Modulation of early immune responses and suppression of Trypanosoma brucei brucei infections by surgical denervation of the spleen

OBJECTIVE

To examine critical interactions between the nervous system and the immune system during experimental African trypanosomiasis.

METHODS AND RESULTS

Inoculation of Trypanosoma brucei brucei resulted in early interferon (IFN)-gamma production, elevated corticosterone and prostaglandin E(2) (PGE(2)) levels and increased splenocyte proliferation, as measured by enzyme-linked immunospot assay, radioimmunoassay and thymidine incorporation assay, respectively. Splenic denervation suppressed IFN-gamma, corticosterone and PGE(2) production, enhanced splenocyte proliferation, and significantly reduced parasitemia and prolonged rat survival.

CONCLUSIONS

Our data show substantial effects of the nervous system on early immune responses that may influence the outcome of this disease. These effects were not dependent on cytokine inhibitory mediators such as prostaglandins or stress hormones. More investigations are required to understand the evident neural control over the immune system during infectious challenges, which may assist in novel therapeutic approaches.

Inhibition of heme oxygenase in the central nervous system potentiates endotoxin-induced vasopressin release in the rat

Previous in vitro studies have shown that increases in endogenous carbon monoxide (CO) generation via activation of the enzyme heme oxygenase (HO) within the rat hypothalamus are associated with the reduced release of the neuropeptides, vasopressin (AVP) and oxytocin, while evidence concerning corticotrophin-releasing hormone (CRH) is controversial. The present study investigated whether there is also a functional relationship between the HO-CO pathway and AVP and corticosterone (Cort) in vivo. Male Wistar rats were challenged with bacterial lipopolysaccharide (LPS) at doses producing significant activation of the hypothalamo-pituitary-adrenal (HPA) axis. LPS was given alone or after pretreatment with the HO inhibitor Sn-protoporphyrin-9 (SnPP9). The latter was injected either intraperitoneally (i.p.) or by intracerebroventricular (i.c.v.) route. SnPP9 given i.p. failed to modify either basal or LPS-stimulated levels of AVP and Cort. On the contrary, i.c.v. SnPP9 strongly potentiated LPS-induced AVP release and significantly enhanced basal serum Cort levels, although it failed to potentiate stimulation by LPS. The LPS + i.c.v. SnPP9 also significantly reduced the hypothalamic stores of AVP compared to controls, correlating with increased circulating levels of AVP. Taken collectively, these data are in concordance with previous in vitro observations showing that the HO-CO pathway acts centrally to attenuate endotoxin-stimulated AVP release, while having less effects on the pituitary-adrenal axis.

Early differentiation of thymic dendritic cells in the absence of glucocorticoids

The possible role of glucocorticoids (GCs) in the maturation of thymic dendritic cells (DCs) during early ontogeny was analyzed in the progeny of adrenalectomized pregnant rats (Adx foetuses). This experimental model ensured the lack of GCs until establishment of foetal hypothalamus-pituitary gland-adrenal (HPA) axis, and showed profound modifications of the development of thymus gland. In the absence of maternal GCs, there was a high percentage of DCs, many of them exhibiting a mature phenotype, in the 15-16 day-old Adx foetal thymus, which sharply decreased to reach control values on foetal day 17. On the other hand, the absolute number of DCs of Sham foetal rats increased throughout ontogeny, whereas the high numbers found in 15-16 day-old Adx foetuses significantly diminished in the following days. This process was closely correlated with the thymocyte life span, previously demonstrated, and the early appearance of DCs in the spleen. Our results demonstrate that like for other cell components of rat thymus, DC maturation is accelerated in an early foetal microenvironment devoid of glucocorticoids.

