Interleukin-1 receptors in brain and pituitary. Characterization and modulation during infection and stress

Modulation of type I IL-1 receptor and IL-1 beta mRNA expression followed by endotoxin treatment in the corticotropin-releasing hormone-deficient mouse

In an attempt to define the possible role of corticotropin-releasing hormone (CRH) on lipopolysaccharide (LPS)-induced type I interleukin-1 receptor (IL-1R1), IL-1alpha, and IL-1beta mRNAs in the pituitary, adrenal gland and spleen, we used CRH-deficient (knockout, KO) mouse in this study. LPS administration resulted in a robust increase in IL-1R1 mRNA levels in the pituitary, adrenal gland and spleen of wild-type (WT) and CRH KO mice, but this elevation was attenuated in the pituitary and adrenal gland of CRH KO mice. CRH deficiency did not affect LPS administration induced increase of IL-1alpha mRNA as well as IL-1beta mRNA in the pituitary and adrenal gland. Lack of CRH attenuated LPS administration induced increase of IL-1beta mRNA expression in the spleen. These data demonstrate the pivotal and organ-specific modulation of CRH for IL-1 and IL-1R1 mRNAs following endotoxin treatment.

Elevated IL-1beta contributes to antibody suppression produced by stress

Acute stressor exposure can facilitate innate immunity and suppress acquired immunity. The present study further characterized the potentiating effect of stress on innate immunity, interleukin-1beta (IL-1beta), and demonstrated that stress-induced potentiation of innate immunity may contribute to the stress-induced suppression of acquired immunity. The long-term effect of stress on IL-1beta was measured by using an ex vivo approach. Sprague-Dawley rats were challenged with lipopolysaccharide (LPS) in vivo, and the IL-1beta response was measured in vitro. Splenocytes, mesenteric lymphocytes, and peritoneal cavity cells had a dose- and time-dependent ex vivo IL-1beta response to LPS. Rats that were exposed to inescapable shock (IS, 100 1.6 mA, 5-s tail shocks, 60-s intertrial interval) and challenged with a submaximal dose of LPS 4 days later had elevated IL-1beta measured ex vivo. To test whether the acute stress-induced elevation in IL-1beta contributes to the long-term suppression in acquired immunity, IL-1beta receptors were blocked for 24 h after stress. Serum anti-keyhole limpet hemocyanin (KLH) immunoglobulin (Ig) was measured. In addition, the acute elevation (2 h post-IS) of splenic IL-1beta in the absence of antigen was verified. Interleukin-1 receptor antagonist prevented IS-induced suppression in anti-KLH Ig. These data support the hypothesis that stress-induced increases in innate immunity (i.e., IL-1beta) may contribute to stress-induced suppression in acquired immunity (i.e., anti-KLH Ig).

Effect of non-peptide corticotropin-releasing factor receptor type 1 antagonist on adrenocorticotropic hormone release and interleukin-1 receptors followed by stress

Previous studies demonstrated that ether-laparotomy significantly increased iodine-125-labeled interleukin-1alpha ([125I]IL-1alpha) binding in the mouse anterior pituitary at 2 h after the onset of stress. Corticotropin-releasing factor (CRF) receptor antagonist, D-Phe CRF (12-41), abolished ether-laparotomy-induced increase in [125I]IL-1alpha binding in the pituitary, showing that CRF plays a pivotal role in the regulation of IL-1 receptors under stress conditions. In an attempt to define the effect of CRA 1000 (2-(N-(2-methylthio-4-isopropylphenyl)-N-ethylamino-4-(4-(3-fluorophenyl)-1,2,3,6-tetrahydropyridin-1-yl)-6-methylpyrimidine), a non-peptide CRF receptor type 1 antagonist on the regulation of hypothalamic-pituitary-adrenal (HPA) axis and IL-1 receptors in the mouse, we measured plasma adrenocorticotropic hormone (ACTH) and corticosterone levels, [125I]IL-1alpha binding and the expression of transcripts for type 1 IL-1 receptor (IL-1R1 mRNA) in the pituitary at 2 h after endotoxin lipopolysaccharide (LPS) treatment or ether-laparotomy stress with or without CRA 1000 pretreatment. A single injection of LPS dramatically increased plasma ACTH and corticosterone levels compared with saline injection. In contrast, plasma ACTH levels were significantly attenuated in response to one LPS injection following oral CRA 1000 pretreatment. LPS-induced plasma corticosterone levels tended to be lower after CRA 1000 pretreatment but it did not reach statistical significance. Ether-laparotomy stress significantly increased plasma ACTH and corticosterone levels at 2 h after the onset of stress and CRA 1000 pretreatment did not affect the peak ACTH and corticosterone levels following stress. Ether-laparotomy stress resulted in a robust increase in [125I]IL-1alpha binding and IL-1R1 mRNA levels in the pituitary. CRA 1000 pretreatment significantly decreased ether-laparotomy stress-induced IL-1R1 mRNA levels but did not affect [125I]IL-1alpha binding. Pretreatment with CRA 1000 without stress significantly increased [125I]IL-1alpha binding and IL-1R1 mRNA levels compared with those in vehicle pretreatment. These data demonstrate differential effects of CRA 1000 in HPA axis following endotoxin and ether-laparotomy stress and complex interactions between CRF and IL-1 receptors during stress.

