anxiety-like behavior, evidence for the induction of anxiety-like processes subsequent to challenge with SEA or SEB is not patently discernable. However, neurobiological events induced by immunological challenge might synergize with reactivity to psychogenic and/or gustatory stimuli, thereby resulting in increased anxiety-like behavior that could be unmasked by standard behavioral tests such as the light-dark box or EPM.

Circulating cytokines and endotoxin are not necessary for the activation of the sickness or corticosterone response produced by peripheral E. coli challenge

Peripheral administration of a variety of inflammatory stimuli, such as endotoxin or cytokines, induces an orchestrated set of brain-mediated events referred to as the sickness response. The mechanism for how immune products signal the brain is not clear, but accumulating evidence supports the existence of neural as well as blood-borne pathways. Although endotoxin or cytokine administration results in sickness responses, few data exist regarding the role of circulating endotoxin or cytokines in the induction of sickness during a real bacterial infection. Thus the present studies examined whether subcutaneously administered Escherichia coli can activate sickness responses and whether circulating endotoxin and/or proinflammatory cytokines are a prerequisite for these responses. Male Sprague-Dawley rats were injected subcutaneously with one of three doses (2.5 x 10(7), 2.5 x 10(8), 2.5 x 10(9) colony-forming units) of replicating E. coli, a ubiquitous bacterial strain, or vehicle. Core body temperature (Tc) and activity were measured for 3 days after the injection. A second set of groups of animals were killed 3, 6, 12, 18, 24, and 48 h after the injection, and blood samples and brains were collected. Injections dose dependently and consistently increased Tc and decreased activity, with increases in Tc beginning 4 h after the injection. In addition, E. coli significantly increased serum interleukin (IL)-1beta, IL-6, and tumor necrosis factor-alpha and brain IL-1beta levels beginning at the 6-h time point. Corticosterone and endotoxin were first elevated in the circulation at 3 and 18 h after the injection, respectively. Because fever onset preceded brain cytokine induction, we also examined cytokine levels in the serum, brain, and inflammation site 2 and 4 h after injection. Cytokines were elevated at the inflammation site but were not detectable in the serum or brain at 2 and 4 h. We conclude that subcutaneous injection of replicating E. coli induces a consistent and naturalistic infection that includes features of the sickness response as well as increases in circulating, brain, and inflammation site tissue cytokines. In addition, injection of replicating E. coli produces a robust fever and corticosterone response at a time when there are no detectable increases in circulating cytokines or endotoxin. These results suggest that elevated levels of circulating cytokines and endotoxin are not necessary for the activation of the sickness or corticosterone response. Therefore, fever, activity reduction, and corticosterone elevation induced by E. coli infection may have been evoked by a neural, rather than a humoral, pathway from the periphery to the brain.

Constitutive expression of p55TNFR mRNA and mitogen-specific up-regulation of TNF alpha and p75TNFR mRNA in mouse brain

Serum tumor necrosis factor (TNF) functions as a mediator of the immune-to-brain axis. Numerous TNF receptor-mediated effects on the nervous system are described but the knowledge about the regional and cellular expression of TNF receptor p55TNFR and p75TNFR in vivo is far from being complete. It is unclear whether TNF mediates its neuroimmune effects alone or in combination with other factors, e.g., bacterial mitogens. Here, we investigated the distribution of TNFalpha, p55TNFR, and p75TNFR in normal mouse brain and examined the stimulus-specific effects of lipopolysaccharide (LPS) and staphylococcal enterotoxin B (SEB) on the expression of the cerebral TNF system. Both mitogens caused enhanced TNFalpha serum levels and induced c-fos mRNA in the paraventricular nucleus but exhibited different effects on the cerebral gene expression of the TNF system. LPS but not SEB rapidly induced TNFalpha mRNA in circumventricular organs (CVOs) followed by spreading of TNFalpha mRNA into brain parenchyma close to the CVOs. The p55TNFR gene was constitutively expressed in many neurons with high levels in brainstem motor nuclei and in neurons of the sensory mesencephalic trigeminal nucleus. Moderate levels of p75TNFR mRNA were seen in single cells scattered throughout the brain in a pattern resembling microglia. Neither LPS nor SEB modulated the p55TNFR gene expression in any region or cell type of the brain, and LPS but not SEB induced p75TNFR mRNA in the CVOs. Thus, enhanced TNF serum levels able to stimulate c-fos mRNA expression in the paraventricular nucleus did not necessarily result in a modulation of the cerebral TNF system.