The inhibitory effect in experimental autoimmune encephalomyelitis by the immunomodulatory drug Linomide (PNU-212616) is not mediated via release of endogenous glucocorticoids

The immunomodulatory drug Linomide (PNU-212616) is an efficient inhibitor of experimental autoimmune encephalomyelitis (EAE) and a variety of other models of autoimmunity. The mechanism of action of the drug is, however, incompletely resolved. It was recently suggested that Linomide might exert its immunomodulatory activity by stimulation of the hypothalamic-pituitary-adrenal axis. To investigate the relevance of this mechanism of action, we monitored the plasma levels of endogenous corticosterone after treatment with Linomide, and also directly compared the inhibitory activity of the drug on acute EAE induced in sham or adrenalectomized SJL/N mice. Treatment with Linomide resulted in a dose related inhibition of EAE in line with previously reported results. Upon onset of clinical signs of EAE, there was a 7-10 fold elevation of plasma corticosterone from the normal baseline level. Administration of Linomide did however not by itself result in any change in plasma corticosterone levels, neither at the pre-symptomatic phase of the disease nor during acute short term treatment. In adrenal ectomized animals immunized for EAE, paralytic disease developed rapidly and was of a more severe and fatal nature as compared to sham-operated controls. Treatment with Linomide had a profound inhibitory effect on development of paralytic disease in both the ectomized and sham-operated groups. These results strongly suggest that Linomide does not exert its immunomodulatory activity via the release of endogenous glucocorticoids.

Cortisol's purpose

It is proposed that cortisol's primary purpose is to mobilize the body's defenses against water-losing intestinal diseases and corticosterone's against serum diseases. They do this by inversely controlling those immune cells, enzymes, and hormones, etc. that affect survival during infection. These glucocorticosteroids affect fight-or-flight mobilization as an adjunct made possible because most processes that enhance immunity have a reverse effect on fight-or-flight.

The role of neuroendocrine immune interactions in the initiation of humoral immunity in chickens

The presence of neuroendocrine immune interaction in mammalian species has been studied extensively and has been established. However, such an interaction is not as well established in avian species. Furthermore, the role of such an interaction in the initiation of humoral immunity is not well understood. Therefore, the present studies were conducted to determine mechanisms involved in the initiation of humoral immunity in chickens. Cornell K-strain White Leghorn immature male chickens were used for all the experiments. Changes in hormonal and leukocyte profiles after antigen stimulation were studied. The ability of different leukocytes to produce ACTH was also investigated. It was concluded that the first step in the initiation of humoral immunity after antigen exposure is the release of interleukin-1 by macrophages, which in turn stimulates the production of CRF by hypothalamus and/or leukocytes. It is important to mention that CRF production could also be a direct effect of antigen stimulation. The CRF will then stimulate ACTH production by anterior pituitary and/or leukocytes. In addition, CRF will directly enhance lymphocyte activities in the spleen. Corticosteroid production will be stimulated by ACTH and will cause redistribution of lymphocytes from circulation to secondary lymphoid organs such as the spleen for antigen processing and eventual production of antibodies against the invading antigens. Finally, both ACTH and corticosteroids will later act in a negative feedback manner to regulate and control the process of antibody production by inhibiting lymphocyte activities and/or reducing the responsiveness to different stimuli.

Real-time measurements of corticosteroids in conscious animals using an antibody-based electrode

An electrochemical immunosensor for real-time determination of corticosteroids, a group of steroidal hormones, is reported. The sensor measures competitive binding of endogenous corticosteroid and a corticosteroid-peroxidase conjugate with antibodies, immobilized on a platinum electrode, by monitoring of peroxidase activity. The electrode is encased within a dialysate membrane, which separates the electrode environment from the sampled fluid, allowing corticosteroid to equilibrate across the membrane. This permits measurements to be made in vivo. The small size of the probe (350 microns D) allows implantation into tissue or circulatory systems. The electrode was viable for 200 to 400 sequential measurements and at least 48 h in vivo. Detection sensitivity is 0.2 to 0.6 microgram/100 ml of cortisol or corticosterone. The results suggest the possibility of monitoring hormones in real-time within the blood or organ systems of conscious animals.

