The neuro-endocrine-immune relationship in pulmonary and pleural tuberculosis: a better local profile in pleural fluid

BACKGROUND

Tuberculosis (TB) is a major health problem worldwide. In TB, the immune and central nervous systems modulate each other. The two main components of this network are the hypothalamic-pituitary-adrenal axis (HPA) and autonomic nervous system (ANS).

OBJECTIVE

To elucidate neuro-endocrine-immune (NEI) interactions in pulmonary (PTB) or pleural (PLTB) TB, we analysed the relationship among compounds from these systems.

METHODS

We quantified levels of catecholamines, hormones and cytokines in plasma from patients with PTB (n = 46) or PLTB (n = 12) and controls (n = 32), and in the pleural fluid from PLTB patients. Transcript expression for genes involved in glucocorticoid-related function (quantitative real-time polymerase chain reaction) was also analysed in mononuclear cells (MCs) from peripheral blood (PBMC) or pleural effusion (PEMC) compartments.

RESULTS

Both patient groups had increased plasma levels of pro- and anti-inflammatory cytokines, cortisol, growth hormone (GH) and dopamine, whereas insulin-like growth factor 1 (IGF-1) and dehydroepiandrosterone levels were decreased. The pleural fluid contained increased levels of pro-inflammatory cytokines, GH and IGF-1 and reduced levels of steroid hormones compared with their plasma counterparts. PBMCs from PTB patients had increased expression of transcripts for 11β-hydroxysteroid dehydrogenase (11βHSD1) and a decreased glucocorticoid receptor (GR) ratio (GRα/GRβ). In PLTB cases, expression of 11βHSD1 and GRα transcripts was higher in PEMCs.

CONCLUSION

PTB patients seem to display adverse NEI dysregulation. Changes in pleural fluid are compatible with a more effective NEI reaction.

Intranasal delivery of dexamethasone efficiently controls LPS-induced murine neuroinflammation

Neuroinflammation is the hallmark of several infectious and neurodegenerative diseases. Synthetic glucocorticoids (GCs) are the first-line immunosuppressive drugs used for controlling neuroinflammation. A delayed diffusion of GCs molecules and the high systemic doses required for brain-specific targeting lead to severe undesirable effects, particularly when lifelong treatment is required. Therefore, there is an urgent need for improving this current therapeutic approach. The intranasal (i.n.) route is being employed increasingly for drug delivery to the brain via the olfactory system. In this study, the i.n. route is compared to the intravenous (i.v.) administration of GCs with respect to their effectiveness in controlling neuroinflammation induced experimentally by systemic lipopolysaccharide (LPS) injection. A statistically significant reduction in interleukin (IL)-6 levels in the central nervous system (CNS) in the percentage of CD45⁺ /CD11b⁺ /lymphocyte antigen 6 complex locus G6D [Ly6G⁺ and in glial fibrillary acidic protein (GFAP) immunostaining was observed in mice from the i.n.-dexamethasone (DX] group compared to control and i.v.-DX-treated animals. DX treatment did not modify the percentage of microglia and perivascular macrophages as determined by ionized calcium binding adaptor molecule 1 (Iba1) immunostaining of the cortex and hippocampus. The increased accumulation of DX in brain microvasculature in DX-i.n.-treated mice compared with controls and DX-IV-treated animals may underlie the higher effectiveness in controlling neuroinflammation. Altogether, these results indicate that IN-DX administration may offer a more efficient alternative than systemic administration to control neuroinflammation in different neuropathologies.

Electric stimulation of the vagus nerve reduced mouse neuroinflammation induced by lipopolysaccharide

Background

Neuroinflammation (NI) is a key feature in the pathogenesis and progression of infectious and non-infectious neuropathologies, and its amelioration usually improves the patient outcome. Peripheral inflammation may promote NI through microglia and astrocytes activation, an increased expression of inflammatory mediators and vascular permeability that may lead to neurodegeneration. Several anti-inflammatory strategies have been proposed to control peripheral inflammation. Among them, electrical stimulation of the vagus nerve (VNS) recently emerged as an alternative to effectively attenuate peripheral inflammation in a variety of pathological conditions with few side effects.

