Adrenergic nerve fibres and mast cells: correlation in rat thymus

Mast cells modulate the pathogenesis of leptin-induced left stellate ganglion activation in canines

BACKGROUND

Leptin is an adipocytokine predominantly secreted by adipose tissue that participates in immune modulation. Mast cells are important immune cells that are related to altered sympathetic activity. Previous study has shown that leptin promotes activation of the left stellate ganglion (LSG) directly via the leptin receptor. This study aims to investigate whether mast cells play a key role in indirect activation.

METHODS

Twenty-eight canines were randomly divided into 3 groups: the control group (saline, n = 8), leptin group (leptin, n = 9), and DSCG group (disodium cromoglycate plus leptin, n = 11). Drugs were locally microinjected into the LSG. The function and neural activity of the LSG were evaluated to investigate LSG activation. Tryptase was adopted to identify activated mast cells in the LSG.

RESULTS

Compared with the control group, leptin injection (18 μg) markedly increased the function and neural activity of the LSG. Leptin also upregulated c-fos, nerve growth factor (NGF), and tryptase expression in the LSG. However, these effects of leptin were attenuated by pre-injection of DSCG (25 mg). Additionally, the immunofluorescence analysis revealed that many mast cells were present in the LSG and that those cells were located close to sympathetic neurons. The presence of leptin receptors on the mast cells was verified.

CONCLUSIONS

Immune mast cells play an important supplementary role in the pathogenesis of leptin-induced LSG activation.

Immunofluorescent Localization of Non-myelinating Schwann Cells and Their Interactions With Immune Cells in Mouse Thymus

The thymus is innervated by sympathetic/parasympathetic nerve fibers from the peripheral nervous system (PNS), suggesting a neural regulation of thymic function including T-cell development. Despite some published studies, data on the innervation and nerve-immune interaction inside the thymus remain limited. In the present study, we used immunofluorescent staining of glial fibrillary acidic protein (GFAP) coupled with confocal microscopy/three-dimensional (3D) reconstruction to reveal the distribution of non-myelinating Schwann cells (NMSC) and their interactions with immune cells inside mouse thymus. Our results demonstrate (1) the presence of an extensive network of NMSC processes in all compartments of the thymus including the capsule, subcapsular region, cortex, cortico-medullary junction, and medulla; (2) close associations/interactions of NMSC processes with blood vessels, indicating the neural control of blood flow inside the thymus; (3) the close "synapse-like" association of NMSC processes with various subsets of dendritic cells (DC; e.g., B220⁺ DCs, CD4⁺ DCs, and CD8⁺ DCs), and lymphocytes (B cells, CD4⁺/CD8⁺ thymocytes). Our novel findings concerning the distribution of NMSCs and the associations of NMSCs and immune cells inside mouse thymus should help us understand the anatomical basis and the mechanisms through which the PNS affects T-cell development and thymic endocrine function in health and disease.

Intrinsic and Extrinsic Thymic Adrenergic Networks: Sex Steroid-Dependent Plasticity

The thymus is sexually differentiated organ providing microenvironment for T-cell precursor differentiation/maturation in the major histocompatibility complex-restricted self-tolerant T cells. With increasing age, the thymus undergoes involution leading to the decline in efficacy of thymopoiesis. Noradrenaline from thymic nerve fibers and "(nor)adrenergic" cells is involved in the regulation of thymopoiesis. In rodents, noradrenaline concentration in thymus and adrenoceptor (AR) expression on thymic cells depend on sex and age. These differences are suggested to be implicated in the development of sexual diergism and the age-related decline in thymopoiesis. The programming of both thymic sexual differentiation and its involution occurs during the critical early perinatal period and may be reprogrammed during peripubertal development. The thymic (re)programming is critically dependent on circulating levels of gonadal steroids. Although the underlying molecular mechanisms have not yet been elucidated fully, it is assumed that the gonadal steroid action during the critical perinatal/peripubertal developmental periods leads to long-lasting changes in the efficacy of thymopoiesis partly through (re)programming of "(nor)adrenergic" cell networks and AR expression on thymic cells.

