Sympathetic innervation of lymph nodes in mice

Origin of noradrenergic innervation of the spleen in rats

Noradrenergic (NA) sympathetic innervation of the spleen was examined in young adult Sprague-Dawley rats (200-250 g) following surgical removal of the superior mesenteric-celiac ganglia (SM-CG) and/or bilateral transection of the subdiaphragmatic vagus nerve. Sham-operated and unoperated rats served as controls. NA sympathetic innervation of spleens from sham-operated and unoperated controls, and from vagotomized rats, was qualitatively similar, with fibers distributing to the capsule, trabeculae, vasculature, and parenchyma of the white pulp. Complete ganglionic extirpation resulted in almost total denervation of NA fibers in all compartments of the spleen. High-performance liquid chromatography with electrochemical detection (LCEC) for catecholamines (CA) and quantitative morphometry of the density of NA varicosities confirmed these observations. LCEC revealed a greater than 85% depletion of norepinephrine (NE) in the spleen following superior mesenteric-celiac ganglionectomy. Stereological evaluation of NA varicosities with a point counting method revealed a decline of 99% in the volume density of NA terminals that occurred uniformly in all compartments of spleens from ganglionectomized rats. In addition, stereological analysis revealed a loss of total NA varicosities (approximately 31% decrease) in spleens from sham-operated rats. This loss in volume density occurred largely due to a loss in parenchymal fibers (approximately 45% decrease). Bilateral subdiaphragmatic vagotomy blocked the effect on NA innervation produced by the surgical stress of sham operation. Retrograde tracing following injection of either fluorogold or true blue into the spleen, coupled with immunocytochemical localization of tyrosine hydroxylase (TH), demonstrated abundant fluorogold (true blue)-labeled neurons in the SM-CG; many, but not all, of these neurons also were TH-positive. These findings indicate that the SM-CG neurons supply NA innervation to the spleen, providing sympathetic innervation as the second neuron in the classical two-neuron sympathetic chain, and suggest additional non-NA innervation of the spleen as well. This study also suggests that surgical stress of sham operation may alter directly the NA innervation of the spleen, possibly by inducing temporary retraction of NA fibers of the parenchymal compartment, which is likely to reduce the availability of NE for interaction with cells of the immune system that possess adrenoceptors and are present adjacent to NA varicosities in this region.4+ Bilateral vagotomy ameliorated the effects of sham operation on NA innervation; since the vagal nerve does not distribute fibers to the spleen, this effect is likely to occur through altered feedback circuits effecting sympathetic outflow, or through altered neuroendocrine outflow.(ABSTRACT TRUNCATED AT 400 WORDS)

Autonomic innervation of the spleen of the coho salmon, Oncorhynchus kisutch. a histochemical demonstration and preliminary assessment of its immunoregulatory role

Regulation of immunity by the nervous system, now a well-established phenomenon in mammals, is effected in part through the autonomic innervation of lymphoid tissues. Noradrenergic fibers specifically target lymphocyte-rich areas in mammalian lymphoid tissues, and their ablation, or the administration of adrenergic agents, can significantly alter immune responses. This study demonstrates that the spleen of the coho salmon is also richly innervated by adrenergic neurons. While this innervation enters the spleen and remains largely associated with the splenic vasculature, fibers can also be observed entering the parenchyma. Although the coho spleen does not possess a well-developed white pulp, aggregations of leukocytes are found adjacent to the major blood vessels in close proximity to the vascular nervous tissue and parenchymal fibers. Chemical sympathectomy with 6-hydroxydopamine results in a significant enhancement of the splenic antibody-secreting cell response to trinitrophenylated sheep red blood cells. These results suggest that sympathectomy is removing a constraint, in the form of inhibitory catecholamines, on the immune response. The potential benefits from a teleost model of neural-immune interactions are discussed.

Sympathetic neural modulation of the immune system. I. Depression of T cell immunity in vivo and vitro following chemical sympathectomy

Chemical sympathectomy of adult mice with 6-hydroxydopamine (6-OHDA) either prior to or following epicutaneous sensitization with the trinitrophenyl (TNP) hapten decreased the delayed hypersensitivity (DH) response to ear challenge. To determine if uptake of 6-OHDA into sympathetic nerve terminals, and their subsequent destruction, was required for suppression of DH, the catecholamine uptake blocker, desipramine, was employed to block 6-OHDA-induced sympathetic denervation. Pretreatment with desipramine prevented the depression of DH. In vivo treatment with the beta blocker, propranolol, did not alter the 6-OHDA effect, eliminating the potential contribution of released catecholamines, acting on beta-adrenoceptors, to DH reduction. Sympathectomy before sensitization also diminished hapten-specific T cell reactivity of sensitized lymph node (LN) cells, as measured in vitro by IL-2 production and CTL generation. In vivo DNA synthesis in draining LN in response to immunization was modestly decreased following 6-OHDA. Thus, sympathetic denervation appears to impair T cell activity in vivo and in vitro. Overall, these results indicate the SNS plays a role in generation of cell-mediated immunity.

