Nerve growth factor and the immune system: old and new concepts in the cross-talk between immune and resident cells during pathophysiological conditions

The causal effects of circulating cytokines on sepsis: a Mendelian randomization study

Background

In observational studies, sepsis and circulating levels of cytokines have been associated with unclear causality. This study used Mendelian randomization (MR) to identify the causal direction between circulating cytokines and sepsis in a two-sample study.

Methods

An MR analysis was performed to estimate the causal effect of 41 cytokines on sepsis risk. The inverse-variance weighted random-effects method, the weighted median-based method, and MR-Egger were used to analyze the data. Heterogeneity and pleiotropy were assessed using MR-Egger regression and Cochran's Q statistic.

Results

Genetically predicted beta-nerve growth factor (OR = 1.12, 95% CI [1.037-1.211], P = 0.004) increased the risk of sepsis, while RANTES (OR = 0.92, 95% CI [0.849-0.997], P = 0.041) and fibroblast growth factor (OR = 0.869, 95% CI [0.766-0.986], P = 0.029) reduced the risk of sepsis. These findings were robust in extensive sensitivity analyses. There was no clear association between the other cytokines and sepsis risk.

Conclusion

The findings of this study demonstrate that beta-nerve growth factor, RANTES, and fibroblast growth factor contribute to sepsis risk. Investigations into potential mechanisms are warranted.

Linking tumor immune infiltrate and systemic immune mediators to treatment response and prognosis in advanced cervical cancer

Cervical cancer (CC) poses a significant burden on individuals in developing regions, exhibiting heterogeneous responses to standard chemoradiation therapy, and contributing to substantial mortality rates. Unraveling host immune dynamics holds promise for innovative therapies and discovery of clinically relevant biomarkers. We studied prospectively locally advanced CC patients pre-treatment, stratifying them as responders (R) or non-responders (NR). R patients had increased tumor-infiltrating lymphocytes (TILs), while NR patients showed elevated PD-1 scores, CD8+ and PD-L2+ TILs, and PD-L1 immune reactivity. NR patients exhibited higher systemic soluble mediators correlating with TIL immune markers. R patients demonstrated functional polarization of CD4 T cells (Th1, Th2, Th17, and Treg), while CD8+ T cells and CD68+ macrophages predominated in the NR group. Receiver operating characteristic analysis identified potential CC response predictors, including PD-L1-immunoreactive (IR) area, PD-L2, CD8, FGF-basic, IL-7, IL-8, IL-12p40, IL-15, and TNF-alpha. Dysfunctional TILs and imbalanced immune mediators contribute to therapeutic insufficiency, shedding light on local and systemic immune interplay. Our study informs immunological signatures for treatment prediction and CC prognosis.

Developing a trans-multisynaptic tracer to map the neural circuit of recovered sciatic nerve after treatment with nerve growth factor

Nerve growth factor (NGF) has been shown to support the survival and differentiation of neurons. In this study, we first developed a retrograde trans-multisynaptic tracer PRV580 expressing the mCherry fluorescent protein based on pseudorabies virus Bartha strain to map the neural circuit of sciatic nerve. Secondly, the newly developed PRV580 was used to map the neural circuit of the recovering sciatic nerve upon treatment with NGF. Our results showed that red signals from PRV580 were observed in various brain regions. Among these regions, many areas of the pyramidal system and the extra-pyramidal system had been mapped, accounting for as much as 56.8 % of the total inputs. Furthermore, we found that NGF could significantly increase the ratio of total input (29.05 %) compared to PBS (3.65 %), indicating that NGF indeed can aid in the repair of injured sciatic nerve. These findings indicated that NGF has therapeutic ability for the treatment of peripheral nerve injuries and virus-based tracers can be used to monitor the recovery.

Lessons from the Cerebrospinal Fluid Analysis of HTLV-1-Infected Individuals: Biomarkers of Inflammation for HAM/TSP Development

HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a neurodegenerative disease that leads to motor impairment due to a chronic inflammatory process in the central nervous system (CNS). However, the HAM/TSP pathogenesis is not completely clear, and biomarkers to define the disease prognosis are still necessary. Thus, we aimed to identify biomarkers for HAM/TSP and potential mechanisms involved in disease development. To that end, the concentrations of VILIP-1, BDNF, VEGF, β-NGF, TGF-β1, fractalkine/CX3CL1, IL-6, IL-18, and TNF-α, and the soluble forms of TREM-1, TREM-2, and RAGE, were assessed using a multiplex bead-based immunoassay in paired cerebrospinal fluid (CSF) and serum samples from HAM/TSP patients (n = 20), asymptomatic HTLV-1 carriers (AC) (n = 13), and HTLV-1-seronegative individuals (n = 9), with the results analyzed according to the speed of HAM/TSP progression. HAM/TSP patients had elevated fractalkine in the serum but not in the CSF, particularly those with low neuroinflammatory activity (CSF/serum ratio of neopterin <1 and of CXCL10 < 2). HAM/TSP patients with normal CSF levels of neurofilament light chain (NfL) showed elevated β-NGF in serum, and serum BDNF levels were increased in HTLV-1-infected individuals, particularly in HTLV-1 AC. Both HTLV-1 AC and HAM/TSP patients had lower TGF-β1 levels in CSF compared to uninfected individuals, and HAM/TSP patients with active CNS inflammation showed higher CSF levels of IL-18, which correlated with markers of inflammation, neuronal death, and blood−brain-barrier permeability. Although none of the factors evaluated were associated with the speed of HAM/TSP progression, reduced TGF-β1 levels in CSF suggest that suppressive responses to control subclinical and/or active neurodegeneration are impaired, while increased CSF IL-18 indicates the involvement of inflammasome-mediated mechanisms in HAM/TSP development.