The localization of primary efferent sympathetic neurons innervating the porcine thymus – a retrograde tracing study

The autonomic nervous system is a sophisticated and independent structure composed of two antagonistic (opposing) divisions (sympathetic and parasympathetic) that control many vital functions including: homeostasis maintenance, heart rate, blood circulation, secretion, etc. Thymus is one of the most important primary lymphoid organs playing a role in the developing of a juvenile’s immune system mainly by maturation, development, and migration of T-cells (T lymphocytes). In the last decades, several studies identifying sources of the thymic autonomic supply have been undertaken in humans and several laboratory rodents but not in higher mammals such as the pig. Therefore, in the present work, retrograde tracing technique of Fast Blue and DiI was used to investigate the sources of sympathetic efferent supply to the porcine thymus. After Fast Blue injection into the right lobe of the thymus, the presence of Fast Blue-positive neurons was found in the unilateral cranial cervical ganglion (82.8 ± 3.0% of total Fast Blue-positive neurons) as well as in the middle cervical ganglion (17.2 ± 3.0%). Injection of DiI resulted in the presence of retrograde tracer in neurons of the cranial cervical ganglion (80.4 ± 2.3% of total amount of DiI-labelled neurons), the middle cervical ganglion (18.4 ± 1.9%), and the cervicothoracic ganglion (1.2 ± 0.8%). The present report provides the first data describing in details the localization of primary efferent sympathetic neurons innervating the porcine thymus.

Neuro-immune modulation of the thymus microenvironment (review)

The thymus is the primary site for T-cell lympho-poiesis. Its function includes the maturation and selection of antigen specific T cells and selective release of these cells to the periphery. These highly complex processes require precise parenchymal organization and compartmentation where a plethora of signalling pathways occur, performing strict control on the maturation and selection processes of T lymphocytes. In this review, the main morphological characteristics of the thymus microenvironment, with particular emphasis on nerve fibers and neuropeptides were assessed, as both are responsible for neuro-immune‑modulation functions. Among several neurotransmitters that affect thymus function, we highlight the dopaminergic system as only recently has its importance on thymus function and lymphocyte physiology come to light.

Vitamin E deficiency induces axonal degeneration in mouse hippocampal neurons

Several lines of evidence demonstrate the relationship between vitamin E deficiency and cognitive dysfunction in rodent models, but little is known about the underlying mechanisms. In this study, we found axonal injury in the hippocampal CA1 region of vitamin E-deficient and normal old mice using immunohistochemical assay. The number of cells in the hippocampal CA1 region of vitamin E-deficient mice and normal old mice was significantly lower than in normal young mice. It is well known that collapsin response mediator protein (CRMP)-2 plays a crucial role in the maintenance of axonal conditions. The expressions of CRMP-2 in the cerebral cortex and hippocampus of vitamin E-deficient mice were significantly lower than both the regions of normal ones. In normal old mice, the expression of CRMP-2 in the cerebral cortex was significantly lower than in the normal ones. In addition, the appearance of microtubule-associated protein (MAP)-light chain 3 (LC3), a major index of autophagy, was higher in the cerebral cortex and hippocampus of vitamin E-deficient mice than in normal young and old mice. These results indicate that axonal degeneration is induced in living tissues, but not cultured cells, and that changes in CRMP-2 and MAP-LC3 may underlie vitamin E-deficiency-related axonal degeneration.

Neonatal androgenization affects the efficiency of β-adrenoceptor-mediated modulation of thymopoiesis

We tested the hypothesis that neonatal androgenization affects the efficacy of β-adrenoceptor (β-AR)-mediated fine tuning of thymopoiesis in adult female rats by modulating the thymic noradrenaline (NA) level and/or β-AR expression. In adult rats administered with 1000 μg testosterone enanthate at postnatal day 2 a higher density of catecholamine (CA)-synthesizing thymic cells, including thymocytes, and a rise in their CA content was found. In addition, in these animals increased thymic noradrenergic nerve fiber fluorescence intensity, reflecting their increased CA content, was detected. These changes were followed by an increase in thymic NA concentration. The rise in thymic NA content in thymic nerve fibers and cells was associated with changes in the expression of mRNA for enzymes controlling pivotal steps in NA biosynthesis (tyrosine hydroxylase, dopamine-β-hydroxylase) and inactivation (monoamine oxidase). In contrast, the thymic level of β(2)-AR mRNA on a per cell basis and the receptor surface density on thymocytes was reduced in testosterone-treated (TT) rats. As a consequence, 14-day-long treatment with propranolol, a β-AR blocker, was ineffective in modulating T-cell differentiation/maturation in TT rats. In conclusion, the study indicates the importance of the neonatal sex steroid milieu for shaping the immunomodulatory capacity of the thymic NA/β-AR signaling system in adult rats.

