Development of immune hyperinnervation in NGF-transgenic mice

Inflammatory Profile of Neurotrophins, IL-6, IL1-β, TNF-α, VEGF, ICAM-1 and TGF-β in the Human Waldeyer's Ring

The palatine tonsils, nasopharyngeal tonsil (adenoid) and lingual tonsil constitute the major part of Waldeyer's ring, with the tubal tonsils and lateral pharyngeal bands as less prominent components. The lymphoid tissue of Waldeyer's ring is located at the gateway of the respiratory and alimentary tract and belongs to the mucosa-associated lymphoid tissue (MALT). Mucosae-associated lymphoid tissues are richly innervated and the mucosae contain peptidergic nerve endings associated with different types of cells and macrophages. The lymphatic tissue is known to interact with the nervous system and several organs implicated in the host response to a wide range of stressors. This study focuses on the expression of some neurotrophins (NTs), their high- and low-affinity receptors in human adenoid tissues, lingual and palatine tonsils via immunohistochemical analysis, as well as on the expression of some inflammatory cytokines and other tissue growth factors. Light microscopy immunohistochemistry showed human samples to be generally positive for all the NTs investigated (NGF, BDNF, NT-3) and their receptors (TrKA, TrKB and TrKC) with some different expression levels. IL-6, IL1-b, TNF-α, VEGF, ICAM-1 and TGF-b were also investigated by immunohistochemistry. These results suggest the presence of a pattern of neurotrophic innervation in the human lymphatic tissues which may play a role in sustaining inflammatory conditions and in modulating a close interaction between the nervous system and the different immune cellular subtypes. Our data also corroborate previous studies, suggesting that neurotrophins and inflammatory cytokines may mediate functional signals in lymphoid aggregates. In this context, owing to their widespread expression in immune organs and immunocompetent cells, NTs and inflammatory cytokines are potential candidates for a prominent role in the regulation of immune and neuroimmune interactions.

Social temperament and lymph node innervation

Socially inhibited individuals show increased vulnerability to viral infections, and this has been linked to increased activity of the sympathetic nervous system (SNS). To determine whether structural alterations in SNS innervation of lymphoid tissue might contribute to these effects, we assayed the density of catecholaminergic nerve fibers in 13 lymph nodes from seven healthy adult rhesus macaques that showed stable individual differences in propensity to socially affiliate (Sociability). Tissues from Low Sociable animals showed a 2.8-fold greater density of catecholaminergic innervation relative to tissues from High Sociable animals, and this was associated with a 2.3-fold greater expression of nerve growth factor (NGF) mRNA, suggesting a molecular mechanism for observed differences. Low Sociable animals also showed alterations in lymph node expression of the immunoregulatory cytokine genes IFNG and IL4, and lower secondary IgG responses to tetanus vaccination. These findings are consistent with the hypothesis that structural differences in lymphoid tissue innervation might potentially contribute to relationships between social temperament and immunobiology.

TLR2 is required for the altered transcription of p75NGF receptors in gram positive infection

Neuroimmune interactions play a decisive role in neuronal cell survival and cell death during neuronal injury, oxidative and free radical stress. In neurons, NGF occupancy of p75 neurotrophin receptor (p75(NTR)) has been shown to promote neuronal apoptosis, while occupancy of tropomyosin receptor kinase A (TrkA) promotes survival of injured neurons. In macrophages, recent results suggest that NGF via TrkA mediates resistance to cell death through the interaction with TLR2. We have investigated the transcriptional regulation of TrkA, p75(NTR) and their ligand nerve growth factor beta (NGFbeta) upon stimulation with the TLR2 ligand Staphylococcus aureus in the spleen of C57BL/6 mice, TLR2 (-/-) and p75(NTR) (-/-) mice. S. aureus challenge (i.p.) resulted in a significant increase in NGFbeta mRNA levels in C57BL/6 (100%), TLR2 (-/-) (300%) and p75(NTR) (-/-) mice (355%). TrkA mRNA levels were upregulated only in p75(NTR) (-/-) mice (87%) whereas in TLR2 (-/-) mice they remained unchanged and even decreased in C57BL/6 mice (46%). p75(NTR) mRNA was increased in spleen of C57BL/6 mice (60%) whereas the levels in TLR2 (-/-) mice remained almost unchanged. Finally, TLR2 mRNA was upregulated by 350% in C57BL/6 mice and by 283% in p75(NTR) (-/-) mice. These data suggest that in splenocytes signaling via TLR2 is required for Gram positive infection mediated alteration of neurotrophin receptor expression as observed in an in vivo infection model with transgenic mice. This observation provides a link between Gram-positive infection and neurotrophic responses, which may be important in preserving neurons at sites of the infection.

