Catecholamine influences and sympathetic neural modulation of immune responsiveness

Primary and secondary lymphoid organs are innervated extensively by noradrenergic sympathetic nerve fibers. Lymphocytes, macrophages, and other cells of the immune system bear functional adrenoreceptors. Norepinephrine fulfills criteria for neurotransmission with cells of the immune system as targets. In vitro, adrenergic agonists can modulate all aspects of an immune response (initiative, proliferative, and effector phases), altering such functions as cytokine production, lymphocyte proliferation, and antibody secretion. In vivo, chemical sympathectomy suppresses cell-mediated (T helper-1) responses, and may enhance antibody (T helper-2) responses. Noradrenergic innervation of spleen and lymph nodes is diminished progressively during aging, a time when cell-mediated immune function also is suppressed. In animal models of autoimmune disease, sympathetic innervation is reduced prior to onset of disease symptoms, and chemical sympathectomy can exacerbate disease severity. These findings illustrate the importance of the sympathetic nervous system in modulating immune function under normal and disease states.

Morphological relationships of choleragenoid horseradish peroxidase-labeled spinal primary afferents with myenteric ganglia and mucosal associated lymphoid tissue in the cat esophagogastric junction

The goal of the present study was to gain insight into the environmental factors influencing the activity of primary spinal afferent fibers in the different layers of the esophagogastric junction of the cat and, thus, to analyze the relationships of these afferents with various cellular components. Spinal primary afferent fibers were selectively labeled by anterogradely transported choleragenoid horseradish peroxidase conjugate (B-HRP). B-HRP was injected into the thoracic dorsal root ganglion at the T8-T13 levels. 6-Hydroxydopamine-induced sympathectomy was performed prior to B-HRP injection in order to prevent otherwise unavoidable labeling of sympathetic fibers in the gut wall. Numerous labeled fibers ran between, around, and within the myenteric ganglia. Others crossed the muscle layers directly and entered the mucosa, where some ran near granulocytes and around or through solitary lymphoid follicles. Labeled fibers were observed in the squamous esophageal epithelium but not in the fundic glandular epithelium. The fibers in the myenteric area are probably connected to the muscular tension receptors that have been detected by electrophysiologic techniques. This assumption is based on the observation that only a few fibers appear to terminate in muscle layers and on the fact that the myenteric area is very narrow and subject to powerful forces. Fibers in the myenteric ganglia could be involved in local efferent functions. Fibers in the mucosa could act as nociceptors and might be involved in local immunological responses.

Noradrenergic and peptidergic innervation of lymphoid organs in the beluga, Delphinapterus leucas: an anatomical link between the nervous and immune systems

The presence of peptidergic and noradrenergic sympathetic nerve fibers in specific compartments of both primary and secondary lymphoid organs of the rodent is well established. These nerve fibers directly contact lymphocytes and macrophages, as well as vascular and trabecular smooth muscle. We investigated the noradrenergic and neuropeptide-Y innervation of lymphoid organs in the cetacean, Delphinapterus leucas (beluga whale). The spleen, thymus, tonsil, gut-associated lymphoid tissue, and assorted lymph nodes were collected from five belugas, obtained during sanctioned hunts, and processed for catecholamine fluorescence histochemistry and for tyrosine hydroxylase and neuropeptide-Y immunocytochemistry. Innervation studies revealed fluorescent nerve fibers, tyrosine hydroxylase, and neuropeptide-Y positive nerve fibers in parenchymal lymphoid compartments, where they were closely associated with cells of the immune system, and in vascular and trabecular compartments. In lymphoid zones, tyrosine hydroxylase and neuropeptide-Y positive nerve fibers were observed in the periarteriolar lymphatic sheath and marginal zone of the spleen; in the outermost portion of the cortex, the corticomedullary zone, and medulla of the lymph nodes; in the parafollicular zones, and diffuse lymphocyte layer below the epithelium of the tonsil; in the outermost portion of some thymic lobules; and in the lamina propria of the gut. These findings are similar to those described for other mammals and substantiate an anatomical link between the nervous and immune systems in the beluga, whereby central nervous system activity may influence autonomic outflow to lymphoid organs and effect immunologic reactivity.

