Expression of nerve growth factor receptors by human peripheral blood mononuclear cells

ProBDNF and its receptors in immune-mediated inflammatory diseases: novel insights into the regulation of metabolism and mitochondria

Immune-mediated inflammatory diseases (IMIDs) consist of a common and clinically diverse group of diseases. Despite remarkable progress in the past two decades, no remission is observed in a large number of patients, and no effective treatments have been developed to prevent organ and tissue damage. Brain-derived neurotrophic factor precursor (proBDNF) and receptors, such as p75 neurotrophin receptor (p75^NTR) and sortilin, have been proposed to mediate intracellular metabolism and mitochondrial function to regulate the progression of several IMIDs. Here, the regulatory role of proBDNF and its receptors in seven typical IMIDs, including multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, allergic asthma, type I diabetes, vasculitis, and inflammatory bowel diseases, was investigated.

p75NTR regulates brain mononuclear cell function and neuronal structure in Toxoplasma infection-induced neuroinflammation

Neurotrophins mediate neuronal growth, differentiation, and survival via tropomyosin receptor kinase (Trk) or p75 neurotrophin receptor (p75^NTR) signaling. The p75^NTR is not exclusively expressed by neurons but also by certain immune cells, implying a role for neurotrophin signaling in the immune system. In this study, we investigated the effect of p75^NTR on innate immune cell behavior and on neuronal morphology upon chronic Toxoplasma gondii (T. gondii) infection‐induced neuroinflammation. Characterization of the immune cells in the periphery and central nervous system (CNS) revealed that innate immune cell subsets in the brain upregulated p75^NTR upon infection in wild‐type mice. Although cell recruitment and phagocytic capacity of p75^NTRexonIV knockout (p75^−/−) mice were not impaired, the activation status of resident microglia and recruited myeloid cell subsets was altered. Importantly, recruited mononuclear cells in brains of infected p75^−/− mice upregulated the production of the cytokines interleukin (IL)‐10, IL‐6 as well as IL‐1α. Protein levels of proBDNF, known to negatively influence neuronal morphology by binding p75^NTR, were highly increased upon chronic infection in the brain of wild‐type and p75^−/− mice. Moreover, upon infection the activated immune cells contributed to the proBDNF release. Notably, the neuroinflammation‐induced changes in spine density were rescued in the p75^−/− mice. In conclusion, these findings indicate that neurotrophin signaling via the p75^NTR affects innate immune cell behavior, thus, influencing the structural plasticity of neurons under inflammatory conditions.

Menstrual cycle and reproductive aging alters immune reactivity, NGF expression, antioxidant enzyme activities, and intracellular signaling pathways in the peripheral blood mononuclear cells of healthy women

Reproductive senescence in women is a process that begins with regular menstrual cycles and culminates in menopause followed by gradual development of diseases such as autoimmune diseases, osteoporosis, neurodegenerative diseases, and hormone-dependent cancers. The age-associated impairment in the functions of neuroendocrine system and immune system results in menopause which contributes to subsequent development of diseases and cancer. The aim of this study is to characterize the alterations in immune responses, compensatory factors such as nerve growth factor (NGF) and antioxidant enzyme activities, and the molecular mechanisms of actions in the peripheral blood mononuclear cells (PBMCs) of young (follicular and luteal phases), middle-aged, and old healthy women. Peripheral blood mononuclear cells were isolated from young women in follicular and luteal phases of the menstrual cycle (n=20; 22.6±2.9 yrs), middle-aged women (n=19; 47.1±3.8 yrs; perimenopausal) and old (n=16; 63.2±4.7 yrs; post-menopausal) women and analyzed for Concanavalin (Con A)-induced proliferation of lymphocytes and cytokine (IL-2 and IFN-γ) production, expression of NGF, p-NF-κB, p-ERK, p-CREB, and p-Akt, antioxidant enzymes [superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx), glutathione-S-transferase (GST)], extent of lipid peroxidation, and nitric oxide (NO) production. Serum gonadal hormones (17β-estradiol and progesterone) were also measured. A characteristic age- and menstrual cycle-related change was observed in the serum gonadal hormone secretion (estrogen and progesterone), T lymphocyte proliferation and IFN-γ production. Salient features include the age-related decline observed in target-derived growth factors (lymphocyte NGF expression), signaling molecules (p-ERK/ERK and p-CREB/CREB ratios) and compensatory factors such as the activities of plasma and PBMC antioxidant enzymes (SOD and catalase) and NO production. Further, an age-associated increase in p-NF-κB expression and lipid peroxidation was observed. Also, serum 17β-estradiol levels were positively correlated with IFN-γ production, SOD activity and NGF expression in the PBMCs. These results suggest that alterations in the levels of gonadal hormones are associated with immunosenescence characterized by decreased IFN-γ production and proliferation of T lymphocytes, decline in NGF expression, SOD and catalase activities, NO production, and signaling mechanisms and thus, may increase the incidence of diseases and cancer in women.

