Cold stress-induced neuroinvasiveness of attenuated arboviruses is not solely mediated by corticosterone

Cold acclimation affects immune composition in skeletal muscle of healthy lean subjects

Low environmental temperatures have a profound effect on biological processes in the body, including the immune system. Cold exposure coincides with hormonal changes, which may directly or indirectly alter the immune system, even in the skeletal muscle. The aim of the present study was to investigate the effect of cold acclimation on immune composition in skeletal muscle. Skeletal muscle biopsies were obtained from 17 healthy lean subjects before and after 10 days of mild cold exposure (15 °: C, 6 h/day). Nonshivering thermogenesis was calculated by indirect calorimetry. We found that cold acclimation increased nonshivering thermogenesis from 10.8 ± 7.5 before to 17.8 ± 11.1% after cold acclimation (P < 0.01), but did not affect plasma catecholamine nor cytokine levels. In contrast, cold acclimation affected mRNA expression of several immune cell markers in skeletal muscle. It downregulated expression of the Th17 markers RORC (-28%, P < 0.01) and NEDD4L (-15%, P < 0.05), as well as the regulatory T-cell marker FOXP3 (-13%, P < 0.05). Furthermore, cold acclimation downregulated expression of the M2 macrophage markers CCL22 (-50%, P < 0.05), CXCL13 (-17%, P < 0.05) and CD209 (-15%, P < 0.05), while the M1 macrophage marker IL12B was upregulated (+141%, P < 0.05). Cold acclimation also enhanced several markers related to interferon (IFN) signaling, including TAP1 (+12%, P < 0.01), IFITM1/3 (+11%, P < 0.05), CD274 (+36%, P < 0.05) and STAT 2 (+10%, P < 0.05). In conclusion, 10 days of intermittent cold exposure induces marked changes in the expression of immune cell markers in skeletal muscle of healthy lean subjects. The physiological consequences and therapeutic relevance of these changes remain to be determined.

Mechanism of West Nile virus neuroinvasion: a critical appraisal

West Nile virus (WNV) is an important emerging neurotropic virus, responsible for increasingly severe encephalitis outbreaks in humans and horses worldwide. However, the mechanism by which the virus gains entry to the brain (neuroinvasion) remains poorly understood. Hypotheses of hematogenous and transneural entry have been proposed for WNV neuroinvasion, which revolve mainly around the concepts of blood-brain barrier (BBB) disruption and retrograde axonal transport, respectively. However, an over‑representation of in vitro studies without adequate in vivo validation continues to obscure our understanding of the mechanism(s). Furthermore, WNV infection in the current rodent models does not generate a similar viremia and character of CNS infection, as seen in the common target hosts, humans and horses. These differences ultimately question the applicability of rodent models for pathogenesis investigations. Finally, the role of several barriers against CNS insults, such as the blood-cerebrospinal fluid (CSF), the CSF-brain and the blood-spinal cord barriers, remain largely unexplored, highlighting the infancy of this field. In this review, a systematic and critical appraisal of the current evidence relevant to the possible mechanism(s) of WNV neuroinvasion is conducted.

The effect of exogenous corticosterone on West Nile virus infection in Northern Cardinals (Cardinalis cardinalis)

The relationship between stress and disease is thought to be unambiguous: chronic stress induces immunosuppression, which likely increases the risk of infection. However, this link has not been firmly established in wild animals, particularly whether stress hormones affect host responses to zoonotic pathogens, which can be transmitted to domesticated animal, wildlife and human populations. Due to the dynamic effects of stress hormones on immune functions, stress hormones may make hosts better or poorer amplifying hosts for a pathogen contingent on context and the host species evaluated. Using an important zoonotic pathogen, West Nile virus (WNV) and a competent host, the Northern Cardinal (Cardinalis cardinalis), we tested the effects of exogenous corticosterone on response to WNV infection. Corticosterone was administered at levels that individuals enduring chronic stressors (i.e., long-term inclement weather, food shortage, anthropogenic pollution) might experience in the wild. Corticosterone greatly impacted mortality: half of the corticosterone-implanted cardinals died between five - 11 days post-inoculation whereas only one of nine empty-implanted (control) birds died. No differences were found in viral titer between corticosterone- and empty-implanted birds. However, cardinals that survived infections had significantly higher average body temperatures during peak infection than individuals that died. In sum, this study indicates that elevated corticosterone could affect the survival of WNV-infected wild birds, suggesting that populations may be disproportionately at-risk to disease in stressful environments.