Parallel development of noradrenergic innervation and cellular compartmentation in the rat spleen

By combining neurochemical measurement of norepinephrine (NE) with double-label immunocytochemistry for tyrosine hydroxylase-positive (TH+) noradrenergic nerves and specific lymphoid markers, we have examined the developmental compartmentation of noradrenergic nerves in the rat spleen. TH+ nerve fibers were present in the white pulp of the spleen at birth, among surface IgM-positive (sIgM+) B lymphocytes at the outer border of the periarteriolar lymphatic sheath (PALS), distant from the central artery. During the first 7 days, noradrenergic innervation developed rapidly, forming plexuses of nerve fibers along the central artery and its branches, among T and B lymphocytes of the PALS, and along the developing marginal sinus where ED3+ macrophages accumulate. The splenic concentration of NE (per mg wet wt.) and 3-methoxy-4-hydroxy-phenetheleneglycol (MHPG), a NE metabolite, increased rapidly during this period, suggesting that NE is available and released from these nerves. From 7-14 days, the white pulp expanded to include an inner PALS, outer PALS, marginal sinus, and marginal zone; during this period, TH+ fibers arborized principally among T lymphocytes of the inner PALS and adjacent to macrophages along the marginal sinus. By 14 days of age, NE concentration reached adult levels, although the MHPG/NE ratio (an index of NE turnover) remained higher throughout development than in adulthood. Finally, from 14-28 days, the outer PALS expanded to include follicles containing sIgM+ B lymphocytes. At the earliest stages of follicular development, a parafollicular rim of noradrenergic fibers was present, providing occasional branches which arborized within the follicle. No further changes were observed in either noradrenergic innervation or cellular compartmentation after 28 days of age. These findings suggest that noradrenergic fibers are present in developing compartments of the spleen at the earliest stages of their development, providing norepinephrine for interaction with a variety of adrenoceptor-bearing lymphoid and nonlymphoid cells.

Neurophysiological and endocrine consequences of immune activity

The studies presented herein demonstrate the potency with which activity of the immune system is able to influence the central nervous system. Electrophysiological recordings have demonstrated significant changes in preoptic area/anterior hypothalamic (PO/AH) multiunit electrical activity (MUA) following sensitization with sheep red blood cells. The peak of activity occurred on the fifth day after immunization, the same day that serum antibodies were first detected. A significant increase in paraventricular nucleus MUA was also demonstrated, but this appeared to be delayed with respect to that in the PO/AH, occurring on the sixth day. Further changes thought to be associated with the immune response also were found: Serum corticosterone levels were elevated on the eighth day of the response, and PO/AH tissue levels of norepinephrine were reduced between the sixth and tenth days. During induction of a secondary response, PO/AH MUA showed a different profile of activity from that recorded during the first response. Chronic administration of the immunosuppressive drug, cyclophosphamide, prevented the recorded changes in PO/AH MUA. These results suggest that some secretory product(s) of the activated immune system may be able to exert effects on the central nervous system. Various immunoactive substances therefore were administered intra-cerebroventricularly in order to examine their effects upon PO/AH MUA, cortical EEG and adrenocortical hormone secretory activity. alpha-Interferon and thymic humoral factor were both found to decrease PO/AH MUA, increase EEG synchronization, and decrease basal levels of circulating corticosterone. In contrast, histamine and interleukin-1 did not alter PO/AH MUA but did cause decreased EEG synchronization and increased serum corticosterone levels. With another preparation, a specific activating effect of interleukin-1 upon putative corticotropin-releasing factor-secreting neurones has also been found, identified vasopressinergic neurones not being affected.