Allergic bronchial airway inflammation in nerve growth factor (NGF)-deprived rats: evidence suggesting a neuroimmunomodulatory role of NGF

In the present study, ovalbumin-sensitized/challenged rats were characterized by an nerve growth factor (NGF) increase in both serum and bronchial alveolar lavage fluid (BALF), but not in the lung. Exogenous administration of NGF or NGF-neutralizing antibodies did not modify immunoglobulin (IgE) and eosinophil parameters. In control rats, NGF administration did not induce increase of IgE or eosinophils in both BALF and lung. The present findings suggest that at least NGF does not act as a proper proinflammatory factor but most probably as a neuroimmune modulator molecule of the allergic state.

Low density of sympathetic nerve fibres and increased density of brain derived neurotrophic factor positive cells in RA synovium

OBJECTIVE

To investigate the correlation between density of nerve fibres and the presence of BDNF(+) cells.

METHODS

Densities of nerve fibres and BDNF(+) cells were detected by quantitative immunohistochemistry in fresh synovial tissue from 52 patients with RA, 59 with OA, and 26 controls (Co). BDNF was also detected by in situ hybridisation.

RESULTS

Sympathetic nerve fibre density was similar in Co and OA but markedly reduced in RA (p = 0.002), whereas density of substance P positive (SP(+)) sensory nerve fibres was lower in OA than in Co and RA (p = 0.002). The ratio of sympathetic/SP(+) sensory nerve fibre density was highest in OA and Co, followed by RA. The correlation between density of sympathetic nerve fibres and SP(+) sensory nerve fibres in OA (R = 0.425, p = 0.001) was strongly positive, had a positive trend in Co (R = 0.243, NS), but was negative in RA (R = -0.292, p = 0.040). In RA and OA tissue the density of BDNF(+) cells was high in sublining areas but markedly lower in Co (p = 0.001). BDNF(+) cell density correlated positively with the ratio of sympathetic/SP(+) sensory nerve fibre density in Co (R = 0.433, p = 0.045) and in OA (R = 0.613, p = 0.015), but not in RA (R = 0.101, NS). Immunohistochemical double staining demonstrated that some macrophages and fibroblasts were positive for BDNF.

CONCLUSIONS

The correlation of density of SP(+) sensory with sympathetic nerve fibres was positive in Co and OA but negative in RA. BDNF may have a stimulatory role on growth of sympathetic in relation to SP(+) sensory nerve fibres in Co and OA, but not in RA.

Nerve growth factor induces increased airway inflammation via a neuropeptide-dependent mechanism in a transgenic animal model of allergic airway inflammation

BACKGROUND

Nerve growth factor (NGF) exerts an important functional impact on the pathogenesis of allergic diseases. Data obtained in animal models of allergic bronchial asthma indicate that NGF alters sensory nerve function and promotes allergic inflammation, bronchial hyper-reactivity, and airway obstruction.

