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 ß-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.

The IgG3 subclass of ß1-adrenergic receptor autoantibodies is an endogenous biaser of ß1AR signaling.

Dysregulation of immune responses has been linked to the generation of immunoglobulin G (IgG) autoantibodies that target human ß1ARs and contribute to deleterious cardiac outcomes. Given the benefits of ß-blockers observed in patients harboring the IgG3 subclass of autoantibodies, we investigated the role of these autoantibodies in human ß1AR function. Serum and purified IgG3(+) autoantibodies from patients with onset of cardiomyopathy were tested using human embryonic kidney (HEK) 293 cells expressing human ß1ARs. Unexpectedly, pretreatment of cells with IgG3(+) serum or purified IgG3(+) autoantibodies impaired dobutamine-mediated adenylate cyclase (AC) activity and cyclic adenosine monophosphate (cAMP) generation while enhancing biased ß-arrestin recruitment and Extracellular Regulated Kinase (ERK) activation. In contrast, the ß-blocker metoprolol increased AC activity and cAMP in the presence of IgG3(+) serum or IgG3(+) autoantibodies. Because IgG3(+) autoantibodies are specific to human ß1ARs, non-failing human hearts were used as an endogenous system to determine their ability to bias ß1AR signaling. Consistently, metoprolol increased AC activity, reflecting the ability of the IgG3(+) autoantibodies to bias ß-blocker toward G-protein coupling. Importantly, IgG3(+) autoantibodies are specific toward ß1AR as they did not alter ß2AR signaling. Thus, IgG3(+) autoantibody biases ß-blocker toward G-protein coupling while impairing agonist-mediated G-protein activation but promoting G-protein-independent ERK activation. This phenomenon may underlie the beneficial outcomes observed in patients harboring IgG3(+) ß1AR autoantibodies.

Sympathetic nervous tone limits the development of myeloid-derived suppressor cells.

Sympathetic nerves that innervate lymphoid organs regulate immune development and function by releasing norepinephrine that is sensed by immune cells via their expression of adrenergic receptors. Here, we demonstrate that ablation of sympathetic nervous system (SNS) signaling suppresses tumor immunity, and we dissect the mechanism of such immune suppression. We report that disruption of the SNS in mice removes a critical α-adrenergic signal required for maturation of myeloid cells in normal and tumor-bearing mice. In tumor-bearing mice, disruption of the α-adrenergic signal leads to the accumulation of immature myeloid-derived suppressor cells (MDSCs) that suppress tumor immunity and promote tumor growth. Furthermore, we show that these SNS-responsive MDSCs drive expansion of regulatory T cells via secretion of the alarmin heterodimer S100A8/A9, thereby compounding their immunosuppressive activity. Our results describe a regulatory framework in which sympathetic tone controls the development of innate and adaptive immune cells and influences their activity in health and disease.

Altered Structural Brain Networks Related to Adrenergic/Muscarinic Receptor Autoantibodies in Chronic Fatigue Syndrome.

BACKGROUND AND PURPOSE: Recent studies suggest that the autoantibodies against adrenergic/muscarinic receptors might be one of the causes and potential markers of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). The purpose of this study was to investigate the structural network changes related to autoantibody titers against adrenergic/muscarinic receptors in ME/CFS by performing a single-subject gray matter similarity-based structural network analysis. METHODS: We prospectively examined 89 consecutive right-handed ME/CFS patients who underwent both brain MRI including 3D T1-wighted images and a blood analysis of autoantibodies titers against ß1 adrenergic receptor (ß1 AdR-Ab), ß2 AdR-Ab, M3 acetylcholine receptor (M3 AchR-Ab), and M4 AchR-Ab. Single-subject gray matter similarity-based structural networks were extracted from segmented gray matter images for each patient. We calculated local network properties (betweenness centrality, clustering coefficient, and characteristic path length) and global network properties (normalized path length λ, normalized clustering coefficient γ, and small-world network value δ). We investigated the correlations between the autoantibody titers and regional gray matter/white matter volumes, the local network properties, and the global network properties. RESULTS: Betweenness centrality showed a significant positive correlation with ß1-AdR-Ab in the right dorsolateral prefrontal cortex. The characteristic path length showed a significant negative correlation with ß2-AdR-Ab in the right precentral gyrus. There were no significant correlations between the antibody titers and the regional gray matter/white matter volumes, and the global network properties. CONCLUSIONS: Our findings suggest that ß1 AdR-Ab and ß2 AdR-Ab are potential markers of ME/CFS.