Neuroimmune modulation: signal transduction and catecholamines

In recent years, much interest has centered on the commonalities and bi-directional interactions between the nervous system and the immune system. This review focuses on mechanisms through which, catecholamines, a class of neuro-endocrine molecules, modulate immune functions. Catecholamines can be immune suppressive and inhibit lymphocyte activation of both T and B cells as well as the generation of immune-mediated anti-tumor responses. Some of these catecholamine-regulated activities appear to be modulated through the second messenger, cyclic AMP, whereas others appear to be catecholamine-dependent but cyclic AMP independent. Further delineation of the interacting ligand-receptor complexes, populations of responding cells and signal transduction mechanisms leading to the activation of specifically involved genes and gene products, will lead to enhanced understanding of the integratory functions of the nervous system in immune responses, the biology of stress, the role of stress-associated molecular mechanisms in perturbations of physiological homeostasis and the development of a new biological psychiatry with accompanying rational therapeutic modalities.

Noradrenergic and peptidergic innervation of secondary lymphoid organs: role in experimental rheumatoid arthritis

Noradrenergic (NA) and peptidergic nerve fibres are present in both primary and secondary lymphoid organs, distributing with the vasculature, trabecular and capsular smooth muscle, and within the parenchyma among cells of the immune system. NA nerve terminals directly abut lymphocytes and macrophages in spleen and lymph nodes. In these organs, norepinephrine has fulfilled the basic criteria for neurotransmission with cells of the immune system as targets. In vitro and in vivo studies have demonstrated NA modulation of primary and secondary antibody responses, cytotoxic T cell responses, natural killer cell activity, and proliferation and differentiation of both T and B lymphocytes. Substance P (SP) has been shown to modulate inflammatory responses, lymphocyte proliferation, and other immunologic reactivity. We investigated the role of NA and SP nerve fibres within lymph nodes in experimental allergic auto-immune arthritis in Lewis rats. Denervation of NA nerve fibres in popliteal and inguinal lymph nodes with 6-hydroxy-dopamine resulted in earlier onset and enhanced severity of arthritic changes as well as inflammation in bilaterally induced experimental arthritis, while denervation of SP nerve fibres in popliteal and inguinal lymph nodes with capsaicin resulted in delayed onset and diminished severity of the inflammatory changes ipsilaterally, and prevention of contralateral arthritic changes in unilaterally induced experimental arthritis. These findings suggest that NA and SP nerve fibres in lymph nodes can modulate the time course of onset and the severity of experimental arthritis in Lewis rats. These modulatory effects are distinctly different from the effects of NA and SP nerve fibres in the joints themselves.

Central nervous system influences on lymphocyte migration

The immune response network is only one of many physiologic adaptive responses to environmental change and there is now substantial evidence that adaptive responses involving the central nervous system have an impact on immune outcome. Effective immune function depends upon a highly mobile population of precursor and effector cells of the lymphoid system. In this review it is proposed that many of the alterations in immunity resulting from CNS activity may be explained in terms of changes in lymphocyte migration patterns in response to endocrine signals, neural signals via neurotransmitter release, or direct contacts between nerves and cells of the immune system.

Innervation of lymphoid organs and implications in development, aging, and autoimmunity

We now have substantial evidence demonstrating noradrenergic sympathetic and peptidergic innervation of both primary and secondary lymphoid organs. We have established criteria for norepinephrine, and some of the neuropeptides, as neurotransmitters, and have found changes in immune responsiveness following pharmacological manipulation of noradrenergic sympathetic or peptidergic nerves. Classic receptor binding studies have demonstrated a wide variety of target cells that possess beta-adrenoceptors and receptors for neuropeptides on cells of the immune system, including lymphocyte subsets, macrophages, accessory cells, or stromal elements. In this chapter we describe noradrenergic and peptidergic innervation of primary and secondary lymphoid organs in development, at maturation and during the normal aging process, and discuss possible functional implications of direct neural signals onto cells of the immune system at critical time points in the lifespan of an animal. Further, we examine for involvement of noradrenergic sympathetic and peptidergic innervation in the development and progression of several autoimmune disorders, including adjuvant-induced arthritis, New Zealand mice strains as a model for hemolytic anemia and lupus-like syndrome, and the experimental allergic encephalomyelitis model for multiple sclerosis.