OBJECTIVE

To further delineate the effects of NGF on airway inflammation, we employed a transgenic (tg) animal model of allergic inflammation and asthma.

METHODS

NGF-tg mice, which overexpress NGF in Clara cells of the airways, were compared with wild-type (wt) littermates regarding their ability to mount IgE-related airway inflammatory responses. Mice were sensitized intraperitoneally to ovalbumin (OVA) and locally challenged via the airways according to established protocols.

RESULTS

NGF-tg mice displayed enhanced levels of OVA-specific IgE antibody titres after repeated OVA aerosol exposure. In the airways, increased numbers of eosinophils were detected. These results were confirmed to be NGF specific, because similar results were obtained following local application of NGF into the airways of wt mice. The effect of NGF was partly mediated via neuropeptides, as treatment of OVA-sensitized NGF-tg mice with the dual neurokinin (NK) receptor NK-1/NK-2 antagonist partly prevented enhanced airway inflammation.

CONCLUSION

The present data indicate an important functional role of NGF in allergic airway inflammation and point to an involvement of tachykinins as mediators of NGF effects.

Changes in plasma nerve growth factor levels in older adults associated with chronic stress

Evidence indicates that the actions of nerve growth factor (NGF) reach beyond the nervous system and might modulate immune function. Based on reports that blood NGF rises following the acute stress of parachute jumping, we investigated whether exposure to a chronic stressor, caregiving for a cognitively impaired spouse, could alter the levels of blood NGF. High perceived stress and depression in caregivers (vs. well-matched controls) were associated with elevated blood NGF. These data suggest that exposure to this chronic stressor can alter the concentrations of circulating NGF, and that psychological stress can induce changes in NGF concentrations in older adults.

Rat alpha1-macroglobulin enhances nerve growth factor-promoted neurite outgrowth, TrkA phosphorylation, and gene expression of pheochromocytoma PC12 cells

Monoamine-activated human alpha2-macroglobulin (alpha2M) has been previously demonstrated to inhibit TrkA-, TrkB-, and TrkC-mediated signal transduction. Rat alpha1-macroglobulin (alpha1M) and alpha2M are structural homologues of human alpha2M, but rat alpha1M is distinctly different from rat alpha2M in many ways and its role in the mammalian nervous system is unknown. In this report, monoamine-activated rat alpha1M was demonstrated to enhance in a dose-dependent manner nerve growth factor (NGF)-promoted neurite outgrowth in pheochromocytoma PC12 cells. Monoamine-activated alpha1M by itself, however, was neither neurotrophic nor mitogenic to PC12 cells. To investigate further its possible mode of action, the ability of monoamine-activated alpha1M and normal alpha1M to bind and to activate the NGF receptor (TrkA) was investigated. Monoamine-activated alpha1M formed a more stable complex with TrkA than normal alpha1 M, but the binding of monoamine-activated alpha1M to TrkA was adversely affected by prior stimulation of TrkA with NGF. In addition, monoamine-activated alpha1M enhanced the NGF-promoted TrkA phosphorylation and up-regulated the expression of NGF-inducible immediate-early genes (c-jun and NGFI-A) and delayed-response genes (SCG10 and transin) in PC12 cells; normal alpha1M, in contrast, produced little or no effect. This study demonstrates that alpha1M, the constitutive form of alpha-macroglobulin in the rat, possesses the ability to promote NGF-mediated differentiation in PC12 cells, possibly via its direct action on TrkA receptors and TrkA-mediated signal transduction and gene expression.

