Disturbed immuno-endocrine communication via the hypothalamo-pituitary-adrenal axis in autoimmune disease

The MRL Model: A Valuable Tool in Studies of Autoimmunity-Brain Interactions

The link between systemic autoimmunity, brain pathology, and aberrant behavior is still a largely unexplored field of biomedical science. Accumulating evidence points to causal relationships between immune factors, neurodegeneration, and neuropsychiatric manifestations. By documenting autoimmunity-associated neuronal degeneration and cytotoxicity of the cerebrospinal fluid from disease-affected subjects, the murine MRL model had shown high validity in revealing principal pathogenic circuits. In addition, unlike any other autoimmune strain, MRL mice produce antibodies commonly found in patients suffering from lupus and other autoimmune disorders. This review highlights importance of the MRL model as a useful preparation in understanding the links between immune system and brain function.

Neonatal corticosterone administration in rodents as a tool to investigate the maternal programming of emotional and immune domains

Neonatal experiences exert persistent influences on individual development. These influences encompass numerous domains including emotion, cognition, reactivity to external stressors and immunity. The comprehensive nature of the neonatal programming of individual phenotype is reverberated in the large amount of experimental data collected by many authors in several scientific fields: biomedicine, evolutionary and molecular biology. These data support the view that variations in precocious environmental conditions may calibrate the individual phenotype at many different levels. Environmental influences have been traditionally addressed through experimental paradigms entailing the modification of the neonatal environment and the multifactorial (e.g. behaviour, endocrinology, cellular and molecular biology) analysis of the developing individual's phenotype. These protocols suggested that the role of the mother in mediating the offspring's phenotype is often associated with the short-term effects of environmental manipulations on dam's physiology. Specifically, environmental manipulations may induce fluctuations in maternal corticosteroids (corticosterone in rodents) which, in turn, are translated to the offspring through lactation. Herein, I propose that this mother-offspring transfer mechanism can be leveraged to devise experimental protocols based on the exogenous administration of corticosterone during lactation. To support this proposition, I refer to a series of studies in which these protocols have been adopted to investigate the neonatal programming of individual phenotype at the level of emotional and immune regulations. While these paradigms cannot replace traditional studies, I suggest that they can be considered a valid complement.

Leptin fails to blunt the lipopolysaccharide-induced activation of the hypothalamic-pituitary-adrenal axis in rats

Obesity is a risk factor for sepsis morbidity and mortality, whereas the hypothalamic-pituitary-adrenal (HPA) axis plays a protective role in the body's defence against sepsis. Sepsis induces a profound systemic immune response and cytokines serve as excellent markers for sepsis as they act as mediators of the immune response. Evidence suggests that the adipokine leptin may play a pathogenic role in sepsis. Mouse endotoxaemic models present with elevated leptin levels and exogenously added leptin increased mortality whereas human septic patients have elevated circulating levels of the soluble leptin receptor (Ob-Re). Evidence suggests that leptin can inhibit the regulation of the HPA axis. Thus, leptin may suppress the HPA axis, impairing its protective role in sepsis. We hypothesised that leptin would attenuate the HPA axis response to sepsis. We investigated the direct effects of an i.p. injection of 2 mg/kg leptin on the HPA axis response to intraperitoneally injected 25 μg/kg lipopolysaccharide (LPS) in the male Wistar rat. We found that LPS potently activated the HPA axis, as shown by significantly increased plasma stress hormones, ACTH and corticosterone, and increased plasma interleukin 1β (IL1β) levels, 2 h after administration. Pre-treatment with leptin, 2 h before LPS administration, did not influence the HPA axis response to LPS. In turn, LPS did not affect plasma leptin levels. Our findings suggest that leptin does not influence HPA function or IL1β secretion in a rat model of LPS-induced sepsis, and thus that leptin is unlikely to be involved in the acute-phase endocrine response to bacterial infection in rats.

Altered neuroendocrine status at the onset of CNS lupus-like disease

Neuropsychiatric (NP) manifestations and brain atrophy are common, etiologically unexplained complications of the systemic autoimmune disease lupus erythematosus (SLE). Similar to patients with NP SLE, behavioral deficits and neurodegeneration occur in aged, lupus-prone MRL/lpr mice. In order to gain a better understanding of the time course and nature of CNS involvement, we compare the neuro-immuno-endocrine profiles of two lupus-prone MRL/lpr stocks, which differ in disease onset and severity. Mice from stock 485 (characterized by early lupus-like manifestations) display blunted responsiveness to palatable solutions and impaired nocturnal activity as early as 7 weeks of age. They also have increased IgG in cerebrospinal fluid (CSF) before high serum autoantibody levels and splenomegaly are detected. Moreover, when compared to age-matched 6825 controls, 485 mice exhibit elevated serum corticosterone, enlarged left adrenal gland, and enhanced haematoxylin/eosin staining in the hypothalamic paraventricular nucleus. Swimming speed and novel object exploration become impaired only when more severe peripheral manifestations are documented in 17 week-old 485 mice. The obtained results suggest that performance deficits during the prodromal phase of NP SLE-like disease are associated with autoantibodies in CSF and asymmetric activation of the hypothalamus-pituitary-adrenal axis. Subsequent deterioration in behavioral performance evolves alongside systemic autoimmunity and inflammation. Although a leaky blood-CSF barrier is a possible explanation, one may hypothesize that, similar to neonatal lupus, maternal antibodies to brain antigens cross blood-placental barrier during embryogenesis and induce early endocrine and behavioral deficits in offspring.

Stress system dynamics during "life as it is lived": an integrative single-case study on a healthy woman

Little is known about the dynamic characteristics of stress system activity during "life as it is lived". Using as representative a study design as possible, this investigation sought to gain insights into this area. A healthy 25-year-old woman collected her entire urine over a period of 63 days in 12-h intervals (126 measurements) to determine cortisol and neopterin (immune activation marker) levels. In addition, she filled out questionnaires on emotional state and daily routine in 12-h intervals, and was interviewed weekly to identify emotionally negative and positive everyday incidents. Adjusted cross-correlational analyses revealed that stressful incidents were associated with cyclic response patterns in both urinary cortisol and urinary neopterin concentrations. Urinary cortisol levels first decreased 12-24 h after stressful incidents occurred (lag 1: -.178; p = 0.048) and then increased a total of 72-84 h later (lag 6: +.224; p = 0.013). Urinary neopterin levels first increased 0-12 h before the occurrence of stressful incidents (-lag 1: +.185; p = 0.040) and then decreased a total of 48-60 h following such stressors (lag 4: -.181; p = 0.044). Decreases in urinary neopterin levels were also found 24-36 and 48-60 h after increases in pensiveness (lag 2: -.215; p = 0.017) and depressiveness (lag 4: -.221; p = 0.014), respectively. Findings on emotionally positive incidents sharply contrasted with those dealing with negative experiences. Positive incidents were followed first by urinary cortisol concentration increases within 12 h (lag 0: +.290; p = 0.001) and then by decreases after a total of 60-72 h (lag 5: -.186; p = 0.039). Urinary neopterin levels first decreased 12-24 h before positive incidents occurred (-lag 2: -.233; p = 0.010) and then increased a total of 12-24 h following these incidents (lag 1: +.222; p = 0.014). As with previous investigations on patients with systemic lupus erythematosus (SLE), this study showed that stress system response can be considerably longer and more complex and differentiated than findings from conventional group studies have suggested. Further integrative single-case studies will need to be conducted in order to draw firm conclusions about stress system dynamics under real-life conditions.