Characterization and visualization of [125I] stromal cell-derived factor-1alpha binding to CXCR4 receptors in rat brain and human neuroblastoma cells

Stromal cell-Derived Factor-1 (SDF-1alpha), binds to the seven-transmembrane G protein-coupled CXCR4 receptor and modulates cell migration, differentiation, and proliferation. CXCR4 has been reported to be expressed in various tissues including brain. Moreover, CXCR4 has recently been shown to be one of the coreceptors for HIV-1 infection which could be implicated in HIV encephalitis. In the present study, the binding properties and autoradiographic distribution of [125I]SDF-1alpha binding to CXCR4 were characterized in the adult rat brain. SDF-1alpha binding and CXCR4 coupling system were also studied in human neuroblastoma cell line SK-N-SH. The binding of [125I]SDF-1alpha on rat brain sections was specific, time-dependent and reversible. The highest densities of CXCR4 were detected in the choroid plexus of the lateral and the dorsal third ventricle. Lower densities of [125I]SDF-1alpha binding sites were observed in various brain regions including cerebral cortex, anterior olfactory nuclei, hippocampal formation, thalamic nuclei, blood vessels and pituitary gland. In the choroid plexus, the IC(50) and K(d) of [125I]SDF-1alpha binding were respectively 0.6 nM and 0. 36 nM. Similar IC(50) values were obtained in other brain structures. A CXCR4 antagonist, bicyclam, competed with SDF-1alpha binding (30% inhibition at 10(-6) M). In SK-N-SH cells, [125I]SDF-1alpha bound to CXCR4 with a K(d) of 5.0 nM and a maximal binding capacity of 460 fmol/mg of protein. SDF-1alpha induced a rapid and transient intracellular calcium increase in SK-N-SH cells. These findings suggest that CXCR4 is highly expressed in some brain structures and have a regulatory role in the nervous system. The significance of this expression in the brain parenchyma and more specifically in the choroid plexus remains to be clarified in the normal as well as in the infected brain.

Modulation of type I interleukin-1 receptor messenger RNA followed by one and repeated endotoxin treatment in the mouse

The expression of transcripts for type 1 interleukin-1 receptors (IL-1R1) were investigated utilizing reverse transcription-polymerase chain reaction (RT-PCR) techniques in male C57BL/6 mice. First, we measured IL-1R1 mRNA 1, 2, 6, and 12 h after a single injection of endotoxin lipopolysaccharide (LPS; 30 microg/mouse). IL-1R1 mRNA was measured in relevant tissues utilizing semiquantitative RT-PCR. IL-1R1 mRNA levels were significantly increased 2 and 6 h after one LPS injection group in comparison with the saline injection group in the hippocampus and testis. Next, we investigated the effect of repeated injections of LPS on IL-1R1 expression. LPS or saline were injected at 24-h intervals for 4 consecutive days. The mice were divided into four groups: (1) LPS injections for 4 days and LPS injection on day 5 (LPS-LPS); (2) LPS injections for 4 days and saline injection on day 5 (LPS-saline); (3) saline injections for 4 days and LPS injection on day 5 (saline-LPS); (4) saline injections for 4 days and saline injection on day 5 (saline-saline). The mice were sacrificed by decapitation 2 h after the last injection. In the hippocampus and pituitary gland, significant increases of IL-1R1 mRNA levels were observed in the saline-LPS group, however, the increases were attenuated in LPS-LPS group. IL-1R1 mRNA levels in the hypothalamus were unchanged in all four groups. In the adrenal gland and testis, IL-1R1 mRNA levels were significantly increased in the LPS-LPS group as well as saline-LPS group. These data demonstrate differential regulation of IL-1R1 mRNA by one and repeated endotoxin treatment and suggest the importance of the cytokines in mediating the effects of infectious challenge on brain, endocrine and immune function during endotoxemia.

