Sympathetic innervation of lymph nodes in mice

Beta Adrenergic Signaling as a Therapeutic Target for Autoimmunity

Background

We recently identified a molecular mechanism involving beta-adrenergic 1 and 2 receptors (β1/2) in the development of T H 17 lymphocytes. Pharmacological and genetic inhibition of these receptors in combination, but not separately, impaired the ability of T-lymphocytes to produce proinflammatory interleukin 17A (IL-17A) and instead promoted the production of protective T reg cells that secrete anti-inflammatory interleukin-10 (IL-10). However, it remained unclear whether this regulatory mechanism could serve as a novel therapeutic approach for autoimmune disorders mediated by IL-17A-producing T-lymphocytes.

Methods

Multiple sclerosis (MS) is an inflammatory demyelinating disorder of the central nervous system (CNS) characterized by an autoimmune response where both T-lymphocytes and IL-17A are implicated in the pathogenesis of the disease. Using an animal model of MS, termed experimental autoimmune encephalomyelitis (EAE), we addressed the impact of beta adrenergic receptor blockade (genetically and pharmacologically) on EAE disease progression, severity, and T H 17/T reg balance.

Results

The genetic deletion β1/2 receptors, either systemically or specifically in T-lymphocytes, significantly attenuated EAE disease severity and animal weight loss. Pharmacological blockade of β1/2 receptors with either propranolol (lipophilic) or nadolol (aqueous) limited disease severity and weight loss similar to the genetic models. All models showed degrees of shifted T H 17/T reg balance (suppressing T H 17 and promoting T reg ) and decreased T-lymphocyte IL-17A production. Importantly, pharmacological blockade was initiated at the time of symptom development, which mimics the typical time where diagnosis of disease would occur.

Conclusions

Our data depict a novel role for β1/2 adrenergic signaling in the control of T H 17/T reg cells in EAE. These findings provide new insight into the disease progression as well as provide a potential new pharmacological therapy for IL-17A-related autoimmune diseases.

Purinergic Receptor P2Y1 Modulates Catecholamine Signaling in Murine Mesenteric Lymph Nodes

Neuroimmune communication is crucial for the body's response to physiological challenges, homeostasis, and immune stress response. Adrenergic and purinergic neurotransmission in the sympathetic nervous system is vital for this communication. This study achieves the first co-detection of adenine-based purines and catecholamines in mesenteric lymph nodes via fast-scan cyclic voltammetry. Additionally, we reveal that manipulating an ATP receptor can impact catecholamine signaling in the lymph node for the first time. The G-protein-coupled receptor P2Y1, which controls intracellular Ca2+ levels, was targeted with the antagonist MRS2179. MRS2179 decreased catecholamine concentrations, increased inter-event times, and prolonged event durations. These results suggest that events became smaller, less frequent, and longer-lasting, possibly attributable to decreased intracellular Ca2+ levels. These findings indicate that ATP release in the lymph node can partially regulate norepinephrine signaling, providing mechanistic insight into sympathetic neuronal neurotransmitter control. A deeper understanding of more complicated neuroimmune mechanisms could potentially influence the development of therapeutic strategies in immunology and neurobiology.

Neuroimmune Interactions in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive primary malignancy, and recent technological advances in surgery have opened up more possibilities for surgical treatment. Emerging evidence highlights the critical roles of diverse immune and neural components in driving the aggressive behavior of PDAC. Recent studies have demonstrated that neural invasion, neural plasticity, and altered autonomic innervation contribute to pancreatic neuropathy in PDAC patients, while also elucidating the functional architecture of nerves innervating pancreatic draining lymph nodes. Research into the pathogenesis and therapeutic strategies for PDAC, particularly from the perspective of neuroimmune network interactions, represents a cutting-edge area of investigation. This review focuses on neuroimmune interactions, emphasizing the current understanding and future challenges in deciphering the reciprocal relationship between the nervous and immune systems in PDAC. Despite significant progress, key challenges remain, including the precise molecular mechanisms underlying neuroimmune crosstalk, the functional heterogeneity of neural and immune cell populations, and the development of targeted therapies that exploit these interactions. Understanding the molecular events governing pancreatic neuroimmune signaling axes will not only advance our knowledge of PDAC pathophysiology but also provide novel therapeutic targets. Translational efforts to bridge these findings into clinical applications, such as immunomodulatory therapies and neural-targeted interventions, hold promise for improving patient outcomes. This review underscores the need for further research to address unresolved questions and translate these insights into effective therapeutic strategies for PDAC.

Neuroimmune communication of the cholinergic system in gut inflammation and autoimmunity

Neuroimmune communication in the body forms a bridge between two central regulatory systems of the body, i.e., nervous and immune systems. The cholinergic system is a crucial modulatory neurotransmitter in the central and peripheral nervous system. It includes the neurotransmitter acetylcholine (ACh), the enzyme required for the synthesis of ACh (choline acetyltransferase, ChAT), the enzyme required for its degradation (acetylcholinesterase, AChE), and cholinergic receptors (Nicotinic acetylcholine receptors and muscarinic acetylcholine receptors). The cholinergic system in neurons is well known for its role in cognitive function, sensory perception, motor control, learning, and memory processes. It has been shown that the non-neuronal cholinergic system (NNCS) is present in various tissues and immune cells and forms a neuroimmune communications system. In the present review, we discussed the NNCS on immune cells, its role in homeostasis and inflammatory reactions in the gut, and how it can be exploited in treating inflammatory responses.

Navigating the Neuroimmunomodulation Frontier: Pioneering Approaches and Promising Horizons-A Comprehensive Review

The research in neuroimmunomodulation aims to shed light on the complex relationships that exist between the immune and neurological systems and how they affect the human body. This multidisciplinary field focuses on the way immune responses are influenced by brain activity and how neural function is impacted by immunological signaling. This provides important insights into a range of medical disorders. Targeting both brain and immunological pathways, neuroimmunomodulatory approaches are used in clinical pain management to address chronic pain. Pharmacological therapies aim to modulate neuroimmune interactions and reduce inflammation. Furthermore, bioelectronic techniques like vagus nerve stimulation offer non-invasive control of these systems, while neuromodulation techniques like transcranial magnetic stimulation modify immunological and neuronal responses to reduce pain. Within the context of aging, neuroimmunomodulation analyzes the ways in which immunological and neurological alterations brought on by aging contribute to cognitive decline and neurodegenerative illnesses. Restoring neuroimmune homeostasis through strategies shows promise in reducing age-related cognitive decline. Research into mood disorders focuses on how immunological dysregulation relates to illnesses including anxiety and depression. Immune system fluctuations are increasingly recognized for their impact on brain function, leading to novel treatments that target these interactions. This review emphasizes how interdisciplinary cooperation and continuous research are necessary to better understand the complex relationship between the neurological and immune systems.