The MRL model: an invaluable tool in studies of autoimmunity-brain interactions

The link between systemic autoimmunity, brain pathology, and aberrant behavior is still largely unexplored field of biomedical science. Accumulating evidence points to causal relationships between immune factors, neurodegeneration, and neuropsychiatric manifestations. By documenting autoimmunity-associated neuronal degeneration and cytotoxicity of the cerebrospinal fluid from disease-affected subjects, the murine MRL model had shown high validity in revealing principal pathogenic circuits. In addition, unlike any other autoimmune strain, MRL mice produce antibodies commonly found in patients suffering from lupus and other autoimmune disorders. This review highlights importance of the MRL model as an indispensible preparation in understanding the links between immune system and brain function.

The MRL/lpr mouse strain as a model for neuropsychiatric systemic lupus erythematosus

To date, CNS disease and neuropsychiatric symptoms of systemic lupus erythematosus (NP-SLE) have been understudied compared to end-organ failure and peripheral pathology. In this review, we focus on a specific mouse model of lupus and the ways in which this model reflects some of the most common manifestations and potential mechanisms of human NP-SLE. The mouse MRL lymphoproliferation strain (a.k.a. MRL/lpr) spontaneously develops the hallmark serological markers and peripheral pathologies typifying lupus in addition to displaying the cognitive and affective dysfunction characteristic of NP-SLE, which may be among the earliest symptoms of lupus. We suggest that although NP-SLE may share common mechanisms with peripheral organ pathology in lupus, especially in the latter stages of the disease, the immunologically privileged nature of the CNS indicates that early manifestations of particularly mood disorders maybe derived from some unique mechanisms. These include altered cytokine profiles that can activate astrocytes, microglia, and alter neuronal function before dysregulation of the blood-brain barrier and development of clinical autoantibody titres.

Intrathecal antibodies and brain damage in autoimmune MRL mice

Neuropsychiatric (NP) manifestations and brain pathology are poorly understood and potentially fatal concomitants of systemic lupus erythematosus (SLE). For many years, autoantibodies to brain tissue (i.e., brain-reactive antibodies, BRA) were proposed as a key factor in pathogenesis of CNS manifestations. Recent evidence suggests that intrathecal BRA, rather than serum autoantibodies, are a better predictor of disturbed brain morphology and function. We presently test this hypothesis by examining the relationship among BRA in cerebrospinal fluid (CSF), behavioral deficits, and brain pathology in a well-established animal model of CNS lupus. We showed earlier that significant diversity in disease manifestations within genetically homogenous MRL-lpr mice allows for constructive and informative correlational analysis. Therefore, levels of CSF antibodies were presently correlated with behavioral, neuropathological and immune measures in a cohort of diseased MRL-lpr males (N=40). ELISA, Western Blotting, standardized behavioral battery, digital planimetry, HE staining, and immunohistochemistry were employed in overall data collection. The IgG antibodies from CSF were binding to different regions of brain parenchyma, with dentate gyrus, amygdale, and subventricular zones showing enhanced immunoreactivity. High levels of CSF antibodies correlated with increased immobility in the forced-swim test and density of HE(+) cells in the paraventricular nucleus. Peripheral measures of autoimmunity were associated with other deficits in behavior and neuropathology. This correlation pattern suggests that etiology of brain damage in lupus-prone mice is multifactorial. Intrathecal BRA may be important in altering motivated responses and activity of major neuroendocrine axes at the onset of SLE-like disease.

Disturbed distribution of proliferative brain cells during lupus-like disease

Brain atrophy and neuronal degeneration of unknown etiology are frequent and severe concomitants of the systemic autoimmune disease lupus erythematosus (SLE). Using the murine MRL/lpr model, we examined populations of proliferative brain cells during the development of SLE-like disease and brain atrophy. The disease onset was associated with reduced expression of Ki67 and BrdU proliferation markers in the dorsal part of the rostral migratory stream, enhanced Fluoro Jade C staining in the subgranular zone of the dentate gyrus, and paradoxical increase in density of Ki67(+)/BrdU(-) cells in the paraventricular nucleus. Protuberances containing clusters of BrdU(+) cells were frequent along the lateral ventricles and in some cases were bridging ventricular walls. Cells infiltrating the choroid plexus were Ki67(+)/BrdU(+), suggesting proliferative leukocytosis in this cerebrospinal fluid-producing organ. The above results further support the hypothesis that systemic autoimmune disease induces complex CNS pathology, including impaired neurogenesis in the hippocampus. Moreover, changes in the paraventricular nucleus implicate a metabolic dysfunction in the hypothalamus-pituitary-adrenal axis, which may account for altered hormonal status and psychiatric manifestations in SLE.

Purine receptor antagonist modulates serology and affective behaviors in lupus-prone mice: evidence of autoimmune-induced pain?

Neurologic and psychiatric (NP) manifestations are severe complications of systemic lupus erythematosus (SLE). As commonly seen in patients, spontaneous disease onset in the MRL/MpJ-Fas(lpr)/J (MRL-lpr) mouse model of NP-SLE is accompanied by increased autoantibodies, pro-inflammatory cytokines and behavioral dysfunction which precede neuroinflammation and structural brain lesions. The role of purinergic receptors in the regulation of immunity and behavior remains largely unexplored in the field of neuropsychiatry. To examine the possibility that purinoception is involved in the development of affective behaviors, the P2X purinoceptor antagonist, suramin, was administered to lupus-prone mice from 5 to 14 weeks of age. In addition to food and water measures, novel object and sucrose preference tests were performed to assess neophobic anxiety- and anhedonic-like behaviors. Enzyme-linked immunosorbant assays for anti-nuclear antibodies (ANA) and pro-inflammatory cytokines were employed in immunopathological analyses. Changes in dendritic morphology in the hippocampal CA1 region were examined by a Golgi impregnation method. Suramin significantly lowered serum ANA and prevented behavioral deficits, but did not prevent neuronal atrophy in MRL-lpr animals. In a new batch of asymptomatic mice, systemic administration of corticosterone was found to induce aberrations in CA1 dendrites, comparable to the "stress" of chronic disease. The precise mechanism(s) through which purine receptor inhibition exerted beneficial effects is not known. The present data supports the hypothesis that activation of the peripheral immune system induces nociceptive-related behavioral symptomatology which is attenuated by the analgesic effects of suramin. Hypercortisolemia may also initiate neuronal damage, and metabolic perturbations may underlie neuro-immuno-endocrine imbalances in MRL-lpr mice.

Systemic sclerosis associated with generalized vasculitis and hypopituitarism

Systemic sclerosis (SSc) is a progressively evolving multisystemic disorder of unknown etiology. Beyond skin, several other organs can also be affected with a severity of involvement that is often heterogeneous. We describe a 53-year-old female patient who was admitted urgently to the hospital almost collapsed, because of numerous bleeding deep skin ulcers, located all over the body. Clinical findings and autoantibody screening were typical of SSc. Moreover, both histopathology and immunofluorescence findings were compatible with scleroderma and vasculitis as well. In addition, pituitary hormone investigation revealed severely damaged function of the gland. We assume that severe skin ulceration and serious hypopituitarism were both implications of underlying SSc-associated vasculitis. To the best of our knowledge, these peculiar clinical manifestations have not been described in the international literature to date.