Development of immune hyperinnervation in NGF-transgenic mice

Sympathetic innervation of lymphoid tissues is localized to specific tissue compartments, but little is known of the "factors" that are important in establishing this pattern during development. Numerous studies have shown interactions of nerve growth factor (NGF) with the immune system, which may include modulation of immune innervation. We previously have shown that NGF transgenic mice, which overexpress NGF in skin and not immune tissues, have a dramatic hyperinnervation of splenic marginal zone and peripheral lymph node medulla and capsule. The purpose of the current studies was to determine if the presence of elevated NGF would alter immune system development and the process of sympathetic ingrowth. The results show that the splenic innervation in NGF transgenics gradually diverged from controls during the first two postnatal weeks, with the greatest change occurring between postnatal days 13 and 16 when the splenic organization was reaching the adult pattern. In contrast, the peripheral lymph nodes were hyperinnervated at an earlier age. mesenteric lymph nodes never diverged from the normal pattern. NGF levels in transgenic spleen were much higher than controls at postnatal days 1 and 2, when little innervation was present, and declined as the tissue matured, possibly because of NGF uptake by the ingrowing sympathetic fibers. This suggests that immune tissues are capable of concentrating NGF, which in turn may modulate the level of innervation by the sympathetic nervous system.

Human CD4+ T cell clones produce and release nerve growth factor and express high-affinity nerve growth factor receptors

BACKGROUND

Increasing evidence shows that nerve growth factor (NGF) plays a role in the complex and fascinating linkage between the nervous and the immune systems due to its ability to modulate functions of several inflammatory cells.

OBJECTIVE

To investigate NGF receptor expression and NGF production and release by human CD4+ cells clones, which have primary relevance in modulating inflammatory events through their different subsets of functional phenotypes.

METHODS

The expression of NGF and a transmembrane tyrosine kinase (TrkA) was evaluated by immunohistochemistry and flow cytometry analysis in five T(H0), six T(H1), and five T(H2) cell clones derived from human circulating mononuclear blood cells. Moreover, the amount of NGF protein was assessed by measuring the NGF levels in culture supernatants of the T cell clones before stimulation and 48 hours after phytohemagglutinin (PHA) activation by use of an immunoenzymatic assay.

RESULTS

Our data have shown that in unstimulated conditions, human CD4+ T cell clones express both immunoreactivity for NGF and the TrkA NGF receptor irrespective of their cytokine profile. Moreover, T(H1) and T(H2) clones, but not T(H0) clones, secrete NGF in basal conditions. PHA activation induces NGF secretion in T(H0) clones and a significant increase of NGF levels in T(H2) (p < 0.05), but not in T(H1) culture supernatants.

CONCLUSIONS

Results obtained represent the first evidence of TrkA expression and NGF production and release in human CD4+ cell clones and suggest a possible functional role of NGF in modulating the immune and inflammatory network.

Nerve growth factors from snake venoms: chemical properties, mode of action and biological significance

An overview of nerve growth factors (NGF) and their receptor system is presented. This general introduction deals with mouse and human NGF, since most of the fundamental knowledge is based on these mammalian proteins. Great emphasis is laid on the nonneuronal NGF effects which are well discussed for their possible toxinological function. The snake venom NGFs were reviewed with respect to their purification, classification and properties. From the date of their discovery about 40 years ago, researchers have been interested in the possible function of mouse salivary and snake venom NGFs. The physiological relevance of snake venom NGF is therefore widely discussed on the base of experimental facts and hypothetical considerations.

Nerve growth-factor and anti-CD40 provide opposite signals for the production of IgE in interleukin-4-treated lymphocytes

Nerve growth factor (NGF) is a well-known neurotrophic factor acting on both the peripheral and the central nervous systems. In addition, it has been shown to play a role in the function of the immune system through specific receptors. Both high-affinity and low-affinity NGF receptors (NGFR) are expressed on human B lymphocytes. The low-affinity NGFR has been shown to have structural homology with another specific B cell surface molecule, CD40, which plays an important role in IgE production. In view of the structural similarities of the p75 NGFR and CD40 we examined whether NGF may also be involved in the regulation of IgE production. We found that NGF and anti-CD40 exerted opposite effects on the induction of IgE by IL-4 in peripheral blood mononuclear cells. NGF inhibited the induction of IgE by IL-4 and this inhibition was not mediated through blocking of the induction of CD23 nor through inhibition of IL-4R expression. The inhibition of IL-4-dependent IgE production was observed on surface (s)IgE+ and sIgE-/sIgM+ B lymphocytes. Anti-CD40 on the other hand, exerted an enhancing effect on IgE production and its addition to IL-4 provided a signal that was resistant to the inhibitory effect of NGF. Antagonistic effects of NGF and IL-4 were also observed for other Ig isotypes since IL-4 prevented the increase in IgA and IgM production induced by NGF. These data indicate that although NGFR and CD40 belong to the same receptor superfamily and exert similar proliferative effects on B lymphocytes, they interact differently with IL-4 in the regulation of IgE production.

