Neurokinin 1 receptor signaling affects the local innate immune defense against genital herpes virus infection

Substance P—Friend or Foe

Substance P (SP), a neuropeptide and pain transmitter has multiple roles and is involved in various processes in the body [...]

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.

The SP-TLR axis, which locally primes the nasal mucosa, is impeded in patients with allergic rhinitis

Background

Substance P (SP) and toll‐like receptors (TLRs) contribute to airway disease, particularly during viral infection. We recently demonstrated that SP can act as an initial response to viral stimuli in the upper airway by upregulating TLRs in the nasal epithelia (the SP‐TLR axis). Patients with allergic rhinitis (AR) suffer from prolonged airway infections. The aim of the present study was to examine if patients with AR exhibit a disturbance in the SP‐TLR axis.

Method

Human nasal biopsies and human nasal epithelial cells (HNEC) from healthy volunteers and patients with AR were cultured in the presence of SP. Epithelial expression of TLR4, neutral endopeptidase (NEP) and neurokinin 1 (NK1) were evaluated with flow cytometry and/or quantitative polymerase chain reaction after 30 min to 24 h. The effect of SP on nasal lipopolysaccharide‐induced interleukin‐8 (IL‐8) release was investigated.

Results

SP stimulation of tissue from healthy volunteers resulted in a transient increase of the TLR4 expression, whereas stimulation of AR patient‐derived material led to a delayed and prolonged upregulation of TLR4. NEP expression in HNEC was lower in AR than healthy controls whereas NK1 receptor expression was increased. SP pretreatment increased TLR4‐dependent IL‐8 expression in healthy controls, but not in AR.

Conclusions

SP‐induced regulation of TLR4 in the human nasal mucosa is disturbed in AR. An altered SP‐mediated innate immune response may contribute to the dysfunctional and often prolonged responses to infection in AR.

Varicella Zoster Virus Induces Nuclear Translocation of the Neurokinin-1 Receptor, Promoting Lamellipodia Formation and Viral Spread in Spinal Astrocytes

Background

Varicella zoster virus (VZV) can present as a myelopathy with spinal astrocyte infection. Recent studies support a role for the neurokinin-1 receptor (NK-1R) in virus infections, as well as for cytoskeletal alterations that may promote viral spread. Thus, we examined the role of NK-1R in VZV-infected primary human spinal astrocytes (HA-sps) to shed light on the pathogenesis of VZV myelopathy.

Methods

Mock- and VZV-infected HA-sps were examined for substance P (subP) production, NK-1R localization, morphological changes, and viral spread in the presence or absence of the NK-1R antagonists aprepitant and rolapitant.

Results

VZV infection of HA-sps induced nuclear localization of full-length and truncated NK-1R in the absence of the endogenous ligand, subP, and was associated with extensive lamellipodia formation and viral spread that was inhibited by NK-1R antagonists.

Conclusions

We have identified a novel, subP-independent, proviral function of nuclear NK-1R associated with lamellipodia formation and viral spread that is distinct from subP-induced NK-1R cell membrane/cytoplasmic localization without lamellipodia formation. These results suggest that binding of a putative viral ligand to NK-1R produces a dramatically different NK-1R downstream effect than binding of subP. Finally, the NK-1R antagonists aprepitant and rolapitant provide promising alternatives to nucleoside analogs in treating VZV infections, including myelopathy.

Role of Substance P Neuropeptide in Inflammation, Wound Healing, and Tissue Homeostasis

Substance P (SP) is an undecapeptide present in the CNS and the peripheral nervous system. SP released from the peripheral nerves exerts its biological and immunological activity via high-affinity neurokinin 1 receptor (NK1R). SP is also produced by immune cells and acts as an autocrine or paracrine fashion to regulate the function of immune cells. In addition to its proinflammatory role, SP and its metabolites in combination with insulin-like growth factor-1 are shown to promote the corneal epithelial wound healing. Recently, we showed an altered ocular surface homeostasis in unmanipulated NK1R^-/- mice, suggesting the role of SP-NK1R signaling in ocular surface homeostasis under steady-state. This review summarizes the immunobiology of SP and its effect on immune cells and immunity to microbial infection. In addition, the effect of SP in inflammation, wound healing, and corneal epithelial homeostasis in the eye is discussed.