Druggable Targets and Compounds with Both Antinociceptive and Antipruritic Effects

Pain and itch are both important manifestations of various disorders, such as herpes zoster, atopic dermatitis, and psoriasis. Growing evidence suggests that both sensations have shared mediators, overlapping neural circuitry, and similarities in sensitization processes. In fact, pain and itch coexist in some disorders. Determining pharmaceutical agents and targets for treating pain and itch concurrently is of scientific and clinical relevance. Here we review the neurobiology of pain and itch and discuss the pharmaceutical targets as well as novel compounds effective for the concurrent treatment of these sensations.

Role of NGF and its receptors in wound healing (Review)

Wound healing is an important and complicated process that includes four highly integrated and overlapping phases, haemostasis, inflammation, proliferation and tissue remodelling. Nerve growth factor (NGF) was the first member of a family of neurotrophic factors to be discovered, and is an essential neurotrophic factor for the development and maintenance of the central and peripheral nervous systems. Several studies have proposed that NGF and its receptors, tropomyosin-related kinase receptor 1 and NGF receptor, are involved in the wound healing process, and are important components of the healing of several wounds both in vivo and in vitro. Topical application of NGF significantly promotes the healing of different types of wounds, including diabetic foot ulcers, pressure ulcers and corneal wounds. The present review summarizes the status of NGF and its receptors in current literature, and discusses data obtained in the last few years on the healing action of NGF in cutaneous, corneal and oral wounds.

Antiviral properties of placental growth factors: A novel therapeutic approach for COVID-19 treatment

The current challenge of the COVID-19 pandemic is complicated by the limited therapeutic options against the virus, with many being anecdotal or still undergoing confirmatory trials, underlining the urgent need for novel strategies targeting the virus. The pulmotropic virus causes loss of oxygenation in severe cases with acute respiratory distress syndrome (ARDS) and need for mechanical ventilation. This work seeks to introduce placental extract-derived biologically active components as a therapeutic option and highlights their mechanism of action relevant to COVID-19 virus. Human placenta has been used in clinical practice for over a century and there is substantial experience in clinical applications of placental extract for different indications. Aqueous extract of human placentacontains growth factors, cytokines/chemokines, natural metabolic and other compounds, anti-oxidants, amino acids, vitamins, trace elements and biomolecules, which individually or in combination show accelerated cellular metabolism, immunomodulatory and anti-inflammatory effects, cellular proliferation and stimulation of tissue regeneration processes. Placental extract treatment is proposed as a suitable therapeutic approach consideringthe above properties which could protect against initial viral entry and acute inflammation of alveolar epithelial cells, reconstitute pulmonary microenvironment and regenerate the lung. We reviewed useful therapeutic information of placental biomolecules in relation to COVID-19 treatment. We propose the new approach of using placental growth factors, chemokines and cytokine which will execute antiviral activity in coordination with innate and humoral immunity and improve patient's immunological responses to COVID-19. Executing a clinical trial using placental extract as preventive, protective and/or therapeutic approach for COVID-19treatment could advance the development of a most promising therapeutic candidate that can join the armamentaria against the COVID-19 virus.

Neurotrophic factors and nerve growth factor in ocular allergy

PURPOSE OF REVIEW

During allergic reaction, nervous and immune systems mutually interact through release of mediators, including neurotrophic factors and nerve growth factor (NGF). These mediators modulate allergic reaction through binding their receptors expressed by immune and structural cells and by stimulating neuropeptide release by nerves. The role of neuropeptides and NGF has been demonstrated in allergic asthma and rhinitis, and, to a lesser extent, in allergic conjunctivitis. The aim of this review are to elucidate the evidence of the role of NGF and neuropeptides in the pathogenesis of allergic conjunctivitis.

RECENT FINDINGS

NGF modulates allergic reaction by stimulating release of cytokines, inflammatory mediators and neuropeptides by immune and structural cells and nerve endings at the site of inflammation. Evidence showed that local and systemic NGF levels increase in patients with allergic conjunctivitis, including allergic rhinoconjuncivitis, vernal keratoconjunctivitis and atopic keratoconjunctivitis. We recently described an increase of conjunctival p75NTR expression in patients with allergic rhinoconjuncivitis, and an increase of tear levels of NGF after conjunctival provocation test with allergen.

SUMMARY

NGF modulates ocular allergic reaction. Increasing understanding of the role of neuropeptides in allergic conjunctivitis may pave the way to the development of novel therapeutic approaches and improvement of patients' management.