T cells at the interface of neuroimmune communication

The immune system protects the host from infection and works to heal damaged tissue after infection or injury. There is increasing evidence that the immune system and the nervous system work in concert to achieve these goals. The sensory nervous system senses injury, infection, and inflammation, which results in a direct pain signal. Direct activation of peripheral sensory nerves can drive an inflammatory response in the skin. Immune cells express receptors for numerous transmitters released from sensory and autonomic nerves, which allows the nervous system to communicate directly with the immune system. This communication is bidirectional because immune cells can also produce neurotransmitters. Both innate and adaptive immune cells respond to neuronal signaling, but T cells appear to be at the helm of neuroimmune communication.

Neuroimmunomodulation of adrenoblockers during liver cirrhosis: modulation of hepatic stellate cell activity

The sympathetic nervous system and the immune system are responsible for producing neurotransmitters and cytokines that interact by binding to receptors; due to this, there is communication between these systems. Liver immune cells and nerve fibres are systematically distributed in the liver, and the partial overlap of both patterns may favour interactions between certain elements. Dendritic cells are attached to fibroblasts, and nerve fibres are connected via the dendritic cell-fibroblast complex. Receptors for most neuroactive substances, such as catecholamines, have been discovered on dendritic cells. The sympathetic nervous system regulates hepatic fibrosis through sympathetic fibres and adrenaline from the adrenal glands through the blood. When there is liver damage, the sympathetic nervous system is activated locally and systemically through proinflammatory cytokines that induce the production of epinephrine and norepinephrine. These neurotransmitters bind to cells through α-adrenergic receptors, triggering a cellular response that secretes inflammatory factors that stimulate and activate hepatic stellate cells. Hepatic stellate cells are key in the fibrotic process. They initiate the overproduction of extracellular matrix components in an active state that progresses from fibrosis to liver cirrhosis. It has also been shown that they can be directly activated by norepinephrine. Alpha and beta adrenoblockers, such as carvedilol, prazosin, and doxazosin, have recently been used to reverse CCl₄-induced liver cirrhosis in rodent and murine models.KEY MESSAGESNeurotransmitters from the sympathetic nervous system activate and increase the proliferation of hepatic stellate cells.Hepatic fibrosis and cirrhosis treatment might depend on neurotransmitter and hepatic nervous system regulation.Strategies to reduce hepatic stellate cell activation and fibrosis are based on experimentation with α-adrenoblockers.

The Sympathetic Nervous System Is Necessary for Development of CD4+ T-Cell Memory Following Staphylococcus aureus Infection

Lymph nodes and spleens are innervated by sympathetic nerve fibers that enter alongside arteries. Despite discovery of these nerve fibers nearly 40 years ago, the role of these nerves during response to infection remains poorly defined. We have found that chemical depletion of sympathetic nerve fibers compromises the ability of mice to develop protective immune memory to a Staphylococcus aureus infection. Innate control of the primary infection was not impacted by sympathectomy. Germinal center formation is also compromised in nerve-depleted animals; however, protective antibody responses are still generated. Interestingly, protective CD4+ T-cell memory fails to form in the absence of sympathetic nerves after S aureus infection.

Neuroanatomy of lymphoid organs: Lessons learned from whole-tissue imaging studies

Decades of extensive research have documented the presence of neural innervations of sensory, sympathetic, or parasympathetic origin in primary and secondary lymphoid organs. Such neural inputs can release neurotransmitters and neuropeptides to directly modulate the functions of various immune cells, which represents one of the essential aspects of the body's neuroimmune network. Notably, recent studies empowered by state-of-the-art imaging techniques have comprehensively assessed neural distribution patterns in BM, thymus, spleen, and LNs of rodents and humans, helping clarify several controversies lingering in the field. In addition, it has become evident that neural innervations in lymphoid organs are not static but undergo alterations in pathophysiological contexts. This review aims to update the current information on the neuroanatomy of lymphoid organs obtained through whole-tissue 3D imaging and genetic approaches, focusing on anatomical features that may designate the functional modulation of immune responses. Moreover, we discuss several critical questions that call for future research, which will advance our in-depth understanding of the importance and complexity of neural control of lymphoid organs.

Fibroblastic reticular cells in lymph node potentiate white adipose tissue beiging through neuro-immune crosstalk in male mice

Lymph nodes (LNs) are always embedded in the metabolically-active white adipose tissue (WAT), whereas their functional relationship remains obscure. Here, we identify fibroblastic reticular cells (FRCs) in inguinal LNs (iLNs) as a major source of IL-33 in mediating cold-induced beiging and thermogenesis of subcutaneous WAT (scWAT). Depletion of iLNs in male mice results in defective cold-induced beiging of scWAT. Mechanistically, cold-enhanced sympathetic outflow to iLNs activates β1- and β2-adrenergic receptor (AR) signaling in FRCs to facilitate IL-33 release into iLN-surrounding scWAT, where IL-33 activates type 2 immune response to potentiate biogenesis of beige adipocytes. Cold-induced beiging of scWAT is abrogated by selective ablation of IL-33 or β1- and β2-AR in FRCs, or sympathetic denervation of iLNs, whereas replenishment of IL-33 reverses the impaired cold-induced beiging in iLN-deficient mice. Taken together, our study uncovers an unexpected role of FRCs in iLNs in mediating neuro-immune interaction to maintain energy homeostasis.

3D anatomy of autonomic innervations in immune organs of a non-human primate and the human

Direct neural inputs to immune organs have been observed for decades, with their functions in neuroimmune regulation being increasingly appreciated. However, the current knowledge of such neural structures, particularly those in primate immune organs, remains incomplete. In this study, we comprehensively assessed the 3D anatomy of autonomic (i.e., sympathetic and parasympathetic) innervations in the immune organs of the rhesus macaque monkey and the human for the first time. Aided with the advanced technique of whole-tissue immunolabeling and lightsheet fluorescence imaging, we revealed the densely organized sympathetic architecture in the parenchyma of the adult monkey and human spleens. On the other hand, only sparse, if any, sympathetic inputs were observed inside the lymph nodes, Peyer's patches, or thymus. In contrast, there were minimal parasympathetic innervations in the parenchyma of these examined immune organs. Together, this work has documented the unique patterns of autonomic innervations in different immune organs of a non-human primate and the human, serving as an essential reference for future research on neuroimmune regulation in the field.