Considering that NI underlies several neurologic pathologies we explored herein the possibility that electrically VNS can also exert anti-inflammatory effects in the brain.

Methods

NI was experimentally induced by intraperitoneal injection of bacterial lipopolysaccharide (LPS) in C57BL/6 male mice; VNS with constant voltage (5 Hz, 0.75 mA, 2 ms) was applied for 30 s, 48 or 72 h after lipopolysaccharide injection. Twenty four hours later, pro-inflammatory cytokines (IL-1β, IL-6, TNFα) levels were measured by ELISA in brain and spleen extracts and total brain cells were isolated and microglia and macrophage proliferation and activation was assessed by flow cytometry. The level of ionized calcium binding adaptor molecule (Iba-1) and glial fibrillary acidic protein (GFAP) were estimated in whole brain extracts and in histologic slides by Western blot and immunohistochemistry, respectively.

Results

VNS significantly reduced the central levels of pro-inflammatory cytokines and the percentage of microglia (CD11b/CD45^low) and macrophages (CD11b/CD45^high), 24 h after the electrical stimulus in LPS stimulated mice. A significantly reduced level of Iba-1 expression was also observed in whole brain extracts and in the hippocampus, suggesting a reduction in activated microglia.

Conclusions

VNS is a feasible therapeutic tool to attenuate the NI reaction. Considering that NI accompanies different neuropathologies VNS is a relevant alternative to modulate NI, of particular interest for chronic neurological diseases.

An adverse immune-endocrine profile in patients with tuberculosis and type 2 diabetes

Diabetes is a risk factor for the development of pulmonary tuberculosis (TB) and both diseases present endocrine alterations likely to play a role in certain immuno-endocrine-metabolic associated disorders. Patients with TB, or with TB and type 2 diabetes (TB + T2DM) and healthy controls (HCo) were assessed for plasma levels of cortisol, dehydroepiandrosterone (DHEA), estradiol, testosterone, growth hormone (GH), prolactin, insulin-like growth factor-1 (IGF-1), cytokines (IL-6, IL-10, IFN-γ) and the specific lymphoproliferative capacity of peripheral blood mononuclear cells. All patients had higher levels of cortisol with a reduction in DHEA, thus resulting in an increased cortisol/DHEA ratio (Cort/DHEA). Increased prolactin and particularly GH levels were found in both groups of TB patients. This was not paralleled by increased concentrations of IGF, which remained within the levels of HCo. Estradiol levels were significantly augmented in patients TB, and significantly more in TB + T2DM, whereas testosterone levels were decreased in both groups of patients. IFN- γ and IL-6 concentrations were significantly increased in all TB, even further in TB + T2DM; while IL-10 was equally increased in both groups of TB patients. The in vitro specific proliferative capacity was decreased in both groups of patients as compared to that of HCo. The adverse immune-endocrine profile of TB seems to be slightly more pronounced in patients who also have T2DM.

The Immuno-endocrine Component in the Pathogenesis of Tuberculosis

Tuberculosis (TB) may be regarded as a disease in which the immune response to Mycobacterium tuberculosis, its etiologic agent, is engaged both in protection and pathology. Different T-lymphocyte subsets are involved in the immune response against M. tuberculosis, but production of interferon-gamma (IFN-gamma) by T cells seems to be fundamental for disease control. Th1-type cytokine responses predominate in patients with mild or moderate forms of pulmonary TB, whereas the production of Th2-type cytokines prevails in the severe disease. Since the immune response fails to definitely eradicate the pathogen, a chronic infection is established, and it is likely that a broad range of regulatory mechanisms operate in this situation. Cytokines released during the course of an immune response activate the hypothalamus-pituitary-adrenal axis leading to the production of glucocorticoids and dehydroepiandrosterone (DHEA), with known immunomodulatory effects. TB patients exhibit increased concentrations of interleukin-6 and cortisol in plasma, reduced DHEA and testosterone levels, together with remarkably increased growth hormone concentrations that were not accompanied by an expected raise in insulin-like growth factor-1. Significant increases in estradiol, prolactin, and thyroid hormone concentrations were also detected in patients. Cortisol inhibits the mycobacterial antigen-driven proliferation and IFN-gamma production, whereas DHEA suppresses transforming growth factor beta production by lymphoid cells from TB patients with advanced disease. Furthermore, supernatants from cultures of M. tuberculosis-stimulated mononuclear cells of TB patients inhibit DHEA secretion by a human adrenal cell line. This type of immuno-endocrine interactions may affect the control of tissue damage and the development of protective immune responses, partly accounting for disease aggravation.