Novel rat models to study primary genital herpes simplex virus-2 infection

In this study we describe that six rat models (SD, WIST, LEW, BN, F344 and DA) are susceptible to intravaginal herpes simplex virus-2 (HSV-2) infection after pre-treatment with progesterone. At a virus dose of 5 × 10(6) PFU of HSV-2, all rat models were infected presenting anti-HSV-2 antibodies, infectious virus in vaginal washes, and HSV-2 DNA genome copies in lumbosacral dorsal root ganglia and the spinal cord. Most of the LEW, BN, F344, and DA rats succumbed in systemic progressive symptoms at day 8-14 post infection, but presented no or mild genital inflammation while SD and WIST rats were mostly infected asymptomatically. Infected SD rats did not reactivate HSV-2 spontaneously or after cortisone treatment. In an HSV-2 virus dose reduction study, F344 rats were shown to be most susceptible. We also investigated whether an attenuated HSV-1 strain (KOS321) given intravaginally, could protect from a subsequent HSV-2 infection. All LEW, BN, and F344 rats survived a primary HSV-1 infection and no neuronal infection was established. In BN and F344 rats, anti-HSV-1 antibodies were readily detected while LEW rats were seronegative. In contrast to naïve LEW, BN, and F344 rats where only 3 of 18 animals survived 5 × 10(6) PFU of HSV-2, 23 of 25 previously HSV-1 infected rats survived a challenge with HSV-2. The described models provide a new approach to investigate protective effects of anti-viral microbicides and vaccine candidates, as well as to study asymptomatic primary genital HSV-2 infection.

Neurokinin-1 receptor agonists bias therapeutic dendritic cells to induce type 1 immunity by licensing host dendritic cells to produce IL-12

Substance-P and hemokinin-1 are proinflammatory neuropeptides with potential to promote type 1 immunity through agonistic binding to neurokinin-1 receptor (NK1R). Dendritic cells (DCs) are professional antigen-presenting cells that initiate and regulate the outcome of innate and adaptive immune responses. Immunostimulatory DCs are highly desired for the development of positive immunization techniques. DCs express functional NK1R; however, regardless of their potential DC-stimulatory function, the ability of NK1R agonists to promote immunostimulatory DCs remains unexplored. Here, we demonstrate that NK1R signaling activates therapeutic DCs capable of biasing type 1 immunity by inhibition of interleukin-10 (IL-10) synthesis and secretion, without affecting their low levels of IL-12 production. The potent type 1 effector immune response observed following cutaneous administration of NK1R-signaled DCs required their homing in skin-draining lymph nodes (sDLNs) where they induced inflammation and licensed endogenous-conventional sDLN-resident and -recruited inflammatory DCs to secrete IL-12. Our data demonstrate that NK1R signaling promotes immunostimulatory DCs, and provide relevant insight into the mechanisms used by neuromediators to regulate innate and adaptive immune responses.

HSV-1 strain McKrae is more neuroinvasive than HSV-1 KOS after corneal or vaginal inoculation in mice

Strains of HSV-1 have been noted to vary in their pathogenesis. We compared the replication of strains KOS and McKrae in mice by two routes of infection, ocular and vaginal. Peripheral replication of KOS was similar (cornea) or attenuated over time (vagina) compared with McKrae; however, McKrae replicated in the nervous system to significantly higher levels than KOS after inoculation by either route. Host genetic background strongly influenced the capacity for virus entry into the nervous system from the vagina. KOS and McKrae replicated equivalently after intracranial inoculation, indicating that McKrae's pathogenic phenotype is linked to neuroinvasiveness rather than neurovirulence.

Substance P induces rapid and transient membrane blebbing in U373MG cells in a p21-activated kinase-dependent manner

U373MG astrocytoma cells endogenously express the full-length neurokinin 1 receptor (NK1R). Substance P (SP), the natural ligand for NK1R, triggers rapid and transient membrane blebbing and we report that these morphological changes have different dynamics and intracellular signaling as compared to the changes that we have previously described in HEK293-NK1R cells. In both cell lines, the SP-induced morphological changes are Gq-independent, and they require the Rho, Rho-associated coiled-coil kinase (ROCK) signaling pathway. Using confocal microscopy we have demonstrated that tubulin is phosphorylated subsequent to cell stimulation with SP and that tubulin accumulates inside the blebs. Colchicine, a tubulin polymerization inhibitor, blocked SP-induced blebbing in U373MG but not in HEK293-NK1R cells. Although p21-activated kinase (PAK) is expressed in both cell lines, SP induced rapid phosphorylation of PAK in U373MG, but failed to phosphorylate PAK in HEK293-NK1R cells. The cell-permeable Rho inhibitor C3 transferase inhibited SP-induced PAK phosphorylation, but the ROCK inhibitor Y27632 had no effect on PAK phosphorylation, suggesting that Rho activates PAK in a ROCK-independent manner. Our study demonstrates that SP triggers rapid changes in cell morphology mediated by distinct intracellular signaling mechanisms in U373MG versus HEK293-NK1R cells.