Neuronal regulation of B-cell immunity: Anticipatory immune posturing?

The brain may sense, evaluate, modulate, and intervene in the operation of immune system, which would otherwise function autonomously in defense against pathogens. Antibody-mediated immunity is one arm of adaptive immunity that may achieve sterilizing protection against infection. Lymphoid organs are densely innervated. Immune cells supporting the antigen-specific antibody response express receptors for neurotransmitters and glucocorticoid hormones, and they are subjected to collective regulation by the neuroendocrine and the autonomic nervous system. Emerging evidence reveals a brain-spleen axis that regulates antigen-specific B cell responses and antibody-mediated immunity. In this article, we provide a synthesis of those studies as pertinent to neuronal regulation of B cell responses in secondary lymphoid organs. We propose the concept of defensive immune posturing as a brain-initiated top-down reaction in anticipation of potential tissue injury that requires immune protection.

Control of lymph node activity by direct local innervation

The nervous system detects environmental and internal stimuli and relays this information to immune cells via neurotransmitters and neuropeptides. This is essential to respond appropriately to immunogenic threats and to support system homeostasis. Lymph nodes (LNs) act as sentinels where adaptive immune responses are generated. They are richly innervated by peripheral sympathetic and sensory nerves, which are responsible for the local secretion of neurotransmitters by sympathetic fibers, such as norepinephrine, and neuropeptides by sensory fibers, including calcitonin gene-related peptide (CGRP) and substance P. Additionally, time-of-day-dependent oscillations in nerve activity are associated with differential immune responses, suggesting a potential role for neuroimmune interactions in coordinating immunity in a circadian fashion. Here, we discuss how LN activity is controlled by local innervation.

Neuroimmune axis of cardiovascular control: mechanisms and therapeutic implications

Cardiovascular diseases (CVDs) make a substantial contribution to the global burden of disease. Prevention strategies have succeeded in reducing the effect of acute CVD events and deaths, but the long-term consequences of cardiovascular risk factors still represent the major cause of disability and chronic illness, suggesting that some pathophysiological mechanisms might not be adequately targeted by current therapies. Many of the underlying causes of CVD have now been recognized to have immune and inflammatory components. However, inflammation and immune activation were mostly regarded as a consequence of target-organ damage. Only more recent findings have indicated that immune dysregulation can be pathogenic for CVD, identifying a need for novel immunomodulatory therapeutic strategies. The nervous system, through an array of afferent and efferent arms of the autonomic nervous system, profoundly affects cardiovascular function. Interestingly, the autonomic nervous system also innervates immune organs, and neuroimmune interactions that are biologically relevant to CVD have been discovered, providing the foundation to target neural reflexes as an immunomodulatory therapeutic strategy. This Review summarizes how the neural regulation of immunity and inflammation participates in the onset and progression of CVD and explores promising opportunities for future therapeutic strategies.

Neural control of immune cell trafficking

Leukocyte trafficking between blood and tissues is an essential function of the immune system that facilitates humoral and cellular immune responses. Within tissues, leukocytes perform surveillance and effector functions via cell motility and migration toward sites of tissue damage, infection, or inflammation. Neurotransmitters that are produced by the nervous system influence leukocyte trafficking around the body and the interstitial migration of immune cells in tissues. Neural regulation of leukocyte dynamics is influenced by circadian rhythms and altered by stress and disease. This review examines current knowledge of neuro–immune interactions that regulate leukocyte migration and consequences for protective immunity against infections and cancer.

Loss of direct adrenergic innervation after peripheral nerve injury causes lymph node expansion through IFN-γ

Peripheral nerve injury can cause debilitating disease and immune cell-mediated destruction of the affected nerve. While the focus has been on the nerve-regenerative response, the effect of loss of innervation on lymph node function is unclear. Here, we show that the popliteal lymph node (popLN) receives direct neural input from the sciatic nerve and that sciatic denervation causes lymph node expansion. Loss of sympathetic, adrenergic tone induces the expression of IFN-γ in LN CD8 T cells, which is responsible for LN expansion. Surgery-induced IFN-γ expression and expansion can be rescued by β2 adrenergic receptor agonists but not sensory nerve agonists. These data demonstrate the mechanisms governing the pro-inflammatory effect of loss of direct adrenergic input on lymph node function.

Adrenergic regulation of the vasculature impairs leukocyte interstitial migration and suppresses immune responses

The sympathetic nervous system (SNS) controls various physiological functions via the neurotransmitter noradrenaline. Activation of the SNS in response to psychological or physical stress is frequently associated with weakened immunity. Here, we investigated how adrenoceptor signaling influences leukocyte behavior. Intravital two-photon imaging after injection of noradrenaline revealed transient inhibition of CD8⁺ and CD4⁺ T cell locomotion in tissues. Expression of β-adrenergic receptor in hematopoietic cells was not required for NA-mediated inhibition of motility. Rather, chemogenetic activation of the SNS or treatment with adrenergic receptor agonists induced vasoconstriction and decreased local blood flow, resulting in abrupt hypoxia that triggered rapid calcium signaling in leukocytes and halted cell motility. Oxygen supplementation reversed these effects. Treatment with adrenergic receptor agonists impaired T cell responses induced in response to viral and parasitic infections, as well as anti-tumor responses. Thus, stimulation of the SNS impairs leukocyte mobility, providing a mechanistic understanding of the link between adrenergic receptors and compromised immunity.