Altered Cortisol/DHEA Ratio in Tuberculosis Patients and its Relationship with Abnormalities in the Mycobacterial-driven Cytokine Production by Peripheral Blood Mononuclear Cells

We have investigated the relationship between cortisol and dehydroepiandrosterone (DHEA) levels and the immune response to mycobacterial antigens in peripheral venous blood, from a male population of active tuberculosis patients and age-matched healthy controls of the same sex (HCo). Peripheral blood mononuclear cells were cultured for 36 or 96 h with whole sonicated Mycobacterium tuberculosis (WSA) for measurement of proliferation, interferon gamma (IFN-gamma) and interleukin-10 (IL-10) in culture supernatants. Comparisons on the in vitro mycobacterial-driven immune responses demonstrated that TB patients had a higher IL-10 production, a decreased lymphoproliferation and a trend to reduced IFN-gamma synthesis, in relation to HCo. Active disease was also characterized by increases in the plasma levels of glucocorticoids (GC) and reduced concentrations of DHEA which resulted in a higher cortisol/DHEA ratio respect the HCo group. Plasma DHEA levels were positively correlated with IFN-gamma values. An inverse correlation was found between the cortisol/DHEA ratio and IFN-gamma levels. Novel evidence is provided showing that the balance between cortisol and DHEA is partly responsible for the immune perturbations seen in TB patients.

Cortisol and dehydroepiandrosterone affect the response of peripheral blood mononuclear cells to mycobacterial antigens during tuberculosis

The effect of cortisol and/or dehydroepiandrosterone (DHEA) on the immune response to antigens obtained from Mycobacterium tuberculosis was studied in vitro by using peripheral blood mononuclear cells obtained from patients at various stages of lung tuberculosis (TB) and from healthy control people (HCo). The results obtained show for the first time that addition of cortisol within concentrations of physiological range can inhibit the mycobacterial antigen-driven proliferation of cells from HCo and TB patients and the production of interferon-gamma (IFN-gamma), indicating that endogenous levels of cortisol may contribute to the decreased lymphoid cell response to mycobacterium antigens observed in TB patients. DHEA did not affect lymphoid cell proliferation, IFN-gamma production and the cortisol-mediated inhibitory effects. Interestingly, we found that DHEA, but not cortisol, suppressed the in vitro transforming growth factor-beta production by lymphoid cells from TB patients with an advanced disease, which is indicative of a selective direct effect of this hormone.

Endotoxin impedes vasoconstriction in the spleen: role of endogenous interleukin-1 and sympathetic innervation

Processes relevant for an appropriate immune response such as immune cell traffic and recirculation require a tight control of blood supply to lymphoid organs. Interactions between endogenous cytokines and sympathetic nerve fibers in lymphoid organs can contribute to this control. The results reported in this paper show that 1) administration of low doses of lipopolysaccharide (LPS), an endotoxin derived from gram-negative bacteria, causes an increase in splenic blood flow (SBF); 2) this increase is mediated by the production of endogenous interleukin-1 (IL-1); 3) the effect of LPS on SBF requires an intact splenic sympathetic innervation; 4) the LPS-induced increase in SBF is exerted at the postganglionic level; 5) the endotoxin inhibits the vasoconstriction induced by the in vivo stimulation of the splenic nerve but does not affect the vasoconstriction induced by norepinephrine (NE); and 6) although IL-1 and LPS stimulate general sympathetic activity as reflected by increased peripheral vascular resistance, they do not increase NE concentration in splenic dialysates. Together these in vivo results indicate that endogenous IL-1 affects blood supply to the spleen by inhibiting the sympathetic vasoconstrictor tonus at a postganglionic, prejunctional level. This effect is expected to be relevant for immune cell recirculation, homing, and traffic as well as antigen trapping in the spleen, an organ specialized in the control of these processes during immune responses.

