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 11ß-hydroxysteroid dehydrogenase (11ßHSD1) and a decreased glucocorticoid receptor (GR) ratio (GRα/GRß). In PLTB cases, expression of 11ßHSD1 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.

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.

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-1ß, 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/CD45low) and macrophages (CD11b/CD45high), 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.

Brain-borne IL-1 adjusts glucoregulation and provides fuel support to astrocytes and neurons in an autocrine/paracrine manner.

It is still controversial which mediators regulate energy provision to activated neural cells, as insulin does in peripheral tissues. Interleukin-1ß (IL-1ß) may mediate this effect as it can affect glucoregulation, it is overexpressed in the 'healthy' brain during increased neuronal activity, and it supports high-energy demanding processes such as long-term potentiation, memory and learning. Furthermore, the absence of sustained neuroendocrine and behavioral counterregulation suggests that brain glucose-sensing neurons do not perceive IL-1ß-induced hypoglycemia. Here, we show that IL-1ß adjusts glucoregulation by inducing its own production in the brain, and that IL-1ß-induced hypoglycemia is myeloid differentiation primary response 88 protein (MyD88)-dependent and only partially counteracted by Kir6.2-mediated sensing signaling. Furthermore, we found that, opposite to insulin, IL-1ß stimulates brain metabolism. This effect is absent in MyD88-deficient mice, which have neurobehavioral alterations associated to disorders in glucose homeostasis, as during several psychiatric diseases. IL-1ß effects on brain metabolism are most likely maintained by IL-1ß auto-induction and may reflect a compensatory increase in fuel supply to neural cells. We explore this possibility by directly blocking IL-1 receptors in neural cells. The results showed that, in an activity-dependent and paracrine/autocrine manner, endogenous IL-1 produced by neurons and astrocytes facilitates glucose uptake by these cells. This effect is exacerbated following glutamatergic stimulation and can be passively transferred between cell types. We conclude that the capacity of IL-1ß to provide fuel to neural cells underlies its physiological effects on glucoregulation, synaptic plasticity, learning and memory. However, deregulation of IL-1ß production could contribute to the alterations in brain glucose metabolism that are detected in several neurologic and psychiatric diseases.

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.

Behavioural endocrine immune-conditioned response is induced by taste and superantigen pairing.

Administration of bacterial superantigen, such as staphylococcal enterotoxin B (SEB), induces in vivo stimulation of T cell proliferation and cytokine production such as interleukin-2 (IL-2). It has been previously reported that SEB administration induces fever, c-Fos expression in the brain, and hypothalamus-pituitary-adrenal axis activation, demonstrating that the brain is able to sense and respond to SEB. Previously it had been shown that immune functions can be behaviourally conditioned pairing a novel gustatory stimulus together with an immunomodulatory drug or an antigen. We designed an experimental protocol using Dark Agouti rats in which saccharin taste, as conditioned stimulus, was paired with an i.p. injection of SEB (2 mg/kg), as unconditioned stimulus. Six days later, when conditioned animals were re-exposed to the conditioned stimulus they displayed strong conditioned taste avoidance to the saccharin. More importantly, re-exposure to the conditioned stimulus significantly increased IL-2, interferon-gamma and corticosterone plasma levels, in comparison with conditioned animals which had not been re-exposed to saccharin taste. These results demonstrate a behavioural-immune-endocrine conditioned response using a superantigen as unconditioned stimulus. In addition, they illustrate the brain abilities to mimic the unconditioned effects of a superantigen by yet unknown mechanisms.

Interleukin-6: a cytokine to forget.

It is known that proinflammatory cytokines such as interleukin-6 (IL-6) are expressed in the central nervous system (CNS) during disease conditions and affect several brain functions including memory and learning. In contrast to these effects observed during pathological conditions, here we describe a physiological function of IL-6 in the "healthy" brain in synaptic plasticity and memory consolidation. During long-term potentiation (LTP) in vitro and in freely moving rats, IL-6 gene expression in the hippocampus was substantially increased. This increase was long lasting, specific to potentiation, and was prevented by inhibition of N-methyl-D-aspartate receptors with (+/-)-2-amino-5-phosphonopentanoic acid (AP-5). Blockade of endogenous IL-6 by application of a neutralizing anti-IL-6 antibody 90 min after tetanus caused a remarkable prolongation of LTP. Consistently, blockade of endogenous IL-6, 90 min after hippocampus-dependent spatial alternation learning resulted in a significant improvement of long-term memory. In view of the suggested role of LTP in memory formation, these data implicate IL-6 in the mechanisms controlling the kinetics and amount of information storage.

Complex phenotype of mice homozygous for a null mutation in the Sp4 transcription factor gene.