Sympathetic nerve distribution in human lymph nodes

Various lymph node functions are regulated by the sympathetic nervous system as shown in rodent studies. If human lymph nodes show a comparable neural regulation, their afferent nerves could represent a potential therapeutic target to treat, for example, infectious or autoimmune disease. Little information is available on human lymph node innervation and the aim of this study is to establish a comprehensive and accurate representation of the presence and location of sympathetic nerves in human lymph nodes. Since previous studies mention sympathetic paravascular nerves to occasionally extent into T cell‐rich regions, the relation of these nerves with T cells was studied as well. A total number of 15 inguinal lymph nodes were resected from six donated human cadavers. Lymph node sections were stained with HE and a double T/B cell staining for evaluation of their morphology and to screen for general pathologies. A triple stain was used to identify blood vessels, sympathetic nerves and T cells, and, to study the presence and location of sympathetic nerves and their relation to T cells. To evaluate whether the observed nerves were en route to other structures or were involved in local processes, adjacent slides were stained with a marker for varicosities (synaptophysin), which presence is suggestive for synaptic activity. All lymph nodes contained sympathetic nerves, both as paravascular and discrete structures. In 15/15 lymph nodes, nerves were observed in their capsule, medulla and hilum, whereas only 13/15 lymph nodes contained nerves in their cortex. The amount of sympathetic nerves varied between compartments and between and within individuals. In general, if a lymph node contained more paravascular nerves in a specific compartment, more discrete nerves were observed as well. Occasionally, discrete nerves were observed in relation to T cells in lymphoid tissues of the cortex and medulla. Furthermore, discrete nerves were frequently present in the capsule and hilum. The presence of varicosities in a portion of these nerves, independently to their compartment, suggested a local regulatory function for these nerves. Human lymph nodes contain sympathetic nerves in their capsule, trabeculae, cortex, medulla and hilum, both as paravascular or as discrete structures. Discrete nerves were observed in relation to T cells and non‐T cell‐rich areas such as the hilar and capsular connective tissue. The presence of discrete structures suggests neural regulation of structures other than blood vessels, which was further supported by the presence of varicosities in a portion of these nerves. These observations are of relevance in further understanding neural regulation of lymph node immune responses and in the development of neuromodulatory immune therapies.

Neuroimmune interactions in cardiovascular diseases

Our body is continuously in contact with external stimuli that need a fine integration with the internal milieu in order to maintain the homoeostasis. Similarly, perturbations of the internal environment are responsible for the alterations of the physiological mechanisms regulating our main functions. The nervous system and the immune system represent the main interfaces between the internal and the external environment. In carrying out these functions, they share many similarities, being able to recognize, integrate, and organize responses to a wide variety of stimuli, with the final aim to re-establish the homoeostasis. The autonomic nervous system, which collectively refers to the ensemble of afferent and efferent neurons that wire the central nervous system with visceral effectors throughout the body, is the prototype system controlling the homoeostasis through reflex arches. On the other hand, immune cells continuously patrol our body against external enemies and internal perturbations, organizing acute responses and forming memory for future encounters. Interesting to notice, the integration of the two systems provides a further unique opportunity for fine tuning of our body's homoeostasis. In fact, the autonomic nervous system guides the development of lymphoid and myeloid organs, as well as the deployment of immune cells towards peripheral tissues where they can affect and control several physiological functions. In turn, every specific immune cell type can contribute to regulate neural circuits involved in cardiovascular function, metabolism, and inflammation. Here, we review current understanding of the cross-regulation between these systems in cardiovascular diseases.

Neuro-Immune Circuits Regulate Immune Responses in Tissues and Organ Homeostasis

The dense innervation of the gastro-intestinal tract with neuronal networks, which are in close proximity to immune cells, implies a pivotal role of neurons in modulating immune functions. Neurons have the ability to directly sense danger signals, adapt immune effector functions and integrate these signals to maintain tissue integrity and host defense strategies. The expression pattern of a large set of immune cells in the intestine characterized by receptors for neurotransmitters and neuropeptides suggest a tight neuronal hierarchical control of immune functions in order to systemically control immune reactions. Compelling evidence implies that targeting neuro-immune interactions is a promising strategy to dampen immune responses in autoimmune diseases such as inflammatory bowel diseases or rheumatoid arthritis. In fact, electric stimulation of vagal fibers has been shown to be an extremely effective treatment strategy against overwhelming immune reactions, even after exhausted conventional treatment strategies. Such findings argue that the nervous system is underestimated coordinator of immune reactions and underline the importance of neuro-immune crosstalk for body homeostasis. Herein, we review neuro-immune interactions with a special focus on disease pathogenesis throughout the gastro-intestinal tract.

Functional circuitry of neuro-immune communication in the mesenteric lymph node and spleen

The peripheral nervous system is an active participant in immune responses capable of blocking aberrant activation of a variety of immune cells. As one of these neuro-immune circuits, the cholinergic anti-inflammatory pathway has been well established to reduce the severity of several immunopathologies. While the activation of this pathway by vagal nerve stimulation requires sympathetic innervation of the spleen, the neuro-immune circuitry remains highly controversial. Neuro-immune pathways in other lymphoid tissues such as mesenteric lymph nodes (MLN) that are critical to the surveillance of the small intestine and proximal colon have not been assessed. Using conditionally expressed Channelrhodopsin, selective stimulation of sympathetic post-ganglionic neurons in the superior mesenteric ganglion (SMG) prevented macrophage activation and LPS-induced TNFα production in the spleen and MLN, but not in the inguinal LN. Site selective stimulation of the SMG induced the release of norepinephrine, resulting in β2AR dependent acetylcholine release in the MLN and spleen. VNS-evoked release of norepinephrine and acetylcholine in the MLN and spleen was significantly reduced using selective optogenetic blockade applied at the SMG. Additionally, this optogenetic blockade restored LPS-induced TNFα production, despite VNS. These studies identify the superior mesenteric ganglion as a critical node in a neuro-immune circuit that can inhibit immune function in the MLN and the spleen.

Immunofluorescence characterization of innervation and nerve-immune cell interactions in mouse lymph nodes

The peripheral nervous system communicates specifically with the immune system via local interactions. These interactions include the “hardwiring” of sympathetic/ parasympathetic (efferent) and sensory nerves (afferent) to primary (e.g., thymus and bone marrow) and secondary (e.g., lymph node, spleen, and gut-associated lymphoid tissue) lymphoid tissue/organs. To gain a better understanding of this bidirectional interaction/crosstalk between the two systems, we have investigated the distribution of nerve fibres and PNS-immune cell associations in situ in the mouse lymph node by using immunofluorescent staining and confocal microscopy/ three-dimensional reconstruction. Our results demonstrate: i) the presence of extensive nerve fibres in all compartments (including B cell follicles) in the mouse lymph node; ii) close contacts/ associations of nerve fibres with blood vessels (including high endothelial venules) and lymphatic vessels/sinuses; iii) close contacts/associations of nerve fibres with various subsets of dendritic cells (e.g., B220⁺CD11c⁺, CD4⁺CD11c⁺, CD8a⁺ CD11c⁺, and Mac1⁺CD11c⁺), Mac1⁺ macrophages, and B/T lymphocytes. Our novel findings concerning the innervation and nerve-immune cell interactions inside the mouse lymph node should greatly facilitate our understanding of the effects that the peripheral nervous system has on cellular- and humoral-mediated immune responses or vice versa in health and disease.