Apical splenic nerve electrical stimulation discloses an anti-inflammatory pathway relying on adrenergic and nicotinic receptors in myeloid cells.

The autonomic nervous system innervates all lymphoid tissues including the spleen therefore providing a link between the central nervous system and the immune system. The only known mechanism of neural inhibition of inflammation in the spleen relies on the production of norepinephrine by splenic catecholaminergic fibers which binds to ß2-adrenergic receptors (ß 2-ARs) of CD4+ T cells. These CD4+ T cells trigger the release of acetylcholine that inhibits the secretion of inflammatory cytokines by macrophages through α7 nicotinic acetylcholine receptor (α7nAchRs) signaling. While the vagal anti-inflammatory pathway has been extensively studied in rodents, it remains to be determined whether it coexists with other neural pathways. Here, we have found that three nerve branches project to the spleen in mice. While two of these nerves are associated with an artery and contain catecholaminergic fibers, the third is located at the apex of the spleen and contain both catecholaminergic and cholinergic fibers. We found that electrical stimulation of the apical nerve, but not the arterial nerves, inhibited inflammation independently of lymphocytes. In striking contrast to the anti-inflammatory pathway mechanism described so far, we also found that the inhibition of inflammation by apical nerve electrical stimulation relied on signaling by both ß 2-ARs and α7nAchRs in myeloid cells, with these two signaling pathways acting in parallel. Most importantly, apical splenic nerve electrical stimulation mitigated clinical symptoms in a mouse model of rheumatoid arthritis further providing the proof-of-concept that such an approach could be beneficial in patients with Immune-mediated inflammatory diseases.

Beta1-adrenergic receptor antibodies in children with dilated cardiomyopathy.

Autoantibodies to beta-1 adrenergic receptor have been reported in adult patients with dilated cardiomyopathy (DCM). Removal of these antibodies has a positive hemodynamic effect. Our aim was to investigate whether these antibodies are present in children with DCM and explore the potential hemodynamic benefit of immunoadsorption (IA). Seventeen children with DCM  were tested for these antibodies. The etiology of DCM was genetic (n=5), myocarditis (n=4), DCM and congenital heart block (n=3), DCM associated to maternal lupus (n=1), DCM and Wolff Parkinson White Syndrome (n=1), and idiopathic (n=3). All patients evidenced ventricular dysfunction. Antibody testing was positive in 8 patients, 7  received IA.  Three patients with high titers had a poor clinical outcome and needed transplantation. Two patients with low titers exhibited a full recovery of heart function. One patient with multiple myocarditis episodes was treated with immunoglobulin IgG and IA ; after 5 years this patient presented a LVEF of 40 percent. Beta-1 adrenergic receptors autoantibodies are present in children with DCM. Immunoadsorption therapy may help improve heart failure in this context.

No evidence for humoral autoimmunity against cardiomyocytes, adrenergic or muscarinic receptors in patients with Tako-Tsubo cardiomyopathy.

BACKGROUND: An association between Tako-Tsubo cardiomyopathy (TTC) and underlying malignancies has been observed, suggesting that TTC might be the consequence of paraneoplastic phenomena. This study investigates the presence of autoantibodies against cardiomyocytes as well as adrenergic (ß1, ß2) and muscarinic (M2) receptors in patients with TTC. METHODS AND RESULTS: Serum from 20 TTC patients and 20 controls with ischemic heart disease was obtained. Indirect immunofluorescence testing for intracellular autoantibodies against cardiomyocytes showed a homogenous distribution, as in both groups 9 of 20 sera displayed a characteristic binding pattern of antibodies including vascular walls and intracellular structures. Flow cytometry analysis revealed no difference between TTC and controls in the binding of autoantibodies to the surface antigens of cardiomyocyte HL-1 cells (p = 0.569, t-test). Flow cytometry analysis of nontransfected wild type cells (p = 0.633, t-test), M2 receptor-transfected cells (p = 0.687, t-test), ß1 receptor-transfected cells (p = 0.444, t-test) and ß2 receptor-transfected cells (p = 0.632, t-test) showed similar results for control and TTC sera. Likewise, the binding pattern of TTC patients with a history of neoplasia compared to those without or to controls did not differ significantly (p > 0.05, u-test). CONCLUSION: Findings suggest that the presumed paraneoplastic etiology of TTC cannot be attributed to the formation of these antibodies.