Using high titer West Nile intravenous immunoglobulin from selected Israeli donors for treatment of West Nile virus infection

BACKGROUND

West Nile Virus (WNV) is endemic in Israel and a significant level of antibodies is present in the population due to natural exposure. Anecdotal cases suggested that the presence of anti-WNV antibodies in intravenous immunoglobulin (IVIG) from Israeli donors (IVIG-IL) assisted the recovery of patients with severe WNV infection.

METHODS

To enhance the therapeutic efficacy of IVIG-IL against WNV infection, OMRIX Biopharmaceuticals, Israel, have developed a strategy for selection of plasma units from a 10% fraction of Israeli blood donors with anti-WNV antibodies. Positive units were processed into pharmaceutical grade WNV IVIG (WNIG). Following inoculation with WNV, mice received i.p. injections of different doses (0.01-8 mg/mouse) of IVIG-IL or WNIG, according to the specific experimental protocol.

RESULTS

WNIG was about 10 times more potent (per gr of IgG) than was regular IVIG-IL when tested by ELISA and neutralization assays. In a mouse lethal WNV infection model, prophylactic treatment with WNIG was at least 5-10-fold more potent as compared to treatment with IVIG-IL. Treatment with WNIG during active encephalitis, three or four days following WNV infection, had a significant protective effect. WNIG was also very effective in protecting immunosuppressed mice. Indeed, treatment of dexamethasone-immunosuppressed mice with 0.2 or 1.0 mg WNIG 4 h after virus infection, led to 100% survival.

CONCLUSION

IVIG produced from selected plasma donated in WNV endemic regions can be used to produce WNV IVIG with superior activity for therapeutic and prophylactic measures.

Pathogenesis of flavivirus encephalitis

Within the flavivirus family, viruses that cause natural infections of the central nervous system (CNS) principally include members of the Japanese encephalitis virus (JEV) serogroup and the tick-borne encephalitis virus (TBEV) serocomplex. The pathogenesis of diseases involves complex interactions of viruses, which differ in neurovirulence potential, and a number of host factors, which govern susceptibility to infection and the capacity to mount effective antiviral immune responses both in the periphery and within the CNS. This chapter summarizes progress in the field of flavivirus neuropathogenesis. Mosquito-borne and tickborne viruses are considered together. Flavivirus neuropathogenesis involves both neuroinvasiveness (capacity to enter the CNS) and neurovirulence (replication within the CNS), both of which can be manipulated experimentally. Neuronal injury as a result of bystander effects may be a factor during flavivirus neuropathogenesis given that microglial activation and elaboration of inflammatory mediators, including IL-1β and TNF-α, occur in the CNS during these infections and may accompany the production of nitric oxide and peroxynitrite, which can cause neurotoxicity.

Cold exposure: human immune responses and intracellular cytokine expression

It is commonly believed that exposure to cold environmental temperatures depresses immune function and increases the risk for infection. This review paper will 1) present an overview of human physiological responses to cold exposure, 2) present the human studies examining the effects of cold exposure on immune responses, and 3) summarize recent experiments from our laboratories examining the effects of exercise and fatigue on immune responses during subsequent cold exposure. Based on the review of the literature, there is no support for the concept that cold exposure depresses immune function.

Clinical signs of West Nile virus encephalomyelitis in horses during the outbreak in Israel in 2000

Between August and October 2000, 76 horses were reported by veterinary practitioners as having signs of a neurological disorder, varying from an involvement of the spinal cord alone to the entire central nervous system; 15 of the horses died or were euthanased as a result of their grave prognosis or secondary complications. At the same time, an outbreak of West Nile virus infection affected people and birds, principally domestic geese. West Nile virus was isolated from four of the horses with encephalomyelitis and five other horses seroconverted, indicating that the virus was the probable cause of the outbreak in horses. Three of the cases from which the virus was isolated are described briefly and one case is described in detail. This horse behaved abnormally and had general proprioceptive deficits in all four limbs. Its neurological condition deteriorated after two days and severe inspiratory dyspnoea due to a failure to abduct the arytenoids necessitated a tracheostomy. It died on the fourth day and histological lesions were observed in the brain stem and grey matter of the spinal cord.