Expression of interleukin-1 genes and interleukin-1 receptors in the mouse brain after hippocampal injury

In order to evaluate the role of IL-1 production in post-traumatic brain, transcripts for IL-1 (alpha, beta, RA) have been quantified following RT-PCR, in hippocampus and cortex after injury of either hippocampus (Hip) or striatum (Stri). Moreover, 125I IL-1alpha binding sites have been directly quantified using binding experiments on brain sections and quantitative autoradiography. Under basal conditions, levels of PCR products were very low. On day 1, IL-1RA transcripts only were strongly increased in the hippocampus after Hip-lesions and in cortex after Stri lesion. Transcripts were back to control values on day 7 post-lesion. IL-1 receptor densities in the hippocampus (dentate gyrus) were decreased at day 1 around the site of the lesion (but not on the contralateral side) and were back to controls on day 7 indicating a transient and local IL-1 production in the surroundings of the lesion. No changes were found following Stri lesion. This study provides further evidence of the role of the IL-1 molecules family, notably IL-1RA, in the brain reaction to trauma.

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-1beta system (ligand, receptor type I, receptor accessory protein and receptor antagonist), TNF-alpha, TGF-beta1 and neuropeptide Y mRNAs in specific brain regions during bacterial LPS-induced anorexia

Bacterial lipopolysaccharide (LPS) or endotoxin induces neurological manifestations including anorexia. It is proposed that LPS-induced cytokine production is involved in the generation of neurological manifestations and in neuroinflammatory/immunological responses during gram-negative infections. For example, LPS-induced effects can be blocked or ameliorated by the interleukin-1 receptor antagonist (IL-1Ra). Here, sensitive and specific RNase protection assays were used to investigate the effects of the intracerebroventricular (i.c.v.) administration of LPS on mRNA levels of interleukin-1beta (IL-1beta) system components, tumor necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta1, and neuropeptide Y (NPY) in the cerebellum, hippocampus, and hypothalamus. The same brain region sample was analyzed with all of the antisense probes. The data show simultaneous local induction of multiple cytokine components messenger ribonucleic acids (mRNAs) within specific brain regions in anorectic rats responding to i.c.v. administered LPS (500 ng/rat). Interleukin-1beta and IL-1Ra had a similar mRNA induction profile (hypothalamus > cerebellum > hippocampus). Interleukin-1 receptor type I (IL-1RI) mRNA also increased in all three brain regions examined, and the soluble form of IL-1 receptor accessory protein (IL-1R AcP II) mRNA was induced in the hypothalamus. Tumor necrosis factor-alpha mRNA levels increased in the hypothalamus > hippocampus > cerebellum. Levels of membrane bound IL-1R AcP, TGF-beta1, and NPY mRNAs did not change significantly in any brain region. The results suggest that: (1) endogenous up-regulation of IL-1beta and TNF-alpha in the hypothalamus contribute to LPS-induced anorexia; and (2) the ratio IL-1Ra/IL-1beta, and IL-1beta <--> TNF-alpha interactions may have implications for gram-negative infections associated with high levels of LPS in the brain-cerebrospinal fluid.

Measles virus modulates human T-cell somatostatin receptors and their coupling to adenylyl cyclase

The possible role of immunomodulatory peptide somatostatin (SRIF) in measles virus (MV)-induced immunopathology was addressed by analysis of SRIF receptors and their coupling to adenylyl cyclase in mitogen-stimulated Jurkat T cells and human peripheral blood mononuclear cells (PBMC). SRIF-specific receptors were assayed in semipurified membrane preparations by using SRIF14 containing iodinated tyrosine at the first position in the amino acid chain ([125I]Tyr1) as a radioligand. A determination of receptor number by saturation of radioligand binding at equilibrium showed that in Jurkat cells, MV infection led to a dramatic decrease in the total receptor number. The virus-associated disappearance of one (Ki2 = 12 +/- 4 nM [mean +/- standard error of the mean [SEM]]; n = 4) of two somatostatin binding sites identified in control Jurkat cells (Ki1 = 78 +/- 3 pM and Ki2 = 12 +/- 4 nM [mean +/- SEM]; n = 4) was also observed. Almost identical results were obtained for phytohemagglutinin-activated human PBMC. In the absence of MV infection, two somatostatin binding sites were present (Ki1 = 111 +/- 31 pM and Ki2 = 17 +/- 2 nM [mean +/- SEM]; n = 2), whereas in MV-infected cells, only the high-affinity (Ki1 = 48 +/- 15 pM [mean +/- SEM]; n = 2) binding site remained. In addition, MV infection reinforced the inhibitory effects of SRIF on adenylyl cyclase activity, since maximal inhibition at 1 microM peptide was 11% +/- 4% in control cells versus 25% +/- 3% (P < 0.05) in infected Jurkat cells. Moreover, MV infection severely impaired the capacity of adenylyl cyclase to be activated directly (by forskolin) or indirectly (via Gs protein-coupled vasoactive intestinal peptide receptor). An assessment of [methyl-3H]thymidine incorporation showed that SRIF increased proliferative responses to mitogens only in control cells, not in MV-infected cells. Altogether, our data emphasize that MV-associated alteration of SRIF transduction appears to be related to the loss of SRIF-dependent increase of mitogen-induced proliferation.

