Chemical sympathectomy increases susceptibility to ocular herpes simplex virus type 1 infection

The sympathetic nervous system drives hyperinflammatory responses to Clostridioides difficile infection

Clostridioides difficile infection (CDI) is a leading cause of hospital-acquired infections in the United States, known for triggering severe disease by hyperactivation of the host response. In this study, we determine the impact of the sympathetic nervous system (SNS) on CDI disease severity. Mouse models of CDI are administered inhibitors of SNS activity prior to CDI. Chemical sympathectomy or pharmacological inhibition of norepinephrine synthesis greatly reduces mortality and disease severity in the CDI model. Pharmacological blockade or genetic ablation of the alpha 2 adrenergic receptor ameliorates intestinal inflammation, disease severity, and mortality rate. These results underscore the role of the SNS and the alpha 2 adrenergic receptor in CDI pathogenesis and suggest that targeting neural systems could be a promising approach to therapy in severe disease.

Crosstalk Between Epithelial Cells, Neurons and Immune Mediators in HSV-1 Skin Infection

Herpes simplex virus type 1 (HSV-1) infection is highly prevalent in humans, with approximately two-thirds of the world population living with this virus. However, only a fraction of those carrying HSV-1, which elicits lifelong infections, are symptomatic. HSV-1 mainly causes lesions in the skin and mucosae but reaches the termini of sensory neurons innervating these tissues and travels in a retrograde manner to the neuron cell body where it establishes persistent infection and remains in a latent state until reactivated by different stimuli. When productive reactivations occur, the virus travels back along axons to the primary infection site, where new rounds of replication are initiated in the skin, in recurrent or secondary infections. During this process, new neuron infections occur. Noteworthy, the mechanisms underlying viral reactivations and the exit of latency are somewhat poorly understood and may be regulated by a crosstalk between the infected neurons and components of the immune system. Here, we review and discuss the immune responses that occur at the skin during primary and recurrent infections by HSV-1, as well as at the interphase of latently-infected neurons. Moreover, we discuss the implications of neuronal signals over the priming and migration of immune cells in the context of HSV-1 infection.

Immuno-metabolic changes in herpes virus infection

Recent evidences indicate that change in cellular metabolic pathways can alter immune response and function of the host; emphasizing the role of metabolome in health and diseases. Human Herpes simplex virus type-1 (HSV-1) and type-2 (HSV-2) causes diseases from asymptomatic to highly prevalent oral and genital herpes, recurrent blisters or neurological complications. Immune responses against HSV are complex with delicate interplay between innate signaling pathways and adaptive immune responses. The innate response involves the induction of protective IFN-1; while Natural Killer (NK) cells and plasmacytoid Dendritic Cells (pDC) confer in vivo adaptive anti-HSV response along with humoral and cellular components in controlling infection and latency. Metabolic changes lead to up-/down-regulation of several cytokines and chemokines like IFN-γ, IL-2, IL-4, IL-10 and MIP1β in HSV infection and recurrences. Recently, the viral protein ICP0 has been identified as an attenuator of TLR signaling, that inhibit innate responses to HSV. This review will summarize the role of metabolome in innate and adaptive effectors in infection, pathogenesis and immune control of HSV, highlighting the delicate interplay between the metabolic changes and immunity.

Autonomic function and rheumatoid arthritis: a systematic review

OBJECTIVES

Rheumatoid arthritis (RA) is a chronic inflammatory condition with increased all-cause and cardiovascular mortality. Accumulating evidence indicates that the immune and autonomic nervous systems (ANS) are major contributors to the pathogenesis of cardiovascular disease. We performed the first systematic literature review to determine the prevalence and nature of ANS dysfunction in RA and whether there is a causal relationship between inflammation and ANS function.

METHODS

Electronic databases (MEDLINE, Central and Cochrane Library) were searched for studies of RA patients where autonomic function was assessed.