Nerve growth factor from the venom of the Chinese cobra Naja naja atra: purification and description of non-neuronal activities

Nerve growth factor (NGF) was separated from crude Naja naja atra venom by using weak cation-exchange chromatography, followed by reversed-phase liquid chromatography. The yield of the purification was 0.2-0.5% (w/w). The mol. wt was determined to be 13,600 and the protein still induced the typical fibre outgrowth of cultured PC-12 cells in a concentration range of 5-10 ng/ml. Beside this neuronal effect we demonstrated non-neuronal effects of cobra venom NGF, such as induction of plasma extravasation and histamine release from whole blood cells. With human leucocyte preparations, including enriched basophils, there was an increase in C5a-induced histamine release, whereas NGF alone was inactive. Cobra NGF was one-tenth as potent as human recombinant NGF, with a half-maximal stimulation occurring at 10 ng/ml. Cobra NGF and human recombinant NGF showed a modulatory effect on histamine release comparable to the haematopoietic growth factor IL-3. Thus, the non-neuronal effects of cobra NGF may account for immunomodulatory activities during inflammatory events.

Comparison of the effects of nerve growth factor and superoxide dismutase on vascular extravasation in experimental burns

Superoxide dismutase (SOD), a free-radical scavenger, inhibits the increase of vascular permeability in experimental burn lesions in rats. In this study the aim was to determine whether Nerve Growth Factor (NGF), which has been implicated in the modulation of some inflammatory reactions, behaves in an analogous way. The study compares the haematocrit (Ht) and haemoglobin (Hb) variations in three groups of rats treated respectively with saline solution, SOD and NGF, immediately after causing a 25 per cent dermal burn injury. Statistical comparison (Student's t test) of the Ht and Hb variations between the Control group (Ht and Hb increase) and the NGF group (Ht and Hb decrease), shows significant differences in the intervals between 15 and 60 min (P < 0.01) and between 60 and 120 min (P < 0.05). Although SOD is able to control extravasation in the immediate postburn period (basal-15 min), NGF has a comparable effect in subsequent periods. The overall action of NGF shows that this agent is able to maintain Ht and Hb values at basal levels even after 120 min postburn. These results seem to be the first evidence of an inhibitory effect of NGF on the vascular permeability in burn lesions.

Correlation between NGF levels in wound chamber fluid and cytological localization of NGF and NGF receptor in axotomized rat sciatic nerve

When a silicone tube is implanted in transected rat sciatic nerve, there is plasma accumulation and formation of a fibrin cable followed by proliferation and migration of neural and nonneural cells from the nerve stumps into the cable. The wound fluid exhibited neurotrophic activity of unknown origin and nature. In this study, we analyzed the NGF level in wound fluid by a sensitive enzyme immunoassay and correlated the NGF level with the cytological localization of NGF, low affinity NGF receptor (p75NGFR), and Trk receptor in the axotomized nerve by immunohistochemistry. We demonstrated a rising NGF level in wound fluid from 490 pg/ml on Day 1 to 950 pg/ml on Day 7; the serum NGF level was 1/20 of that in the wound fluid. The infiltrating leukocytes expressed strong NGF but no p75NGFR. The proliferative fibroblasts and vascular cells exhibited a short period of NGF but no p75NGFR staining. Schwann cells in the distal segment showed a prolonged period of NGF and p75NGFR expression. No Trk receptor was demonstrated on leukocytes or non-neural cells. These findings suggest that locally synthesized NGF is mainly responsible for the neurotrophic activity in the wound chamber fluid. The NGF produced by the nonneural cells may be bound and stored in the p75NGFR in Schwann cells in the distal segment prior to the arrival of the regenerating axons.