Auditory stress induces changes in membrane functions of mouse peritoneal macrophages

Stressful events induce responses in the endocrine and immune systems. The authors analysed the influence of repetitive noise stress on peritoneal macrophage oxidative and phagocytic responses. Plasma corticosterone levels were also measured. Different groups of 6- to 8-week-old C57BL/6 male mice were exposed for 1 night (n = 14) and 3 nights (n = 21) to a sound stress of 110 dB in an audiogenic stress chamber. Control animals were submitted to a sham stress for 1 night (n = 13) and 3 nights (n = 17). A marked decrease was observed in the phagocytic response to yeast (P = 3 x 10(-4)) while a mild increase in the oxidative response stimulated by opsonized zymosan was noted only after the 3 night stress (P = 0.02). Corticosterone levels of control and stressed mice did not differ. These results indicate that the stress resulting from repetitive noise causes modifications in peritoneal macrophage activity, and that these changes are dependent on the duration of stress. These functional alterations seem more complex than a simple general suppression or activation.

Towards artificial antibodies prepared by molecular imprinting

The new technique of molecular imprinting has increasingly been adopted by research laboratories worldwide during the last few years. We have studied the use of such imprints against drugs as artificial antibody-binding mimics in competitive radioimmuno-style binding assays. The recognition sites "molded" in the polymers mimic the binding sites of natural antibodies in their interactions with the target antigen. Binding constants are as low as 4.0 nmol/L for a small number of well-defined sites, and cross-reactivities are similar to or better than those observed with biological antibodies. In some cases, the polymers have been used to determine drug concentrations in human serum specimens.

The interaction between interleukin-1 and glucocorticoids in the in vivo antibody response of mice to three concentrations of antigen

Antigenic challenge leads to a transient increase of serum glucocorticoids, a phenomenon that has been implicated in regulation of the magnitude of the immune response. In the present study, we determined the effects of immunization with three different doses of the T-dependent antigen, sheep red blood cells (SRBC), on glucocorticoid levels, IL-1 production by splenic macrophages, and number of splenic antibody-forming cells in mice. Immunization with three doses of antigen caused a dose-dependent increase in serum glucocorticoid after 2-4 h. No effect of immunization on serum corticosteroid-binding globulin levels was found, suggesting that the concentration of free, hormonally active corticosterone was increased. Antigenic challenge resulted in a significant rise of IL-1 production in a dose-related manner 2 h after immunization, except for the group given the highest dose of SRBC, which demonstrated strong elevation of serum corticosterone level by this time. However, IL-1 production by splenic macrophages, isolated at the peak of the hormonal reaction to SRBC (4 h after immunization), was suppressed in a dose-dependent fashion. An inverse relationship between endogenous levels of glucocorticoids and splenic plaque-forming cells number was also revealed. It is concluded that the interaction of IL-1 and glucocorticoids during the first hours after antigenic challenge is one of the factors controlling the magnitude of the immune response.

The role of central corticoliberin in the hyperosmosis-induced secretion of neurohypophysial hormones and corticosterone in the rat

Although synthetic corticotropin-releasing hormone (CRH) is known to influence the secretion of the neurohypophysial hormones, the role of endogenous CRH in the rat brain is still unclear in this respect. Accordingly, experiments were scheduled to study the effects of intracerebroventricularly (i.c.v.) administered CRH-antiserum (AS) on the hyperosmosis-induced secretion of arginine-8-vasopressin (AVP), oxytocin (OXT) and corticosterone in Wistar male rats. A 2 microliters CRH-AS injection was given, and repeated 24 h later, 30 min prior to intraperitoneal administration of hypertonic saline (HS; 2.5% NaCl, 2 ml/100 g body weight) followed by decapitation in 15 min. Plasma AVP and OXT were measured by radioimmunoassay and corticosterone by fluorimetry. HS increased the levels of AVP, OXT and corticosterone. CRH-AS did not change the plasma concentrations of these hormones in 0.9% NaCl-treated animals. CRH-AS pretreatment prevented the corticosterone-releasing action of HS, and significantly moderated the HS-induced AVP and OXT increase. These findings suggest that the central CRH system may participate in the regulation of corticosterone and neurohypophysial hormone secretion evoked by acute osmotic challenge.