RESULTS

A total of 40 studies were included. ANS function was assessed by clinical cardiovascular reflex tests (CCTs) (n = 18), heart rate variability (HRV) (n = 15), catecholamines (n = 5), biomarkers of sympathetic activity (n = 5), sympathetic skin responses (n = 5), cardiac baroreflex sensitivity (cBRS) (n = 2) and pupillary light reflexes (n = 2). A prevalence of ~60% (median, range: 20-86%) of ANS dysfunction (defined by abnormal CCTs) in RA was reported in 9 small studies. Overall, 73% of studies (n = 27/37) reported at least one of the following abnormalities in ANS function: parasympathetic dysfunction (n = 20/26, 77%), sympathetic dysfunction (n = 16/30, 53%) or reduced cBRS (n = 1/2, 50%). An association between increased inflammation and ANS dysfunction was found (n = 7/19, 37%), although causal relationships could not be elucidated from the studies available to date.

CONCLUSIONS

ANS dysfunction is prevalent in ~60% of RA patients. The main pattern of dysfunction is impairment of cardiovascular reflexes and altered HRV, indicative of reduced cardiac parasympathetic (strong evidence) activity and elevated cardiac sympathetic activity (limited evidence). The literature to date is underpowered to determine causal relationships between inflammation and ANS dysfunction in RA.

Corneal nerves in health and disease

Corneal nerves are responsible for the sensations of touch, pain, and temperature and play an important role in the blink reflex, wound healing, and tear production and secretion. Corneal nerve dysfunction is a frequent feature of diseases that cause opacities and result in corneal blindness. Corneal opacities rank as the second most frequent cause of blindness. Technological advances in in vivo corneal nerve imaging, such as optical coherence tomography and confocal scanning, have generated new knowledge regarding the phenomenological events that occur during reinnervation of the cornea following disease, injury, or surgery. The recent availability of transgenic neurofluorescent murine models has stimulated the search for molecular modulators of corneal nerve regeneration. New evidence suggests that neuroregenerative and inflammatory pathways in the cornea are intertwined. Evidence-based treatment of neurotrophic corneal diseases includes using neuroregenerative (blood component-based and neurotrophic factors), neuroprotective, and ensconcing (bandage contact lens and amniotic membrane) strategies and avoiding anti-inflammatory therapies, such as cyclosporine and corticosteroids.

Comparison of the host immune response to herpes simplex virus 1 (HSV-1) and HSV-2 at two different mucosal sites

A study was undertaken to compare the host immune responses to herpes simplex virus 1 (HSV-1) and HSV-2 infection by the ocular or genital route in mice. Titers of HSV-2 from tissue samples were elevated regardless of the route of infection. The elevation in titers of HSV-2, including cell infiltration and cytokine/chemokine levels in the central nervous system relative to those found following HSV-1 infection, was correlative with inflammation. These results underscore a dichotomy between the host immune responses to closely related alphaherpesviruses.

Substance P in the corneal stroma regulates the severity of herpetic stromal keratitis lesions

PURPOSE

To determine whether substance P (SP) in herpes simplex virus-1 (HSV-1) infected cornea regulates the severity of herpetic stromal keratitis (HSK) lesions in a mouse model.

METHODS

C57BL/6 mice were infected ocularly with HSV-1 (RE). The corneas with HSK lesions, on Day 15 postinfection, were grouped on the basis of the corneal opacity as mild (≤2) or severe (>2). The amount of SP was determined in the corneas with mild or severe HSK lesions by enzyme immunosorbent assay (EIA) and confocal microscopy. Subconjunctival inoculation of spantide I, SP receptor antagonist, was carried out during the clinical phase of HSK. ELISA and flow cytometry were used to determine the level of cytokines, chemokines, and influx of immune cell types in the corneal lesions.