Neuropsychological correlates of serum lymphocytotoxic antibodies in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by frequent neuropsychiatric (NP) manifestations. At least two different pathogenetic mechanisms have been proposed for NP-SLE, including vasculitis and antibodies against neuronal antigens, the latter as expressed by the presence of brain cross-reactive lymphocyte antibodies. We have previously reported a high prevalence of cognitive dysfunction in SLE which can remain subclinical and which cannot be accounted for on the basis of disease activity, general distress, or steroid medication. In the present study, we undertook the same extensive, standardized neuropsychological testing in 98 consecutive female SLE patients in order to evaluate central nervous system functioning in relation to serum lymphocyte antibodies which were measured at the time of neuropsychological testing by a microcytotoxicity test. A significant association was observed between the presence of serum lymphocytotoxic antibodies (LCA) and cognitive impairment in patients with SLE. The pattern of impairment which predominated in the LCA-positive patients involved deficits in anteriorly associated, primarily visuospatial functions. These findings support the hypothesis of localization of a particular antigen-antibody interaction in the brain in SLE, suggesting the existence of immunological control mechanisms for normal brain functioning.

The localization of sensory nerve fibers and receptor binding sites for sensory neuropeptides in canine mesenteric lymph nodes

Previous work has established that the central nervous system can modulate the immune response. Direct routes through which this regulation may occur are the sympathetic and sensory innervation of lymphoid organs. We investigated the innervation of canine mesenteric lymph nodes using immunohistochemistry and the expression of binding sites for sensory neuropeptides using quantitative receptor autoradiography. The sympathetic innervation of lymph nodes was examined by immunohistochemical methods using an antiserum directed against tyrosine hydroxylase (TOH), the rate limiting enzyme in catecholamine synthesis. TOH-containing fibers were associated with 90% of the blood vessels (arteries, veins, arterioles and venules) in the hilus, medullary and internodular regions of lymph nodes and in trabeculae with no obvious relationship to blood vessels. The sensory innervation of lymph nodes was investigated using antisera directed against the putative sensory neurotransmitters calcitonin gene-related peptide (CGRP) and substance P (SP). CGRP- and SP-containing fibers were detected in the hilus, the medullary region, and the internodular region of lymph nodes usually in association with arterioles and venules. About 50% of the arterioles and venules exhibited a CGRP innervation and a smaller fraction (5-10%) were innervated by SP-containing fibers. Few if any TOH, CGRP, and SP nerve fibers were detected in the germinal centers of lymph nodes. Using quantitative receptor autoradiography we studied the distribution of receptor binding sites for the sensory neuropeptides CGRP, SP, substance K (SK), vasoactive intestinal peptide (VIP), somatostatin (SOM), and bombesin. Specific CGRP binding sites were expressed throughout lymph nodes by trabeculae, arterioles, venules and 25% of the germinal centers. SP receptor binding sites were localized to arterioles and venules in the T cell regions and 25-30% of the germinal centers. VIP binding sites were localized to the internodular and T cell regions, to medullary cords, and to 10-20% of germinal centers. SK, SOM, and bombesin binding sites were not detected in the lymph nodes, although receptor binding sites for these peptides were detected with high specific/nonspecific binding ratios in other canine peripheral tissues. Taken together with previous results these findings suggest that the sympathetic and sensory innervation of mesenteric lymph nodes appears to be involved with the regulation of their blood and lymph flow. The neuropeptide receptor binding sites in lymph node germinal centers may be expressed by lymphocytes upon activation by antigens.(ABSTRACT TRUNCATED AT 400 WORDS)

Suppression of the immune response by benzodiazepine receptor inverse agonists

24 h after administration of a single dose of the benzodiazepine receptor inverse agonists N'-methyl-beta-carboline-3-carboxamide (FG 7142) and 3-carbomethoxy-4-ethyl-6,7-dimethoxy-beta-carboline (DMCM), a profound suppression of the immune response was observed in rodents. This immunosuppression was manifest as a decrease in phytohemagglutinin (PHA) and concanavalin-A (Con-A) stimulated T cell proliferation in rats and mice administered FG 7142 and a decrease in allogeneic cytotoxic T lymphocyte activity in mice administered either FG 7142 or DMCM. The effects of FG 7142 were antagonized by the prior administration of Ro 15-1788, a benzodiazepine receptor antagonist. These findings demonstrate that the neural pathways subserved by benzodiazepine receptors can modulate immune function, and suggest that these receptors may be involved in the stress-induced modulation of immune function.