Lipocortin 1 (annexin 1) immunoreactivity in the cervical spinal cord of Lewis rats with acute experimental allergic encephalomyelitis

Spontaneous recovery from acute experimental allergic encephalomyelitis (EAE) by the Lewis rat is probably mediated by endogenous corticosteroids. It has been proposed that the anti-inflammatory actions of the glucocorticoids may be effected via the induction of mediator proteins termed lipocortins and recently we have demonstrated increased levels of lipocortin 1 in the central nervous system (CNS) of EAE-diseased rats (Bolton C., A-J. Elderfield and R.J. Flower (1990), J. Neuroimmunol. 29: 173-181). In this study, utilizing antisera raised against recombinant human lipocortin 1, immunohistochemistry and light microscopy have been used to determine the distribution of the protein in the cervical spinal cord of Lewis rats during EAE. In normal animals lipocortin 1 immunoreactivity was localized predominantly in the walls of larger blood vessels and to a lesser extent capillaries. The same staining pattern was found in adjuvant-inoculated controls. In sections from EAE-inoculated animals there was no change during the induction phase, but with the onset of clinical symptoms and the appearance of inflammatory infiltrates in the CNS, a marked increase in lipocortin 1 immunostaining was observed. This additional staining was due to widespread immunoreactivity of the lesions, was maximal at the height of disease and decreased following recovery and lesion regression. Within the lesions the vast majority of infiltrating lymphocytes and macrophages were positive for lipocortin 1, including some very heavily stained macrophage-like cells. Measurement of corticosterone in the sera of these animals showed that changes in lipocortin 1 immunostaining in the CNS during EAE closely parallel serum corticosterone levels.

The effect of transportation stress on splenic natural killer cell activity in C57BL/6J mice

Splenic natural killer cell activity and plasma corticosterone levels were measured in air- and truck-transported C57BL/6J mice (Mus musculus) on days 0, 1, 3 and 5 post-arrival. These data are important in determining adequate stabilization periods for transported animals before studies involving natural killer cells are begun. Three control groups (phosphate buffered saline, polyinosinic-polycytidylic acid, and hydrocortisone injected mice) were stabilized in the animal facilities 3 weeks before the start of experiments. Natural killer activity in transported mice was reduced significantly (p less than 0.05) on day 0 and returned to normal levels by 24 hours. Plasma corticosterone levels were increased significantly (p less than 0.005) on day 0 and returned to control levels by day 1, correlating inversely with splenic natural killer activity. This study indicates that stress resulting from transportation causes a short-term decrease in the splenic natural killer cell activity of mice, and this decrease may be related to the increased plasma corticosterone levels induced by the stressful event. We conclude that mice should be stabilized at least 24 hours before experiments involving the natural killer cell system are begun.

Affinity chromatography using competitive elution separates polyclonal glucocorticoid antisera into fractions of varying cross-reactivity

Affinity chromatography of glucocorticoid antisera using cross-reacting steroid-Sepharose columns and competitive elution with the immunising steroid has allowed the separation of polyclonal antibodies into fractions of varying cross-reactivity. Elution was at neutral pH in the presence of 20% acetonitrile followed by dissociation of the eluted immunoglobulin-steroid complex, by dialysis. A polyclonal cortisol antibody with an initial 70% cross-reactivity to 11-deoxycortisol yielded a fraction with 10% cross reactivity and improved affinity. This fraction was suitable for determining plasma cortisol on patients undergoing the metyrapone test whereas another fraction of similar affinity but higher cross reactivity to 11-deoxycortisol, as well as the intact antiserum, grossly over-estimated plasma cortisol on these patients. This technique should permit the use of antibody fractions for immunoassay when the intact antiserum may be unsatisfactory due to lack of specificity.