The potential role of Staphylococcal enterotoxin B in rats with postburn Staphylococcus aureus sepsis

Staphylococcal enterotoxin B (SEB) is an important member of the superantigen family, which exerts a number of pathological effects in the human, as well as susceptible animals. The present study was conducted to observe the time course and tissue distribution of SEB in postburn Staphylococcus aureus infection; meanwhile, the relationship between SEB and multiple organ dysfunction was also studied. Eighty-six male Wistar rats were randomly divided into four groups as follows: normal control group (n = 10); scald control group (n = 10); postburn sepsis group (n = 50) in which rats inflicted with 20% total body surface area (TBSA) III degrees scald followed by SEB-producing S. aureus challenge were further divided into 0.5-, 2-, 6-, 12-, and 24-h subgroups, with 10 rats in each subgroup; and SEB monoclonal antibody (MAb) treatment group (n = 16) in which a dose of 4 mg/kg SEB MAb was given intravenously just before S. aureus challenge, and the rats were further divided into 2- and 6-h subgroups. It was found that after thermal injury combined with S. aureus infection, SEB was widely distributed to the liver, kidneys, lungs, and heart, exacerbating the pathophysiology of multiple organ dysfunction induced by postburn sepsis. At the same time, the gene and protein expressions of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) were also markedly upregulated in various tissues. Early treatment with SEB-specific MAb-MAb2D(1)-could markedly decrease SEB levels in plasma as well as in various tissues, and could significantly reduce the 6-h mortality rate (17.64% [3/17] vs. 55.6% [20/36], P = 0.02). These data suggested that neutralization of SEB is effective in ameliorating S. aureus sepsis and subsequent multiple organ damage, which might be attributed to its inhibitory effect on inflammatory mediator formation.

Neural correlates of IgE-mediated food allergy

Although many authors have considered the possibility of a direct interaction between food allergy and behavioral changes, the evidence supporting this hypothesis is elusive. Here, we show that after oral ovalbumin (OVA) challenge, allergic mice present higher levels of anxiety, increased Fos expression in emotionality-related brain areas, and aversion to OVA-containing solution. Moreover, treatment with anti-IgE antibody or induction of oral tolerance abrogate both food aversion and the expression of c-fos in the central nervous system (CNS). Our findings establish a direct relationship between brain function and food allergy, thus creating a solid ground for understanding the etiology of psychological disorders in allergic patients.

Correlation of body temperature with protection against staphylococcal enterotoxin B exposure and use in determining vaccine dose-schedule

The immunoprotective potential of a recombinant vaccine against the incapacitating effect of aerosolized staphylococcal enterotoxin B (SEB) in nonhuman primates is reported. SEB belongs to a family of structurally related superantigens responsible for serious, life threatening pathologies. Injecting the recombinant SEB vaccine did not induce temperature elevation in rhesus monkeys, a classical symptom of toxic-shock syndrome. No temperature elevation was noted following injection with control tetanus toxoid. In addition to 100% survival, we observed a clear correlation between vaccine dose and mitigation of temperature elevation after a lethal SEB aerosol challenge. We conclude that the recombinant SEB vaccine is non-pyrogenic and that monitoring changes in body temperature is an important biomarker of toxic shock in a primate animal model.

Inhibition of rostral basal forebrain neurons promotes wakefulness and induces FOS in orexin neurons

The present study examined whether the activities of the rostral basal forebrain neurons alter the activities of the orexin (also known as hypocretin) neurons in the tuberal part of the hypothalamus in rats. We performed microdialysis perfusion of the ventromedial portion of the rostral basal forebrain with the GABAA receptor agonist muscimol to inhibit focally the neuronal activities in the rostral basal forebrain. Then, we monitored sleep/wake behaviour and investigated the pattern of activities of orexin neurons by examining the expression of FOS as an indicator of cellular activation. Bilateral perfusion with muscimol (5, 15, and 50 micro m) produced a dose-dependent decrease in the amount of sleep. This perfusion with muscimol at 50 micro m produced FOS-like immunoreactivity in 37% of the orexin neurons located in the tuberal part of the hypothalamus, whereas the FOS-like immunoreactivity was sparse in orexin neurons of the sleeping control rats (P = 0.001 by Mann-Whitney U-test). Unilateral perfusion with muscimol (50 micro m) also suppressed sleep. In this case, FOS-like immunoreactivity was seen in 40% of the orexin neurons on the side ipsilateral to the perfusion site but only in 10% of orexin neurons on the contralateral side (P = 0.018 by Wilcoxon signed rank test). These functional data suggested that a sleep-generating element in the ventromedial part of the rostral basal forebrain provides an inhibitory influence on the activities of the orexin neurons in the tuberal part of the hypothalamus.

Peripheral protein immunization induces rapid activation of the CNS, as measured by c-Fos expression

To investigate immune-to-brain communication, we challenged rats intraperitoneally with a protein antigen (keyhole limpet hemocyanin, KLH), and measured c-Fos expression in different brain structures. We found a rapid c-Fos expression 120 min after immunization in brain stem and forebrain structures, using a dose of KLH not inducing fever or malaise. Using proper controls, we found that this central response is related to the immunogenicity of the antigen and the magnitude of the immune response. Our results suggest that different interconnected brain cell groups respond rapidly to an immune challenge in the periphery, constituting an afferent pathway of neuroimmune communication.