BACKGROUND: Sp4 is a zinc finger transcription factor which is closely related to Sp1 and Sp3. All three proteins recognize the same DNA elements and can act as transcriptional activators through glutamine-rich activation domains. Unlike Sp1 and Sp3, which are ubiquitous proteins, Sp4 is highly abundant in the central nervous system, but also detectable in many other tissues. RESULTS: We have disrupted the mouse Sp4 gene by a targeted deletion of the exons encoding the N-terminal activation domains. Sp4 knockout mice show a complete absence of Sp4 expression. They develop until birth without obvious abnormalities. After birth, two-thirds die within 4 weeks. Surviving mice are growth retarded. Male Sp4null mice do not breed. The cause for the breeding defect remains obscure since they show complete spermatogenesis. In addition, pheromone receptor genes in the vomeronasal organ appear unaffected. Female Sp4null mice have a smaller thymus, spleen and uterus. In addition, they exhibit a pronounced delay in sexual maturation. CONCLUSIONS: The phenotype of the Sp4null mice differs significantly from those described for Sp1-/- and Sp3-/- mice. Thus, the structural similarities, the common recognition motif and the overlapping expression pattern of these three transcription factors do not reflect similar physiological functions.

Endocrine host responses during early and late phases of tumor development.

It is well established that hormones affect tumor growth. Conversely, inoculation of cells obtained from tumors that had been transplanted for many generations causes changes in the concentration of different hormones before and after tumor detection. We aimed at answering the question of whether hormonal alterations also occur during the development of primary tumors and following transplantation of tumors from early generations. Primary tumors were induced in mice by either the carcinogenic agent 3-methylcholanthrene, which produces fibrosarcomas, or the milk-transmitted mammary tumor virus, which induces adenocarcinomas. The results showed that (i) in both models, an early reduction in plasma insulin and prolactin levels occurred, and in the case of insulin, this reduction was sustained for a prolong period prior to tumor detection, indicating that recognition by the host of emergent tumor cells triggers an endocrine response; (ii) in contrast with multiply transplanted tumors, cells from early transplant generations produced no significant endocrine changes during latency; (iii) irrespective of whether they were primary or transplanted, large tumor burdens caused similar hormonal alterations, consisting of increased corticosterone and growth hormone and decreased insulin, thyroxin, prolactin and sex steroid levels in blood. Our comprehensive longitudinal study demonstrates host endocrine responses during different stages of neoplastic development.

The cytokine-HPA axis feed-back circuit.

Due to their anti-inflammatory effects and their capacity to affect the synthesis of most cytokines and the Th1/Th2 balance, endogenous glucocorticoids contribute to control the basal operation of immune cells. Immune processes result in the production of cytokines, such as IL-1, IL-2, IL-6, IL-11, IL-12, TNF-alpha, and INF-gamma, which can activate the HPA axis. In turn, the resulting increase in glucocorticoid blood levels can affect immune cell activity directly or by controlling the production of cytokines, suggesting the existence of an immunoregulatory cytokine-HPA axis circuit. There is evidence that this circuit plays a relevant role in controlling excessive inflammatory reactions and the non-specific expansion of immune cells with no or low affinity for the antigen that triggers an immune response.

The cytokine-HPA axis circuit contributes to prevent or moderate autoimmune processes.

There is evidence that an immunoregulatory circuit integrated by immune-derived cytokines and the hypothalamus-pituitary-adrenal (HPA) axis operates during certain pathological conditions. For example, it has been shown that IL-1 is the main mediator of the increase in ACTH and corticosterone blood levels detected in models of viral infection and bacterial endotoxins. This endocrine response has protective effects during septic shock. In experimental models of tumors, there are also clear indications that the increase in glucocorticoid levels detected during the growth of a lymphoma is mediated by immune-derived products and contributes to the inhibition of the inflammatory response. The disruption of the cytokine-HPA axis circuit can predispose to autoimmunity. This has been shown in animal models of spontaneous autoimmune thyroiditis, lupus-like disease, and experimental arthritis. More recently, it has been shown that the proper operation of this circuit contributes to preventing or moderating autoimmunity. The recovery of animals from experimental autoimmune encephalomyelitis (EAE) is clearly dependent on an increase in endogenous glucocorticoid levels. It has been recently shown that this endocrine response is, at least in part, triggered by the immune response to the encephalitogenic antigen and mediated by the endogenous IL-1 produced during the disease. These examples support the concept that the cytokine-HPA circuit plays a protective role during certain pathologies and that its disruption can lead to predisposition to or aggravation of autoimmune diseases.

Increased sensitivity of the baroreceptor reflex after bacterial endotoxin.

Lipopolysaccharide (LPS), an endotoxin that elicits the production of several cytokines, induces cardiovascular changes characterized by increased perfusion of immune organs and compensatory sympathetic vasoconstriction in other tissues. We therefore hypothesized that to adapt to altered blood flow distribution following LPS administration, changes in the sensitivity of reflexes that control blood pressure would occur. Our data show that the sensitivity of the baroreceptor reflex increases significantly two and three hours after the intravenous administration of a subpyrogenic dose of the endotoxin. This change in sensitivity that could occur at peripheral or central levels may underlie necessary adjustments of cardiovascular mechanisms during the course of certain immune responses.

Not all peripheral immune stimuli that activate the HPA axis induce proinflammatory cytokine gene expression in the hypothalamus.