Adrenergic Signaling at the Interface of Allergic Asthma and Viral Infections.

Upper respiratory viral infections are a major etiologic instigator of allergic asthma, and they drive severe exacerbations of allergic inflammation in the lower airways of asthma sufferers. Rhinovirus (RV), in particular, is the main viral instigator of these pathologies. Asthma exacerbations due to RV infections are the most frequent reasons for hospitalization and account for the majority of morbidity and mortality in asthma patients. In both critical care and disease control, long- and short-acting ß2-agonists are the first line of therapeutic intervention, which are used to restore airway function by promoting smooth muscle cell relaxation in bronchioles. While prophylactic use of ß2-agonists reduces the frequency and pathology of exacerbations, their role in modulating the inflammatory response is only now being appreciated. Adrenergic signaling is a component of the sympathetic nervous system, and the natural ligands, epinephrine and norepinephrine (NE), regulate a multitude of autonomic functions including regulation of both the innate and adaptive immune response. NE is the primary neurotransmitter released by post-ganglionic sympathetic neurons that innervate most all peripheral tissues including lung and secondary lymphoid organs. Thus, the adrenergic signaling pathways are in direct contact with both the central and peripheral immune compartments. We present a perspective on how the adrenergic signaling pathway controls immune function and how ß2-agonists may influence inflammation in the context of virus-induced asthma exacerbations.

The role of autoantibodies in the syndromes of orthostatic intolerance: a systematic review.

Orthostatic intolerance is defined as the provocation of symptoms upon standing, commonly caused by neurogenic orthostatic hypotension (OH) and postural tachycardia syndrome (POTS), the etiology for which has not been fully uncovered yet. Many reports have described the occurrence of dysautonomia, orthostatic intolerance and POTS following febrile illness, presumably viral and post-vaccine. Furthermore, patients with dysautonomia have higher rates of autoimmune disorders such as Hashimoto thyroiditis and SLE. Recent evidence has shown the presence of adrenergic and cholinergic receptor antibodies in patients with POTS and orthostatic hypotension. In patients with cholinergic receptor antibodies, higher titers correlate with the disease severity. Few reports have shown that immunomodulation therapy resulted in significant improvement in symptoms. In this article, we review the available literature correlating autoimmunity with orthostatic intolerance syndromes. Future studies are warranted to evaluate the prevalence of such antibodies and examine different treatment modalities in this sub group of patients.

Increased circulating ß2-adrenergic receptor autoantibodies are associated with smoking-related emphysema.

Smoking is a dominant risk factor for chronic obstructive pulmonary disease (COPD) and emphysema, but not every smoker develops emphysema. Immune responses in smokers vary. Some autoantibodies have been shown to contribute to the development of emphysema in smokers. ß2-adrenergic receptors (ß2-ARs) are important targets in COPD therapy. ß2-adrenergic receptor autoantibodies (ß2-AAbs), which may directly affect ß2-ARs, were shown to be increased in rats with passive-smoking-induced emphysema in our current preliminary studies. Using cigarette-smoke exposure (CS-exposure) and active-immune (via injections of ß2-AR second extracellular loop peptides) rat models, we found that CS-exposed rats showed higher serum ß2-AAb levels than control rats before alveolar airspaces became enlarged. Active-immune rats showed increased serum ß2-AAb levels, and exhibited alveolar airspace destruction. CS-exposed-active-immune treated rats showed more extensive alveolar airspace destruction than rats undergoing CS-exposure alone. In our current clinical studies, we showed that plasma ß2-AAb levels were positively correlated with the RV/TLC (residual volume/total lung capacity) ratio (r = 0.455, p < 0.001) and RV%pred (residual volume/residual volume predicted percentage, r = 0.454, p < 0.001) in 50 smokers; smokers with higher plasma ß2-AAb levels exhibited worse alveolar airspace destruction. We suggest that increased circulating ß2-AAbs are associated with smoking-related emphysema.