Nerve growth factor promotes ASIC1a expression via the NF-κB pathway and enhances acid-induced chondrocyte apoptosis

Nerve growth factor (NGF) is a neurotrophic factor that is thought to have a broad role in the nervous system and tumors, and has recently been described as a mediator of inflammation. It is not clear whether or not NGF participates in apoptosis of articular chondrocytes. In this study, we determined if NGF affects ASIC1a expression and NF-κB P65 activation in rat chondrocytes, and measured the effectiveness of NGF on apoptotic protein expression in acid-induced chondrocytes. NGF was shown to up-regulate the level of ASIC1a in a dose- and time-dependent fashion. Simultaneously, NGF activated NF-κB P65 in chondrocytes. Additionally, the elevated ASIC1a expression induced by NGF was eliminated by the NF-κB inhibitor (PDTC) in chondrocytes. Moreover, NGF reduced cell viability and induced LDH release under the premise of acid-induced articular chondrocytes. Furthermore, NGF could enhance cleaved-caspase 9 and cleaved-PARP expression in acid-pretreated chondrocytes, and which could be inhibited by using psalmotoxin 1(PcTX1) or PDTC. Together, these results indicated that NGF may up-regulate ASIC1a expression through the NF-κB signaling pathway, and further promote acid-induced apoptosis of chondrocytes.

Neutralization of nerve growth factor (NGF) inhibits the Th2 response and protects against the respiratory syncytial virus (RSV) infection

Increasing evidence suggests that respiratory syncytial virus (RSV) infection during the early life is an important risk factor for the development of asthma. RSV infection is associated with neurogenic inflammation in the airways along with the increased expression of nerve growth factor (NGF). However, the role of NGF in RSV infection is not clear. In this study, we infected the rat with RSV and treated these animals with anti-NGF neutralization antibody. We found that anti-NGF treatment significantly alleviated the lung inflammation as evidenced by decreased inflammatory infiltration and decreased airway resistance. Importantly, anti-NGF treatment resulted in increased Th1, but decreased Th2 immune responses, and facilitated the viral control in the tissues and blood. Therefore, NGF inhibited Th2 but increased Th1 responses in RSV infection. Pharmacological intervention of NGF signaling during severe RSV infections could prevent or decrease further asthma symptoms.

Changes in Plasma β-NGF and Its Receptors Expression on Peripheral Blood Monocytes During Alzheimer's Disease Progression

Alzheimer's disease (AD), the most common cause of dementia, is characterized by the deposition of extracellular amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles, and by neuroinflammation. During the pathogenesis of AD, monocyte-macrophage lineage cells become increasingly ineffective in clearing Aβ deposits, less able to differentiate, and shift toward pro-inflammatory processes. Beta-nerve growth factor (β-NGF) and its receptors, TrKA and p75NTR, produce several biological responses, including cell apoptosis and survival, and inflammation. In the central nervous system, the involvement of these receptors in several critical hallmarks of AD is well known, but their role in circulating monocytes during the progression of dementia is unclear. We investigated the relationship between plasma β-NGF concentration and TrkA/p75NTR receptor expression in monocytes of patients with mild cognitive impairment (MCI), mild AD, and severe AD. We observed that plasma β-NGF concentration was increased with a higher expression of TrKA, but not of p75NTR, in monocytes from patients with MCI and mild AD, whereas β-NGF concentration and TrKA expression were decreased and p75NTR expression was increased, associated with caspase 3-mediated apoptosis, in patients with severe AD. In our study, we show evidence of variation in plasmatic β-NGF and monocytic TrkA/p75NTR receptor expression during the progression of dementia. These novel findings add evidence to support the hypothesis for the involvement of β-NGF and its receptors on monocytes during AD progression.

β-NGF and β-NGF receptor upregulation in blood and synovial fluid in osteoarthritis

Osteoarthritis (OA) of the knee is the most common form of non-traumatic joint disease. Previous studies have shown the involvement of β-NGF and its receptors TrKA and p75NTR in OA-related pain, but their role in its pathogenesis is still unclear. The aim of our study was to investigate the amount of β-NGF and the expression levels of its receptors on cells isolated from synovial fluid and blood from OA patients who had undergone total knee arthroplasty, in order to check any possible correlation with the disease staging. Our results show a progressive stage-related increase of β-NGF and its receptors both in serum and synovial fluid. Furthermore, with respect to control subjects, OA patients show an increased amount of inflammatory monocytes along with an increased expression of β-NGF, TrKA and p75NTR. In conclusion, our study suggests a stage-related modulation of β-NGF and its receptors in the inflammatory process of OA.

Expression and signaling of NGF in the healthy and injured retina

This review summarizes the present knowledge concerning the retinal localization of the nerve growth factor (NGF), its precursor proNGF, and the receptors TrkA and p75NTR in the developing and mature rodent retina. We further discuss the changes in the expression of NGF and the receptors in experimental models of retinal disorders and diseases like inherited retinitis pigmentosa, retinal detachment, glaucoma, and diabetic retinopathy. Since proNGF is now recognized as a bioactive signaling molecule which induces cell death through p75NTR activation, the role of proNGF in the induction of retinal cell loss under neurodegenerative conditions is also highlighted. In addition, we present the evidences for a potential therapeutic intervention with NGF for the treatment of retinal neurodegenerative diseases. Different strategies have been developed and experimentally tested in mice and rats in order to reduce cell loss and Müller cell gliosis, e.g., increasing the availability of endogenous NGF, administration of exogenous NGF, activation of TrkA, and inhibition of p75NTR. Here, we discuss the several lines of evidence supporting a protective effect of NGF on retinal cell loss, with specific emphasis on photoreceptor and retinal ganglion cell degeneration. A better understanding of the mechanisms underlying the effects of NGF and proNGF in the modulation of neurodegeneration and gliosis in the retina will help to develop efficient therapeutic strategies for various retinal diseases.