Neuroimmunopathology in a murine model of neuropsychiatric lupus

Animal models are extremely useful tools in defining pathogenesis and treatment of human disease. For many years researchers believed that structural damage to the brain of neuropsychiatric (NP) patients lead to abnormal mental function, but this possibility was not extensively explored until recently. Imaging studies of NP-systemic lupus erythematosus (SLE) support the notion that brain cell death accounts for the emergence of neurologic and psychiatric symptoms, and evidence suggests that it is an autoimmunity-induced brain disorder characterized by profound metabolic alterations and progressive neuronal loss. While there are a number of murine models of SLE, this article reviews recent literature on the immunological connections to neurodegeneration and behavioral dysfunction in the Fas-deficient MRL model of NP-SLE. Probable links between spontaneous peripheral immune activation, the subsequent central autoimmune/inflammatory responses in MRL/MpJ-Tnfrsf6(lpr) (MRL-lpr) mice and the sequential mode of events leading to Fas-independent neurodegenerative autoimmune-induced encephalitis will be reviewed. The role of hormones, alternative mechanisms of cell death, the impact of central dopaminergic degeneration on behavior, and germinal layer lesions on developmental/regenerative capacity of MRL-lpr brains will also be explored. This model can provide direction for future therapeutic interventions in patients with this complex neuroimmunological syndrome.

Impaired response to amphetamine and neuronal degeneration in the nucleus accumbens of autoimmune MRL-lpr mice

Spontaneous development of lupus-like disease in MRL-lpr mice is accompanied by a constellation of behavioral deficits, including blunted responsiveness to sucrose. Although autoimmunity-induced damage of limbic areas is proposed to underlie this deficit, the systemic nature of the disease precludes inference of a causal relationship between CNS damage and functional loss. Based on the stimulatory effects of d-amphetamine sulfate (AMPH) on sucrose intake, the present study pharmacologically probes the functional status of central dopaminergic circuits involved in control of behavioral reward. The response rates were compared between diseased MRL-lpr mice and congenic MRL +/+ controls tested in the sucrose preference paradigm. Neuronal loss was assessed by Fluoro Jade B (FJB) staining of nucleus accumbens and the CA2/CA3 region. While control mice significantly increased intake of sucrose solutions 60 min after administration of AMPH (i.p., 0.5 mg/kg), the intake in drugged MRL-lpr mice was comparable to those given saline injection. Increased FJB staining was detected in the nucleus accumbens and hippocampus of diseased mice, and AMPH treatment neither altered this nor other measures of organ pathology. The results obtained are consistent with previously observed changes in the mesolimbic dopamine system of MRL-lpr mice and suggest that the lesion in the nucleus accumbens and deficits in dopamine release underlie impaired responsiveness to palatable stimulation during the progress of systemic autoimmune disease. As such, they point to a neurotransmitter-specific regional brain damage which may account for depressive behaviors in neuropsychiatric lupus erythematosus.

Behavioral heterogeneity in an animal model of neuropsychiatric lupus

BACKGROUND

Various psychiatric manifestations of unknown etiology are common in systemic autoimmune disease lupus erythematosus (SLE). Profound heterogeneity at clinical and neuropathological levels suggests distinct subpopulations of SLE patients and multiple mechanisms in the pathogenesis of aberrant behavior. Using inbred mice prone to SLE-like condition, we presently examine whether subpopulations of diseased mice can be identified on the basis of their behavioral performance.

METHODS

Hierarchical cluster analysis was used to classify 105 MRL-lpr males into clusters. Multivariate analysis of variance (MANOVA) and discriminant function analysis were used to detect overall differences and identify discriminative variables.

RESULTS

Cluster 1 was characterized by blunted responsiveness to palatable stimulation, as well as increased spleen mass and serum levels of interleukin-1. Cluster 2 comprised of animals with reduced ambulation speed and enlarged spleen. Mice from cluster 3 showed profound dilatation of brain ventricles, reduced brain mass, impaired nutrition and performance in task reflective of emotional reactivity.

CONCLUSIONS

Present results suggest that systemic autoimmunity compromises brain function via non-Mendelian mechanisms. Although neuroactive cytokines may impair reward systems, brain atrophy seems to underlie deficits in ingestive behavior and emotional reactivity. This study supports the hypothesis that multiple neuroimmunological pathways are involved in the etiology of aberrant behavior during SLE-like disease.

Brain-immune interactions and disease susceptibility

Many studies have established the routes by which the immune and central nervous (CNS) systems communicate. This network of connections permits the CNS to regulate the immune system through both neuroendocrine and neuronal pathways. In turn, the immune system signals the CNS through neuronal and humoral routes, via immune mediators and cytokines. This regulatory system between the immune system and CNS plays an important role in susceptibility and resistance to autoimmune, inflammatory, infectious and allergic diseases. This review focuses on the regulation of the immune system via the neuroendocrine system, and underlines the link between neuroendocrine dysregulation and development of major depressive disorders, autoimmune diseases and osteoporosis.

Diminished transforming growth factor β2 production leads to increased expression of a profibrotic procollagen α2 type I messenger RNA variant in embryonic fibroblasts of UCD-200 chickens, a model for systemic sclerosis

OBJECTIVE

A procollagen alpha2(I) messenger RNA (mRNA) variant, with a 115-bp band and an expected band of 180 bp, was found to be increased during early, acute scleroderma-like disease in UCD-200 chickens. The present study investigated the influence of cytokines on the expression of these 2 proalpha2(I) mRNA variants.

METHODS

Embryonic fibroblasts of UCD-200 chickens (UCD-200-CEF) and normal white leghorns (NWL-CEF) were grown in 3-dimensional collagen gels. Procollagen mRNA expression was analyzed by RNase protection assay, and proliferation was determined by (3)H-thymidine incorporation. Transforming growth factor beta1 (TGFbeta1) and TGFbeta2 were measured in culture supernatants by enzyme-linked immunosorbent assay.

RESULTS

Compared with NWL-CEF, UCD-200-CEF expressed 7.2 times more of the smaller profibrotic proalpha2(I) mRNA variant. TGFbeta1 stimulated the proliferation of UCD-200-CEF, but not NWL-CEF. The 115 bp:180 bp ratio was increased by TGFbeta1 in both NWL-CEF and UCD-CEF. TGFbeta2 and TGFbeta3 reduced the expression of the profibrotic proalpha2(I) mRNA in UCD-200-CEF to the same levels observed in healthy control NWL-CEF. In culture supernatants, NWL-CEF produced 4.1 times more TGFbeta2 than that produced by UCD-CEF. Inhibition of endogenous TGFbeta2 in NWL-CEF resulted in the same 115 bp:180 bp ratio as seen in untreated UCD-CEF.

CONCLUSION

TGFbeta2 reduces the expression of a profibrotic proalpha2(I) mRNA variant in UCD-200-CEF. The constitutive overproduction of this proalpha2(I) mRNA variant and the diminished synthesis of TGFbeta2 in untreated UCD-200-CEF suggest that TGFbeta2 can act as an antifibrotic cytokine and might be a key player during fibrosis onset. These results shed light on the contradictory observations regarding the role of TGFbeta2 in human systemic sclerosis.

Stress and thyroid autoimmunity

While many studies have shown a connection between stress and autoimmune disease, most of the evidence for stress contributing to the onset and course of autoimmune disease is circumstantial and the mechanisms by which stress affects autoimmune disease are not fully understood. The best circumstantial evidence for an effect of stress on autoimmune thyroid disease is the well-known relationship between the onset of Graves' hyperthyroidism and major stress but even this is debated. However, most of the recent case-control studies have supported stress as a factor that affects the onset and clinical course of Graves' disease. On the other hand, there have been few reports concerning the possible relationship between stress and Hashimoto's thyroiditis. Because the onset and course of Hashimoto's thyroiditis is generally insidious, the effect of stress on Hashimoto's thyroiditis might be overlooked. Numerous human and animal studies have demonstrated that psychological and physiologic stressors induce various immunologic changes. Stress affects the immune system either directly or indirectly through the nervous and endocrine systems. These immune modulations may contribute to the development of autoimmunity as well as the susceptibility to autoimmune disease in genetically predisposed individuals. Stress can be one of the environmental factors for thyroid autoimmunity.