Induction of cytokine transcripts in the central nervous system and pituitary following peripheral administration of endotoxin to mice

The regional distribution and inducibility of cytokines in the normal brain is still a matter of controversy. As an attempt to clarify this issue, we studied the constitutive and induced expression of interleukin (IL)-1beta, IL-6, tumor necrosis factor (TNF)-alpha, and interferon (IFN)-gamma mRNAs in the brain, pituitary, and spleen of mice using qualitative and semiquantitative reverse-transcription polymerase chain reaction. The contribution of nonbrain cells to the cytokine transcripts detected was considered. With the exception of IFN-gamma mRNA, transcripts for the other cytokines were found to be constitutively present in the brain. Following i.p. injection of lipopolysaccharide (LPS) at a dose below those described to disrupt the blood-brain barrier (BBB), cytokine mRNA expression was increased in the spleen, the pituitary, and the brain. In the brain, the onset of transcription varied from 45 min (IL-1beta, TNF-alpha) to 4 hr (IFN-gamma), and the peak of mRNA accumulation was observed at different times depending on the cytokine and the brain region studied. IL-1 and IL-6 were highly expressed in the hypothalamus and hippocampus, while TNF-alpha expression was more marked in the thalamus-striatum. The cortex was the region in which cytokines were less inducible. The inducible expression of cytokine mRNAs in the brain was paralleled by stimulation of the hypothalamus-pituitary-adrenal axis. These results show the capacity of brain cells to synthesize different cytokine mRNAs in vivo and define the kinetics of their expression in several brain areas and in the periphery in parallel to the activation of a neuroendocrine pathway by endotoxin.

On the mechanism of antiinflammation induced by tumor transplantation, surgery, and irritant injection

Tumor transplantation, major surgery, and injection of nonspecific irritants elicit inflammation locally while suppressing inflammation induced subsequently and at distant sites. Such systemic antiinflammation in rodents occurs via corticosterone-independent and -dependent pathways. Based upon hormone measurements and the response to adrenalectomy, antiinflammation induced by irritants and certain surgical procedures is corticosterone independent while that which follows tumor transplantation is corticosterone dependent. However, injection of tumorous ascites stimulates both pathways since it contains two antiinflammatory factors: Factor A (molecular weight less than 2,000) does not alter hormone balance while Factor B (molecular weight 30,000-100,000) increases corticosterone levels and is corticosterone dependent. Desensitization of systemic antiinflammation develops rapidly regardless of whether it is corticosterone dependent (Factor B) or independent (Factor A or irritants). However, tumor transplantation resists desensitization possibly by inducing an immune response since lymphocytic mitogens prevent development of and break established desensitization. Nevertheless, abolition of tumor-induced antiinflammation follows injection of tumorous ascites by a mechanism that involves Factor B suppression of the corticosterone response to the tumor while Factor A apparently raises the threshold at which physiological increases in corticosterone inhibit leukocyte emigration. We conclude that systemic antiinflammation is a general consequence of a localized inflammatory reaction and that desensitization of such antiinflammation develops rapidly. Recent evidence indicates that certain mediators of inflammation are proinflammatory when administered intradermally but antiinflammatory when given intravenously. Thus, systemic antiinflammation may arise when chemical mediators of inflammation generated by a local reaction gain access to the circulation.

