Herpes simplex virus infections in male and female mice following pinna inoculation: responses to primary infection and artificially induced recurrent disease

Neuroendocrine-immune interactions and responses to exercise

This article reviews the interaction between the neuroendocrine and immune systems in response to exercise stress, considering gender differences. The body's response to exercise stress is a system-wide effort coordinated by the integration between the immune and the neuroendocrine systems. Although considered distinct systems, increasing evidence supports the close communication between them. Like any stressor, the body's response to exercise triggers a systematic series of neuroendocrine and immune events directed at bringing the system back to a state of homeostasis. Physical exercise presents a unique physiological stress where the neuroendocrine and immune systems contribute to accommodating the increase in physiological demands. These systems of the body also adapt to chronic overload, or exercise training. Such adaptations alleviate the magnitude of subsequent stress or minimize the exercise challenge to within homeostatic limits. This adaptive capacity of collaborating systems resembles the acquired, or adaptive, branch of the immune system, characterized by the memory capacity of the cells involved. Specific to the adaptive immune response, once a specific antigen is encountered, memory cells, or lymphocytes, mount a response that reduces the magnitude of the immune response to subsequent encounters of the same stress. In each case, the endocrine response to physical exercise and the adaptive branch of the immune system share the ability to adapt to a stressful encounter. Moreover, each of these systemic responses to stress is influenced by gender. In both the neuroendocrine responses to exercise and the adaptive (B lymphocyte) immune response, gender differences have been attributed to the 'protective' effects of estrogens. Thus, this review will create a paradigm to explain the neuroendocrine communication with leukocytes during exercise by reviewing (i) endocrine and immune interactions; (ii) endocrine and immune systems response to physiological stress; and (iii) gender differences (and the role of estrogen) in both endocrine response to physiological stress and adaptive immune response.

Susceptibility to HSV-1 infection and exercise stress in female mice: role of estrogen

Exhaustive exercise has been associated with an increased risk for upper respiratory tract infections in mice and humans. We have previously shown (Brown AS, Davis JM, Murphy AE, Carmichael MD, Ghaffer A, Mayer EP. Med Sci Sports Exerc 36: 1290–1295, 2004) that female mice are better protected from the lethal effects of herpes simplex virus type 1 (HSV-1) infection, both at rest and following exercise stress, but little is known about possible mechanisms. This study tested the effects of estrogen on HSV-1 infection and macrophage antiviral resistance following repeated exhaustive exercise. Female mice were assigned to either exercise (Ex) or control (C): intact female (I-C or I-Ex), ovariectomized female (O-C or O-Ex), or ovariectomized estrogen-supplemented female (E-C or E-Ex). Exercise consisted of treadmill running to volitional fatigue (∼125 min) for 3 consecutive days. Intact female mice had a later time to death than O and E ( P < 0.05) and fewer deaths than both O and E ( P < 0.05). Exercise stress was associated with increased time to sickness ( P < 0.05) and symptom severity at days 6 and 12–21 postinfection ( P < 0.05) and decreased macrophage antiviral resistance ( P < 0.001) in all groups. E had increased symptom severity at days 6 and 13–21 postinfection ( P < 0.05). Results indicate that intact female mice are better protected from the lethal effects of HSV-1 infection and that exercise stress had a similar negative impact in all groups. This protective effect was lost in ovariectomized mice, but it was not reinstated by 17β-estradiol replacement. This indicates that other ovarian factors, alone or in combination with estrogen, are responsible for the protective effects in females.

Gender Differences in Macrophage Antiviral Function following Exercise Stress

INTRODUCTION

In male mice, exhaustive exercise increases susceptibility to respiratory infection following intranasal inoculation with herpes simplex virus-1 (HSV-1), whereas moderate exercise decreases the risk of infection. These responses have been linked with altered macrophage antiviral resistance, among other immune mechanisms. Female mice appear to be better protected from death than male mice following HSV-1 infection, although their response to exercise stress is similar. The possible immune mechanisms, however, have not been explored.

PURPOSE

This study was conducted to examine gender differences in macrophage antiviral resistance following repeated moderate and exhaustive treadmill exercise.

METHODS

Male (M, N = 36) and female (F, N = 36) CD-1 mice were randomly assigned to moderate exercise (Mod), exhaustive exercise (Exh), or control (C) groups. Exercise was done daily for 3 d; moderate exercise consisted of treadmill running for 90 min, whereas exhaustive exercise consisted of running to volitional fatigue (approximately 50 min).

RESULTS

Females had greater macrophage antiviral resistance to HSV-1 than males in C and Mod (P < 0.05), but not Exh; Mod increased resistance, whereas Exh decreased resistance similarly in both genders (P < 0.001).

CONCLUSIONS

These data suggest that altered macrophage antiviral resistance to HSV-1 may contribute to gender differences in in vivo resistance to HSV-1 respiratory infection at rest, as well as following moderate and exhaustive exercise.