Induction of immunoreactive interleukin-1 beta and tumor necrosis factor-alpha in the brains of rabies virus infected rats

Interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF alpha) are important cytokines in the development of brain inflammation during pathological process. During rabies virus infection, the level of these proinflammatory cytokines are enhanced in the brain. In the present study we determined the cellular localization of these two cytokines by immunocytochemistry in brains of rats infected with rabies virus, at different time-intervals of the disease (day 1, 3, 4, 5 and at final stage day 6 post-infection (p.i.)). Cellular identification of IL-1 beta (irIL-1 beta) and TNF alpha (irTNF alpha) immunopositive cells was studied using a polyclonal antibody against these cytokines and against glial fibrillary acidic protein (GFAP) to detect astrocytes and GSA-I-B4 isolectin to detect microglial cells and/or infiltrating macrophages. In brains of control and early infected rats, irIL-1 beta was only detected in fibers located in the hypothalamus, supraoptic and tractus optic nuclei and infundibular nucleus. From day 4 onwards until day 6 p.i., enhanced irIL-1 beta was found and identified either in activated ameboid and/or infiltrated macrophages (amygdala, thalamus, internal capsula, subtantia nigra, septal nuclei and around blood vessels), or in activated ramified cells (hypothalamus and periventricular nucleus, piriformis and cingulate cortex, hippocampus). IrTNF alpha was observed in the brains of rats at a final stage of disease (day 5 and 6 p.i.): in the hypothalamus, the amygdala, the internal capsula, the thalamus, the septal nuclei, the hippocampus, the habenular nuclei and around the blood vessels. Ir-TNF alpha was detected in round cells identified as ameboid microglia and/or infiltrated macrophages. A marked activation of microglial and astroglial cells was observed mainly in the hypothalamus, the thalamus and hippocampus and around the blood vessels, at day 4 p.i. and later, revealing a high central inflammatory reaction in brains of rabies virus infected rats. These results showed that IL-1 beta and TNF alpha are produced in the brain both by local microglial cells and infiltrating macrophages during rabies infection. Thus, these cytokines may play an important role in coordinating the dramatic inflammatory response associated with the rabies-encephalopathy as well as in the neural modification and alteration of brain functions.

Interleukin-1 receptors type I and type II in the mouse brain: kinetics of mRNA expressions after peripheral administration of bacterial lipopolysaccharide

The expression of transcripts for Interleukin-1 (IL-1) type I and type II receptors (IL-1R1, IL-1R2) was investigated in the mouse brain and spleen using reverse transcription-polymerase chain reaction techniques under basal conditions and following injection of endotoxin (LPS, i.p., 4 mg/kg). Under basal conditions, mRNAs for both receptor types were found in various parts of the brain, in pituitary as well as in spleen. Following LPS stimulation, mRNA expressions were increased in all studied tissues. IL-1R1 mRNAs were predominant in the brain and pituitary while, IL-1R2 mRNAs were more abundant in the spleen. The maximal quantity of transcripts (IL-1R1, IL-1R2) was obtained 6 h after LPS injection in all studied tissues. The decrease to basal level was observed within 48 h in the brain. In the spleen, IL-1R1 mRNAs remained elevated 48 h after LPS while IL-1R2 mRNAs had already reached basal level. These results indicate a LPS-induced stimulation of IL-1 receptors mRNAs in the brain and a differential expression of IL-1R1 and IL-1R2 transcripts in brain and immune tissues.