Antidiabetic effects of interleukin 1

Interleukin 1 (IL-1), a cytokine released mainly by activated macrophages-monocytes, affects glucose homeostasis and may mediate some of the metabolic derangements observed during certain inflammatory and infectious processes. In this report, it is shown that IL-1 acts as a hypoglycemic agent not only in normal animals but also in mice at early stages of alloxan-induced diabetes and in genetically diabetic, insulin-resistant C57BL/Ks db/db mice and C57BL/6J ob/ob mice. In these animal models, a single injection of a low dose of human recombinant IL-1 normalized glucose blood levels for several hours. This effect was not mediated by possible insulin secretagogue actions of the cytokine. Furthermore, IL-1 markedly reduced the levels of triglycerides in blood of streptozotocin-induced diabetic mice at later stages of the disease. Although the final mechanism of action is at present unknown, the results showed that IL-1 is a hormone with powerful antidiabetic properties. Defective production of this cytokine associated with diabetes could contribute to aggravate the course of the disease during infectious and inflammatory processes.

Interactions between endogenous glucocorticoids and inflammatory responses in normal and tumor-bearing mice: role of T cells

Appropriately stimulated lymphocytes and macrophages produce factors in vitro that increase serum corticosterone levels when injected in vivo. In this study, we used euthymic and congenitally athymic mice on a BALB/c background to explore the role of T cells in controlling corticosterone levels and the leukocyte response to inflammation. Adult athymic mice had more intense inflammatory reactions than euthymic mice despite higher basal corticosterone levels. This latter condition may be due to interleukin-1 (IL-1) since macrophages from athymic mice when stimulated in vitro by lipopolysaccharide produced more IL-1 than macrophages from euthymic mice. In response to mitogen stimulation, however, splenocytes from athymic mice produced a factor (not IL-1), which, upon injection, increased corticosterone levels and suppressed inflammation. Production of this factor was enhanced by T cells since splenocyte supernatants from euthymic mice were more potent in eliciting both effects. Evidence for in vivo participation of T cells in regulating corticosterone levels was obtained by tumor transplantation. Injection of syngeneic tumor cells or cell-free tumorous ascites rapidly increased corticosterone levels in euthymic but not athymic mice. Anti-inflammation correlated with increased corticosterone levels but was observed also in athymic mice receiving syngeneic tumor transplants. These studies demonstrate that T cells enhance production of a lymphokine that increases corticosterone levels and are required for the corticosterone response to tumor transplantation. In addition, the data suggest two pathways of anti-inflammation in tumor-bearing hosts: a corticosterone-independent, T cell-independent mechanism and a T cell-dependent mechanism that involves a lymphokine-mediated increase in corticosterone blood levels.

Hormonal changes following tumor transplantation: factors increasing corticosterone and the relationship of corticosterone to tumor-induced anti-inflammation

EL-4 lymphoma cells transplanted to syngeneic C57BL/6J mice induced a biphasic decrease in inflammation and a bi-phasic increase in serum levels of corticosterone. In addition, this tumor altered serum levels of 3 other hormones, resulting in a biphasic decrease in insulin, an early decrease in prolactin, and a terminal severe deficiency in thyroxine. Early changes occurred 16 to 48 hr after tumor transplantation and were of variable duration, while late-phase defects developed during the last few days of life. Soluble factors associated with tumor growth may mediate certain hormonal changes since serum levels of corticosterone increased and insulin decreased following injection of tumorous ascites into normal mice. Further, injection of cell-free tumor culture supernatants increased corticosterone levels. Hormonal changes following injection of soluble factors occurred after a delay of 16 hr indicating that the factors acted indirectly. Surgical adrenalectomy blocked the corticosterone increase induced by tumor transplantation or ascites injection and eliminated the anti-inflammatory effect of tumor transplantation while significantly decreasing the effect associated with injection of tumorous ascites. Thus, the physiologically induced increase in serum levels of corticosterone reached anti-inflammatory levels. Further, elevated levels of corticosterone are a major contributing factor to anti-inflammation induced by tumorous ascites injection and constitute the principal mechanism of anti-inflammation following tumor transplantation.