Nerve Growth Factor: A Focus on Neuroscience and Therapy

Nerve growth factor (NGF) is the firstly discovered and best characterized neurotrophic factor, known to play a critical protective role in the development and survival of sympathetic, sensory and forebrain cholinergic neurons. NGF promotes neuritis outgrowth both in vivo and in vitro and nerve cell recovery after ischemic, surgical or chemical injuries. Recently, the therapeutic property of NGF has been demonstrated on human cutaneous and corneal ulcers, pressure ulcer, glaucoma, maculopathy and retinitis pigmentosa. NGF eye drops administration is well tolerated, with no detectable clinical evidence of systemic or local adverse effects. The aim of this review is to summarize these biological properties and the potential clinical development of NGF.

Nerve growth factor: role in growth, differentiation and controlling cancer cell development

Recent progress in the Nerve Growth Factor (NGF) research has shown that this factor acts not only outside its classical domain of the peripheral and central nervous system, but also on non-neuronal and cancer cells. This latter observation has led to divergent hypothesis about the role of NGF, its specific distribution pattern within the tissues and its implication in induction as well as progression of carcinogenesis. Moreover, other recent studies have shown that NGF has direct clinical relevance in certain human brain neuron degeneration and a number of human ocular disorders. These studies, by suggesting that NGF is involved in a plethora of physiological function in health and disease, warrant further investigation regarding the true role of NGF in carcinogenesis. Based on our long-lasting experience in the physiopathology of NGF, we aimed to review previous and recent in vivo and in vitro NGF studies on tumor cell induction, progression and arrest. Overall, these studies indicate that the only presence of NGF is unable to generate cell carcinogenesis, both in normal neuronal and non-neuronal cells/tissues. However, it cannot be excluded the possibility that the co-expression of NGF and pro-carcinogenic molecules might open to different consequence. Whether NGF plays a direct or an indirect role in cell proliferation during carcinogenesis remains to demonstrate.

Progress in corneal wound healing

Corneal wound healing is a complex process involving cell death, migration, proliferation, differentiation, and extracellular matrix remodeling. Many similarities are observed in the healing processes of corneal epithelial, stromal and endothelial cells, as well as cell-specific differences. Corneal epithelial healing largely depends on limbal stem cells and remodeling of the basement membrane. During stromal healing, keratocytes get transformed to motile and contractile myofibroblasts largely due to activation of transforming growth factor-β (TGF-β) system. Endothelial cells heal mostly by migration and spreading, with cell proliferation playing a secondary role. In the last decade, many aspects of wound healing process in different parts of the cornea have been elucidated, and some new therapeutic approaches have emerged. The concept of limbal stem cells received rigorous experimental corroboration, with new markers uncovered and new treatment options including gene and microRNA therapy tested in experimental systems. Transplantation of limbal stem cell-enriched cultures for efficient re-epithelialization in stem cell deficiency and corneal injuries has become reality in clinical setting. Mediators and course of events during stromal healing have been detailed, and new treatment regimens including gene (decorin) and stem cell therapy for excessive healing have been designed. This is a very important advance given the popularity of various refractive surgeries entailing stromal wound healing. Successful surgical ways of replacing the diseased endothelium have been clinically tested, and new approaches to accelerate endothelial healing and suppress endothelial-mesenchymal transformation have been proposed including Rho kinase (ROCK) inhibitor eye drops and gene therapy to activate TGF-β inhibitor SMAD7. Promising new technologies with potential for corneal wound healing manipulation including microRNA, induced pluripotent stem cells to generate corneal epithelium, and nanocarriers for corneal drug delivery are discussed. Attention is also paid to problems in wound healing understanding and treatment, such as lack of specific epithelial stem cell markers, reliable identification of stem cells, efficient prevention of haze and stromal scar formation, lack of data on wound regulating microRNAs in keratocytes and endothelial cells, as well as virtual lack of targeted systems for drug and gene delivery to select corneal cells.

Molecular immunology of allergic conjunctivitis

PURPOSE OF REVIEW

Successful treatment of allergic eye disease depends on understanding the pathophysiology of ocular allergy. Thus, in this review, recent experimental and clinical research that has provided significant information about the immunopathology of allergic eye disease will be discussed.

RECENT FINDINGS

Recently, role of various cells, cytokines and chemokines has been scrutinized in the immunopathogenesis of ocular allergy. In this respect, current research highlights contribution of special molecules and cells in the development and clinical features of immunoglobulin E (IgE) and T-cell-mediated eye allergies.

SUMMARY

Recent findings in molecular immunology of ocular allergy, which comprise complex inflammatory conditions of the conjunctiva, have enabled us to better understand the pathophysiology of these diseases and have aided in the potential development of new therapeutic agents.

What can we learn about stroke from retinal ischemia models?