Innervation of mucosal immune cells in the gastrointestinal tract

There is mounting evidence for interactions between the immune and peripheral nervous systems. Many regulatory molecules are candidate mediators for communication between inflammatory cells and nerves; however, the extent of targeting of neurotransmitters (and interleukins) as intersystem messengers has been somewhat overlooked. Lymphoid tissues are well supplied by nerves and the gastrointestinal lamina propria, which is populated by a variety of immune cell types, is densely innervated. One-half to two-thirds of mast cells are closely apposed to nerves in the intestinal mucosa, in both rodents and humans, and nerve stimulation has been reported to cause mast cell activation. Although less extensively studied, both eosinophils and plasma cells in the gastrointestinal mucosa are also positioned for interaction with nerves, and intra-epithelial leukocytes may be subject to diffusible neurally-derived mediators. Peyer's patches are relatively sparsely innervated but appear to express neuropeptide receptors in inflammatory conditions. Although the nerves in the mucosa have traditionally been thought of as a static component, recent experiments suggest that these may undergo extensive remodelling during nematode-induced inflammation. Such data suggest a dynamic interplay between the immune and nervous systems during inflammatory episodes in the gut, although considerable work is still needed to determine the importance of neuro-immune interactions in gastrointestinal homeostasis and inflammation.

Stress--mechanisms of immunosuppression

Stress, a term commonly used to describe varied phenomena, should be restricted to describe an adaptive response by an animal to threats to homeostasis. The threats to homeostasis are called stressors. Stressors include a variety of physical, psychological, chemical, or infectious causes that are modified by intrinsic and extrinsic factors. Examples of modifiers include stressor severity, duration, novelty, host genetics and immune status. What may be a stressor to an animal in one situation, when modified, may not be a stressor in another situation. Mechanisms of stress once thought to involve a single pathway described by Seyle as the General Adaptation Syndrome, have been rejected. Four pathways, some incompletely defined, have been implicated in modulation of the immune system. They include autonomic nervous system, the hypothalamic adrenal axis, extra-adrenal pathways involving neuropeptides and neurotransmitters and neuroimmunological mediators. The mechanisms of stress-induced immunosuppression resistance are poorly defined in domestic fowl and will require careful experimentation linking defined stressors with altered physiological responses that affect specific immune function and result in increased disease susceptibility.

[The effect of in vitro X-irradiated blood transfusions on the morphostructure of immunocompetent organs and their nerve elements]

A study was made of changes that occur in the rat thymus, spleen, lymph nodes, their nerve elements, and spinal ganglia under the effect of the in vitro X-irradiated blood transfusions. Parallelism was noted in the activation of the immunocompetent organ morphostructures, the rate of reactive alterations in nerve elements, and the improvement of the immunity indices.

Peptidergic innervation of rat lymphoid tissue and lung: relation to mast cells and sensitivity to capsaicin and immunization

The peptidergic innervation of lymphoid tissue and the lung in relation to mast cells was studied in rat. The sensitivity of neuropeptide-containing nerves to capsaicin treatment and immunization was also examined. Measurements of the content of neurokinin A and calcitonin gene-related peptide revealed that the lung contained the highest content of both neuropeptides; lymph nodes had intermediate levels, whereas the spleen had the lowest content. Immunohistochemistry showed that the calcitonin gene-related peptide- and neurokinin A-immunoreactive nerves in lymph nodes were mainly found around blood vessels, whereas in the lung the nerves were present within the lining respiratory epithelium, bronchial smooth muscle, around blood vessels and close to lymphoid aggregates. Combined immunohistochemistry for serotonin (5-hydroxytryptamine), as a marker for mast cells, and tachykinins or calcitonin gene-related peptide revealed that a close association was often present between the nerves and 5-hydroxytryptamine-positive cells in the bronchi of the lung, while 5-hydroxytryptamine-positive cells were not observed in lymph nodes. The neurokinin A and calcitonin gene-related peptide content in lymph nodes, spleen and lung, but not the content of neuropeptide Y, was markedly decreased by capsaicin treatment, suggesting a sensory origin for the two former peptides. Aerosol immunization increased the levels of calcitonin gene-related peptide in the lung, whereas the content in mediastinal lymph nodes was not affected. These data demonstrate a peptidergic innervation mainly of blood vessels in lymphoid tissue and a close relation between sensory nerves and mast cells as well as lymphoid aggregates in the bronchi of the lung.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of peptidergic nerve fibers in rat bronchus-associated lymphoid tissue: light microscopic observations