Human placental mast cells as an in vitro model system in aspects of neuro-immunotoxicity testing

1. In both the developing and adult nervous systems, nerve growth factor (NGF) influences neuronal survival, differentiation and recovery following insult. 2. The effect of NGF upon human placental mast cells (HPMC) was investigated, since it is known that rodent mast cells express a functional receptor for NGF and secrete histamine upon challenge with this neurotrophic factor. Furthermore, human placental tissue contains a significant amount of NGF and expresses a NGF receptor. 3. HPMC were shown to secrete histamine in a concentration dependent manner in response to NGF (0.001-10.0 micrograms ml-1) in the presence of the lipid cofactor phosphatidylserine (10.0 micrograms ml-1). 4. NGF induced histamine release from isolated HPMC with an EC50 of 0.1 microgram ml-1 NGF and maximal secretion of total cellular histamine of 22.3 +/- 3.4% at 3.0 micrograms ml-1. 5. The response was shown to be a secretory process, dependent upon the presence of exogenous calcium ions and to be pH- and temperature-sensitive. 6. HPMC are suggested to be a suitable primary cell model for use in aspects of in vitro toxicity testing, in terms of assessing the neuro-immunotoxic potential of neurotrophic therapeutics. In addition, mechanistic studies concerning those xenobiotics which may exert their neurotoxic effect via interaction with neurotrophic factors and, or their receptors, may be studied in this human cell model.

Substance P-, calcitonin gene-related peptide, growth-associated protein-43, and neurotrophin receptor-like immunoreactivity associated with unmyelinated axons in feline ventral roots and pia mater

The spinal pia mater receives a rich innervation of small sensory axons via the ventral roots. Other sensory axons enter the ventral roots but end blindly or turn abruptly in hairpin loop-like formations and continue in a distal direction. In the present study, the content of substance P (SP)-, calcitonin gene-related peptide (CGRP)-, growth-associated protein (GAP-43)-, and low-affinity neurotrophin receptor protein (p75NGFr)-like immunoreactivity (-LI) associated with these different types of sensory axons was assessed with light and electron microscopic immunohistochemical techniques. In addition, the binding of antibodies against synthetic peptides representing unique sequences of residues in the products of the trk and trkB protooncogenes was analyzed. These genes encode membrane spanning proteins, which have been shown to constitute specific high affinity binding sites for several members of the nerve growth factor family of neurotrophic factors. The results of the present study imply that the ventral root afferents comprise several different types of sensory axons, which all contain SP-, CGRP-, GAP-43-, and p75NGFr-like immunoreactivities. In addition, at least some of the presumed sensory fiber bundles in ventral roots and the pia mater were immunoreactive for the trkB gene product. Moreover, leptomeningeal cells and nonneuronal cells of the ventral roots were shown to bind antibodies to both the trk and trkB gene products. The ventral root afferents seem to share their immunohistochemical pattern with pain-transducing axons at some other locations, such as the tooth pulp. The contents of SP- and CGRP-LI in sensory axons that reach the central nervous system (CNS) through the ventral root indicate that ventral root afferents may be involved in sensory mechanisms, such as the ventral root pain reaction, as well as in the control of the pial blood vessels. The demonstration of GAP-43 and neurotrophin receptor-immunoreactivities associated with unmyelinated fibers in ventral roots and the pia mater is discussed in relation to previous reports on postnatal plasticity in these axonal populations.