Retinal ischemia is a very useful model to study the impact of various cell death pathways, such as apoptosis and necrosis, in the ischemic retina. However, it is important to note that the retina is formed as an outpouching of the diencephalon and is part of the central nervous system. As such, the cell death pathways initiated in response to ischemic damage in the retina reflect those found in other areas of the central nervous system undergoing similar trauma. The retina is also more accessible than other areas of the central nervous system, thus making it a simpler model to work with and study. By utilizing the retinal model, we can greatly increase our knowledge of the cell death processes initiated by ischemia which lead to degeneration in the central nervous system. This paper examines work that has been done so far to characterize various aspects of cell death in the retinal ischemia model, such as various pathways which are activated, and the role neurotrophic factors, and discusses how these are relevant to the treatment of ischemic damage in both the retina and the greater central nervous system.

Therapeutic potential of andrographolide for treating endometriosis

BACKGROUND

Mounting evidence shows that nuclear factor-κB (NF-κB) plays an important role in endometriosis. We therefore evaluated the therapeutic potential of andrographolide, an NF-κB inhibitor.

METHODS

Primary cell cultures were performed using ectopic endometrial tissue specimens and their homologous eutopic endometrial specimens from 16 women with endometriosis, as well as control samples from 4 women without endometriosis. Andrographolide was evaluated for an effect on cell proliferation and cell cycle, DNA-binding activity of NF-κB and expression of cyclooxygenase-2 (COX-2) and tissue factor (TF). In a rat model of endometriosis, andrographolide treatment was evaluated for an effect on lesion size, hotplate response latency and expression of phosphorylated p50 and p65, COX-2 and nerve growth factor (NGF) in ectopic endometrium.

RESULTS

Andrographolide dose dependently suppressed proliferation and cell cycle progression, attenuated DNA-binding activity of NF-κB in endometriotic stromal cells and inhibited COX-2 and TF expression. In the rat experiment, induced endometriosis resulted in reduced response latency. Andrographolide treatment significantly reduced lesion size in a dose-dependent manner and significantly increased response latency. Andrographolide treatment also significantly reduced immunoreactivity of COX-2, phosphorylated p50 and p65, and NGF in ectopic endometrium.

CONCLUSIONS

Treatment with andrographolide significantly suppresses the growth of ectopic endometrium in vitro and in vivo, and results in a significant improvement in generalized hyperalgesia in rats with induced endometriosis. Therefore, andrographolide may be cytoreductive and may relieve pain symptoms in women with endometriosis. With excellent safety and cost profiles, andrographolide could be a promising therapeutic agent for endometriosis.

Natural antibodies against nerve growth factor inhibit in vitro prostate cancer cell metastasis

Prostate cancer is a major cause of death in older men, and bone metastasis is the primary cause of morbidity and mortality in prostate cancer. Prostate is an abundant source of nerve growth factor (NGF) that is secreted by malignant epithelial cells and utilized as an important autocrine factor for growth and metastasis. We previously showed that intravenous gammaglobulin (IVIg) contains natural antibodies against NGF, which inhibit growth and differentiation of the NGF-dependent cell line PC-12. In the present study, we examined the effects of these natural antibodies on in vitro migration or metastasis of two prostate cancer cell lines namely DU-145 and PC-3. Cancer cell migration was assessed using these cell lines in the upper chambers of Matrigel invasion chambers. The effects of IVIg and affinity-purified anti-NGF antibodies on cell migration through membrane into the lower chamber were assessed in dose/response experiments by a colorimetric method. Affinity-purified natural IgG anti-NGF antibody inhibited DU-145 migration by 38% (p = 0.01) and PC-3 migration by 25% (p = 0.02); whereas, a monoclonal anti-NGF antibody inhibited DU-145 migration by 40% (p = 0.01) and PC-3 migration by 37% (p = 0.02), at the same concentration. When IVIg was depleted of NGF-specific IgG by affinity chromatography, there was no significant inhibition of migration of the DU-145 and PC-3 cells at a concentration of 1 mg/well. Removal of the NGF-specific antibody from the IVIg was also demonstrated by a lack of effect on PC-12 cell differentiation. Therefore, IVIg is able to inhibit the migration of prostate cancer cell lines, through Matrigel chambers in vitro, only when the natural NGF-specific antibodies actively are present in IVIg.

Mouse natural killer (NK) cells express the nerve growth factor receptor TrkA, which is dynamically regulated

BACKGROUND

Nerve growth factor (NGF) is a neurotrophin crucial for the development and survival of neurons. It also acts on cells of the immune system which express the NGF receptors TrkA and p75(NTR) and can be produced by them. However, mouse NK cells have not yet been studied in this context.

METHODOLOGY/PRINCIPAL FINDINGS

We used cell culture, flow cytometry, confocal microscopy and ELISA assays to investigate the expression of NGF receptors by NK cells and their secretion of NGF. We show that resting NK cells express TrkA and that the expression is different on NK cell subpopulations defined by the relative presence of CD27 and CD11b. Expression of TrkA is dramatically increased in IL-2-activated NK cells. The p75(NTR) is expressed only on a very low percentage of NK cells. Functionally, NGF moderately inhibits NK cell degranulation, but does not influence proliferation or cytokine production. NK cells do not produce NGF.

CONCLUSIONS/SIGNIFICANCE

We demonstrate for the first time that mouse NK cells express the NGF receptor TrkA and that this expression is dynamically regulated.