Inhalation anesthetic-induced neuroinvasion by an attenuated strain of West Nile virus in mice

There are contradictory reports regarding the effects of inhalation anesthetics on the immune system. Measurable immune responses have been studied in vitro, but little is known about the in vivo effects in the intact organism. We used an attenuated, non-neuroinvasive, nonlethal strain of the encephalitic West Nile virus, termed WN-25, which can become lethal in combination with environmental stressors, to study possible modulatory immune effects of inhalation anesthetics in mice. Both single short-term exposure and repeated exposure to halothane and nitrous oxide were studied. Exposure to 30% CO2 served as a positive control. Mortality, brain invasion, spleen weight, and antiviral antibodies served as the experimental endpoints. Halothane and nitrous oxide led to viral brain invasion, increased mortality, and suppressed immune response in a concentration- and time-dependent manner. Repeated exposures had a cumulative effect. Assessment of the stability of the viral attenuation did not demonstrate any alteration in the character of the virus, suggesting an increased access to the brain by inhalation anesthetics that led to the fatal encephalitis. These findings may be of special concern to populations at risk, such as operating room staff and patients undergoing general anesthesia in endemic areas of encephalitic virus species, in which subclinical infection may develop into an overt disease.

Melatonin prolongs survival of immunodepressed mice infected with the Venezuelan equine encephalomyelitis virus

Male albino mice immunodepressed after the injection of dexamethasone (DEX) were inoculated intraperitoneally with the Guajira strain of Venezuelan equine encephalomyelitis (VEE) virus. Melatonin (MLT) was administered daily, at a dose of 500 micrograms/kg bodyweight, for 3 days before virus inoculation and 10 days after. Serum levels of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-2 (IL-2) were determined in all the experimental groups (control, DEX, DEX + MLT, DEX + VEE, DEX + VEE + MLT, VEE and MLT). At day 6 after the virus inoculation, the survival rate was significantly increased from 0% in group DEX + VEE to 32.5% in the group of immunodepressed infected mice treated with MLT (DEX + VEE + MLT). By day 10 a survival rate of 10% was found in group DEX + VEE + MLT and 0% in group VEE. No alterations in IL-2 serum levels were observed. MLT increased GM-CSF in control and in DEX-treated mice. In the VEE virus-infected mice treated with DEX, serum levels of GM-CSF increased progressively from day 1 to 5 postinoculation. In contrast, the levels of GM-CSF in infected immunodepressed mice treated with MLT decreased significantly from day 1 to 5 postinoculation. At day 5 after viral inoculation, no differences were detected in the cerebral viral titres in groups VEE, DEX + VEE and DEX + MLT + VEE. These results show that MLT does not inhibit VEE viral replication in the brain of immunodepressed mice.

CNS penetration by noninvasive viruses following inhalational anesthetics

The effects of inhalational anesthetics on brain penetration by the neurovirulent noninvasive West Nile virus (WN-25) were studied in mice. WN-25 injected intracerebrally causes encephalitis and kills adult mice, but when injected intraperitoneally (i.p.) it is unable to invade the brain and kill. Under stress conditions, this strain causes encephalitis and death even after i.p. inoculation. In the study described in this paper, we used two inhalational anesthetics, a single short-term exposure to 2% halothane for 10 min in oxygen, or 70% nitrous oxide (N2O) for 30 min in air. Both inhalational anesthetics induced WN-25 encephalitis and death in 33% and 20% of the tested mice, respectively. Exposure of inoculated mice to halothane for prolonged periods or for repeated exposures (two or three times) markedly increased the mortality rate (up to 75%). Exposure to 30% CO2, a known modulator of blood-brain barrier (BBB) activity, was used as a positive control (80% mortality). No death was observed in the control non-exposed injected mice. Virus levels were found to be more than 10(7) plaque-forming units (PFU)/brain in all moribund mice. Additional parameter demonstrating the "stressor-like" nature of inhalation anesthetics was the induction of a significant decrease in weight of the lymphoid organs of inoculated mice. We suggest that inhalational anesthetics induces BBB breaching with subsequent entrance of the noninvasive WN-25 virus into the brain, causing encephalitis and death.