Hippocampal damage in mouse and human forms of systemic autoimmune disease

Systemic lupus erythematosus (SLE) is frequently accompanied by neuropsychiatric (NP) and cognitive deficits of unknown etiology. By using autoimmune MRL-lpr mice as an animal model of NP-SLE, we examine the relationship between autoimmunity, hippocampal damage, and behavioral dysfunction. Fluoro Jade B (FJB) staining and anti-ubiquitin (anti-Ub) immunocytochemistry were used to assess neuronal damage in young (asymptomatic) and aged (diseased) mice, while spontaneous alternation behavior (SAB) was used to estimate the severity of hippocampal dysfunction. The causal relationship between autoimmunity and neuropathology was tested by prolonged administration of the immunosuppressive drug cyclophosphamide (CY). In comparison to congenic MRL +/+ controls, SAB acquisition rates and performance in the "reversal" trial were impaired in diseased MRL-lpr mice, suggesting limited use of the spatial learning strategy. FJB-positive neurons and anti-Ub particles were frequent in the CA3 region. Conversely, CY treatment attenuated the SAB deficit and overall FJB staining. Similarly to mouse brain, the hippocampus from a patient who died from NP-SLE showed reduced neuronal density in the CA3 region and dentate gyrus, as well as increased FJB positivity in these regions. Gliosis and neuronal loss were observed in the gray matter, and T lymphocytes and stromal calcifications were common in the choroid plexus. Taken together, these results suggest that systemic autoimmunity induces significant hippocampal damage, which may underlie affective and cognitive deficits in NP-SLE.

Novel repression of the glucocorticoid receptor by anthrax lethal toxin

Death from anthrax has been reported to occur from systemic shock. The lethal toxin (LeTx) is the major effector of anthrax mortality. Although the mechanism of entry of this toxin into cells is well understood, its actions once inside the cell are not as well understood. LeTx is known to cleave and inactivate MAPKKs. We have recently shown that LeTx represses the glucocorticoid receptor (GR) both in vitro and in vivo. This repression is partial and specific, repressing the glucocorticoid, progesterone, and estrogen receptor alpha, but not the mineralocorticoid or estrogen receptor beta. This toxin does not affect GR ligand or DNA binding, and we have suggested that it may function by removing/inactivating one or more of the many cofactors involved in nuclear hormone receptor signaling. Although the precise involvement of this nuclear hormone receptor repression in LeTx toxicity is unknown, examples of blunted HPA axis and glucocorticoid signaling in numerous autoimmune/inflammatory diseases suggest that such repression of critically important receptors could have deleterious effects on health.

Daily psychosocial stressors and cyclic response patterns in urine cortisol and neopterin in a patient with systemic lupus erythematosus

This study investigated the complex biochemical responses to personally meaningful everyday stressors in a patient with systemic lupus erythematosus (SLE). For this purpose, a 52 year-old woman with SLE collected her entire urine for 56 days on a 12-h basis for the determination of cortisol as well as neopterin, a cellular immune parameter. Additionally, using questionnaires, daily notes and interviews, extensive psychosocial and psychological time-series data were collected every 12 h. Cross-correlational analyses of the resulting time-series revealed that stressful incidents were associated with cyclic fluctuations in both urine cortisol and urine neopterin. Specifically, whenever the patient anticipated a moderately stressful incident, urine cortisol initially increased 24 h before the incident and then decreased 12 h before the incident. Moderate stressors not anticipated by the patient were associated with an initial increase 24 h following the incident and then with a decrease after a total of 36 h. Moreover, stressors having to do with the patient's extramarital relationship were followed initially by a decrease in urine neopterin after 36 h and then by an increase after a total of 60 h. Our findings indicate that when investigating the relationship between psychosocial stressors and biochemical activity in SLE, appropriate consideration of the data's dynamic nature may be necessary to avoid flawed conclusions.

Neurodegeneration in autoimmune MRL-lpr mice as revealed by Fluoro Jade B staining

As in many humans suffering from lupus erythematosus, the development of systemic autoimmunity and inflammation in Fas-deficient MRL-lpr mice is accompanied by CNS dysfunction of unknown etiology. Experimental studies revealed infiltration of lymphoid cells into the choroid plexus, reduced neuronal complexity, retarded brain growth, and enlargement of cerebral ventricles. Moreover, an increased presence of cells with nicked-DNA (TUNEL+ cells) in the periventricular areas suggested accelerated apoptosis in brain cells of MRL-lpr mice. However, direct evidence that the dying cells were neurons was lacking. For this purpose, we presently use Fluoro-Jade B (FJB), a novel fluorescent dye which has high affinity for dying neurons (both apoptotic and necrotic). As expected, in comparison to the control groups, the brains of diseased, 5-month-old MRL-lpr mice showed increased numbers of FJB-positive (+) cells in cortical and periventricular regions. The FJB+ cells were significantly more numerous than TUNEL+ cells, and only approximately 7% co-localized with TUNEL. Immunostaining for CD4 and CD8 markers did not correlate with the number of FJB+ cells, suggesting that T-lymphocyte infiltration into the brain tissue is not a reliable predictor of neuronal demise. Conversely, indices of systemic autoimmunity (splenomegaly and high serum anti-nuclear antibody levels) were associated with increased FJB+ cell numbers in brains of autoimmune MRL-lpr mice, supporting the causal link between autoimmunity and neurodegeneration. Taken together, the above results suggest that factors other than T-cell infiltration and cell death mechanisms other than Fas-mediated apoptosis dominate neuronal degeneration in lupus-prone MRL-lpr mice.

Altered neurotransmission in brains of autoimmune mice: pharmacological and neurochemical evidence

Depressive-like behavior is the most profound manifestation of autoimmunity-associated behavioral syndrome in lupus-prone MRL-lpr mice. This led to the hypothesis that chronic autoimmunity and inflammation alter the activity of central serotonergic and dopaminergic systems. Three drugs with a selective mode of action were used to probe the functional status of these two systems in vivo. The behavioral effects of single and repeated intraperitoneal (i.p.) injections of sertraline, quinpirole (QNP) and risperidone were measured in the forced swim and brief sucrose preference tests. In comparison to MRL +/+ controls, autoimmune MRL-lpr mice did not show a reduction in sucrose intake after the administration of sertraline. Acute injection of quinpirole increased floating more in the MRL-lpr than in the control group, while intermittent administration induced self-injurious behavior in both groups. Acute injection of risperidone significantly increased floating in MRL-lpr mice, while repeated administration abolished the difference between the substrains in sucrose intake. These discrepancies in responsiveness implied that the central neurotransmitter activity is dissimilar in the two MRL substrains. This notion was confirmed in a cohort of untreated MRL-lpr and MRL +/+ mice by comparing their neurotransmitter/metabolite levels in several brain regions. In particular, MRL-lpr brains showed increased dopamine (DA) levels in the paraventricular nucleus (PVN) and median eminence (ME), decreased concentrations of serotonin in the PVN and enhanced levels in the hippocampus, as well as decreased norepinephrine (NE) levels in the prefrontal cortex. Behavioral deficits correlated with the changes in PVN and median eminence. These results are consistent with the hypothesis that imbalanced neurotransmitter regulation of the hypothalamus-pituitary axis plays an important role in the etiology of behavioral dysfunction induced by systemic autoimmune disease.