The role of neurotrophins in the pathophysiology of allergic rhinitis

PURPOSE OF REVIEW

Allergic rhinitis is characterized by allergic airway inflammation and a hyperresponsiveness to nonspecific stimuli which is partly neuronally controlled. In this regard, neurotrophins are prime candidates as mediators of neuronal and immunological plasticity and they will be the focus of the current review.

RECENT FINDINGS

Neurotrophins including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are expressed in the nasal mucosa. The majority of NGF expression has been found in eosinophil granulocytes, the glandular apparatus and peripheral nerves. As shown recently, nasal allergen provocation upregulates BDNF expression in nasal mucosa and NGF expression on peripheral nerves and nasal lavage in patients with allergic rhinitis. In this regard, increased BDNF expression positively correlates with the maximum increase in total nasal symptom score. The neurotrophin receptors including pan-neurotrophin receptor p75, tyrosine kinase A (trkA) and trkB are expressed in nasal tissue. TrkA is expressed on endothelial, p75 on peripheral nerves and trkB on nasal mucosa mast cells that decreases after allergen provocation. The expression of these neurotrophin receptors is increased on peripheral blood eosinophils in allergic rhinitis compared with nonatopic controls. Further, BDNF and NGF exert immunomodulatory functions on eosinophils of patients with allergic rhinitis. Finally, eosinophils of patients with allergic rhinitis are capable of BDNF and NGF production.

SUMMARY

Neurotrophins represent prime candidates in upper airway pathophysiology in allergic rhinitis. Research on neurotrophins in allergic rhinitis is thus becoming a progressively more exciting field and may reveal new and promising therapeutic options for the future.

Helminth infections associated with multiple sclerosis induce regulatory B cells

OBJECTIVE

To assess the importance of B-cell control during parasite infections in multiple sclerosis (MS) patients.

METHODS

Peripheral blood CD19+ B cells from 12 helminth-infected MS patients, 12 MS patients without infection, 10 patients infected with Trypanosoma cruzi, 8 subjects infected with Paracoccidioides brasiliensis, and 12 healthy control subjects were purified using magnetic cell sorting. Interleukin (IL)-4, IL-6, IL-10, tumor necrosis factor-alpha, lymphotoxin, transforming growth factor-beta, brain-derived neurotrophic factor, and nerve growth factor secretion were evaluated after stimulation with CDw32 L cells and CD40 antibody using enzyme-linked immunosorbent assays. The production of anti-myelin oligodendrocyte glycoprotein IgG and IgM antibodies was evaluated by enzyme-linked immunosorbent spot assays. Cell phenotype was assessed by flow cytometry.

RESULTS

Helminth infections in MS patients created a B-cell population producing high levels of IL-10, dampening harmful immune responses through a mechanism mediated, at least in part, by the ICOS-B7RP-1 pathway. The IL-10-producing B-cell phenotype detected expressed high levels of CD1d and was similar to the one observed in mature naive B2 cells (namely, CD11b(-), CD5(-), CD27(-), and IgD+). Moreover, B cells isolated from helminth-infected MS patients also produced greater amounts of brain-derived neurotrophic factor and nerve growth factor compared with those of normal subjects, T. cruzi-infected subjects, P. brasiliensis-infected subjects, or uninfected MS patients, raising the possibility that these cells may exert a neuroprotective effect on the central nervous system.

INTERPRETATION

Increased production of B-cell-derived IL-10 and of neurotrophic factors are part of the parasite's regulation of host immunity and can alter the course of MS, potentially explaining environmental-related MS suppression observed in areas with low disease prevalence.

Modulation of neurotrophin and neurotrophin receptor expression in nasal mucosa after nasal allergen provocation in allergic rhinitis

BACKGROUND

Patients with allergic rhinitis (AR) feature both allergic airway inflammation and a hyperresponsiveness to nonspecific stimuli which is partly neuronally controlled. Still, it is unclear whether or not neurotrophins are involved in airway pathophysiology of AR and in nasobronchial interaction.

METHODS

Nine AR patients with mono-allergy to grass pollen and nine healthy controls underwent nasal allergen provocation (NP). Serum samples, nasal and bronchial biopsies were taken before (T(0)) and 24 h after (T(24)) NP. Pan-neurotrophin receptor p75(NTR), tyrosine kinase A (trkA), trkB, nerve growth factor (NGF), and brain-derived neurotrophic factor (BDNF) were assessed with immunohistochemistry, and NGF and BDNF levels with ELISA.

RESULTS

At T(24), BDNF and NGF were upregulated in nasal mucosa (P < 0.05) and increased in the peripheral blood of AR compared with T(0). The increase in nasal BDNF expression correlated positively with the maximum increase in total nasal symptom score in AR (P = 0.02). p75(NTR) was expressed on peripheral nerves and epithelial layer, trkA on endothelial cells, and trkB on mast cells. trkB + mast cells significantly decreased after NP in AR (P < 0.01). NP did not modulate p75(NTR) and trkA expression in nasal mucosa and had no effect on the expression of neurotrophins and receptors in bronchial mucosa.