Gender Differences in Viral Infection after Repeated Exercise Stress

Fatiguing exercise can increase susceptibility to respiratory infection after intranasal inoculation with herpes simplex virus-1 (HSV-1) in male mice. Although gender differences in susceptibility to certain pathogens do exist, it is unknown whether female mice will respond differently than males in response to strenuous exercise and HSV-1 infection.

PURPOSE

To test the effects of gender on susceptibility to HSV-1 respiratory infection after repeated exhaustive exercise.

METHODS

Male (N = 86) and female (N = 89) CD-1 mice (approximately 60 d old) were randomly assigned to exercise (Ex) or control (C) groups. Exercise consisted of 3 d of treadmill running at 36 m x min(-1) at 8% grade until volitional fatigue (135 +/- 5min). Fifteen minutes after the last bout of exercise, Ex and C mice were inoculated intranasally with a standard dose (LD30) of HSV-1. Mice were monitored for 21 d for morbidity (time to sickness and symptom severity) and mortality.

RESULTS

Run time to fatigue was significantly longer in females than males (P = 0.027). Significant gender differences in susceptibility to infection were found after exercise stress. In males, exercise stress resulted in increased morbidity (66%, P < 0.05) and mortality (30%, P < 0.05) whereas in females, exercise stress only resulted in increased morbidity (66%, P < 0.05).

CONCLUSION

Results suggest that although males and females have similar morbidity rates after infection and exercise stress, females recover to a greater extent and are ultimately better protected from death.

Effect of a beta-adrenergic antagonist, propranolol, on induced HSV-1 ocular recurrence in latently infected rabbits

PURPOSE

Propranolol, a beta-adrenergic antagonist, has been shown to block hyperthermically-induced ocular recurrence of HSV-1 in mice and reduce spontaneous ocular viral shedding and herpetic corneal lesions in latently infected rabbits. The present study was performed to determine the effect of propranolol on epinephrine iontophoresis-induced ocular recurrence and immunosuppression-induced ocular recurrence in the rabbit eye model.

METHODS

New Zealand white rabbits were infected with HSV-1 strain 17Syn+ or McKrae. After latency was established, the animals were injected intramuscularly with saline (placebo), or propranolol (5-200 mg/kg) twice daily, and then induced with epinephrine iontophoresis or cyclophosphamide and dexamethasone administration. Tear film swabs were cultured to determine the frequency of viral shedding.

RESULTS

Propranolol administered at a range of doses did not affect the frequency or duration of viral shedding following epinephrine or cyclophosphamide/dexamethasone induction as compared to saline treatment.

CONCLUSION

These results demonstrate that propranolol does not significantly reduce ocular HSV-1 shedding following induction by epinephrine iontophoresis or immunosuppression. By inference, these results suggest two possibilities: (1) that viral pathways leading to spontaneous and induced shedding of virus are under separate control mechanisms or (2) in rabbits, these inducers are of such potency that propranolol is ineffectual.

Propranolol suppresses reactivation of herpesvirus

Herpes simplex virus type 1 (HSV-1) reactivates from the nervous system and causes recurrent disease in end organs such as the eye and the lips. We found that the beta-adrenergic receptor blocker, propranolol, reduces HSV-1 reactivation in an animal model. Mice latent for McKrae strain HSV-1 were injected with propranolol or saline once a day for 3 successive days, and subjected to a brief period of hyperthermia on the second day to induce reactivation. Twenty-four hours after the third injection, swabs of the ocular surface and homogenates of the corneas and trigeminal ganglia were analyzed for the presence of infectious virus and viral DNA. Treatment with propranolol significantly decreased the appearance of infectious virus in the tear film, cornea, and trigeminal ganglia (P < 0.05, chi 2-test). The results suggest a possible new pharmacologic approach to suppressing herpesvirus reactivation in the nervous system and thereby preventing recurrent disease.

In vitro reactivation of latent herpes simplex virus by the demethylating compound hexamethylene-bis-acetamide

We have characterized previously a model of herpes simplex virus (HSV) infection of rat dorsal root ganglia (DRG) following cutaneous infection. During acute infection HSV can be isolated from co-cultivated rat ganglia in (mean +/- S.E.M.) 4.8 +/- 0.33 days (d) and from latently infected ganglia in 7.8 +/- 0.53 (d) (P < or = 0.0001). We treated co-cultivated rat ganglia from acute and latent infected rats with the demethylating compound hexamethylene-bis-acetamide (HEX) to see what effect, if any, it would have on HSV infection. HEX-treated ganglia from rats with acute infection did not differ significantly from controls in the proportion of rats, skin or ganglia positive for HSV. The mean time to detect virus was not different between treated (3.6 +/- 0.38 d) and control (3.1 +/- 0.46 d) (P > 0.05) groups. In latent infected rats there was no difference between treated and controlled groups in the proportions of rats, skin and ganglia positive for HSV. There was a significant difference in the mean time to CPE between the HEX and control groups respectively (4.5 +/- 0.72 d vs 8.92 +/- 1.42 d, P < 0.01). We conclude that HEX converted latent HSV infection to a productive one.