Neuroendocrine regulation of immunity

A reciprocal regulation exists between the central nervous and immune systems through which the CNS signals the immune system via hormonal and neuronal pathways and the immune system signals the CNS through cytokines. The primary hormonal pathway by which the CNS regulates the immune system is the hypothalamic-pituitary-adrenal axis, through the hormones of the neuroendocrine stress response. The sympathetic nervous system regulates the function of the immune system primarily via adrenergic neurotransmitters released through neuronal routes. Neuroendocrine regulation of immune function is essential for survival during stress or infection and to modulate immune responses in inflammatory disease. Glucocorticoids are the main effector end point of this neuroendocrine system and, through the glucocorticoid receptor, have multiple effects on immune cells and molecules. This review focuses on the regulation of the immune response via the neuroendocrine system. Particular details are presented on the effects of interruptions of this regulatory loop at multiple levels in predisposition and expression of immune diseases and on mechanisms of glucocorticoid effects on immune cells and molecules.

Neurotoxic properties of cerebrospinal fluid from behaviorally impaired autoimmune mice

The chronic, lupus-like autoimmune disease in MRL-lpr mice is associated with leucocyte infiltration into the choroid plexus, brain cell death, and deficits in motivated behavior. The presence of lymphoid cells in the ventricular lumen and the increased number of TUNEL-positive cells in periventricular areas led to the hypothesis that immune cells enter into the cerebrospinal fluid (CSF) and induce primary neuronal damage in regions bordering the cerebral ventricles. Using an in vitro approach, we presently examine the possibility that CSF from autoimmune mice is neurotoxic and/or gliotoxic. The CSF and serum from diseased MRL-lpr mice, less symptomatic MRL +/+ controls, and healthy Swiss/Webster mice (non-autoimmune controls) were frozen until their effects on the viability of pyramidal neurons and astrocytes were assessed in a two-color fluorescence assay. Significant reduction in neuronal viability (in some cases as low as 67%) was observed in the co-cultures of hippocampal neurons and astrocytes incubated for 24 h with CSF from autoimmune MRL-lpr mice. The viability of astrocytes did not differ among the groups, and the CSF from autoimmune mice appeared more toxic than the serum. The behavior of MRL-lpr mice differed significantly from the control groups, as indicated by impaired exploration, reduced intake of palatable food, and excessive immobility in the forced swim test. The present results suggest that CSF from the behaviorally impaired lupus-prone mice is neurotoxic and are consistent with the hypothesis that neuroactive metabolites are produced intrathecally in neuropsychiatric lupus erythematosus.

Immunosuppression prevents neuronal atrophy in lupus-prone mice: evidence for brain damage induced by autoimmune disease?

An early onset of systemic, lupus-like disease in MRL-lpr mice is accompanied by deterioration in their behavioral performance and atrophy of pyramidal neurons in the parietal cortex and the hippocampal CA1 area. Using the immunosuppressive drug cyclophosphamide (CY) to attenuate the disease, we have tested the hypothesis that the autoimmune/inflammatory process is responsible for changes in brain morphology. A modified Golgi impregnation method revealed that, in comparison to saline-treated controls, immunosuppressive treatment with CY (100 mg/kg/week i.p. over 8 weeks) increased dendritic branching and spine numerical density in the CA1 region of MRL-lpr mice and MRL +/+ mice, which develop less severe manifestations of the disease. More interestingly, CY selectively prevented the atrophy and aberrant morphology of pyramidal neurons in the parietal cortex of MRL-lpr mice. The neuropathological measures (in particular reduced dendritic spine density) significantly correlated with increased serum levels of antinuclear antibodies and splenomegaly. The present results support the hypothesis that chronic autoimmune disease induces functionally important changes in neuronal morphology, and provide an empirical basis for understanding the behavioral dysfunction in systemic lupus erythematosus and autoimmune phenomena reported in some forms of mental illness.

Reciprocal interactions between the neuroendocrine and immune systems during inflammation

The neuroendocrine and immune responses to inflammatory stress represent important integrated physiologic circuits for the regulation of inflammation whose basis has been reviewed. Proinflammatory cytokines such as IL-1 beta, TNF alpha, and IL-6 released from inflammatory foci initiate a local inflammatory response and travel by way of the blood-stream to the central nervous system, where they trigger a variety of neuroendocrine counterregulatory mechanisms. There is an important NEI loop. Stimulatory signals are received by the neural systems from inflammatory foci and are transduced by the hypothalamus, thereby initiating a complex hormonal and cytokine cascade of reactions aimed at modulating inflammation and returning the organism to normal physiologic homeostasis once the trigger has been neutralized. Conversely, a number of mechanisms that modulate the anti-inflammatory activity of the neuroendocrine responses to inflammation are also activated. Defects in the neuroendocrine-immune interactions can profoundly affect the susceptibility to developing chronic inflammatory disease and influencing survival after bacterial infections. The NEI loop has important pathophysiologic implications for disease processes.

Intracerebroventricular corticotropin-releasing factor decreases food intake in white-crowned sparrows

Neuropeptides such as corticotropin-releasing factor (CRF) may play a role in regulating the pronounced seasonal changes in food intake shown by white-crowned sparrows (Zonotrichia leucophrys gambelii). White-crowned sparrows held on short day length received injections into the third ventricle (icv) of saline or 5.0, 15.0, and 30 microg/kg. Meal size over the subsequent 180 min was significantly depressed in a dose-dependent fashion. Other non-specific behaviors such as preening, hopping, and immobile behaviors appeared to not be affected by a dose that suppressed food intake. This experiment suggests that white-crowned sparrows, when weight-stable, respond to CRF in a manner comparable with several mammalian species.

Altered circadian rhythms of the stress hormone and melatonin response in lupus-prone MRL/MP-fas(Ipr) mice

The immune system interacts with the hypothalamo-pituitary-adrenal axis via so-called glucocorticoid increasing factors, which are produced by the immune system during immune reactions, causing an elevation of systemic glucocorticoid levels that contribute to preservation of the immune reactions specificities. Previous results from our laboratory had already shown an altered immuno-neuroendocrine dialogue via the hypothalamo-pituitary-adrenal axis in autoimmune disease-prone chicken and mouse strains. In the present study, we further investigated the altered glucocorticoid response via the hypothalamo-pituitary-adrenal axis in murine lupus. We established the circadian rhythms of corticosterone, dehydroepiandrosterone-sulfate, adrenocorticotropic hormone and melatonin, as well as the time response curves after injection of interleukin-1 of the first three parameters in normal SWISS and lupus-prone MRL/MP-fas(Ipr) mice. The results show that lupus-prone MRL/ MP-fas(Ipr) mice do not react appropriately to changes of the light/dark cycle, circadian melatonin rhythms seem to uncouple from the light/dark cycle, and plasma corticosterone levels are elevated during the resting phase. Diurnal changes of dehydroepiandrosterone-sulfate and adrenocorticotropic hormone were normal compared to healthy controls. These data indicate that MRL/ MP-fas(Ipr) mice not only show an altered glucocorticoid response mediated via the hypothalamo pituitary adrenal axis to IL-1, but are also affected by disturbances of corticosterone and melatonin circadian rhythms. Our findings may have implications for intrathymic T cell development and the emergence of autoimmune disease.