The bidirectional interaction between the sympathetic nervous system and immune mechanisms in the pathogenesis of hypertension

Over the last few years, evidence has accumulated to suggest that hypertension is, at least in part, an immune-mediated inflammatory disorder. Many links between immunity and hypertension have been established and provide a complex framework of mechanistic interactions contributing to the rise in BP. These include immune-mediated inflammatory processes affecting regulatory brain nuclei and interactions with other mediators of cardiovascular regulation such as the sympathetic nervous system. Sympathoexcitation differentially regulates T-cells based upon activation status of the immune cell as well as the resident organ. Exogenous and endogenous triggers activate signalling pathways in innate and adaptive immune cells resulting in pro-inflammatory cytokine production and activation of T-lymphocytes in the cardiovascular and renal regions, now considered major factors in the development of essential hypertension. The inflammatory cascade is sustained and exacerbated by the immune flow via the brain-bone marrow-spleen-gastrointestinal axis and thereby further aggravating immune-mediated pathways resulting in a vicious cycle of established hypertension and target organ damage. This review summarizes the evidence and recent advances in linking immune-mediated inflammation, sympathetic activation and their bidirectional interactions with the development of hypertension. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

Interaction of neurotransmitters and neurochemicals with lymphocytes

Neurotransmitters and neurochemicals can act on lymphocytes by binding to receptors expressed by lymphocytes. This review describes lymphocyte expression of receptors for a selection of neurotransmitters and neurochemicals, the anatomical locations where lymphocytes can interact with neurotransmitters, and the effects of the neurotransmitters on lymphocyte function. Implications for health and disease are also discussed.

Toward the Existence of a Sympathetic Neuroplasticity Adaptive Mechanism Influencing the Immune Response. A Hypothetical View-Part I

The nervous system exerts a profound influence on the function of the immune system (IS), mainly through the sympathetic arm of the autonomic nervous system. In fact, the sympathetic nervous system richly innervates secondary lymphoid organs (SLOs) such as the spleen and lymph nodes. For decades, different research groups working in the field have consistently reported changes in the sympathetic innervation of the SLOs during the activation of the IS, which are characterized by a decreased noradrenergic activity and retraction of these fibers. Most of these groups interpreted these changes as a pathological phenomenon, referred to as "damage" or "injury" of the noradrenergic fibers. Some of them postulated that this "injury" was probably due to toxic effects of released endogenous mediators. Others, working on animal models of chronic stimulation of the IS, linked it to the very chronic nature of processes. Unlike these views, this first part of the present work reviews evidence which supports the hypothesis of a specific adaptive mechanism of neural plasticity from sympathetic fibers innervating SLOs, encompassing structural and functional changes of noradrenergic nerves. This plasticity mechanism would involve segmental retraction and degeneration of these fibers during the activation of the IS with subsequent regeneration once the steady state is recovered. The candidate molecules likely to mediate this phenomenon are also here introduced. The second part will extend this view as to the potential changes in sympathetic innervation likely to occur in inflamed non-lymphoid peripheral tissues and its possible immunological implications.

Adrenergic Signaling: A Targetable Checkpoint Limiting Development of the Antitumor Immune Response

An immune response must be tightly controlled so that it will be commensurate with the level of response needed to protect the organism without damaging normal tissue. The roles of cytokines and chemokines in orchestrating these processes are well known, but although stress has long been thought to also affect immune responses, the underlying mechanisms were not as well understood. Recently, the role of nerves and, specifically, the sympathetic nervous system, in regulating immune responses is being revealed. Generally, an acute stress response is beneficial but chronic stress is detrimental because it suppresses the activities of effector immune cells while increasing the activities of immunosuppressive cells. In this review, we first discuss the underlying biology of adrenergic signaling in cells of both the innate and adaptive immune system. We then focus on the effects of chronic adrenergic stress in promoting tumor growth, giving examples of effects on tumor cells and immune cells, explaining the methods commonly used to induce stress in preclinical mouse models. We highlight how this relates to our observations that mandated housing conditions impose baseline chronic stress on mouse models, which is sufficient to cause chronic immunosuppression. This problem is not commonly recognized, but it has been shown to impact conclusions of several studies of mouse physiology and mouse models of disease. Moreover, the fact that preclinical mouse models are chronically immunosuppressed has critical ramifications for analysis of any experiments with an immune component. Our group has found that reducing adrenergic stress by housing mice at thermoneutrality or treating mice housed at cooler temperatures with β-blockers reverses immunosuppression and significantly improves responses to checkpoint inhibitor immunotherapy. These observations are clinically relevant because there are numerous retrospective epidemiological studies concluding that cancer patients who were taking β-blockers have better outcomes. Clinical trials testing whether β-blockers can be repurposed to improve the efficacy of traditional and immunotherapies in patients are on the horizon.

The immunology of hypertension

Although systemic hypertension affects a large proportion of the population, its etiology remains poorly defined. Emerging evidence supports the concept that immune cells become activated and enter target organs, including the vasculature and the kidney, in this disease. Mediators released by these cells, including reactive oxygen species, metalloproteinases, cytokines, and antibodies promote dysfunction of the target organs and cause damage. In vessels, these factors enhance constriction, remodeling, and rarefaction. In the kidney, these mediators increase expression and activation of sodium transporters, and cause interstitial fibrosis and glomerular injury. Factors common to hypertension, including oxidative stress, increased interstitial sodium, cytokine production, and inflammasome activation promote immune activation in hypertension. Recent data suggest that isolevuglandin-modified self-proteins in antigen-presenting cells are immunogenic, promoting cytokine production by the cells in which they are formed and T cell activation. Efforts to prevent and reverse immune activation may prove beneficial in preventing the long-term sequelae of hypertension and its related cardiovascular diseases.