CONCLUSION

This study shows that neurotrophins and their receptors are expressed in human airways. Allergic rhinitis was characterized by a modulation of BDNF, NGF, and trkB in nasal mucosa after NP and a correlation of nasal BDNF with the maximal increase of total nasal symptom score. Therefore, our data suggest that neurotrophins participate in upper-airway pathophysiology in AR, whereas their role in nasobronchial interaction remains unclear.

TLR4 signaling induces functional nerve growth factor receptor p75NTR on mouse dendritic cells via p38MAPK and NF-kappa B pathways

Many neuropeptides that are produced by immune cells have been shown to be involved in the pathogenesis of immunological disorders. Nerve growth factor (NGF) and its receptors are found to be widely expressed in the immune system and regulate both innate and adaptive immune responses. However, the underlying mechanisms by which NGF contributes to pathogenesis of inflammatory diseases remain to be fully understood. Dendritic cells (DCs) are potent initiator for inflammatory and immune responses upon recognization and activation of Toll-like receptors (TLRs). In this study, we demonstrated that stimulation with TLR ligand lipopolysaccharide (LPS), but not lipoteichoic acid (LTA), Poly (I:C) and CpG oligodeoxynucleotide (ODN), could significantly induce expression of NGF and NGF receptor p75(NTR) on mouse bone marrow-derived DCs (BMDCs) in vitro in dose- and time-dependent manners. The expression of NGF and NGF receptor p75(NTR) also increased on splenic DCs isolated from the mice injected with LPS in vivo. However, there was no such effect on DCs derived from TLR4-deficient mice, indicating the LPS-induced upregulation of NGF and p75(NTR) was TLR4 pathway-dependent. Furthermore, LPS-induced upregulation of NGF and p75(NTR) could be inhibited by p38MAPK inhibitor SB203580 and NF-kappaB inhibitor PDTC, suggesting TLR4-triggered activation of p38MAPK and NF-kappaB pathways are responsible for the process. Interestingly, NGF could markedly promote LPS-pretreated BMDCs to secret IL-12p40 and TNF-alpha, which could be abolished by pretreatment with p75(NTR) antagonist or the specific small interference RNA duplex targeting p75(NTR) (p75-siRNA), suggesting the inducible p75(NTR) is critical for the TLR4-initiated inflammatory effect of NGF on BMDCs. Thus, TLR4 signaling can induce expression of NGF and p75 (NTR) on DCs via activation of p38 MAPK and NF-kappaB pathways, suggesting that NGF may be involved in the pathogenesis of inflammatory diseases.

Nerve growth factor stimulates proliferation, adhesion and thymopoietic cytokine expression in mouse thymic epithelial cells in vitro

Thymic epithelial cells, which constitute a major component of the thymic microenvironment, provide a crucial signal for intrathymic T cell development and selection. Neuroimmune networks in the thymic microenvironment are thought to be involved in the regulation of T cell development. NGF is increasingly recognized as a potent immunomodulator, promoting "cross-talk" between various types of immune system cells. The present study clearly shows that NGF stimulates mouse thymic epithelial cell activities in vitro including cell proliferation, thymocyte adhesion to thymic epithelial cells, and the expression of cell adhesion molecules such as ICAM-1 and VCAM-1, and thymopoietic factors including IL-7, GM-CSF, SDF-1, TARC and TECK. Thus, our data are of considerable clinical importance showing that trophic NGF activity could be used to enhance the thymus regeneration and develop methods to improve host immunity when the immune function is depressed due to thymic involution.

Expression of nerve growth factor is upregulated in the rat thymic epithelial cells during thymus regeneration following acute thymic involution

Neuroimmune networks in the thymic microenvironment are thought to be involved in the regulation of T cell development. Nerve growth factor (NGF) is increasingly recognized as a potent immunomodulator, promoting "cross-talk" between various types of immune system cells. The present study describes the expression of NGF during thymus regeneration following acute involution induced by cyclophosphamide in the rat. Immunohistochemical stain demonstrated not only the presence of NGF but also its upregulated expression mainly in the subcapsular, paraseptal, and perivascular epithelial cells, and medullary epithelial cells including Hassall's corpuscles in both the normal and regenerating thymus. Biochemical data obtained using Western blot and RT-PCR supported these results and showed that thymic extracts contain NGF protein and mRNA, at higher levels during thymus regeneration. Thus, our results suggest that NGF expressed in these thymic epithelial cells plays a role in the T lymphopoiesis associated with thymus regeneration during recovery from acute thymic involution.

Nerve growth factor effect on human primary fibroblastic-keratocytes: Possible mechanism during corneal healing

In response to corneal injury, cytokines and growth factors play a crucial role by influencing epithelial-stromal interaction during the healing and reparative processes which may resolve in tissue remodeling and fibrosis. While transforming growth factor-beta1 (TGF-beta1) is considered the main profibrogenic modulator of these process, recently the nerve growth factor (NGF) appears as a pleiotropic modulator of wound-healing and inflammatory responses. Interestingly in the cornea, where NGF, trkA(NGFR) and p75(NTR) are expressed by epithelial cells and keratocytes, the NGF eye-drop induces the healing of neurotrophic or autoimmune corneal ulcers. During corneal healing, quiescent keratocytes are replaced by active fibroblast-like keratocytes/myofibroblasts. While the NGF effect on epithelial cells has been investigated, no data are reported for NGF effects on fibroblastic-keratocytes, during corneal healing. NGF, trkA(NGFR) and p75(NTR) were found expressed by fibroblastic-keratocytes. NGF was able to induce fibroblastic-keratocyte differentiation into myofibroblasts, migration, Metalloproteinase-9 expression/activity and contraction of a 3D collagen gel, without affecting their proliferation and collagen production. These data also show a two-directional control of fibroblastic-keratocytes by NGF and TGF-beta1. To sum up, the findings of this study indicate that NGF can modulate some functional activities of fibroblastic-keratocytes, thus substantiating the healing effects of NGF on corneal wound-healing.