Alterations of monoamines in specific central autonomic nuclei following immunization in mice

At the peak of an immune response (Day 4 following immunization) in mice, norepinephrine (NE) was selectively decreased in the paraventricular nucleus (PVN) of the hypothalamus. At times before (Day 2) and after (Day 8) the peak immune response, no changes in NE were found in this nucleus. Decreases in NE were not seen in other hypothalamic sites or in the A1 cell group of the medulla, which sends noradrenergic projections to the hypothalamus, suggesting that the effect is selective and regional. Morphometric evaluation of varicosities revealed no alterations in density of catecholamine-containing varicosities in the PVN, further suggesting that the decrease in NE is a metabolic effect and not a loss or redistribution of fibers. NE also was decreased in the hippocampus on Day 2 at the rising phase of the immune response. In addition, alterations in serotonin levels were found in the brain during an immune response. Serotonin was decreased in the hippocampus on Day 2, was decreased in the PVN and supraoptic nucleus on Day 4, and was increased in the nucleus tractus solitarius (NTS) on Day 2. These results support the presence of a functional link from the activated immune system to central autonomic nuclei interconnecting the hypothalamus, the limbic system, and the autonomic nervous system. In view of the role of the PVN in corticotropin-releasing factor secretion and regulation of autonomic outflow, evidence from lesion studies for hippocampal involvement in immune regulation, and a key role for NTS in regulation of autonomic outflow, the present findings reinforce the potential importance of these brain regions in reciprocal communication between the nervous and immune systems.

Decreased sympathetic innervation of spleen in aged Fischer 344 rats

Splenic noradrenergic innervation in young adult and aged Fischer 344 rats was examined using fluorescence histochemistry for catecholamines and high performance liquid chromatography with electrochemical detection (LCEC) for the quantitation of norepinephrine (NE). In young adult rats, abundant noradrenergic plexuses followed the vasculature and trabeculae into splenic white pulp. In aged rats, noradrenergic innervation was reduced in density and in overall intensity of fluorescence, and splenic NE levels were significantly lower. The relationship between diminished noradrenergic innervation and diminished immune responsiveness in aging mammals, while not clear on a causal level, is presented as a hypothesis for further testing.

Noradrenergic sympathetic innervation of the spleen: IV. Morphometric analysis in adult and aged F344 rats

Noradrenergic postganglionic sympathetic innervation of the spleen in 8-month-old (adult) and 27-month-old (aged) Fischer 344 (F344) rats was examined using fluorescence histochemistry for catecholamines coupled with stereologic point-counting analysis for quantitation of noradrenergic varicosities. Noradrenergic varicosities in the spleen were evaluated in four compartments: (1) vascular-, (2) trabecular-, (3) capsular-, and (4) parenchymal-associated fibers. The 27-month-old rats were subdivided further into two groups based upon behavioral testing for gustatory neophobia, a condition reported to be associated with acute locus coeruleus lesions in young rats and with diminished norepinephrine (NE) levels in central noradrenergic neurons in aged rats. In the 8-month-old rats, spleens displayed abundant innervation. Noradrenergic plexuses entered the spleen with the splenic artery and its branches, distributed into capsular and trabecular compartments, and followed the vasculature and trabeculae into splenic white pulp. Noradrenergic fibers entered the white pulp mainly in association with the central artery and its branches; liner and punctate varicosities branched mainly from vascular plexuses into the large, well-defined parenchyma of the white pulp, ending primarily among fields of T lymphocytes. Some fibers extended along the inner edge of the marginal zone and the parafollicular zone. Few noradrenergic varicosities were found in the red pulp. In both groups of aged rats, sympathetic noradrenergic innervation was diminished markedly.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of the immune system by sympathetic neural mechanisms

The immune system is made up of primary and secondary lymphoid organs, containing lymphocytes and several accessory cell types, which are the key agents of immunological reactivity. Some of the basic features of immune responses are reviewed. Several pathways from the CNS to the immune system are of potential importance in physiological regulation. The sympathetic nervous system innervates all lymphoid organs with noradrenergic fibers. Furthermore, lymphocytes have receptors for sympathetic neurotransmitters, e.g., beta adrenoceptors. Sympathetic denervation by pharmacologic treatment with 6-hydroxydopamine has a marked affect on several immune responses, including antibody production, delayed hypersensitivity, and generation of cytotoxic T lymphocytes. Norepinephrine, epinephrine, and synthetic adrenergic agonists potentiate cytotoxic T lymphocyte responses in vitro. This appears to be mediated via beta 2 adrenoceptors. Studies with adrenoceptor blockers also indicate a possible role for alpha receptors. In sum, our studies indicate that intact noradrenergic innervation is required for normal immune function. Sympathetic neural influence, via norepinephrine release, may be exerted at the cellular (activation, proliferation, secretion of products) as well as the physiologic (antigen localization, lymphocyte migration) levels.