Experimental stress suppresses recruitment of macrophages but enhanced their P. gingivalis LPS-stimulated secretion of nitric oxide

BACKGROUND

Epidemiological studies have suggested that stress can alter the onset and progression of periodontal disease. However, the mechanisms involved are not clear. The present study was designed to examine whether the functional response of mouse macrophages stimulated by Porphyromonas gingivalis lipopolysaccharide (LPS) is affected by experimental stress, and to investigate the role of corticosterone (CS) in the stress-related effects.

METHODS

Two models of stress were used: emotional (isolation) and physical (cold). We measured thioglycollate-induced macrophage recruitment in vivo, and LPS-induced nitric oxide (NO) secretion by the macrophages in vitro. Two groups of mice were exposed to the stress conditions: isolation or cold. A third group was injected daily with CS, and a fourth group was used as a control (no stress). After 3 days of stress conditions, thioglycollate was injected into the peritoneal cavity. Four days later, peritoneal macrophages were isolated, counted, and cultured. The secretion of NO by the cultured cells was evaluated with and without P. gingivalis LPS stimulation.

RESULTS

The number of cells in the peritoneal lavage of stressed mice was significantly reduced in comparison to macrophages isolated from non-stressed animals. The number of macrophages from CS-treated mice did not differ from controls. NO secretion from unstimulated macrophages did not differ between the stressed and control groups. Stimulation of the macrophages with P. gingivalis LPS significantly enhanced NO secretion by macrophages from the control and stressed animals, but not by the CS-treated group. NO levels secreted by P. gingivalis-stimulated cells from the two stressed groups were significantly higher than the levels secreted by controls, and the isolation group released significantly higher levels than the cold group. Stimulation of the macrophages with P. gingivalis LPS and interferon (IFN)-gamma resulted in enhanced NO secretion in the 4 groups compared to LPS alone, with no significant differences between the groups.

CONCLUSIONS

The results suggest that experimental stress modulates the response of macrophages to inflammatory stimulants, and that CS is not the sole mediator involved. The presence of IFN-gamma in the culture may mask the functional differences induced by stress. The stress-induced upregulation of NO secretion might be involved in the accelerated periodontal destruction in stressed subjects.

Immune changes in humans during cold exposure: effects of prior heating and exercise

This study examined the immunological responses to cold exposure together with the effects of pretreatment with either passive heating or exercise (with and without a thermal clamp). On four separate occasions, seven healthy men [mean age 24.0 +/- 1.9 (SE) yr, peak oxygen consumption = 45.7 +/- 2.0 ml. kg(-1). min(-1)] sat for 2 h in a climatic chamber maintained at 5 degrees C. Before exposure, subjects participated in one of four pretreatment conditions. For the thermoneutral control condition, subjects remained seated for 1 h in a water bath at 35 degrees C. In another pretreatment, subjects were passively heated in a warm (38 degrees C) water bath for 1 h. In two other pretreatments, subjects exercised for 1 h at 55% peak oxygen consumption (once immersed in 18 degrees C water and once in 35 degrees C water). Core temperature rose by 1 degrees C during passive heating and during exercise in 35 degrees C water and remained stable during exercise in 18 degrees C water (thermal clamping). Subsequent cold exposure induced a leukocytosis and granulocytosis, an increase in natural killer cell count and activity, and a rise in circulating levels of interleukin-6. Pretreatment with exercise in 18 degrees C water augmented the leukocyte, granulocyte, and monocyte response. These results indicate that acute cold exposure has immunostimulating effects and that, with thermal clamping, pretreatment with physical exercise can enhance this response. Increases in levels of circulating norepinephrine may account for the changes observed during cold exposure and their modification by changes in initial status.