Glial cell line-derived neurotrophic factor family members sensitize nociceptors in vitro and produce thermal hyperalgesia in vivo

Nerve growth factor (NGF) has been implicated as an effector of inflammatory pain because it sensitizes primary afferents to noxious thermal, mechanical, and chemical [e.g., capsaicin, a transient receptor potential vanilloid receptor 1 (TRPV1) agonist] stimuli and because NGF levels increase during inflammation. Here, we report the ability of glial cell line-derived neurotrophic factor (GDNF) family members artemin, neurturin and GDNF to potentiate TRPV1 signaling and to induce behavioral hyperalgesia. Analysis of capsaicin-evoked Ca2+ transients in dissociated mouse dorsal root ganglion (DRG) neurons revealed that a 7 min exposure to GDNF, neurturin, or artemin potentiated TRPV1 function at doses 10-100 times lower than NGF. Moreover, GDNF family members induced capsaicin responses in a subset of neurons that were previously insensitive to capsaicin. Using reverse transcriptase-PCR, we found that artemin mRNA was profoundly upregulated in response to inflammation induced by hindpaw injection of complete Freund's adjuvant (CFA): artemin expression increased 10-fold 1 d after CFA injection, whereas NGF expression doubled by day 7. No increase was seen in neurturin or GDNF. A corresponding increase in mRNA for the artemin coreceptor GFRalpha3 (for GDNF family receptor alpha) was seen in DRG, and GFRalpha3 immunoreactivity was widely colocalized with TRPV1 in epidermal afferents. Finally, hindpaw injection of artemin, neurturin, GDNF, or NGF produced acute thermal hyperalgesia that lasted up to 4 h; combined injection of artemin and NGF produced hyperalgesia that lasted for 6 d. These results indicate that GDNF family members regulate the sensitivity of thermal nociceptors and implicate artemin in particular as an important effector in inflammatory hyperalgesia.

Post-traumatic application of brain-derived neurotrophic factor and glia-derived neurotrophic factor on the rat spinal cord enhances neuroprotection and improves motor function

We examined the potential efficacy of brain-derived neurotrophic factor (BDNF) and glial-derived neurotrophic factor (GDNF) applied over traumatized spinal cord, alone or in combination, for attenuating motor dysfunction, blood-spinal cord barrier (BSCB) breakdown, edema formation, and cell injury in a rat model. Under Equithesin anesthesia, spinal cord injury (SCI) was performed by making a unilateral incision into the right dorsal horn of the T10-11 segment. The rats were allowed to survive 5 hours after trauma. The BDNF or GDNF was applied (0.1 to 1 microg/10 microl in phosphate buffer saline) 30, 60, or 90 minutes after SCI. Topical application of BDNF or GDNF 30 minutes after SCI in high concentration (0.5 microg and 1 microg) significantly improved motor function and reduced BSCB breakdown, edema formation, and cell injury at 5 hours. These beneficial effects of neurotrophins were markedly absent when administered separately either 60 or 90 minutes after injury. However, combined application of BDNF and GDNF at 60 or 90 minutes after SCI resulted in a significant reduction in motor dysfunction and spinal cord pathology. These novel observations suggest that neurotrophins in combination have potential therapeutic value for the treatment of SCI in clinical situations.

Neuroimmunological findings in allergic skin diseases

PURPOSE OF REVIEW

Recent studies have gained widespread information about the complex regulation of genetic, environmental, immunologic, and pharmacologic factors that contribute to the development of allergic inflammatory skin diseases such as atopic dermatitis. Neuroimmune mechanisms, however, still remain to be elucidated. This review will focus on the interaction between the cutaneous immune and peripheral nervous system in allergic inflammatory skin such as atopic dermatitis.

RECENT FINDINGS

Neuropeptides and neuropeptide-positive nerve fibres are prominently increased in lesions of atopic dermatitis. The density of nerve fibres is increased while peripheral nerve endings are in an active state of excitation. In this regard, neurotrophins particularly described for their functional role on nerve cells are also expressed in atopic dermatitis skin. In addition, neurotrophins modulate the functional role of eosinophils as main target effector cells in atopic dermatitis, as described recently. Interestingly, eosinophils are capable of neurotrophin as well as neuropeptide production itself, pointing to a bidirectional communication between neuronal cell populations and main target effector cells.

SUMMARY

Neurotrophins and neuropeptides modulate both the functional activity of sensory neurons and immune cells. We have therefore developed the concept of a neuroimmune network between target effector cells and sensory nerves that links pathogenic events to dysfunctions of the cutaneous immune and peripheral nervous system in allergic inflammatory skin diseases.