Noradrenergic sympathetic innervation of the spleen: I. Nerve fibers associate with lymphocytes and macrophages in specific compartments of the splenic white pulp

Sympathetic noradrenergic nerve fibers, stained with antiserum for tyrosine hydroxylase (TH), richly innervate the splenic white pulp. These fibers distribute with the vascular and trabecular systems, and associate mainly with the central artery and its branches, the periarteriolar lymphatic sheath (PALS), the marginal sinus, and the parafollicular zone, with occasional delicate fibers also present in the follicles. Simultaneous staining of TH-positive nerve fibers and markers for specific lymphoid cells has shown several regions of contact between nerves and lymphocytes or macrophages. The TH-positive nerve fibers in the plexuses around the central arterial system and in the PALS are present among T lymphocytes (OX-19-positive cells) including both T helper and T suppressor cells, and interdigitating cells. At the marginal sinus, TH-positive fibers run adjacent to macrophages (ED3-positive cells), B lymphocytes (IgM-positive), and intensely fluorescent IgM-positive cells. Along the parafollicular zone, TH-positive nerve fibers run adjacent to T lymphocytes, peripheral follicular B lymphocytes, and intensely fluorescent IgM-positive cells. Within some follicles, delicate fibers end adjacent to both T and B lymphocytes. These relationships suggest a direct interaction between norepinephrine release from the TH-positive nerve terminals and the lymphocytes and macrophages closely associated with them, and focuses attention on the potential neural modulation of related functions such as T and B lymphocyte entry into the spleen and antigen capture (marginal zone), antigen presentation and T cell activation (PALS), B cell activation (parafollicular zone and marginal zone), and lymphocyte egress (outer marginal zone).

Noradrenergic sympathetic innervation of the spleen: III. Development of innervation in the rat spleen

The ontogeny of noradrenergic innervation and its compartmental development were studied in the rat spleen using glyoxylic acid histofluorescence and high-performance liquid chromatography (HPLC). Noradrenergic nerves were present at birth in bundles adjacent to the splenic artery and vein. On days 1-3, fluorescent profiles largely were associated with the vasculature and with the perivascular zone. By day 6, these fibers formed increasingly elaborate and tortuous plexuses around the central arteries and their branches. By day 10, fibers were present along the marginal sinus and extended into the developing marginal zone. Between day 10 and day 13 the largest increase in norepinephrine (NE) levels (per mg protein) were noted, and the periarteriolar lymphatic sheath (PALS) achieved its adult form, with increased innervation of the parenchyma. In contrast, the venous/trabecular system developed relatively late. The first trabecular fibers were evident at day 10, and the capsule was not innervated until day 13. From 13 days to adulthood, there was a gradual refinement and extension of existing patterns with no change in NE levels as measured by HPLC (per mg protein), suggesting that the innervation was keeping pace with rapid increases in spleen growth. The pattern of growth and development for noradrenergic nerves in the PALS remarkably parallels changes in T cell compartmentation during this period. We propose that norepinephrine is available for interaction with T cells at the earliest stages of development and could play a role in such processes as lymphocyte packing and the onset of immunocompetence.

Involvement of peripheral and central catecholamine systems in neural-immune interactions

In this review, we have attempted to delineate the current state of knowledge of the relationships between the immune system and one chemically specific component of the nervous system, the noradrenergic system, both in the brain and the periphery. We have discussed recent work describing the presence of noradrenergic innervation in lymphoid tissues in the major lymphatic organs. Our findings demonstrate clearly that the regions in which lymphocytes (mainly T cells) reside, and through which they recirculate, receive direct sympathetic neural input. The immune system can, therefore, be considered 'hard-wired' to the brain. The evidence for receptors on cells of the immune system capable of receiving signals from the brain is discussed. The significance of this 'hard-wiring' to the function of the immune system is considered, both with regard to the effect of its disruption on immune responses, and to the direct and indirect effects of sympathetic neurotransmitter substances on lymphocytes and their behavior in vitro and in vivo. Finally, our detailed analysis of changes occurring in central noradrenergic pathways as a result of stimulation of the immune system leads to an emerging picture of feedback loops from the immune system to the brain. Such circuits employ endocrine, and probably autonomic, outflow to modulate and regulate immune responses.