The localization of neuropeptide Y (NPY), substance P (SP), calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) in the nerve fibers of rat bronchus-associated lymphoid tissue (BALT) was investigated by light microscopic immunohistochemistry. Nerve fiber bundles revealing NPY-like immunoreactivity were shown to enter the BALT together with pulmonary artery branches. They frequently reached the central zone of the BALT to give rise to fine, tortuous fibers. On the other hand, nerve fibers immunoreactive for SP and CGRP seemed to distribute in the subepithelial zone of the BALT after dissociating from fiber networks in the walls of bronchi, although small numbers of SP and CGRP fibers were also seen in the BALT central zone. CGRP fibers formed a more intense network than SP fibers in the BALT. Scattered VIP fibers were found only in the subepithelial zone of the BALT. These findings not only suggest that the four kinds of peptidergic fibers act on BALT in multiple ways, but also that these neuropeptides may be involved in the control of mucosal immunity, lymphocyte migration and proliferation within the BALT.

Neuroimmunomodulatory interactions of norepinephrine and serotonin

Monoamine neuroleptics alter rodents responses to immunization, suggesting that norepinephrine (NE) and serotonin (5HT) are neuroimmunomodulatory in these animals. Although endocrine factors participate in their mechanism(s) of action, recent studies suggest that NE and 5HT also interact more directly with immunocompetent cells. This review provides an overview of evidence for a direct regulatory link between the nervous and immune systems and further speculates on the process by which NE and 5HT realize in part, their neuroimmunomodulatory potential. Anatomical data show that noradrenergic fibers of the sympathetic nervous system innervate lymphoid organs providing a channel of communication between neurons and lymphocytes. Presumably neural signals transmitted by NE are received by platelets that in turn, transduce them via 5HT into immunomodulatory messages. It is proposed that NE alters the capacity of platelets to sequester and/or catabolize 5HT, thus regulating its physiologically active pool in the plasma. Macrophages possess a 5HT uptake system, the kinetic properties of which make them sensitive to changes in plasma levels of the amine. Thus, through its ability to regulate plasma levels of 5HT, an immunosuppressive amine with access to macrophages, the nervous system can influence cells involved in antigen recognition. Support for this hypothetical immunomodulatory mechanism is gleaned from clinical and experimental studies. For example, individuals suffering emotional trauma are more susceptible than others to developing physical illness. It is of interest that platelet 5HT pharmacodynamics are often abnormal in patients with psychological disorders characterized by catecholamine deficits. Similar platelet changes have been achieved experimentally by treating rats with catecholamine antimetabolites. Additional support for the hypothesis derives from aging research since 'monoamine imbalance' and immune dysfunction are co-characteristics of senescence. In aging rodents and humans, central catecholamine deficits are associated with a decreased platelet affinity for 5HT and an increased plasma content of 5HT. Thus, emotional, spontaneous (age-related), or experimental changes in monoamine homeostasis have the potential to increase the risk of disease in affected individuals. Perhaps part of this effect results from endocrine perturbations associated with the trauma. However, a direct interaction between the nervous and immune systems involving monoamines is also possible, and a need for future study of this potentially significant mechanism for neuroimmunomodulation is indicated.