Age-associated remodeling of neural and nonneural thymic catecholaminergic network affects thymopoietic productivity

Ageing is associated with a progressive decline in thymic cytoarchitecture followed by a less efficient T cell development and decreased emigration of naïve T cells to the periphery. These thymic changes are linked to increased morbidity and mortality from infectious, malignant and autoimmune diseases in old age. Therefore, it is of paramount importance to understand the thymic homeostatic processes across the life span, as well as to identify factors and elucidate mechanisms driving or contributing to the thymic involution. Catecholamines (CAs) derived from sympathetic nerves and produced locally by thymic cells represent an important component of the thymic microenvironment. In young rats, they provide a subtle tonic suppressive influence on T cell development acting via β(2)- and α(1)-adrenoceptors (ARs) expressed on thymic nonlymphoid cells and thymocytes. In the face of thymic involution, a progressive increase in the thymic noradrenaline level, reflecting a rise in the density of noradrenergic nerve fibers and CA-synthesizing cells, occurs. In addition, the density of β(2)- and α(1)-AR-expressing thymic nonlymphoid cells and the α(1)-AR thymocyte surface density also exhibit a pronounced increase with age. The data obtained from studies investigating effects of AR blockade on T cell development indicated that age-related changes in CA-mediated thymic communications, certainly those involving α(1)-ARs, may contribute to diminished thymopoietic efficiency in the elderly. Having in mind thymic plasticity in the course of ageing, and broadening possibilities for pharmacological modulation of CA signaling, we here present and discuss the progress in research related to a role of CAs in thymic homeostasis and age-related decay in the thymic naïve T cell output.

Intrinsic innervation and dopaminergic markers after experimental denervation in rat thymus

The aim of this study was to examine rat thymus innervation using denervation techniques and to explore the related microanatomical localization of dopamine, D1, D2 receptors and dopamine membrane transporter (DAT).

In the thymus subcapsular region, the parenchymal cholinergic fibers belong exclusively to phrenic nerve branching. No somatic phrenic nerve branching was detected in any other analysed thymus lobule regions.

In rats subjected to sympathetic or parasympathetic ablation, it was observed that catecholaminergic and cholinergic nerve fibers respectively contributed to forming plexuses along vessel walls.

In the subcapsular and septal region, no parenchymal nerve branching, belonging to sympathetic or parasympathetic nervous system was noted. Instead, in the deep cortical region, cortico-medullary junction (CM-j) and medulla, catecholaminergic and cholinergic nerve fibers were detected along the vessels and parenchyma.

Dopamine and dopamine receptors were widely diffused in the lobular cortico-medullary junction region and in the medulla, where the final steps of thymocyte maturation and their trafficking take place.

No variation in dopamine and DAT immune reaction was observed following total or partial parasympathectomy or phrenic nerve cutting. After chemical or surgical sympathectomy however, neither dopamine nor DAT immune reaction was noted again. Instead, D1 and D2 dopamine receptor expression was not affected by thymus denervation.

In rats subjected to specific denervation, it was observed the direct intraparenchymal branching of the phrenic nerve and sympathetic and parasympathetic fibers into thymus parenchyma along vessels. These findings on the dopaminergic system highlight the importance of neurotransmitter receptor expression in the homeostasis of neuroimmune modulation.

Expression of the onconeural CV2/CRMP5 antigen in thymus and thymoma

Anti-CV2 antibodies (AB) react with the developmentally regulated neural proteins CRMPs and particularly with CRMP5. They occur with small cell lung cancer (SCLC) and thymoma. SCLCs universally express CRMP5. We investigated the expression of CRMPs in thymoma and thymus. In thymoma, none of the CRMPs were detected by immunohistochemistry in tumorous epithelial cells with specific antibodies including CRMP5 but an antibody reacting with a peptide common to the CRMPs labeled a 66-kDa protein in Western blot of rat brain, thymus, and thymoma extracts. Thus, the normal CRMP5 is probably not expressed by tumorous epithelial cells. These results indicate that the mechanisms leading to CRMP5 autoimmunization are different in SCLC and thymoma.

Without nerves, immunology remains incomplete -in vivo veritas

Interest in the interactions between nervous and immune systems involved in both pathological and homeostatic mechanisms of host defence has prompted studies of neuroendocrine immune modulation and cytokine involvement in neuropathologies. In this review we concentrate on a distinct area of homeostatic control of both normal and abnormal host defence activity involving the network of peripheral c-fibre nerve fibres. These nerve fibres have long been recognized by dermatologists and gastroenterologists as key players in abnormal inflammatory processes, such as dermatitis and eczema. However, the involvement of nerves can all too easily be regarded as that of isolated elements in a local phenomenon. On the contrary, it is becoming increasingly clear that neural monitoring of host defence activities takes place, and that involvement of central/spinal mechanisms are crucial in the co-ordination of the adaptive response to host challenge. We describe studies demonstrating neural control of host defence and use the specific examples of bone marrow haemopoiesis and contact sensitivity to highlight the role of direct nerve fibre connections in these activities. We propose a host monitoring system that requires interaction between specialized immune cells and nerve fibres distributed throughout the body and that gives rise to both neural and immune memories of prior challenge. While immunological mechanisms alone may be sufficient for local responsiveness to subsequent challenge, data are discussed that implicate the neural memory in co-ordination of host defence across the body, at distinct sites not served by the same nerve fibres, consistent with central nervous mediation.