[Autoimmunity and Prognosis of Patients With Morphologically Documented Myocarditis].

AIM: to assess clinical and prognostic value of circulating cardiospecific autoantibodies (AAB) and CD4+ T-regulatory cells in patients with myocarditis. MATERIAL AND METHODS: We included into this study 47 patients with lymphocytic myocarditis verified by analysis of histological and immunohistochemical data. Comparison group consisted of 30 practically healthy persons. Content of marker cardiotropic AAT were measured with the help of standardized immune enzyme test-systems. Number of circulating CD4+CD25+ and CD4+CD25+FoxP3+ T-lymphocytes were evaluated by flow cytometry. RESULTS: Among factors determining prognosis of patients with lymphocytic myocarditis factors of key significance were the presence of clinically overt heart failure at the disease debut, and degree of reduction of left ventricular ejection fraction. Distinctive feature of active myocarditis was elevation of titer of AABs to sarcomeric, cytoskeleton, and cytoplasmic proteins of cardiomyocytes, as well as elevated level of AABs to various epitopes of adenine nucleotide translocator. Elevated level of AAB to 1-adrenoreceptors was an independent predictor of unfavorable outcome in patients with lymphocytic myocarditis. Increased population of circulating CD4+CD25+ T-regulatory cells was as sociated with elevated concentration of of natriuretic peptide. CONCLUSION: Abnormalities in the system of autoimmunity play key role not only in pathogenesis but also in prognosis of inflammatory myocardial diseases. Changes of profile of circulating cardiospecific AABs and T-regulatory cells can bear a protective function.

Autoimmune basis for postural tachycardia syndrome.

BACKGROUND: Patients with postural tachycardia syndrome (POTS) have exaggerated orthostatic tachycardia often following a viral illness, suggesting autoimmunity may play a pathophysiological role in POTS. We tested the hypothesis that they harbor functional autoantibodies to adrenergic receptors (AR). METHODS AND RESULTS: Fourteen POTS patients (7 each from 2 institutions) and 10 healthy subjects were examined for α1AR autoantibody-mediated contractility using a perfused rat cremaster arteriole assay. A receptor-transfected cell-based assay was used to detect the presence of ß1AR and ß2AR autoantibodies. Data were normalized and expressed as a percentage of baseline. The sera of all 14 POTS patients demonstrated significant arteriolar contractile activity (69±3% compared to 91±1% of baseline for healthy controls, P<0.001) when coexisting ß2AR dilative activity was blocked; and this was suppressed by α1AR blockade with prazosin. POTS sera acted as a partial α1AR antagonist significantly shifting phenylephrine contractility curves to the right. All POTS sera increased ß1AR activation (130±3% of baseline, P<0.01) and a subset had increased ß2AR activity versus healthy subjects. POTS sera shifted isoproterenol cAMP response curves to the left, consistent with enhanced ß1AR and ß2AR agonist activity. Autoantibody-positive POTS sera demonstrated specific binding to ß1AR, ß2AR, and α1AR in transfected cells. CONCLUSIONS: POTS patients have elevated α1AR autoantibodies exerting a partial peripheral antagonist effect resulting in a compensatory sympathoneural activation of α1AR for vasoconstriction and concurrent ßAR-mediated tachycardia. Coexisting ß1AR and ß2AR agonistic autoantibodies facilitate this tachycardia. These findings may explain the increased standing plasma norepinephrine and excessive tachycardia observed in many POTS patients.

Importance of adrenergic pathways in women's cancers.

The importance of adrenergic pathways in cancer has long been suspected, but now there is mounting epidemiological, preclinical, and clinical evidence of its importance in gynecologic cancers. To date, most of these effects are mediated primarily through the beta 2 adrenergic receptor activation of the tumor cell cyclic AMP-protein kinase A signaling pathway. This review will discuss the current knowledge about the neuroendocrine stress response in gynecologic tumor biology.

A leading role for the immune system in the pathophysiology of preeclampsia.