Interleukin 1 affects glucose homeostasis

Alterations in glucose metabolism are known to occur during certain types of inflammation and infectious diseases. Interleukin 1 (IL 1), an immune-derived cytokine released during these processes, is proposed to function as a mediator of such alterations, since administration of low subpyrogenic doses of human rIL 1 to mice and rats produced hypoglycemia. In mice this effect was paralleled by increased insulin, glucagon, and corticosterone blood levels. When IL 1 was repeatedly injected, mice remained hypoglycemic for at least 14 h after the last injection. Furthermore, these animals responded normally to a challenge with glucose, thus suggesting that the proper function of the pancreas was preserved. A moderate hypoglycemia, paralleled by increased glucagon and corticosterone blood levels, was also observed in IL 1-injected rats, but no increase in insulin levels was detected. IL 1 administration to adrenalectomized rats resulted in a more marked hypoglycemia and in a profound hypoinsulinemia. The results suggest that IL 1 causes hypoglycemia by increasing insulin blood levels and probably also by mechanisms independent of the insulin secretagogue action of this cytokine.

Corticotropin-releasing factor-producing neurons in the rat activated by interleukin-1

Intraperitoneal administration of human recombinant interleukin-1 (IL-1) to rats can increase blood levels of corticosterone and adrenocorticotropic hormone (ACTH). The route by which IL-1 affects pituitary-adrenal activity is unknown. That the IL-1-induced pituitary-adrenal activation involves an increased secretion of corticotropin-releasing factor (CRF) is indicated by three lines of evidence. First, immunoneutralization of CRF markedly attenuated the IL-1-induced increase of ACTH blood levels. Second, after blockade of fast axonal transport in hypothalamic neurons by colchicine, IL-1 administration decreased the CRF immunostaining in the median eminence, indicating an enhanced release of CRF in response to IL-1. Third, IL-1 did not stimulate ACTH release from primary cultures of anterior pituitary cells. These data further support the notion of the existence of an immunoregulatory feedback circuit between the immune system and the brain.

Neuroendocrine and metabolic responses induced by interleukin-1

We have previously demonstrated that Interleukin-1 (IL-1), a cytokine mainly produced by activated monocytes, stimulates the pituitary-adrenal axis and affects glucose homeostasis. Comparative studies revealed that a beta form of recombinant human IL-1, similar to the mature peptide secreted naturally, is more powerful than other preparations of this monokine in stimulating adrenocorticotrophic hormone (ACTH) and corticosterone output. Another monokine, tumor necrosis factor (TNF), does not share with IL-1 the capacity to induce such effects. In extending our studies to rats, we showed that increased ACTH and blood corticosterone levels are also induced by IL-1 in this species. Another in vivo activity of IL-1 relates to its capacity to induce a reduction in blood glucose levels. Our studies strongly suggest that, as opposed to other effects elicited by IL-1, blockade of prostaglandin synthesis does not affect the capacity of IL-1 to stimulate insulin output and produce hypoglycemia. Administration of IL-1 to adrenalectomized mice, which are defective in counterregulatory mechanisms of glucose homeostasis, resulted in marked hypoglycemia. In contrast to the response observed in normal mice, in adrenalectomized animals this effect was paralleled by decreased blood insulin levels. IL-1 was also injected into alloxan-diabetic mice. A marked reduction in blood glucose levels occurred in these animals. This effect was already noticeable 1 hr after injection. After 2 hr and for at least another 6 hr, glucose levels of alloxan-treated mice injected with IL-1 remained within the normal range.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunoregulatory feedback between interleukin-1 and glucocorticoid hormones

The production and action of immunoregulatory cytokines, including interleukin-1 (IL-1), are inhibited by glucocorticoid hormones in vivo and in vitro. Conversely, glucocorticoid blood levels were increased by factors released by human leukocytes exposed to Newcastle disease virus preparations. This activity was neutralized by an antibody to IL-1. Therefore the capacity of IL-1 to stimulate the pituitary-adrenal axis was tested. Administration of subpyrogenic doses of homogeneous human monocyte-derived IL-1 or the pI 7 form of human recombinant IL-1 to mice and rats increased blood levels of adrenocorticotropic hormone (ACTH) and glucocorticoids. Another monokine, tumor necrosis factor, and the lymphokines IL-2 and gamma-interferon had no such effects when administered in doses equivalent to or higher than those of IL-1. The stimulatory effect of IL-1 on the pituitary-adrenal axis seemed not to be mediated by the secondary release of products from mature T lymphocytes since IL-1 was endocrinologically active when injected into athymic nude mice. These results strongly support the existence of an immunoregulatory feedback circuit in which IL-1 acts as an afferent and glucocorticoid as an efferent hormonal signal.