Effects of glucocorticoid and antiglucocorticoid hormones on leukocyte numbers and function

Hormones were administered to mice in seven daily intraperitoneal injections of saline suspensions. Progesterone and cortexolone, which often fail to act as antiglucocorticoids in vivo, were found to have antiglucocorticoid effects on the immune system under these conditions. The effects seen were increases in numbers of lymphocytes, monocytes, neutrophils and total leukocytes in the blood, increases in the number of peritoneal exudate cells and splenic plaque-forming cells, and increased splenocyte responses to the mitogen phytohemagglutinin. Deoxycorticosterone, sometimes also considered to be an antiglucocorticoid, acted only as a glucocorticoid here. Both deoxycorticosterone and the glucocorticoid corticosterone had effects opposite to those produced by progesterone and cortexolone on these parameters.

Evidence for differences in the steroid binding domains of the glucocorticoid receptor versus the idiotype antibody

Triamcinolone acetonide (TA), coupled to bovine serum albumin, was used to obtain a polyclonal anti-TA antibody in the rabbit. This idiotype differed from rat glucocorticoid receptor and transcortin in several respects. RU 38486, a synthetic antagonist with high affinity for the receptor, could neither bind the anti-TA antibody nor displace the idiotype bound 3H-TA. Similarly, corticosterone, the natural rodent ligand, had no affinity for the idiotype. These results imply differences in the conformation and topology of the corticoid binding domains, contrary to the current notion where all agonists and antagonists would saturate an identical configuration.

Synthesis of 7 alpha- and beta-carboxymethyl derivatives of cortisol, corticosterone, deoxycorticosterone and cortisone. Immunogenic properties of cortisol, corticosterone and deoxycorticosterone derivatives

7 alpha- and 7 beta-Carboxymethylderivatives of cortisol, corticosterone and deoxycorticosterone have been synthetized. After coupling to bovine serum albumin, they were used to elicit antibodies in rabbits. Highly specific antisera were obtained which may possibly be used for a direct radioimmunoassay of these steroids in human and rodent plasma. In the case of the derivatives of cortisol and corticosterone and stereoisomery of the coupling had an effect on the affinity and the specificity of the antisera. In all immunized rabbits the antisera obtained with the 7 alpha-derivative had a higher affinity and a narrower specificity than the antiserum obtained with the 7 beta-derivative.

Malarial immunity in pregnant mice, in relation to total and unbound plasma corticosterone

A pregnancy dependent loss of malarial immunity is accompanied by an (excessive) increase of total as well as free plasma corticosterone. This loss of immunity was largely prevented by adrenalectomy. Moreover, malarial immunity was more sensitive to dexamethasone immunosuppression during pregnancy. Primary infections are more virulent during pregnancy and like in recrudescent mice, cause excessive total and free plasma corticosterone levels. Corticosterone may be considered an immuno-regulatory serum factor during pregnancy, the endocrine regulation of which is disturbed in pregnant, infected mice.

Plasma corticosterone radioimmunoassay and levels in the neonate chick

The objective was to develop and validate a rapid, precise plasma corticosterone radioimmunoassay using a commercially available antiserum, for use in Gallus domesticus. Sample preparation consisted of sequential 2,2,4-trimethylpentane and dichloromethane extraction to partition progestins and glucocorticoids, respectively. Progesterone, 11 beta-Hydroxyprogesterone, and deoxycorticosterone significantly cross reacted with the antiserum used. However, progesterone was effectively removed prior to assay by the 2,2,4-trimethylpentane plasma washings while 11 beta-Hydroxyprogesterone and deoxycorticosterone interference is doubtful for reasons discussed. Standard curve data showed a linear range from 0 to 150 pg by log-logit transformation with a 5 pg assay sensitivity. Mean percent unlabeled corticosterone recovery was 96% with intraassay and interassay coefficients of variation being 3.75 and 5.62%, respectively. The assay was utilized to characterize corticosterone fluctuations during day one post hatch in broiler chicks. Method of blood collection, rapid decapitation vs. heart stab, resulted in no difference in mean plasma corticosterone levels. Corticosterone levels differed over a 24 hr sampling period, such that highest levels were found upon receipt of the chicks at the hatchery (approximately 20 ng/ml) and 20 hr later (approximately 11 ng/ml). Lowest plasma corticosterone concentrations occurred from 10 to 14 hr (approximately 6 ng/ml) after receipt of the chicks.