Altered host response to murine gammaherpesvirus 68 infection in mice lacking the tachykinin 1 gene and the receptor for substance P

The tachykinins are implicated in neurogenic inflammation and the neuropeptide substance P in particular has been shown to be a proinflammatory mediator. A role for the tachykinins in host response to viral infection has been previously demonstrated using either TAC1- or NK1 receptor-deficient transgenic mice. However, due to redundancy in the peptide-receptor complexes we wished determine whether a deficiency in TAC1 and NK1(R) in combination exhibited an enhanced phenotype. TAC1 and NK1(R)-deficient mice were therefore crossed to generate transgenic mice in both (NK1(-/-)×TAC1(-/-)). As expected, after infection with the respiratory pathogen murine gammaherpesvirus (MHV-68), TAC1 and NK1(R)-deficient mice were more susceptible to infection than wild-type C57BL/6 controls. However, unexpectedly, NK1(-/-)×TAC1(-/-) mice were more resistant to infection arguing for a lack of feedback inhibition through alternative receptors in these mice. Histopathological examination did not show any great differences in the inflammatory responses between groups of infected animals, except for the presence of focal perivascular B cell accumulations in lungs of all the knockout mice. These were most pronounced in the NK1(-/-)×TAC1(-/-) mice. These results confirm an important role for TAC1 and NK1(R) in the control of viral infection but reinforce the complex nature of the peptide-receptor interactions.

Substance P primes lipoteichoic acid- and Pam3CysSerLys4-mediated activation of human mast cells by up-regulating Toll-like receptor 2

Substance P (SP) is a neuropeptide with neuroimmunoregulatory activity that may play a role in susceptibility to infection. Human mast cells, which are important in innate immune responses, were analysed for their responses to pathogen-associated molecules via Toll-like receptors (TLRs) in the presence of SP. Human cultured mast cells (LAD2) were activated by SP and TLR ligands including lipopolysaccharide (LPS), Pam3CysSerLys4 (Pam3CSK4) and lipoteichoic acid (LTA), and mast cell leukotriene and chemokine production was assessed by enzyme-linked immunosorbent assay (ELISA) and gene expression by quantitative PCR (qPCR). Mast cell degranulation was determined using a β-hexosaminidase (β-hex) assay. SP treatment of LAD2 up-regulated mRNA for TLR2, TLR4, TLR8 and TLR9 while anti-immunoglobulin E (IgE) stimulation up-regulated expression of TLR4 only. Flow cytometry and western blot confirmed up-regulation of TLR2 and TLR8. Pretreatment of LAD2 with SP followed by stimulation with Pam3CSK4 or LTA increased production of leukotriene C4 (LTC(4) ) and interleukin (IL)-8 compared with treatment with Pam3CSK4 or LTA alone (>2-fold; P<0·01). SP alone activated 5-lipoxygenase (5-LO) nuclear translocation but also augmented Pam3CSK4 and LTA-mediated 5-LO translocation. Pam3CSK4, LPS and LTA did not induce LAD2 degranulation. SP primed LTA and Pam3CSK4-mediated activation of JNK, p38 and extracellular-signal-regulated kinase (ERK) and activated the nuclear translocation of c-Jun, nuclear factor (NF)-κB, activating transcription factor 2 (ATF-2) and cyclic-AMP-responsive element binding protein (CREB) transcription factors. Pretreatment with SP followed by LTA stimulation synergistically induced production of chemokine (C-X-C motif) ligand 8 (CXCL8)/IL-8, chemokine (C-C motif) ligand 2 (CCL2)/monocyte chemotactic protein 1 (MCP-1), tumour necrosis factor (TNF) and IL-6 protein. SP primes TLR2-mediated activation of human mast cells by up-regulating TLR expression and potentiating signalling pathways associated with TLR. These results suggest that neuronal responses may influence innate host defence responses.