Preeclampsia syndrome is characterized by inadequate placentation, because of deficient trophoblastic invasion of the uterine spiral arteries, leading to placental hypoxia, secretion of proinflammatory cytokines, the release of angiogenic and antiangiogenic factors and miRNAs. Although immune-system alterations are associated with the origin of preeclampsia, other factors, including proinflammatory cytokines, neutrophil activation, and endothelial dysfunction, are also related to the pathophysiology of this syndrome. The pathophysiology of preeclampsia may involve several factors, including persistent hypoxia at the placental level and the release of high amounts of STBMs. DAMP molecules released under hypoxic conditions and STBMs, which bind TLRs, may activate monocytes, DCs, NK cells, and neutrophils, promoting persistent inflammatory conditions in this syndrome. The development of hypertension in preeclamptic women is also associated with endothelial dysfunction, which may be mediated by various mechanisms, including neutrophil activation and NET formation. Furthermore, preeclamptic women have higher levels of nonclassic and intermediate monocytes and lower levels of lymphoid BDCA-2(+) DCs. The cytokines secreted by these cells may contribute to the inflammatory process and to changes in adaptive-immune system cells, which are also modulated in preeclampsia. The changes in T cell subsets that may be seen in preeclampsia include low Treg activity, a shift toward Th1 responses, and the presence of Th17 lymphocytes. B cells can participate in the pathophysiology of preeclampsia by producing autoantibodies against adrenoreceptors and autoantibodies that bind the AT1-R.

Association between the presence of autoantibodies against adrenoreceptors and severe pre-eclampsia: a pilot study.

BACKGROUND: Pre-eclampsia is the leading cause of maternal and neonatal morbidity and mortality with incompletely understood etiopathogenesis. The purpose of the current study is to determine whether there is a relationship between the presence of autoantibodies against ß1, ß2 and α1 adrenoreceptors and severe pre-eclampsia. METHODOLOGY/PRINCIPAL FINDINGS: Synthetic peptides corresponding to amino acid sequences of the second extracellular loops of ß1, ß2 and α1 adrenoreceptors were synthesized as antigens to test 34 patients with severe pre-eclampsia, 36 normal pregnancy women and 40 non-pregnant controls for the presence of autoantibodies using enzyme-linked immunosorbent assay. The respective frequencies of autoantibodies against ß1, ß2 and α1 adrenoreceptors were 50.0% (17/34), 52.9% (18/34) and 55.9% (19/34) in patients with severe pre-eclampsia, 19.4% (7/36) (p = 0.011), 19.4% (7/36) (p = 0.006) and 17.6% (6/36) (p = 0.001) in normal pregnancy women and 10% (4/40), 7.5% (3/40) and 10% (4/40) (p<0.001) in non-pregnant controls. Titers of these autoantibodies were also significantly increased in patients with severe pre-eclampsia. By logistic regression analysis, the presence of these three autoantibodies significantly increased the risk of neonatal death (odds ratio, 13.5; 95% confidence interval, 1.3-141.3; p = 0.030) and long-term neonatal hospitalization (odds ratio, 5.0; 95% confidence interval, 1.3-19.1; p = 0.018). The risk of hypertension and fetal distress were also associated with the presence of these three autoantibodies. CONCLUSIONS/SIGNIFICANCE: This novel pilot study demonstrated for the first time that the presence of autoantibodies against ß1, ß2 and α1 adrenoreceptors are increased in patients with severe pre-eclampsia. Pregnant women who are positive for the three autoantibodies are at increased risks of neonatal mortality and morbidity. We posit that these autoantibodies may be involved in the pathogenesis of severe pre-eclampsia.

Differential TNF production by monocyte subsets under physical stress: blunted mobilization of proinflammatory monocytes in prehypertensive individuals.