Chronic inflammatory stress

A major mechanism involved in maintaining homeostasis in response to chronic inflammation is the hypothalamo-pituitary-adrenal (HPA) axis, resulting in the release of anti-inflammatory glucocorticoids from the adrenal cortex. An inadequate HPA axis response may result in the development of a pathology or an increase in susceptibility and/or severity of disease. Other neuroendocrine systems are also implicated. Increasingly considered important are circadian rhythms, not only of hormones, but also of components of the immune system. Recent evidence concerning changes in hypothalamic control of the HPA axis following development of disease, the implication of these for the response to stress and the use of the HPA axis as a predictor of susceptibility to disease will also be considered. Finally, the influence of stress on autoimmune disease will be discussed. This chapter will concentrate principally on rheumatoid arthritis, although other autoimmune diseases and animal models will be discussed.

The role of the hypothalamic-pituitary-adrenal axis in rheumatoid arthritis

It has become clear that there is a bidirectional communication between the neuroendocrine and the immune system and that both systems influence each other and interact under physiological conditions and in response to inflammatory stimuli. The hypothalamic-pituitary axis plays an important role in regulating and controlling immune responses and dysfunction of the axis has been implicated in the pathogenesis of rheumatoid arthritis (RA). Corticotrophin-releasing hormone (CRH), one of the main hormones of the axis, is also released extra-hypothalamically, peripherally at the site of inflammation and may modulate inflammatory responses locally. In this chapter we will discuss the role of the hypothalamic-pituitary-adrenal (HPA) axis and peripheral CRH, its influences on immune function and what is known about the possible pathogenetic role of the HPA axis and peripheral CRH in RA.

Animal models of neuroimmune interactions in inflammatory diseases

Animal models have been used successfully to study various aspects of neural-immune interactions. Although different approaches carry certain advantages and disadvantages, current high sensitivity screening and manipulation methods coupled with molecular and genetic approaches can be successfully used to tease out the neural pathways that regulate inflammatory disease and the effects of immune molecules, such as interleukins, on neuronal function and pathology. Newer methodologies that measure gene expression of thousands of genes will in the future add to the ability to evaluate complex systems interactions in whole animal models. This review addresses the advantages and disadvantages of some of these approaches in the context of application to neural-immune interactions.

Reduced corticotropin-releasing factor and enhanced vasopressin gene expression in brains of mice with autoimmunity-induced behavioral dysfunction

The spontaneous development of autoimmune disease in MRL-lpr mice induces behavioral and endocrine changes that resemble effects of chronic stressors. To further examine the correspondence between autoimmune disease and chronic stress, we asked whether the brains of autoimmune mice show a shift in the corticotropin-releasing factor (CRF) to vasopressin (AVP) ratio. Using in situ hybridization histochemistry with 35S-labelled mouse riboprobes, the levels of mRNA transcripts encoding CRF and AVP were compared between autoimmune MRL-lpr and control MRL +/+ brains. CRF transcript levels were lower in the hypothalamic paraventricular nucleus and in the central nucleus of the amygdala in MRL-lpr mice. AVP transcript levels were higher in the paraventricular and the supraoptic nuclei in MRL-lpr mice compared to controls. CRF mRNA levels were inversely related to performance in stress-sensitive tasks and to measures of autoimmunity. As found previously for behavioral performance, immunosuppressive treatment with cyclophosphamide abolished the group difference in neuropeptide gene expression. These results indicate that an autoimmune disease process is necessary for the shift in the brain CRF:AVP ratio. Furthermore, they support the parallel between chronic stress and chronic autoimmunity/inflammation, and suggest common central mechanisms relevant to endocrine function and behavior.

Regulation of the hypothalamic-pituitary-adrenal axis by cytokines: actions and mechanisms of action

Glucocorticoids are hormone products of the adrenal gland, which have long been recognized to have a profound impact on immunologic processes. The communication between immune and neuroendocrine systems is, however, bidirectional. The endocrine and immune systems share a common "chemical language," with both systems possessing ligands and receptors of "classical" hormones and immunoregulatory mediators. Studies in the early to mid 1980s demonstrated that monocyte-derived or recombinant interleukin-1 (IL-1) causes secretion of hormones of the hypothalamic-pituitary-adrenal (HPA) axis, establishing that immunoregulators, known as cytokines, play a pivotal role in this bidirectional communication between the immune and neuroendocrine systems. The subsequent 10-15 years have witnessed demonstrations that numerous members of several cytokine families increase the secretory activity of the HPA axis. Because this neuroendocrine action of cytokines is mediated primarily at the level of the central nervous system, studies investigating the mechanisms of HPA activation produced by cytokines take on a more broad significance, with findings relevant to the more fundamental question of how cytokines signal the brain. This article reviews published findings that have documented which cytokines have been shown to influence hormone secretion from the HPA axis, determined under what physiological/pathophysiological circumstances endogenous cytokines regulate HPA axis activity, established the possible sites of cytokine action on HPA axis hormone secretion, and identified the potential neuroanatomic and pharmacological mechanisms by which cytokines signal the neuroendocrine hypothalamus.

Cytokines mediate protective stimulation of glucocorticoid output during autoimmunity: involvement of IL-1

Endogenous glucocorticoid levels are increased during experimental autoimmune encephalomyelitis (EAE) in Lewis rats. Although this endocrine response is essential for survival, the mechanism that triggers the stimulation of glucocorticoid output during the disease remains unknown. We report here that 1) after immunization with the encephalitogenic antigen myelin basic protein (MBP), increased blood glucocorticoid levels are not only observed in Lewis rats, but also in PVG rats, which do not develop EAE; 2) immune cells obtained from animals with EAE and stimulated in vitro with MBP produced mediators that increased glucocorticoid levels when administered to naive recipients; and 3) acute in vivo blockade of interleukin-1 (IL-1) receptors inhibited, to a large extent, the increase in corticosterone levels during EAE. These results show that the increase in corticosterone levels after immunization with MBP can be dissociated from the stress of the paralytic attack that characterizes EAE. Furthermore, they indicate that an endocrine response, which is decisive for the prevention or moderation of EAE, is mainly the result of the stimulation of the hypothalamic-pituitary-adrenal axis by cytokines produced during the immune response that induces the autoimmune disease.

Detrimental effects of chronic hypothalamic-pituitary-adrenal axis activation. From obesity to memory deficits

Increasing evidence suggests that the detrimental effects of glucocorticoid (GC) hypersecretion occur by activation of the hypothalamic-pituitary-adrenal (HPA) axis in several human pathologies, including obesity, Alzheimer's disease, AIDS dementia, and depression. The different patterns of response by the HPA axis during chronic activation are an important consideration in selecting an animal model to assess HPA axis function in a particular disorder. This article will discuss how chronic HPA axis activation and GC hypersecretion affect hippocampal function and contribute to the development of obesity. In the brain, the hippocampus has the highest concentration of GC receptors. Chronic stress or corticosterone treatment induces neuropathological alterations, such as dendritic atrophy in hippocampal neurons, which are paralleled by cognitive deficits. Excitatory amino acid (EAA) neurotransmission has been implicated in chronic HPA axis activation. EAAs play a major role in neuroendocrine regulation. Hippocampal dendritic atrophy may involve alterations in EAA transporter function, and decreased EAA transporter function may also contribute to chronic HPA axis activation. Understanding the molecular mechanisms of HPA axis activation will likely advance the development of therapeutic interventions for conditions in which GC levels are chronically elevated.