Cervical and vaginal cytokine determinations in pregnant women: methodologic issues

Investigations of the role cytokines play in preterm birth are complicated by a number of methodologic issues that arise as to the most feasible and efficient methods to measure cytokines. The purpose of this article is to review methodologic issues surrounding the measurement of vaginal and cervical cytokines, specifically IL-1beta, IL-6, and TNF-alpha, in pregnant women experiencing preterm labor. Specifically, two quantification methods, weight and protein assay, and cytokine specimens from two different sites, vaginal and cervical, were compared. There were no significant correlations between cytokine levels using the protein versus weight quantification method. The weight method had more negative values and thus the protein quantification method was more accurate. There were high correlations between cervical and vaginal IL-1beta levels and IL-6 levels, but cervical and vaginal TNF-alpha levels were not correlated.

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

The cornea is one of the most highly innervated tissues in the mammalian host. We hypothesized changes to cornea innervation through chemical sympathectomy would significantly alter the host response to the neurotropic viral pathogen, herpes simplex virus type 1 (HSV-1) following ocular infection. Mice treated with 6-hydroxydopamine hydrobromide displayed reduced tyrosine hydroxylase-positive fibers residing in the cornea. Sympathectomized mice were also found to show a transient rise in virus recovered in infected tissues and succumbed to infection in greater numbers. Whereas there were no differences in infiltrating leukocyte populations including HSV-1-specific cytotoxic T lymphocytes in the infected tissue, an increase in substance P and a decrease in IFN-gamma levels in the trigeminal ganglion but not brain stem of sympathectomized mice were noted. Sympathectomized mice treated with the neurokinin-1 receptor antagonist L703,606 had delayed mortality implicating the involvement of substance P in HSV-1-mediated death.

‘Sensing’ autoimmunity in type 1 diabetes

Type 1 diabetes (T1D) results from autoimmune-mediated loss of insulin-producing beta-cells. Recent findings suggest that the events controlling T1D development are not only immunological, but also neuronal in nature. In the non-obese diabetic (NOD) mouse model of T1D, a mutant sensory neuron channel, TRPV1, initiates chronic, progressive beta-cell stress, inducing islet cell inflammation. This novel mechanism of organ-specific damage requires a permissive, autoimmune-prone host, but ascribes tissue specificity to the local secretory dysfunction of sensory afferent neurons. In NOD mice, normalizing this neuronal function by administration of the neurotransmitter substance P clears islet cell inflammation, reduces insulin resistance and restores normoglycemia. Here, we discuss this neuro-immuno-endocrine model, its implications and the involvement of sensory neurons in other autoimmune disorders. These developments might provide novel neuronal-based therapeutic interventions, particularly in diabetes.

Therapeutic dendritic cell vaccination with Ag coupled to cholera toxin in combination with intratumoural CpG injection leads to complete tumour eradication in mice bearing HPV 16 expressing tumours

We have evaluated whether cholera toxin (CT) can enhance the efficiency of therapeutic dendritic cell (DC) vaccination in mice bearing a human papilloma virus (HPV) 16 antigen (Ag) expressing tumour. Mice were therefore injected with the TC-1 cancer cell line expressing E6 and E7, which are the major oncogenic proteins produced in HPV-induced cervical cancer, and they were then vaccinated with Ag pulsed DCs. While vaccination with E7 pulsed DCs had no impact on tumour growth, DCs pulsed with CT conjugated E7 (CT-E7) significantly reduced tumour size. However, this treatment was only able to eradicate the tumour in 11% of the affected animals. For complete tumour eradication, combinational therapy with CT-E7 pulsed DCs and local treatment of the tumour with CpG oligodeoxynucleotides (CpG) was required. Combinational therapy was associated with increased expression of MHC I and MHC II and increased levels of chemokine production in the tumour. These results suggest that combined treatment with CT-Ag pulsed DCs and local CpG administration offers an efficient strategy to eradicate an already existing HPV-E7 expressing tumour in mice.