Immunofluorescent characterization of non-myelinating Schwann cells and their interactions with immune cells in mouse mesenteric lymph node

The central nervous system (CNS) influences the immune system in a general fashion by regulating the systemic concentration of humoral substances, whereas the autonomic nervous system communicates specifically with the immune system according to local interactions. Data concerning the mechanisms of this bidirectional crosstalk of the peripheral nervous system (PNS) and immune system remain limited. To gain a better understanding of local interactions of the PNS and immune system, we have used immunofluorescent staining of glial fibrillary acidic protein (GFAP), coupled with confocal microscopy, to investigate the non-myelinating Schwann cell (NMSC)-immune cell interactions in mouse mesenteric lymph nodes. Our results demonstrate i) the presence of extensive NMSC processes and even of cell bodies in each compartment of the mouse mesenteric lymph node; ii) close associations/interactions of NMSC processes with blood vessels (including high endothelial venules) and the lymphatic vessel/sinus; iii) close contacts/associations of NMSC processes with various subsets of dendritic cells (such as CD4+CD11c+, CD8+CD11c+ dendritic cells), macrophages (F4/80+ and CD11b+ macrophages), and lymphocytes. Our novel findings concerning the distribution of NMSCs and NMSC-immune cell interactions inside the mouse lymph node should help to elucidate the mechanisms through which the PNS affects cellular- and humoral-mediated immune responses or vice versa in health and disease.

Autonomic nervous system and immune system interactions

The present review assesses the current state of literature defining integrative autonomic-immune physiological processing, focusing on studies that have employed electrophysiological, pharmacological, molecular biological, and central nervous system experimental approaches. Central autonomic neural networks are informed of peripheral immune status via numerous communicating pathways, including neural and non-neural. Cytokines and other immune factors affect the level of activity and responsivity of discharges in sympathetic and parasympathetic nerves innervating diverse targets. Multiple levels of the neuraxis contribute to cytokine-induced changes in efferent parasympathetic and sympathetic nerve outflows, leading to modulation of peripheral immune responses. The functionality of local sympathoimmune interactions depends on the microenvironment created by diverse signaling mechanisms involving integration between sympathetic nervous system neurotransmitters and neuromodulators; specific adrenergic receptors; and the presence or absence of immune cells, cytokines, and bacteria. Functional mechanisms contributing to the cholinergic anti-inflammatory pathway likely involve novel cholinergic-adrenergic interactions at peripheral sites, including autonomic ganglion and lymphoid targets. Immune cells express adrenergic and nicotinic receptors. Neurotransmitters released by sympathetic and parasympathetic nerve endings bind to their respective receptors located on the surface of immune cells and initiate immune-modulatory responses. Both sympathetic and parasympathetic arms of the autonomic nervous system are instrumental in orchestrating neuroimmune processes, although additional studies are required to understand dynamic and complex adrenergic-cholinergic interactions. Further understanding of regulatory mechanisms linking the sympathetic nervous, parasympathetic nervous, and immune systems is critical for understanding relationships between chronic disease development and immune-associated changes in autonomic nervous system function.

Mouse models of sepsis elicit spontaneous action potential discharge and enhance intracellular Ca2+ signaling in postganglionic sympathetic neurons

Sepsis is a severe systemic inflammatory disorder that rapidly activates the sympathetic nervous system to enhance catecholamine secretion from postganglionic sympathetic neurons and adrenal chromaffin cells. Although an increase in preganglionic drive to postganglionic sympathetic tissues has been known to contribute to this response for quite some time, only recently was it determined that sepsis also has direct effects on adrenal chromaffin cell Ca2+ signaling and epinephrine release. In the present study, we characterized the direct effects of sepsis on postganglionic sympathetic neuron function. Using the endotoxemia model of sepsis in mice, we found that almost a quarter of postganglionic neurons acquired the ability to fire spontaneous action potentials, which was absent in cells from control mice. Spontaneously firing neurons possessed significantly lower rheobases and fired a greater number of action potentials at twice the rheobase compared to neurons from control mice. Sepsis did not significantly affect voltage-gated Ca2+ currents. However, global Ca2+ signaling was enhanced in postganglionic neurons isolated from 1 to 24 h endotoxemic mice. A similar increase in the amplitude of high-K+-stimulated Ca2+ transients was observed during the cecal ligation and puncture model of sepsis. The enhanced excitability and Ca2+ signaling produced during sepsis likely amplify the effect of increased preganglionic drive on norepinephrine release from postganglionic neurons. This is important, as sympathetic neurons are integral to the anti-inflammatory autonomic reflex that is activated during sepsis.

Spinal cord injury impacts B cell production, homeostasis, and activation

Complex interactions govern the interplay of central nervous and immune systems, including the generation, homeostatic maintenance, and activation of B cells. Accordingly, spinal cord injury will likely impact all of these processes. Several laboratories have recently explored this possibility, and their observations in aggregate reveal both acute and chronic consequences that can vary based on the injury location. Acute effects include a transient cessation of bone marrow B lymphopoiesis, with a corresponding drop in the peripheral follicular and transitional B cell subsets, whereas the marginal zone subset is preserved. Despite recovery of B lymphopoiesis by 28 days post injury, follicular B cell numbers remain depressed; this may reflect reduced levels of the homeostatic cytokine BLyS. In general, the ability to mount T dependent antibody responses after injury are intact, as are pre-existing memory B cell pools and antibody levels. In contrast, T-independent responses are chronically compromised. Both glucocorticoid-dependent and -independent processes mediate these effects, but a detailed understanding of the mechanisms involved awaits further study. Nonetheless, these observations in toto strengthen the growing appreciation for bidirectional interactions between the CNS and immune system, highlighting the need for further basic and translational efforts.