Progressive atrophy of pyramidal neuron dendrites in autoimmune MRL-lpr mice

The autoimmune-prone MRL-lpr substrain of mice develop an autoimmunity-associated behavioral syndrome (AABS) which resembles in many respects the behavior of animals exposed to chronic stress. The present study examined whether these mice show changes in the morphology of neuronal dendrites, as found in animals exposed to chronic stress. A modified Golgi-Cox procedure was used to visualize the dendrites of pyramidal neurons in the parietal cortex and in the CA1 hippocampal field of 5-week and 14-week old MRL-lpr mice and MRL + / + controls. Reduced dendritic branching and length, and an up to 20% loss of dendritic spines were observed in parietal and hippocampal pyramidal neurons of MRL-lpr mice at both ages. In the parietal cortex, there was an age-dependent potentiation in the reduction of basilar, but not apical, dendrite branching and length, as well as in the loss of spines on basilar segments. Loss of spines in the hippocampus followed an age-related course for apical but not basilar dendrites. Moreover, compared to age-matched controls, brain weight was smaller in MRL-lpr mice at 14 but not 5 weeks of age. Considering that dendritic atrophy becomes more extensive when autoimmune disease is florid in MRL-lpr mice, it is proposed that immune/inflammatory factor(s) produce dendritic loss. Reduced dendritic complexity may represent, at least in part, a structural basis for the altered behavioral profile of MRL-lpr mice.

Neuroendocrine-immune disturbances in animal models with spontaneous autoimmune diseases

According to our concept, the development of autoimmune disease depends on the presence of two sets of essential genes, one coding for an abnormal autoreactivity of the immune system, the other for a primary susceptibility of the target organ/structure for the immune attack. The final outcome of the disease in a given individual is then fine tuned by modulatory factors, such as diet or hormones. With regard to the latter, the immuno-endocrine interaction via the hypothalamo-pituitary-adrenal (HPA) axis has proven to be of special importance. Investigating the so-called Obese strain (OS) of chickens, an animal model with a spontaneously occurring Hashimoto-like autoimmune thyroiditis, we have first shown an impaired surge of glucocorticoid hormones after stimulation of the HPA axis by antigens or certain cytokines (glucocorticoid-increasing factors--GIFs). More recently, we have found a similar behavior in models with systemic autoimmune diseases, that is, murine lupus erythematosus and avian scleroderma. More detailed studies have, however, proven that the mechanisms underlying this altered immuno-endocrine communication via the HPA axis differs in different models. Finally, recent data point to the possibility that the classical pathways of glucocorticoid-T-cell interactions also take place in the thymus itself, which has been shown to be a site of steroid hormone production.

Interleukin-1 receptor defect in autoimmune NZB mouse brain

Interleukin-1 receptors (IL-1R type I and II) have been characterized in murine nervous structures (hippocampus and frontal cortex), in vascular structures (vessels, choroid plexus), and in the anterior pituitary. Because interleukin-1 (IL-1), injected or induced in the brain, is a powerful regulator of the stress axis and immune functions, it was of interest to investigate IL-1Rs and IL-1 in autoimmune mice. In control mice, bacterial lipopolysaccharide (LPS), administered i.p. or i.c.v., induces a sharp decrease in available brain IL-1 receptors, in spite of a moderate increase in mRNAs for both receptor types. This is concomitant with an increase in IL-1 alpha, beta, and ra mRNA. Ligand production clearly overcomes receptor turnover. In autoimmune mice (NZB and NZB/NZW F1), a strong defect in IL-1R (type I) is demonstrated in the dentate gyrus. This tissue-specific defect cannot be explained by increased occupancy by endogeneous ligands as for LPS-treated mice. The transmission of the defect is Mendelian and suggests the involvement of a single gene. However patterns of IL-1R mRNAs (evaluated by RT-PCR) are similar in NZB and in controls, suggesting a translational or post-translational abnormality. The contribution of this genetic disorder in the development of autoimmunity remains to be clarified. Because the brain IL-1 system sends inhibitory signals towards immune functions, this lack of functional IL-1 binding sites might participate in the disregulations observed in NZB autoimmune mice.

Interleukin-1 receptor deficiency in the hippocampal formation of (NZB x NZW)F2 mice: genetic and molecular studies relating to autoimmunity

Interleukin-1 receptor (IL-1R) deficiency has been previously described in the dentate gyrus of autoimmune NZB and (NZB x NZW) F1 (or BWF1) mice. In this study, the genetic and molecular characterization of this defect were investigated in BWF2 mice in relation to anti-DNA antibody production and microsatellite D1Nds4 (near the IL1r1 gene) polymorphism. IL-1R density was quantified in the brain, spleen and pancreas, using in vitro quantitative autoradiography with recombinant human [125I]-IL-1alpha as the ligand. This study of the dentate gyrus of F2 mice revealed three phenotypes: NZW-like, NZB-like and F1-like, which occurred in a ratio of 1:1:2, with IL-1R densities of 100%, 17% and 59%, respectively as compared to control NZW mice (100%). In contrast, IL-1R densities observed in the choroid plexus and peripheral organs were similar. Moreover a high production of IgG2a anti-DNA antibodies was observed in F2 mice, as in their parents, particularly those with the NZB-like phenotype. Microsatellite mapping of D1Nds4 revealed polymorphism in both parents and BWF2 mice in relation to the level of IL-1R density in the dentate gyrus. In spite of the acute defect in IL-1 binding in the dentate gyrus of NZB mice, molecular analysis of IL-1R mRNA (type I, II and accessory protein) showed similar amounts of mRNA, measured following RT-PCR amplification, in the hippocampal formation of both NZB and control C3H/He mice. In conclusion, the transmission of the IL-1R defect in the dentate gyrus of NZB mice is monofactorial and the defect appears to be at the post-transcriptional level of IL-1R synthesis. The lack of IL-1R in the dentate gyrus seems to correlate with some autoimmune characteristics. Correlation of D1Nds4 polymorphism with the level of IL-1R density suggests that it could be a predisposing gene to disease or a marker for other closely linked predisposing genes.

Modulation of hypothalamic-pituitary-adrenal function by transgenic expression of interleukin-6 in the CNS of mice

Interleukin-6 (IL-6) and IL-6 receptor mRNA and protein have been reported in different brain regions under normal and pathophysiological conditions. Although much is known about the hypothalamic-pituitary-adrenal (HPA) axis stimulation after acute administration, less is known about the chronic effects of IL-6 on the function of the HPA axis. In the present study, we examined the function of the HPA axis in transgenic mice in which constitutive expression of IL-6 under the control of the glial fibrillary acidic protein (GFAP) promoter was targeted to astrocytes in the CNS. GFAP-IL6 mice heterozygous or homozygous for the IL-6 transgene had normal basal plasma corticosterone levels but, after restraint stress, showed abnormally increased levels in a gene dose-dependent manner. The increased plasma corticosterone levels in the IL-6 transgenic mice were associated with increased adrenal corticosterone content and hyperplasia of both adrenal cortex and medulla. Notably, plasma adrenocorticotrophic hormone (ACTH) levels and pituitary ACTH content were either not changed or decreased in these mice, whereas plasma arginine vasopressin (AVP) was increased, supporting a role for AVP in response to acute immobilization stress. The reduced ACTH response together with the adrenal hyperplasia in the IL-6 transgenic mice suggests direct activation at the level of the adrenal gland that may be directly activated by AVP or sensitized to ACTH. A similar mechanism may play a role in the blunted ACTH response and elevated corticosterone levels under pathophysiological conditions observed in humans with high brain levels of IL-6.

Reduced aggressiveness and low testosterone levels in autoimmune MRL-lpr males

Autoimmune, lupus-prone MRL-lpr mice float excessively in the forced swim test, explore novel objects and places less, and show blunted responsiveness to palatable stimuli, which is consistent with the hypothesis that the development of chronic autoimmune disease alters emotional reactivity and/or motivation. The present study measures isolation-induced fighting, a model of "affective" aggression, in lupus-prone MRL-lpr and control MRL +/+ males. When compared with controls, autoimmune MRL-lpr mice show reduced aggressiveness, as evidenced by fewer fighting contacts, longer attack latency, shorter fighting episodes and shorter duration of fighting. In addition, reduced testosterone levels accompany serological signs of autoimmunity in the MRL-lpr males. The present results support the hypothesis that affective responsiveness is altered in lupus-prone mice and may suggest limbic system dysfunction during chronic autoimmune/inflammatory disease. The question of whether immune activation alters behavior by a direct effect on the nervous system, or also via the endocrine system, requires further study.