Noradrenergic and peptidergic innervation of lymphoid tissue

Sympathetic noradrenergic nerve fibers innervate both the vasculature and parenchymal fields of lymphocytes and associated cells in several lymphoid organs, including the thymus, spleen, lymph nodes, gut-associated lymphoid tissue (GALT), and bone marrow, in a variety of mammalian species. This innervation is both regional and specific, and generally is directed into zones of T lymphocytes and plasma cells rather than into nodular regions or B lymphocyte regions. In the thymus, noradrenergic fibers enter with nerve bundles and plexuses around blood vessels, travel into the cortex from subcapsular plexuses and with the vasculature, and branch into the parenchyma of the thymic cortex. The vasculature and parenchymal regions of both the outer and deep cortex are innervated by these fibers. In the spleen, noradrenergic fibers enter with the vasculature, travel along the trabeculae and along the branching vasculature, and are distributed mainly in the white pulp along the central artery and associated periarterial lymphatic sheath. Fibers branch from a dense plexus around the central artery and travel into the parenchyma, where they end among fields of lymphocytes and other cell types. In lymph nodes, noradrenergic fibers enter at the hilus, travel along the vasculature and in a subcapsular plexus, and branch into the parenchyma in paracortical and cortical regions, where they end among lymphocytes. In the GALT, represented in these studies by rabbit appendix, sacculus rotundus, and Peyer's patches, noradrenergic fibers enter at the serosal surface, travel longitudinally with the muscularis interna, turn radially into internodular plexuses, plunge directly through the thymus-dependent zones, and ramify profusely among lymphocytes, enterochromaffin cells, and plasma cells in the interdomal regions. In the bone marrow, noradrenergic fibers enter with blood vessels, distribute deeply into the marrow on those vessels, and branch sparsely into the substance of the marrow. Immunocytochemical observations revealed the presence of neuro-peptide-like immunoreactivity in the thymus and spleen. Vasoactive intestinal peptide (VIP)-like immunoreactivity is found in varicose profiles in the thymus within the cortex. In the spleen, immunoreactive profiles showing neuropeptide Y-like, Met-enkephalin-like, cholecystokinin-8 (CCK)-like, and neurotensin-like immunoreactivity are present along the central artery of the white pulp and its smaller branches, with only sparse fibers of most of these peptides entering the parenchyma. CCK-like profiles are present in abundance in the white pulp among parenchymal elements.(ABSTRACT TRUNCATED AT 400 WORDS)

Immune-neuroendocrine interactions

Concepts and facts concerning immune-neuroendocrine interactions are discussed. The immune response elicits endocrine, autonomic, and brain functional changes. These changes can be mediated by soluble factors released by activated immunologic cells. As a result of these immune-neuroendocrine interactions the content of powerful agents such as hormones, neurotransmitters, and neuropeptides in the microenvironment of immunologic cells is modified. This leads to external immunoregulatory signals imposed upon autoregulatory mechanisms.

Autonomic nervous system innervation of thymic-related lymphoid tissue in wildtype and nude mice

A study was undertaken to determine the source and terminal distribution of the autonomic nervous system (ANS) innervation of lymphoid tissue in the mediastinum of male and female B10 and Balb/c wildtype and syngeneic nude (nu/nu) mice. Acetylcholinesterase (AChE) histochemistry was used to localize this hydrolytic enzyme in neural tissue and glyoxylic acid fluorescent histochemistry was used to characterize catecholaminergic (CA) innervation. The thymus was innervated by AChE-positive fibers of the vagus, the recurrent laryngeal, and the phrenic nerves. Catecholaminergic innervation was derived from the stellate ganglia and other small ganglia of the thoracic sympathetic nervous system chain. Whereas intrinsic AChE-positive innervation of the thymus was evident at the cortico-medullary boundaries and under the capsule, CA innervation was observed along the trabeculae with perivascular plexuses at the cortico-medullary boundaries and interlobular septa. Free CA fibers were noted in the medulla and in the cortex, where they were often proximal to cortical autofluorescent (CAF) cells. The rudimentary thymus of the adult nude mouse received limited ANS innervation. Only a few CA or AChE-positive fibers were evident, with the majority of fibers associated with the acinar cells of the gland. Mediastinal lymph nodes in male and female wildtype mice varied in their distribution and were frequently found clustered around nerves and ganglia. The intrinsic innervation of lymph nodes by AChE-positive fibers was confined to the subcapsular marginal sinus, with a few vascular-associated fibers in the parenchyma. Catecholaminergic perivascular plexuses were present in the hilar zone, whereas some free fibers were noted under the capsule and in the parenchyma. The mediastinal lymph nodes of male and female nude mice when compared to the lymph nodes of male and female wildtype mouse were found to be increased in number and in distribution. Clusters of these lymph nodes were found in close proximity to ANS tissue. The intrinsic innervation of the nude mediastinal lymph nodes was comparable to that present in the wildtype mouse tissue. The functional implication of these data is discussed with regard to nervous:immune system interactions.