Nerve growth factor and autoimmune diseases

The initiation of a humoral immune response to a foreign antigen is a complex biologic process involving the interaction of many cell types and their secreted products. Autoimmune diseases, which are characterized by an abnormal activation of the immune system, probably result from the failure of normal self-tolerance mechanisms. The etiology of such illnesses, however, is far from being understood. While there have been extensive studies on the participation of the immune and endocrine systems in autoimmune diseases, few have dealt with nervous system-mediated immunoregulation in such situations. Evidence continues to grow suggesting that nerve growth factor (NGF), first identified for its activity in promoting the growth and differentiation of sensory and sympathetic neurons, may exert a modulatory role on neuroimmunoendocrine functions of vital importance in the regulation of homeostatic processes. Newly detected NGF-responsive cells belong to the hemopoietic-immune system and to populations in the brain involved in neuroendocrine functions. NGF levels are elevated in a number of autoimmune states, along with increased accumulation of mast cells. NGF and mast cells both appear to be involved in neuroimmune interactions and tissue inflammation. Moreover, mast cells themselves synthesize, store, and release NGF, proposing that alterations in normal mast cell behaviors may provoke maladaptive neuroimmune tissue responses whose consequences could have profound implications in inflammatory disease states, including those of an autoimmune nature. This review focuses on these cellular events and presents a working model which attempts to explain the close interrelationships of the neuroendocrinoimmune triade via a modulatory action of NGF.

Expression of functional trk protooncogene in human monocytes

There is increasing evidence that neurotrophins, including nerve growth factor (NGF), exert specific effects on cells of the immune system in addition to their neurotrophic actions. This report shows that human monocytes express the trk protooncogene, encoding the signal-transducing receptor unit for NGF. This receptor is functional, since interaction of NGF with monocytes triggered a respiratory burst, the major component of monocyte cytotoxic activity. During in vitro differentiation of human blood monocytes to macrophages trk expression decreased, suggesting a maturation-dependent trk expression decreased, suggesting a maturation-dependent trk regulation. Treatment of monocytes with Staphylococcus aureus Cowan I, a potent activator of monocytes, stimulated trk mRNA synthesis in a time-dependent way, implying a modulatory role for NGF in immune functions. The finding that dibutyryl cAMP elicited a time-dependent trk induction in monocytes as well as in phorbol ester-differentiated promonocytic U937 cells indicates that adenylate cyclase is involved in monocytic trk regulation. These results suggest that NGF, in addition to its neurotrophic function, is an immunoregulatory cytokine acting on monocytes.

NGF retards apoptosis in chick embryo bursal cell in vitro

Recent studies have demonstrated that the action of nerve growth factor (NGF) is not restricted to neuronal cells but also affects cells of the immune system. In a previous work on the effect of NGF on the chick embryo bursa of Fabricius both in vivo and in vitro, we observed that NGF prolongs bursal cell survival in vitro. In the present study we report that the increase of viable cells in NGF-treated cultures is not due to a proliferative effect of NGF on bursal cells but to a reduction of cell mortality. The morphological analysis revealed that bursal cells in cultures die by apoptosis, which was also shown by the typical pattern of DNA fragmentation, a hallmark of this cell death process. It is concluded that NGF, with an action similar to that described in sympathetic neurons and PC12, could retard bursal cell death by influencing apoptosis.

Nerve growth factor receptor gene expression in human peripheral blood lymphocytes in aging

Nerve growth factor (NGF) has a modulating effect on immune function, which may occur as a consequence of binding to the NGF receptor (NGF-R). To determine if mRNA for the gene coding for p75NGFR (low affinity NGF-R) is present in lymphocytes, Northern blot analysis of mRNA from human peripheral blood lymphocytes (PBL) and purified T lymphocytes was initiated using cDNA probe for human p75NGFR. p75NGFR mRNA was present in PBL and T lymphocytes, and the mRNA in response to phytohemagglutinin stimulation showed maximum levels at 14 hr of stimulation. p75NGFR mRNA content when analyzed in PBL and T cells from volunteers of various ages showed that p75NGFR mRNA expression does not change with the age of the cell donor.