Neurobehavioral alterations in autoimmune mice

Inbred MRL, NZB and BXSB strains of mice spontaneously develop a systemic, lupus-like autoimmune disease. The progress of autoimmunity is accompanied with a cascade of behavioral changes, most consistently observed in tasks reflective of emotional reactivity and the two-way avoidance learning task. Given the possibility that behavioral alterations may reflect a detrimental consequence of autoimmune-inflammatory processes and/or an adaptive response to chronic malaise, they are tentatively labeled as autoimmunity-associated behavioral syndrome (AABS). It is hypothesized that neuroactive immune factors (pro-inflammatory cytokines, brain-reactive antibodies) together with endocrine mediators (corticotropin-releasing factor, glucocorticoids) participate in the etiology of AABS. Since AABS develops natively, and has a considerable face and predictive validity, and since the principal pathway to autoimmunity is known, AABS may be a useful model for the study of CNS involvement in human autoimmune diseases and by extension, for testing autoimmune hypotheses of several mental disorders (major depression, schizophrenia, Alzheimer's disease, autism and AIDS-related dementia).

Neuroimmunomodulation via limbic structures--the neuroanatomy of psychoimmunology

During the last 20 years, mutual communications between the immune, the endocrine and the nervous systems have been defined on the basis of physiological, cellular, and molecular data. Nevertheless, a major problem in the new discipline "Psychoneuroimmunology" is that controversial data and differences in the interpretation of the results make it difficult to obtain a comprehensive overview of the implications of immunoneuroendocrine interactions in the maintenance of physiological homeostasis, as well as in the initiation and the course of pathological conditions within these systems. In this article, we will first discuss the afferent pathways by which immune cells may affect CNS functions and, conversely, how neural tissues can influence the peripheral immune response. We will then review recent data, which emphasize the (patho)physiological roles of hippocampal-amygdala structures and the nucleus accumbens in neuroimmunomodulation. Neuronal activity within the hippocampal formation, the amygdaloid body, and the ventral parts of the basal ganglia has been examined most thoroughly in studies on neuroendocrine, autonomic and cognitive functions, or at the level of emotional and psychomotor behaviors. The interplay of these limbic structures with components of the immune system and vice versa, however, is still less defined. We will attempt to review and discuss this area of research taking into account recent evidences for neuroendocrine immunoregulation via limbic neuronal systems, as well as the influence of cytokines on synaptic transmission, neuronal growth and survival in these brain regions. Finally, the role of limbic structures in stress responses and conditioning of immune reactivity will be commented. Based on these data, we propose new directions of future research.

Neuroendocrine immune responses to inflammation: the concept of the neuroendocrine immune loop

The neuroendocrine and immune responses to inflammatory stress represents an integrated circuit whose basis is reviewed in this chapter. Pro-inflammatory cytokines such as IL-1 beta, TNF-alpha and IL-6 released from inflammatory foci initiate local anti-inflammatory mechanisms and travel via the blood stream to the brain where they trigger a variety of neuroendocrine counter-regulatory mechanisms. There is therefore an important neuroendocrine-immune loop in which stimulatory signals are received by the neural systems from inflammatory foci. These signals are transduced by the hypothalamus which initiates a complex hormonal cascade reaction aimed at modulating inflammation and returning the organism to normal physiological homeostasis once the trigger has been neutralized. Abnormalities in this cross-talk can profoundly influence the susceptibility to developing chronic inflammatory disease. Thus, in conclusion, the neuroendocrine-immune loop has important pathophysiological implications for disease processes.

Neuroendocrine changes in systemic lupus erythematosus and Sjögren's syndrome

It has become clear that the neuroendocrine and immune systems are closely linked and interdependent. The exact mechanisms of this interaction are only beginning to be unravelled. The complexity of these connections may partly explain why the aetiopathogenesis of autoimmune diseases remains obscure and why genetic, hormonal, microbial, environmental, as well as a host of other factors, have all been put forward as explanations. What has become clear is that a number of neuroendocrine and hormonal factors have important immunomodulatory roles in health and disease.

Disturbed emotionality in autoimmune MRL-lpr mice

MRL-lpr mice develop symptoms of autoimmune lupus-like disease early in the life and MRL(-)+/+ mice develop it substantially later. The present study examines our previous suggestion that autoimmune MRL-lpr mice show altered emotional reactivity. In addition, it aims to identify the set of measures which best discriminate the behavior of MRL-lpr mice from their congenic controls (MRL +/+). Behavior of males from these two substrains (n = 40/substrain; 3-4 mo of age) was compared on a battery of tests presumed to be reflective of emotional reactivity. MRL-lpr mice explored the open field less, spent more time at home-base, and defecated less in comparison to congenic MRL +/+ controls. Moreover, MRL-lpr mice hesitated to step down from an elevated platform and to make contact with a novel object. They also visited open-arms of a plus-maze less often and showed extensive floating in the Porsolt's swim test. Discriminant analysis revealed that the performance of the MRL-lpr and MRL +/+ mice differed most profoundly on measures taken in the Porsolt's swim and step-down tests. In addition, in the MRL-lpr group high titers of serum antinuclear antibodies were associated with impaired exploration of a novel object. These results are consistent with the previously proposed notion of increased "timidity" in autoimmune MRL-lpr mice and of an immune factor contribution to altered emotional reactivity. Considering that behavior of autoimmune MRL-lpr mice resembles behavior of stressed animals, it is speculated that disturbed emotional reactivity reflects the effect of autoimmunity on the hypothalamic-pituitary-adrenal axis.

Interleukin-1 receptor deficiency in brains from NZB and (NZB/NZW)F1 autoimmune mice

Interleukin-1 receptors (IL-1R) are expressed in the brain and the anterior pituitary of normal mice (C3H/He, Swiss), and appear to be involved in the neuroendocrine control of the immune response. Here we have studied the IL-1R density in the brain and the pituitary from several strains of autoimmune mice (NZB, (NZB/NZW)F1, MRL/MP-lpr), using quantitative autoradiography with recombinant human [125I]IL-1 alpha as a ligand. IL-1R was similar in the brain of C3H/He, Swiss and NZW (controls) and MRL/MP-lpr mice. In NZB mice a profound deficit (10% of control mice) in IL-1R was observed exclusively in the dentate gyrus. In (NZB/NZW)F1 the deficit was about 50%. These observations were independent of sex and age. Pituitary receptors were not affected in all the strains except NZW (30% increase). Competition experiments demonstrated that the affinity of IL-1R was not modified in dentate gyrus of (NZB/NZW)F1 and NZW mice. Thus, the number of IL-1R was the only parameter affected. This deficit was not reversed by corticosterone treatment (0.2 mg/20 g body weight, i.p.) and was poorly modified by lipopolysaccharide treatment (0.1 mg/20 g body weight, i.p.) compared to C3H/He mice. In conclusion, this central IL-1R deficit is unlikely to be the consequence of occupancy by abnormal synthesis of brain IL-1. This abnormality is tissue-specific with hereditary autosomal transmission. The role of central IL-1R in neuroimmunoendocrine interactions and in autoimmunity remains to be clarified.