Ovarian expression of alpha (1)- and beta (2)-adrenoceptors and p75 neurotrophin receptors in rats with steroid-induced polycystic ovaries

Polycystic ovary syndrome (PCOS) is the main cause of infertility in women. Despite extensive research aimed at identifying the pathogenetic mechanism underlying this condition, the aetiology of the disease is still unknown. Evidence from studies on women with PCOS and on an experimental rat polycystic ovary (PCO) model suggests that the sympathetic regulatory drive to the ovary may be unbalanced. The present study was designed to investigate this hypothesis. Accordingly, we used the well-defined rat PCO model, where PCO is induced by a single intramuscular (i.m.) injection of estradiol valerate (EV), and compared the model with oil-injected controls. We studied the ovarian expression of the alpha1- and beta2-adrenoceptors (ARs), the neurotrophin receptor p75 (p75NTR), and the sympathetic marker tyrosine hydroxylase (TH) at two time points: 30 and 60 days after EV injection. Our data demonstrate for the first time that all of the alpha1-AR subtypes are expressed in normal rat ovaries at both the mRNA and the protein levels. Furthermore, the expression of the alpha1-AR subtypes was differentially modulated in a time- and subtype-dependent manner in rats with EV-induced PCO. The ovaries in rats with steroid-induced PCO are characterised by an early overexpression of these molecules and p75NTR, while the beta2-AR was downregulated. An increase in the expression of ovarian TH after EV injection was also detected, suggesting a structural and functional remodelling of ovarian sympathetic innervation in PCO rats. Our evidence strongly indicates that the role of the sympathetic nervous system is crucial in the pathogenesis of EV-induced PCO. Overall, our findings suggest that therapeutical approaches aimed at down-regulating the sympathetic tone to the ovary could be useful in the prevention and clinical treatment of PCOS.

Vertebrate thymus and the neurotrophin system

An immunomodulary role has been proposed for growth factors included in the family of neurotrophins. This is supported by the presence of both neurotrophins and neurotrophin receptors in the immune organs and some immunocompetent cells, the in vitro and in vivo effects of the neurotrophins on the immune cells, and the structural changes of lymphoid organs in mice deficient in neurotrophins and their receptors. The current data strongly indicate that neurotrophins regulate the biology of thymic stromal cells and T cells, including survival, and are involved in the thymic organogenesis. This review compiles the available data about the occurrence and distribution of neurotrophins and their signaling receptors (Trk proteins and p75(NTR)) in the vertebrate thymus and the possible contribution of these molecules to the thymic microenvironment and, therefore, to the T cells differentiation.

Neurotrophins and the immune system

The neurotrophins are a family of polypeptide growth factors that are essential for the development and maintenance of the vertebrate nervous system. In recent years, data have emerged indicating that neurotrophins could have a broader role than their name might suggest. In particular, the putative role of NGF and its receptor TrkA in immune system homeostasis has become a much studied topic, whereas information on the other neurotrophins is scarce in this regard. This paper reviews what is known about the expression and possible functions of neurotrophins and their receptors in different immune tissues and cells, as well as recent data obtained from studies of transgenic mice in our laboratory. Results from studies to date support the idea that neurotrophins may regulate some immune functions. They also play an important role in the development of the thymus and in the survival of thymocytes.

p75NTR in the spleen: age-dependent changes, effect of NGF and 4-methylcatechol treatment, and structural changes in p75NTR-deficient mice

In addition to their well-known actions within the nervous system, neurotrophins and their receptors are involved in immune system functioning, as demonstrated by their wide distribution in lymphoid tissues and their in vitro actions on immunocompetent cells. Nevertheless, the in vivo roles of neurotrophin-receptor systems in lymphoid tissues, as well as the scope of their influence throughout development and adulthood, are yet to be clarified. In the present study, we used combined morphological and immunohistochemical techniques to investigate the presence and cellular localization of p75NTR, the pan-neurotrophin receptor protein, in rat spleen from newborns to aging individuals, and the structural and innervation changes in the spleens of p75NTR-deficient mice. In rats, p75NTR was expressed by splenic nerve fibers and dendritic cells in an age-regulated fashion, with maximal expression detected at 2 weeks. Consistently, the spleens of newborn mice lacking this receptor protein showed no signs of ingrowing sympathetic fibers, along with an absence of defined white pulp areas. The present findings suggest a prolonged role of p75NTR in the physiology of the spleen; at least during the embryonic development period, the receptor may be critical for correct innervation and compartmentalization processes to occur.