Differential potencies of corticosterone and hydrocortisone in immune and immune-related processes in the mouse

The effects of corticosterone and hydrocortisone on the thymus, the pituitary--adrenal axis, delayed hypersensitivity, the corticosterone plasma level and the numbers of circulating nucleated and monocytic cells were investigated in the mouse. Short-term effects within 48 h after one or two corticoid injections and late effects 7 days after a regimen of 4 corticoid injections were discerned. In short-term experiments hydrocortisone was more active than corticosterone upon the induction of leukopenia and monocytopenia and the inhibition of delayed hypersensitivity. However, regarding late effects and the short-term effect on adrenal weight, corticosterone far exceeded hydrocortisone in activity. Our results could be explained by assuming two feedback-inhibition systems for glycocorticoids. The first, likely to be responsible for the changes observed for the adrenal weight and the numbers of ciruclating white cells after a single glucocorticoid injection, was shown to be expressed in a soluble factor released in the blood stream tentatively designated "glucocorticoid inhibiting factor. The factor was more readily induced by hydrocortisone but displayed a greater specificity in inhibiting effects of corticosterone. The second feedback-inhibition system, responsible for increased numbers of circulating monocytes paralleled by an enhanced delayed hypersensitivity response, was expressed in a decreased corticosterone plasma level, most probably secondary to a diminished release of ACTH from the pituitary gland. With the glucocorticoid doses we used the second feedback-inhibition system was only triggered by the more physiological hormone, corticosterone.

Imprinting behavior: pituitary-adrenocortical modulation of the approach response

Plasma corticosterone concentrations in newly hatched ducklings exposed to an imprinting model are inversely related to the strength of approach behavior. Injections of corticosterone before imprinting reduces following, whereas alpha1-10-adrenocorticotropin or antiserum to corticosterone augments following behavior. The sensitive period for imprinting may be regulated by changes in the pituitary-adrenocortical axis.

A radioimmunoassay for corticosterone and its application to the measurement of stress in poultry

A radioimmunoassay for corticosterone was developed using an antibody to corticosterone-21-hemisuccinate:bovine serum albumin. The assay possessed good specificity, sensitivity and reproducibility and required minimal sample preparation. Tests of adrenal function showed that stimulation of the adrenal with exogenous ACTH and with dexamethasone caused an increase and decrease, respectively, in plasma concentrations of corticosterone. Exposure to cold environmental temperatures caused an increase in plasma corticosterone. Handling and the removal of blood samples by venepuncture had no effect upon the concentration of corticosterone. It was concluded that this assay would accurately measure the response to stresses which affect the pituitary-adrenal axis.

The determination of five steroids in avian plasma by radioimmunoassay and competitive protein-binding

A method has been developed for the simultaneous determination of testosterone, 5alpha-dihydrotestosterone and corticosterone, or of estrone, estradiol-17beta and corticosterone, after separation on a Celite:propylene glycol:ethylene glycol column (6:1.5:1.5 w/v/v). The lower quarter of the column was packed with a Celite: water mixture (3:1 w/v) as a stationary phase (glycol) 'trap'. This effectively prevented leaching of the glycols into the eluate as the concentration of ethyl acetate in the mobile phase was increased to elute the more polar steroids. In addition, a second system utilizing a Celite: ethylene glycol column (2:1 w/v) for the separation of estrone and estradiol-17beta is described. Testosterone, 5alpha-dihydrotestosterone, estrone and estradiol-17beta were measured by radioimmunoassay and corticosterone by a competitive protein-binding technique. Reliability criteria are presented showing that the assay systems used are accurate and reproducible. Plasma-steroid levels of eight avian species are also presented and compared with those found by other investigators.