Elevated blood pressure (BP) and infiltration of the vasculature by monocytes contribute to vascular pathology; but, monocyte migratory characteristics based on differing inflammatory potential under adrenergic activation remains unclear. We compared nonclassical (CD14(+)CD16(++); HLA-DR(+)), intermediate (CD14(++)CD16(+); HLA-DR(++)), and classical (CD14(++)CD16(-); HLA-DR(+/-)) monocyte trafficking and their LPS-stimulated TNF production in response to a physical stressor (20-min treadmill exercise at 65-70% VO(2peak)) in participants with high prehypertension (PHT), mild PHT or normal BP (NBP). To determine adrenergic receptor (AR) sensitivity, pre-exercise cells were also treated with isoproterenol (Iso). When cells were stimulated with LPS, the CD16 molecules were downregulated, and monocyte subsets were differentiated based on HLA-DR expression. Monocyte subpopulations (as % of total monocytes) and intracellular TNF production were evaluated by flow cytometry. TNF production in all subsets decreased post-exercise and with ex-vivo incubation with Iso, irrespective of BP (p<0.001), with nonclassical and intermediate monocytes being a major source of TNF production. Overall, % nonclassical monocytes increased, % intermediate did not change, whereas % classical decreased post-exercise (p<0.001). However, % increase in nonclassical monocytes under exercise-induced adrenergic activation was blunted in high PHT individuals (p<0.05), but not in individuals with mild PHT and NBP. These findings extend our previous reports by showing that the mobilization of proinflammatory monocytes under physical stress is attenuated with even mild BP elevation. This may be indicative of monocytic AR desensitization and/or greater adhesion of "proinflammatory" monocytes to the vascular endothelium in hypertension with potential clinical implications of vascular pathology.

Drug-like actions of autoantibodies against receptors of the autonomous nervous system and their impact on human heart function.

Antibodies against cholinergic and adrenergic receptors (adrenoceptors) are frequent in serum of patients with chronic heart failure. Their prevalence is associated with Chagas' disease, idiopathic dilated cardiomyopathy (DCM), and ischaemic heart disease. Among the epitopes targeted are first and second extracellular loops of the ß-adrenergic (ß-adrenoceptor) and M2 muscarinic receptor. ß(1)-adrenoceptor autoantibodies affect radioligand binding and cardiomyocyte function similar to agonists. Corresponding rodent immunizations induce symptoms compatible with chronic heart failure that are reversible upon removal of the antibodies, transferable via the serum and abrogated by adrenergic antagonists. In DCM patients, prevalence and stimulatory efficacy of ß(1)-adrenoceptor autoantibodies are correlated to the decline in cardiac function, ventricular arrhythmia and higher incidence of cardiac death. In conclusion, such autoantibodies seem to cause or promote chronic human left ventricular dysfunction by acting on their receptor targets in a drug-like fashion. However, the pharmacology of this interaction is poorly understood. It is unclear how the autoantibodies trigger changes in receptor activity and second messenger coupling and how that is related to the pathogenesis and severity of the associated diseases. Here, we summarize the available evidence regarding these issues and discuss these findings in the light of recent knowledge about the conformational activation of the human ß(2)-adrenoceptor and the properties of bona fide cardiopathogenic autoantibodies derived from immune-adsorption therapy of DCM patients. These considerations might contribute to the conception of therapy regimen aimed at counteracting or neutralizing cardiopathogenic receptor autoantibodies.

Neuroendocrine-immune interactions and responses to exercise.

This article reviews the interaction between the neuroendocrine and immune systems in response to exercise stress, considering gender differences. The body's response to exercise stress is a system-wide effort coordinated by the integration between the immune and the neuroendocrine systems. Although considered distinct systems, increasing evidence supports the close communication between them. Like any stressor, the body's response to exercise triggers a systematic series of neuroendocrine and immune events directed at bringing the system back to a state of homeostasis. Physical exercise presents a unique physiological stress where the neuroendocrine and immune systems contribute to accommodating the increase in physiological demands. These systems of the body also adapt to chronic overload, or exercise training. Such adaptations alleviate the magnitude of subsequent stress or minimize the exercise challenge to within homeostatic limits. This adaptive capacity of collaborating systems resembles the acquired, or adaptive, branch of the immune system, characterized by the memory capacity of the cells involved. Specific to the adaptive immune response, once a specific antigen is encountered, memory cells, or lymphocytes, mount a response that reduces the magnitude of the immune response to subsequent encounters of the same stress. In each case, the endocrine response to physical exercise and the adaptive branch of the immune system share the ability to adapt to a stressful encounter. Moreover, each of these systemic responses to stress is influenced by gender. In both the neuroendocrine responses to exercise and the adaptive (B lymphocyte) immune response, gender differences have been attributed to the 'protective' effects of estrogens. Thus, this review will create a paradigm to explain the neuroendocrine communication with leukocytes during exercise by reviewing (i) endocrine and immune interactions; (ii) endocrine and immune systems response to physiological stress; and (iii) gender differences (and the role of estrogen) in both endocrine response to physiological stress and adaptive immune response.