Administration of low doses of lipopolysaccharide (LPS) that do not disrupt the blood-brain barrier (BBB) results in the expression of interleukin-1 beta (IL-1 beta), IL-6, and tumor necrosis factor-alpha (TNF alpha) in the hypothalamus in parallel to stimulation of the hypothalamus-pituitary-adrenal (HPA) axis. This endocrine response is triggered by peripheral cytokines, and we recently obtained evidence that brain-borne IL-1 contributes to its maintenance. LPS preferentially stimulates cells of the macrophage lineage and B lymphocytes. The possibility that primarily stimulation of other types of peripheral immune cells also results in the expression of proinflammatory cytokines in the brain and in the activation of the HPA axis was investigated. Our results showed that, in contrast to LPS, administration of the superantigen staphylococcal enterotoxin B (SEB), which stimulates T cells by binding to appropriate V beta domains of the T-cell receptor, did not result in induction of IL-1 beta, IL-6, and TNF alpha expression in the hypothalamus. Furthermore, although IL-2 transcripts in the spleen were highly increased, expression of this gene was not detected in the brain. However, as with LPS, SEB administration also results in elevated levels of glucocorticoids in blood. Therefore, our data suggest that increased expression of proinflammatory cytokines in the brain is not a necessary step in the stimulation of the HPA axis by SEB.

Sympathetic innervation affects superantigen-induced decrease in CD4V beta 8 cells in the spleen.

The stimulation by superantigens of T cells expressing an appropriate V beta chain results in a strong proliferative response that is followed by a state of energy specific for the antigen used. This model was used to continue our studies on immunoregulatory host neuroendocrine responses. We have recently found that four days after administration of the superantigen staphylococcal enterotoxin B (SEB) into mice, that is, at an early stage of the anergic phase, the decrease in the percentage of splenic CD4V beta 8 was accompanied by a decrease in the splenic concentration of the sympathetic neurotransmitter noradrenaline (NA) as compared to vehicle-injected mice. No comparable changes were detected in the kidney. At this point, blood levels of NA, adrenaline, and corticosterone were comparable in SEB- and vehicle-injected mice. We have also found that the decrease in splenic CD4V beta 8 cells was not observed in animals that had been chemically sympathectomized prior to the administration of the superantigen. These results indicate that the sympathetic response induced by SEB may have immunoregulatory implications.

A reduction in blood insulin levels as a host endocrine response during tumor development.

It has been previously reported that endogenous insulin levels decrease during tumor growth. We have now studied whether this host endocrine response is independent of the way in which the tumor is induced. For this purpose, animals transplanted with tumor cells induced by 3-methylcholanthrene (MCA) or 7,12-dimethylbenz(a) anthracene (DMBA), or with EL-4 lymphoma cells, and animals that develop autochthonous tumors induced by MCA or the murine mammary tumor virus (MMTV) were used. These procedures result in the induction of tumors of different histologic types: fibrosarcoma, mammary adenocarcinoma and lymphoma. The results obtained showed that a reduction in insulin levels preceded the overt appearance of tumors in all models of syngeneic or autochthonous tumors studied but not when DMBA-induced tumor cells were administered into allogeneic recipients. Reduced levels of insulin before tumor detection appeared to affect the onset of MCA-induced tumors. Indeed, those mice with a late tumor onset were those that had a more pronounced decrease in insulin blood levels during the induction phase of autochthonous MCA-induced tumors. Soluble factors associated with tumor growth seem to mediate the reduction in insulin blood levels in mice transplanted with EL-4 tumor cells. The results obtained indicate that the reduction in insulin levels detected is a consequence of the recognition of tumor cells by the host, and seems to be independent of the histologic type of the neoplastic cells that develop. Pharmacological interventions at the levels of mechanisms that control insulin output should clarify the relevance of decreased levels of this hormone for tumor development.

Norepinephrine stimulates lymphoid cell mobilization from the perfused rat spleen via beta-adrenergic receptors.

The possibility that norepinephrine (NE) influences lymphoid cell outflow independently of its vasoconstrictor action was investigated in the perfused rat spleen. Using agents that affect the vasoconstrictor tonus of the spleen, we observed an inverse correlation between flow resistance and splenic cell output. The curve obtained served as a reference for evaluating effects of different treatments on the number of cells that are mobilized at defined levels of flow resistance. Perfusion of the beta-adrenergic blocker propranolol either alone or in combination with NE lowered splenic leukocyte outflow clearly beyond the number of cells expected at the corresponding flow resistance. No comparable effects were observed when the alpha-adrenergic blocker phentolamine was perfused. When the vasoconstrictor effect of NE was counteracted by papaverine, splenic cell outflow was significantly higher than expected for the level of flow resistance attained. Furthermore, when NE was perfused together with endotoxin, which does not inhibit the vasoconstriction induced by catecholamines, splenic cell mobilization was severalfold higher than expected at increased flow resistance. Propranolol abrogated this effect to a large extent. Furthermore, perfusion of the beta-agonist isoproterenol stimulated lymphoid cell outflow from the spleen despite increased flow resistance. These studies show a dual effect of NE on cell mobilization from the spleen: cell retention by decreasing blood flow and stimulation of cell output by a beta-adrenergically mediated, smooth muscle-independent mechanism.