A triple entente: virus, neurons, and CD8+ T cells maintain HSV-1 latency

Herpes simplex virus type 1 (HSV-1) travels by retrograde transport to sensory ganglia where latency is established. Recurrent disease results from virus reactivation and anterograde transport to nerve termini. Prevention of reactivation requires a complex interplay among virus, neuron, and immune response. Study of this tripartite relationship suggests possible interaction, and even communication among these components, that direct an immune response that allows for control of virus while preserving the viability of host tissue. Exciting new evidence supports the view that CD8+ effector T cells employ both lytic granule-dependent and interferon gamma-dependent effector mechanisms in maintaining HSV-1 latency.

The effect of substance P on nitric oxide production by HSV-1 infected macrophages

The regulatory role of neuro-immune pathways in various infectious disease states is an interesting area of investigation due to its important therapeutic potential. In this study the effect of substance P (SP) on nitric oxide (NO) production of HSV-infected macrophages and its relation with incubation time and also the cytopathic effect of virus in the presence of SP are considered. As we have observed, substance P enhances NO production both in HSV- and mock-infected macrophages and this effect has been diminished or disappeared after 24 h. It has also been observed that SP enhances the cytopathic effect of HSV in a time dependent manner with the most effect at 10 h after stimulation with SP. We have also observed that HSV-1 cytopathic effect has not been significantly affected by pretreatment of macrophages with SP (2, 10 or 24 h before HSV infection). It can be concluded that the neurotransmitter SP has a significant role in modulating macrophage function and thus innate immunity processes in healthy and HSV-infected cells.

Role of IFN-alpha/beta signaling in the prevention of genital herpes virus type 2 infection

This study has shown that IFN-alpha/beta signaling is crucial for combating primary herpes simplex virus type 2 (HSV-2) infection and for responding to immunotherapy using ligands to TLR3, 7 and 9, but not for vaccine-induced immunity. Both genital viral replication and the disease progression were enhanced in HSV-2-infected mice lacking the IFN-alpha/beta receptor (IFN-alpha/betaR-/-). IFN-alpha/betaR-/- mice were, however, able to mount a normal HSV-2-specific Th1 response and acquired sterilizing immunity following vaccination. Anti-viral treatments using agonists to TLR3, 7 and 9 by administration of synthetic dsRNA, imiquimod and oligonucleotides containing unmethylated CpG motifs, respectively, were strongly dependent on IFN-alpha/beta receptor signaling for their efficacy. Even though all treatments had a weak impact on local vaginal viral replication in infected IFN-alpha/betaR-/- animals, they did not affect disease progression or mortality in these animals as opposed to wild type controls where all three treatments reduced viral replication as well as disease severity and mortality. Lack of IFN-alpha/betaR signaling also blocked production of IFN-gamma and TNF-alpha in response to TLR9 activation. These studies have shown that IFN-alpha/beta receptor signaling is important for multiple events in the anti-viral defense.

MHC expression and chemokine production in the murine vagina following intra-vaginal administration of ligands to toll-like receptors 3, 7 and 9

The expression of MHC class I, MHC class II and the chemokines IP-10, MIP-1alpha, RANTES, fractalkine and I-TAC has been analyzed after intra-vaginal treatment with three synthetic toll-like receptors (TLR) agonists-double-stranded RNA (poly I:C), imiquimod and CpG-rich oligonucleotides (CpG-ODN). These compounds act mainly through TLR3, TLR7 and TLR9, respectively. CpG-ODN induced an accumulation of leucocytes in the vagina, and a strong up-regulation of MHC class I expression on both leucocytes and epithelial cells. Imiquimod and poly I:C induced a weak MHC class I up-regulation in the epithelium but not in the lamina propria. Neither treatment had any profound effect on expression of MHC class II on epithelial cells but poly I:C and to a lesser extent CpG-ODN, up-regulated MHC class II staining intensity which, in the case of CpG-ODN, treatment, was associated with a strong accumulation of CD11c-positive dendritic cells. All three treatments induced an early (8h) but transient IP-10 response. Imiquimod and CpG-ODN, but not poly I:C induced an early MIP-1alpha response which remained for at least 7 days in CpG-ODN-treated animals but not in imiquimod-treated mice. Poly I:C and CpG-ODN, but not imiquimod, induced significant levels of RANTES at different time-points post-treatment. None of the treatments induced any significant changes in the levels of fractalkine, I-TAC or IFN-alpha. These studies have implications for the manipulation of the genital immune response and also improving the outcome of vaginal immunotherapy.

Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ

This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.