The Effect of Stress on the Inflammatory Response toPorphyromonas gingivalisin a Mouse Subcutaneous Chamber Model

BACKGROUND

The impact of emotional stress on the outcome of infectious diseases was studied in animal models and humans, but data related to the effect of stress on periodontal infection are limited. Using the subcutaneous chamber model in mice, the present study was carried out to investigate the effect of stress on the host response to Porphyromonas gingivalis.

METHODS

Mice with subcutaneous chambers (2 per animal) were divided into 4 treatment groups: cold-stress; isolation-stress; corticosterone (CS)-injected; and controls. On the third day of stress conditions, heat-killed P. gingivalis were injected into the chambers. The chambers were sampled 1 and 5 days later and analyzed for leukocyte number, tumor necrosis factor (TNF)-alpha levels, and interferon (IFN)-gamma levels.

RESULTS

Injection of P. gingivalis induced the migration of leukocytes into the chambers and increased the intrachamber levels of IFN-gamma and TNF-alpha. There were no significant differences in cell number and IFN-gamma levels between the different treatment groups, but the levels of TNF-alpha were significantly lower in the isolation-stress and cold-stress groups compared to control animals. CS-injected animals were not different from controls. In addition, the levels of TNF-alpha in the stressed animals were lower on the fifth day post-injection than on the first day, but not in the CS and control group.

CONCLUSIONS

The results suggest that the levels of TNF-alpha induced by P. gingivalis in the infection site are downregulated in stressed animals, and CS is not the sole mediator responsible. The stress-induced reduction in TNF-alpha levels might have an impact on the pathogenesis of periodontal disease in humans experiencing emotional stress.

Role of the Hypothalamic Pituitary Adrenal Axis and IL-6 in Stress-Induced Reactivation of Latent Herpes Simplex Virus Type 1

Hyperthermic stress induces reactivation of herpes simplex virus type 1 (HSV-1) in latently infected mice and also stimulates corticosterone release from the adrenals via activation of the hypothalamic pituitary adrenal axis. In the present study, we tested the hypothesis that stress-induced elevation of corticosterone potentiates HSV-1 reactivation in latently infected mice. Because of the putative role of IL-6 in facilitating HSV-1 reactivation in mice, the effect of hyperthermic stress and cyanoketone treatment on IL-6 expression in the trigeminal ganglion was also measured. Preadministration of cyanoketone, a glucocorticoid synthesis inhibitor, blocked the stress-induced elevation of corticosterone in a dose-dependent manner. Furthermore, inhibition of corticosterone synthesis was correlated with reduced levels of HSV-1 reactivation in latently infected mice. Hyperthermic stress elicited a transient rise in IL-6 mRNA levels in the trigeminal ganglion, but not other cytokine transcripts investigated. In addition, there was a significant reduction in MAC-3+, CD8+, and DX5+ (NK cell marker) cells in the trigeminal ganglion of latent HSV-1-infected mice 24 h after stress. Cyanoketone blocked the stress-induced rise in IL-6 mRNA and protein expression in the trigeminal ganglion latently infected with HSV-1. Collectively, the results indicate that the activation of the hypothalamic pituitary adrenal axis plays an important role in stimulating IL-6 expression and HSV-1 reactivation in the trigeminal ganglion following hyperthermic stress of mice.

Newcastle disease vaccines

Newcastle disease (ND) is a worldwide problem with severe economic implications, affecting chickens, turkeys and other birds. Newcastle disease virus (NDV), a member of the Paramyxoviridae group can cause disease of diverse severity in accordance with environmental factors. NDV strains are classified according to their virulence into three categories. The lentogenic strains are very mild and naturally inhabit healthy flocks. They can be used as live vaccines even for young chicks. Killed vaccines can be produced from the same viruses following inactivation. Mesogenic ND viruses, which cause mild or inapparent respiratory infections, have recently been banned in many countries even for killed vaccine production due to fears of disease emergence. Velogenic strains are the causative agents of the disease and can be used for the purpose of vaccine challenge test. Production and use of Newcastle disease vaccines are discussed in this review.