Direct contacts between nerve endings and lymphoid cells in the jugular body of Rana pipiens

The ultrastructure of contacts between nerve terminals and lymphoid cells in a lymphoid myeloid organ, the jugular body, of Rana pipiens, has been analyzed. The results are discussed emphasizing their importance for functional relationships between the neuroendocrine and lymphoid systems.

A contribution to the study of lymphopoiesis in the bursa of Fabricius in Gallus domesticus

It has been proposed that the anatomical connection between the bursa of Fabricius and the cloaca is the pathway for unknown intestinal factors which are necessary for the induction of normal bursal lymphopoiesis. It has also been suggested that normal lymphopoiesis occurs only if nerve and vascular connections are intact. Experiments were performed to test these hypotheses. To test the influence of the intestinal contents, the bursal stalk was cut on the 16th day of incubation or at hatching. In this way, contact between the bursa and the intestinal flow in embryos was avoided and bacterial contamination of the bursa at hatching was also avoided. No change in the bursal follicles was observed. To study the influence of the nervous system on bursal lymphopoiesis, the bursa was isolated from the cloaca at hatching, and by maintaining vascularization the bursa was sutured to the peritoneum of the abdominal wall after scratching the contact surfaces. Once a new vascular network was established, one fragment of bursa was completely isolated from its normal anatomical site, causing interruption of the blood vessels and nerves of the bursa. The histological appearance of the bursa was not changed. It would appear that the integrity of the anatomical relation between bursa and cloaca and an intact nerve supply is not necessary for normal lymphopoiesis to occur in the bursa of Fabricius. In contrast, sufficient vascularization appears to be essential.

[Functional morphology of the adrenergic innervation and adrenocontaining structures of the lymphoid organs]

Topography of adrenergic neural fibres and adrenodependent structures in lymphoid organs of some mammals (rat, cat, dog, guinea-pig, golden hamster) has been studied by means of Falck's method with other histochemical methods applied simultaneously. In thymus, spleen, tonsils, lymph nodes and appendix adrenergic innervation is performed at the expense of adventitial vascular plexus and some neural fibres directed towards the organs' parenchyma. In the parenchyma of the lymphoid organs some fluorescent interfollicular macrophages and intrafollicular cells with serotonin and catecholamines in their cytoplasm were detected spectroscopically. These two types of cells respond differently to increasing amount of free amines in the organism. Orthochromic mast cells and elastic fibres also possess fluoresent properties which are connected with the presence of serotonin and catecholamines in the lymphoid organs.

[Bronchial lympho-epithelial nodules in the rat. Definition and morphological characteristics in optical and electron microscopy (author's transl)]

Among the bronchial lymphoid tissue, lympho-epithelial nodules are an original component, easily distinguished from other structures, particularly from lymphoid cell infiltrates. Such structures are encountered in many species and may be characterized by a flattened epithelium, containing a few ciliated cells, devoid of mucus producing cells, and infiltrated with lymphocytes. Inter and intracellular vacuoles are described in the lympho-epithelium and the underlying mucosa. Electron microscope studies support the view that lymphoepithelium has a "trapping" function of particulate matter, more direct evidence is however attempted. Peripheral lymphatic vessels and high endothelium veins contribute to the important lymphocyte transfer. An hypothesis of capacity for antigenic recognition of the lymphoepithelial nodule is discussed.