The immune system in hypertension

While hypertension has predominantly been attributed to perturbations of the vasculature, kidney, and central nervous system, research for almost 50 yr has shown that the immune system also contributes to this disease. Inflammatory cells accumulate in the kidneys and vasculature of humans and experimental animals with hypertension and likely contribute to end-organ damage. We and others have shown that mice lacking adaptive immune cells, including recombinase-activating gene-deficient mice and rats and mice with severe combined immunodeficiency have blunted hypertension to stimuli such as ANG II, high salt, and norepinephrine. Adoptive transfer of T cells restores the blood pressure response to these stimuli. Agonistic antibodies to the ANG II receptor, produced by B cells, contribute to hypertension in experimental models of preeclampsia. The central nervous system seems important in immune cell activation, because lesions in the anteroventral third ventricle block hypertension and T cell activation in response to ANG II. Likewise, genetic manipulation of reactive oxygen species in the subfornical organ modulates both hypertension and immune cell activation. Current evidence indicates that the production of cytokines, including tumor necrosis factor-α, interleukin-17, and interleukin-6, contribute to hypertension, likely via effects on both the kidney and vasculature. In addition, the innate immune system also appears to contribute to hypertension. We propose a working hypothesis linking the sympathetic nervous system, immune cells, production of cytokines, and, ultimately, vascular and renal dysfunction, leading to the augmentation of hypertension. Studies of immune cell activation will clearly be useful in understanding this common yet complex disease.

Autonomic regulation of cellular immune function

The nervous system and the immune system (IS) are two integrative systems that work together to detect threats and provide host defense, and to maintain/restore homeostasis. Cross-talk between the nervous system and the IS is vital for health and well-being. One of the major neural pathways responsible for regulating host defense against injury and foreign antigens and pathogens is the sympathetic nervous system (SNS). Stimulation of adrenergic receptors (ARs) on immune cells regulates immune cell development, survival, proliferative capacity, circulation, trafficking for immune surveillance and recruitment, and directs the cell surface expression of molecules and cytokine production important for cell-to-cell interactions necessary for a coordinated immune response. Finally, AR stimulation of effector immune cells regulates the activational state of immune cells and modulates their functional capacity. This review focuses on our current understanding of the role of the SNS in regulating host defense and immune homeostasis. SNS regulation of IS functioning is a critical link to the development and exacerbation of chronic immune-mediated diseases. However, there are many mechanisms that need to be further unraveled in order to develop sound treatment strategies that act on neural-immune interaction to resolve or prevent chronic inflammatory diseases, and to improve health and quality of life.

Inflammation in dorsal root ganglia after peripheral nerve injury: effects of the sympathetic innervation

Following a peripheral nerve injury, a sterile inflammation develops in sympathetic and dorsal root ganglia (DRGs) with axons that project in the damaged nerve trunk. Macrophages and T-lymphocytes invade these ganglia where they are believed to release cytokines that lead to hyperexcitability and ectopic discharge, possibly contributing to neuropathic pain. Here, we examined the role of the sympathetic innervation in the inflammation of L5 DRGs of Wistar rats following transection of the sciatic nerve, comparing the effects of specific surgical interventions 10-14 days prior to the nerve lesion with those of chronic administration of adrenoceptor antagonists. Immunohistochemistry was used to define the invading immune cell populations 7 days after sciatic transection. Removal of sympathetic activity in the hind limb by transecting the preganglionic input to the relevant lumbar sympathetic ganglia (ipsi- or bilateral decentralization) or by ipsilateral removal of these ganglia with degeneration of postganglionic axons (denervation), caused less DRG inflammation than occurred after a sham sympathectomy. By contrast, denervation of the lymph node draining the lesion site potentiated T-cell influx. Systemic treatment with antagonists of α1-adrenoceptors (prazosin) or β-adrenoceptors (propranolol) led to opposite but unexpected effects on infiltration of DRGs after sciatic transection. Prazosin potentiated the influx of macrophages and CD4(+) T-lymphocytes whereas propranolol tended to reduce immune cell invasion. These data are hard to reconcile with many in vitro studies in which catecholamines acting mainly via β2-adrenoceptors have inhibited the activation and proliferation of immune cells following an inflammatory challenge.

Suppression of phagosome proteolysis and Matrigel migration with the α2-adrenergic receptor agonist dexmedetomidine in murine dendritic cells

Dexmedetomidine is a highly-selective α2-adrenergic receptor agonist used for sedation of critically ill patients in an intensive care setting. Dendritic cells (DCs) in peripheral tissues sense certain foreign antigens and ingest and process them, while migrating to the regional lymph node. Then, DCs present the processed antigen on their surface to stimulate the clonal proliferation of cognitive lymphocytes, leading to the establishment of adaptive immunity. In murine bone marrow-derived DCs, dexmedetomidine significantly delayed the intracellular proteolytic degradation of ovalbumin, while it did not affect phagocytosis, decreased the expression of the surface molecules I-A(b) and CD86, and suppressed cognitive helper T-cell proliferation. Furthermore, dexmedetomidine significantly suppressed DC migration both in vitro, using a Matrigel migration assay, and in vivo, using a foot pad-popliteal lymph node migration assay, which may be ascribed to the inhibition of type IV collagenase/gelatinase activity. Finally, vaccination with dexmedetomidine-treated DCs significantly suppressed the contact hypersensitivity reaction in vivo. These results indicate that dexmedetomidine may suppress immunity by inhibiting DC antigen processing/presentation and migration.

Treatment of chronic lymphocytic leukemia requires targeting of the protective lymph node environment with novel therapeutic approaches

Chronic lymphocytic leukemia (CLL) remains associated with low complete response rates and high relapse rates. This is in part due to poor understanding of CLL biology and thus inadequate targeting of therapy. For years CLL has been proposed as bi-compartmental: the quiescent tumor in the periphery and the proliferating cells within specific microenvironments. Historically the bone marrow was considered the major tissue of the CLL microenvironment. However, many recent innovative studies have categorically shown that peripheral CLL cells are derived from the lymph nodes (LN). Proliferation here is largely driven by helper T cells via CD40-CD40L engagement. Critically, in vitro studies have shown that such engagement additionally protects LN CLLs from apoptosis. Agents inducing apoptosis in non-CD40 engaged CLL cells are frequently ineffective against those continually engaged with CD40L. This emphasizes that, in order to improve responses and prevent relapse, novel therapies must be assessed against CD40L engaged CLL cells to show effective targeting against the LN. This review discusses the evidence supporting the superior involvement of the LN in CLL, how CD40L engaged CLL studies should be conducted, and the novel therapies studied in vitro and in vivo that have been proposed to be effective in this setting.