Changes in nerve growth factor receptor-like immunoreactivity in the spinal cord after ventral funiculus lesion in adult cats

Spinal motoneurons have a capability to regenerate CNS-type axons after intramedullary lesions in the adult cat. Regrowing axons have been traced through CNS-type scar tissue in the ventral funiculus of the spinal cord and into adjacent ventral root fascicles. This scar tissue, which appears to support and sustain regenerating axons, has been shown to have a persistent defect in the blood-brain barrier. It has been suggested that the blood-brain barrier may play a vital role in CNS regeneration by regulating the access of blood-borne trophic factors to the lesion area. In the present study, the binding of antibodies to the human nerve growth factor receptor in the cat spinal cord was examined with immunohistochemical methods 2 days to 8 weeks after a ventral funiculus lesion. The results show that, while no neurons in the ventral horn of the control material contained nerve growth factor receptor-like immunoreactivity as revealed by fluorescence microscopy, affected motoneurons expressed nerve growth factor receptor after ventral funiculus lesion. Nerve growth factor receptor-like immunoreactivity associated to both capillaries and interstitium was present in the scar tissue. Electron microscopic examination of sections labelled with the immunogold-silver method showed that perivascular nerve growth factor receptor-like immunoreactivity was located exclusively to non-pericytic perivascular cells. These cells were abundant in the expanded capillary perivascular spaces adjacent to the traumatic lesion. Similar cells, with or without relation to blood vessels, were observed in the scar tissue and in the pia mater. In a separate set of specimens it was observed that a ventral funiculus lesion combined with ventral root avulsion, which removes denervated PNS tissue, resulted in an expression of nerve growth factor receptor-like immunoreactivity which was similar to the one observed after ventral funiculus lesion only. The results of the present study show that affected motoneurons and cells in the scar tissue express nerve growth factor receptor after ventral funiculus lesion which implies that neurotrophic factors related to nerve growth factor may be of importance for the regenerative response.

In vivo and in vitro effect of NGF on bursa of Fabricius cells during chick embryo development

NGF exerts a broader biological action than previously believed. The growing-evidence of NGF's effect on lymphocytes and the presence of high levels of mRNA for NGF receptors in the embryonic bursa of Fabricius led us to study the action of NGF on bursal cells during chick embryo development. Our in vivo experiments indicate that NGF administration in ovo caused a significant increase in size of the lymphoid follicles in the embryonic bursa at E15. The in vitro experiments demonstrated that NGF exhibits different effects on bursal cells depending on the stage of development. At E9 bursal cells survive for longer periods when NGF is added to the medium. At E15 NGF act as a colony-stimulating factor by significantly increasing the number of colonies in soft agar cultures.

Nerve growth factor and neuronal cell death

The regulation of neuronal cell death by the neuronotrophic factor, nerve growth factor (NGF), has been described during neural development and following injury to the nervous system. Also, reduced NGF activity has been reported for the aged NGF-responsive neurons of the sympathetic nervous system and cholinergic regions of the central nervous system (CNS) in aged rodents and man. Although there is some knowledge of the molecular structure of the NGF and its receptor, less is known as to the mechanism of action of NGF. Here, a possible role for NGF in the regulation of oxidant--antioxidant balance is discussed as part of a molecular explanation for the known effects of NGF on neuronal survival during development, after injury, and in the aged CNS.

The cholinergic neuronal differentiation factor from heart cells is identical to leukemia inhibitory factor

A protein secreted by cultured rat heart cells can direct the choice of neurotransmitter phenotype made by cultured rat sympathetic neurons. Structural analysis and biological assays demonstrated that this protein is identical to a protein that regulates the growth and differentiation of embryonic stem cells and myeloid cells, and that stimulates bone remodeling and acute-phase protein synthesis in hepatocytes. This protein has been termed D factor, DIA, DIF, DRF, HSFIII, and LIF. Thus, this cytokine, like IL-6 and TGF beta, regulates growth and differentiation in the embryo and in the adult in many tissues, now including the nervous system.