RESULTS

The authors determined a significantly higher level of SP in the corneas with severe HSK lesions in comparison with mild lesions. The corneas with a higher level of SP also exhibited higher amounts of proinflammatory cytokines (IL-6, IFN-γ) and chemokines (CCL3, CXCL2) when compared with the corneas with a lower level of SP. SP receptor NK1R expression was determined in CD45- and CD45+ cells in infected cornea. SP present in the corneal stroma of the eyes with severe HSK lesions colocalized with β-III tubulin(+) and IA(b+) cell types. Subconjunctival inoculation of spantide I during the clinical phase of HSK resulted in significant reduction in the corneal opacity and angiogenesis.

CONCLUSIONS

Collectively, these results demonstrate the relative contribution of substance P in regulating the clinical severity of HSK lesions in a mouse model.

Mice lacking adrenergic signaling have normal cochlear responses and normal resistance to acoustic injury but enhanced susceptibility to middle-ear infection

The vasculature and neurons of the inner ear receive adrenergic innervation from the cervical sympathetic chain, and adrenergic receptors may be expressed by cells of the organ of Corti and stria vascularis, despite a lack of direct sympathetic innervation. To assess the functional role of adrenergic signaling in the auditory periphery, we studied mice with targeted deletion of the gene for dopamine beta-hydroxylase (DBH), which catalyzes the conversion of dopamine to noradrenaline; thus, these mutant mice have no measurable adrenaline or noradrenaline. Dbh (-/-) mice were more susceptible to spontaneous middle-ear infection than their control littermates, consistent with a role for sympathetics in systemic and/or local immune response. At 6-8 weeks of age, cochlear thresholds and suprathreshold responses assessed by auditory brainstem responses and distortion product otoacoustic emissions, as well as light-microscopic morphology, were indistinguishable from controls, if ears with conductive hearing loss were eliminated. Dbh (-/-) mice were no more susceptible to acoustic injury than controls, despite prior reports that sympathectomy reduces noise damage. Dbh (-/-) mice showed enhancement of shock-evoked olivocochlear suppression of cochlear responses, which may arise from the loss of adrenergic inputs to olivocochlear neurons in the brainstem. However, adrenergic modulation of olivocochlear efferents does not mediate the protective effect of contralateral cochlear destruction on ipsilateral response to acoustic overexposure.

Cutting edge: Sympathetic nervous system increases proinflammatory cytokines and exacerbates influenza A virus pathogenesis

Although the sympathetic nervous system innervates the lung, little is known about its participation in host immunity to pulmonary pathogens. In this study, we show that peripheral sympathectomy reduces mouse morbidity and mortality from influenza A virus-induced pneumonia due to reduced inflammatory influx of monocytes, neutrophils, and NK cells. Mortality was also delayed by treating mice with an alpha-adrenergic antagonist. Sympathectomy diminished the immediate innate cytokine responses, particularly IL-1, which was profoundly reduced. These findings demonstrate an unexpected role for the sympathetic nervous system in innate antiviral immunity and in exacerbating the pathology of a virus of great significance to human and animal health.

Sympathetic nervous system control of anti-influenza CD8+ T cell responses

Despite the longstanding appreciation of communication between the nervous and the immune systems, the nature and significance of these interactions to immunity remain enigmatic. Here, we show that 6-hydroxydopamine-mediated ablation of the mouse peripheral sympathetic nervous system increases primary CD8(+) T cell responses to viral and cellular antigens presented by direct priming or cross-priming. The sympathetic nervous system also suppresses antiviral CD4(+) T cell responses, but this is not required for suppressing CD8(+) T cell responses. Adoptive transfer experiments indicate that enhanced CD8(+) responses do not result from permanent alterations in CD8(+) T cell function in sympathectomized mice. Rather, additional findings suggest that the sympathetic nervous system tempers the capacity of antigen-presenting cells to activate naïve CD8(+) T cells. We also show that antiviral CD8(+) T cell responses are enhanced by administration of a beta(2) (but not beta(1) or alpha) adrenergic antagonist. These findings demonstrate a critical role for the sympathetic nervous system in limiting CD8(+) T cell responses and indicate that CD8(+) T cell responses may be altered in patients using beta-blockers, one of the most widely prescribed classes of drugs.