Ventral tegmental area-basolateral amygdala-nucleus accumbens shell neurocircuitry controls the expression of heroin-conditioned immunomodulation

The present investigations sought to determine whether the ventral tegmental area (VTA), basolateral amygdala (BLA), and nucleus accumbens shell (NAC) comprise a circuitry that mediates heroin-induced conditioned immunomodulation. Rats were given conditioning trials in which they received an injection of heroin upon placement into a distinctive environment. Prior to testing, rats received unilateral intra-BLA microinfusion of a D(1) antagonist concomitantly with unilateral intra-NAC shell microinfusion of an NMDA antagonist. Disconnection of the VTA-BLA-NAC circuit impaired the ability of the heroin-paired environment to suppress lipopolysaccharide-induced immune responses, defining for the first time a specific neural circuit involved in conditioned neural-immune interactions.

Neural pathways in allergic inflammation

Allergy is on the rise worldwide. Asthma, food allergy, dermatitis, and systemic anaphylaxis are amongst the most common allergic diseases. The association between allergy and altered behavior patterns has long been recognized. The molecular and cellular pathways in the bidirectional interactions of nervous and immune systems are now starting to be elucidated. In this paper, we outline the consequences of allergic diseases, especially food allergy and asthma, on behavior and neural activity and on the neural modulation of allergic responses.

The central nervous system and inflammation in hypertension

In recent years a major research effort has focused on the role of inflammation, and in particular adaptive immunity, in the genesis of hypertension. Hypertension stimulates the accumulation of inflammatory cells including macrophages and T lymphocytes in peripheral tissues important in blood pressure control, such as the kidney and vasculature. Angiotensin II modulates blood pressure via actions on the central nervous system (CNS) and the adaptive immune system. Recent work suggests that the central actions of angiotensin II via the circumventricular organs lead to activation of circulating T-cells and vascular inflammation. The neuro-immune system plays an essential role in the pathogenesis of hypertension and further understanding of this relationship could lead to the development of new treatment strategies.

Age-associated alterations in sympathetic noradrenergic innervation of primary and secondary lymphoid organs in female Fischer 344 rats

Normal aging processes, as well as, psychological stress affect the immune system; each can act alone, or interact with each other, to cause dysregulation of immune function substantially altering physical and mental health. The sympathetic nervous system (SNS), a major mediator of stress effects on immune function, is significantly affected by normal aging process, and stress can affect aging of the SNS. Previously, we have shown age-associated changes in sympathetic noradrenergic (NA) innervation of lymphoid organs in male rodents that affect immune regulation. The purpose of this study was to investigate sympathetic innervation of lymphoid organs and associated alterations in immune responses in young and aging female Fischer 344 (F344) rats. Histofluorescence and immunocytochemistry for NA innervation, and neurochemistry for norepinephrine (NE) levels were performed in the thymus, spleen, and mesenteric lymph nodes (MLN) isolated from 3-month-old young (normal estrous cycle), 8- to 9-month-old (onset of irregular estrous cycling), and 24-25 month, and 30-31 month female F344 rats (acyclic) at diestrus based on vaginal smears. Age-related alterations in natural killer (NK) cell activity, interleukin-2 (IL-2) and interferon-γ (IFN-γ) production, T and B lymphocyte proliferation were examined in splenocytes. Sympathetic NA innervation and NE levels increased with aging in the thymus, declined in spleen and MLN, and was accompanied by significant reductions in NK cell activity, IL-2 and IFN-γ production, and T and B cell proliferation in old female rats. In 8-9 mo rats, NE levels in the hilar region of the spleen and IFN-γ production were unaltered, while NE levels in the end region of the spleen and IL-2 production were reduced. Collectively, these results suggest that aging is characterized by significant alterations in sympathetic NA innervation in the thymus, spleen, and MLN associated with immunosuppression, and that there is a marked shift in NA activity and immune reactivity occurring during middle-aged female rats.

Dopamine D1 receptors within the basolateral amygdala mediate heroin-induced conditioned immunomodulation

This study investigates the role of basolateral amygdala (BLA) dopamine in heroin-induced conditioned immunomodulation. Animals underwent conditioning in which heroin administration was repeatedly paired with placement into a conditioning chamber. Six days after the final conditioning session animals were returned to the chamber and received intra-BLA microinfusions of dopamine, D(1) or D(2), antagonist. Antagonism of D(1), but not D(2), receptors within the BLA blocked the suppressive effect of heroin-associated environmental stimuli on iNOS, TNF-α and IL-1β. This study is the first to demonstrate that the expression of heroin's conditioned effects on proinflammatory mediators require dopamine D(1) receptors within the BLA.

The sympathetic nervous system modulates CD4(+)FoxP3(+) regulatory T cells via a TGF-beta-dependent mechanism

CD4(+)FoxP3(+) Tregs are essential mediators of the peripheral immune response to self-antigens. Accordingly, the homeostatic regulation of Treg activity and number would impact on the immune response to both self- and non-self antigens. Because the sympathetic nervous system (SNS) interacts chemically and physically with the central and peripheral immune system and exerts a direct influence on antigen-presenting cells and effector lymphocytes, we have investigated the effect of chemical ablation of the SNS on the number and function of peripheral Treg. Removal of murine peripheral sympathetic innervation by 6-hydroxydopamine induced an increase in splenic and lymph node CD4(+)FoxP3(+) Tregs by a TGF-beta-dependent mechanism. Further, this increase in Tregs coincides with an inhibition of the induction of experimental autoimmune encephalomyelitis. Our results demonstrate that the SNS is an important contributor to the maintenance of peripheral Treg and TGF-beta acts as a bridge between the immune system and the nervous system. Neurological events mediated by the SNS, such as a stress response, may affect the number of T cells that regulate an immune response. Additionally, targeting Tregs via the SNS may be a novel approach to the prevention or treatment of autoimmune diseases.

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.

Sympathetic modulation of immunity: relevance to disease

Optimal host defense against pathogens requires cross-talk between the nervous and immune systems. This paper reviews sympathetic-immune interaction, one major communication pathway, and its importance for health and disease. Sympathetic innervation of primary and secondary immune organs is described, as well as evidence for neurotransmission with cells of the immune system as targets. Most research thus far has focused on neural-immune modulation in secondary lymphoid organs, has revealed complex sympathetic modulation resulting in both potentiation and inhibition of immune functions. SNS-immune interaction may enhance immune readiness during disease- or injury-induced 'fight' responses. Research also indicate that dysregulation of the SNS can significantly affect the progression of immune-mediated diseases. However, a better understanding of neural-immune interactions is needed to develop strategies for treatment of immune-mediated diseases that are designed to return homeostasis and restore normal functioning neural-immune networks.