Endogenous blood levels of corticosterone control the immunologic cell mass and B cell activity in mice

An inverse relation between endogenous levels of glucocorticoids and splenic mass and cellularity was detected. Decreased endogenous corticosterone blood levels result in an increased number of immunoglobulin-secreting cells in the spleen, a fact that cannot be attributed only to the expansion of the lymphoid cell mass. The opposite phenomenon was observed in animals with high corticosterone blood levels, which showed reduced numbers of immunoglobulin-secreting cells. It is concluded that endogenous glucocorticoid levels contribute to the control of B cell activity and possibly to the interaction of these cells with other immunologic cells.

Endogenous blood levels of corticosterone control the immunologic cell mass and B cell activity in mice

An inverse relation between endogenous levels of glucocorticoids and splenic mass and cellularity was detected. Decreased endogenous corticosterone blood levels result in an increased number of immunoglobulin-secreting cells in the spleen, a fact that cannot be attributed only to the expansion of the lymphoid cell mass. The opposite phenomenon was observed in animals with high corticosterone blood levels, which showed reduced numbers of immunoglobulin-secreting cells. It is concluded that endogenous glucocorticoid levels contribute to the control of B cell activity and possibly to the interaction of these cells with other immunologic cells.

The immune response evokes changes in brain noradrenergic neurons

A decreased noradrenaline turnover in the hypothalami of rats was observed at the peak of the immune response to sheep red blood cells. The decrease in noradrenergic neuronal activity was mimicked by injection of soluble r mediators released by immunological cells activated in vitro. Noradrenaline also tended to decrease in the brainstem but not in the residual brain. It is suggested that products released from activated immunological cells during the immune response may induce the previously described autonomic and endocrine mechanisms that contribute to immunoregulation.

Hypothalamic changes during the immune response

The immune system is subject to an array of identified autoregulatory processes, but immunoregulation may also have a further basis in a network of immune-neuroendocrine interactions. Two antigens each produced an increase of more than 100% in electrical activity of individual neurones in the ventromedial but not in the anterior nucleus of the rat hypothalamus. Animals that failed to respond to antigen manifested no increase in the firing rate. These findings constitute the first evidence for a flow of information from the activated immune system to the hypothalamus, suggesting that the brain is involved in the immune response.

Network of immune-neuroendocrine interactions

In order to bring the self-regulated immune system into conformity with other body systems its functioning within the context of an immune-neuroendocrine network is proposed. This hypothesis is based on the existence of afferent--efferent pathways between immune and neuroendocrine structures. Major endocrine responses occur as a consequence of antigenic stimulation and changes in the electrical activity of the hypothalamus also take place; both of these alterations are temporally related to the immune response itself. This endocrine response has meaningful implications for immunoregulation and for immunospecificity. During ontogeny, there is also evidence for the operations of a complex network between the endocrine and immune system, a bidirectional interrelationship that may well affect each developmental stage of both functions. As sequels the functioning of the immune system and the outcome of this interrelation could be decisive in lymphoid cell homeostasis, self-tolerance, and could also have significant implications for pathology.

Changes in blood hormone levels during the immune response

Injection of three different antigens into rats or mice led in the course of several days to about a threefold increase in serum corticosterone levels and concommitantly to a decrease in thyroxine (rats). In view of the known immuno-suppressive effect of the glucocorticoids the possibility is considered that the endocrine changes induced during the immune response could significantly modulate the subsequent character of the immune response, e.i. magnitude, duration and lymphoid cell proliferation, however, a more complete pattern of hormonal variations and their cause needs to be established. These findings while admittedly preliminary, suffice to provide an indication of a temporal pattern of hormonal change during the immune response which could be important in immunoregulation.