Interleukin 1 binding to its type I, but not type II receptor, modulates the in vivo acute phase response

Interleukin-1 reduces food intake and body weight in rat by acting in the arcuate hypothalamus

A reduction in food intake is commonly observed after bacterial infection, a phenomenon that can be reproduced by peripheral administration of Gram-negative bacterial lipopolysaccharide (LPS) or interleukin-1beta (IL-1β), a pro-inflammatory cytokine released by LPS-activated macrophages. The arcuate nucleus of the hypothalamus (ARH) plays a major role in food intake regulation and expresses IL-1 type 1 receptor (IL-1R1) mRNA. In the present work, we tested the hypothesis that IL-1R1 expressing cells in the ARH mediate IL-1β and/or LPS-induced hypophagia in the rat. To do so, we developed an IL-1β-saporin conjugate, which eliminated IL-R1-expressing neurons in the hippocampus, and micro-injected it into the ARH prior to systemic IL-1β and LPS administration. ARH IL-1β-saporin injection resulted in loss of neuropeptide Y-containing cells and attenuated hypophagia and weight loss after intraperitoneal IL-1β, but not LPS, administration. In conclusion, the present study shows that ARH NPY-containing neurons express functional IL-1R1s that mediate peripheral IL-1β-, but not LPS-, induced hypophagia. Our present and previous findings indicate that the reduction of food intake after IL-1β and LPS are mediated by different neural pathways.

Acute phase response impairs host defense against Pseudomonas aeruginosa pneumonia in mice

OBJECTIVE

Pseudomonas aeruginosa is a common pathogen in hospital-acquired pneumonia. Especially trauma and postsurgical patients display a profound acute phase protein response and are susceptible to acquiring pneumonia. The objective was to study the influence of the acute phase response induced by sterile tissue injury on pulmonary host defense.

DESIGN

Laboratory investigation.

SETTING

Academic medical center.

SUBJECTS

Female C57Bl/6 wild-type mice, 8-10 wks old.

INTERVENTIONS

Mice were injected subcutaneously with either turpentine or sterile saline (control) in both hind limbs 1 day before intranasal infection with P. aeruginosa.

MEASUREMENTS AND MAIN RESULTS

The turpentine-induced acute phase response was associated with 100% lethality after induction of pneumonia, whereas control mice all survived the Pseudomonas infection. In addition, turpentine-injected mice demonstrated much higher bacterial loads in their lungs and an increased dissemination of the infection. The acute phase reaction attenuated lung inflammation during pneumonia, as reflected by histopathology, reduced pulmonary levels of proinflammatory cytokines, and a strongly diminished recruitment of neutrophils to the site of infection. Blood neutrophils harvested from turpentine injected mice displayed a reduced capacity to up-regulate their CD11b/CD18 expression upon stimulation with Pseudomonas ex vivo and during Pseudomonas pneumonia in vivo. Administration of a blocking anti-CD11b antibody to turpentine-injected and control mice almost completely abrogated the difference in bacterial outgrowth, whereas inhibition of the sympathetic nervous system did not affect the impaired pulmonary host defense in mice with an acute phase response.

CONCLUSIONS

These data suggest that a systemic acute phase response might impair host defense against P. aeruginosa pneumonia, possibly in part by inhibition of CD11b/CD18-dependent neutrophil recruitment.

The role of plasminogen activator inhibitor type 1 in the inflammatory response to local tissue injury

BACKGROUND

The plasma levels of the plasminogen activator-inhibitor type 1 (PAI-1) are consistently elevated in patients with sterile tissue injury, often accompanied by a systemic acute phase protein response. It remains unknown, however, whether and to what extent PAI-1 affects the host response to trauma.

METHODS AND RESULTS

By using the well-established murine model of turpentine-induced tissue injury we compared local and systemic inflammatory responses in PAI-1 gene-deficient (PAI-1-/-) and normal wild-type (Wt) mice. Subcutaneous turpentine injection elicited strong increases in PAI-1 protein concentration in plasma and at the site of injury, but not in liver. PAI-1 mRNA was locally increased and expressed mainly by macrophages and endothelial cells. PAI-1 deficiency greatly enhanced the early influx of neutrophils to the site of inflammation, which was associated with increased edema and necrosis at 8 h after injection. Furthermore, PAI-1-/- mice showed a reduced early interleukin (IL)-6 induction with subsequently lower acute phase protein levels and a much slower recovery of body weight loss.

CONCLUSION

These findings suggest that PAI-1 is not merely a marker of tissue injury but plays a functional role in the local and systemic host response to trauma.

Expression of interleukin-1 receptors and their role in interleukin-1 actions in murine microglial cells

Interleukin (IL)-1 is an important mediator of acute brain injury and inflammation, and has been implicated in chronic neurodegeneration. The main source of IL-1 in the CNS is microglial cells, which have also been suggested as targets for its action. However, no data exist demonstrating expression of IL-1 receptors [IL-1 type-I receptor (IL-1RI), IL-1 type-II receptor (IL-1RII) and IL-1 receptor accessory protein (IL-1RAcP)] on microglia. In the present study we investigated whether microglia express IL-1 receptors and whether they present target or modulatory properties for IL-1 actions. RT-PCR analysis demonstrated lower expression of IL-1RI and higher expression of IL-1RII mRNAs in mouse microglial cultures compared with mixed glial or pure astrocyte cultures. Bacterial lipopolysaccharide (LPS) caused increased expression of IL-1RI, IL-1RII and IL-1RAcP mRNAs, induced the release of IL-1beta, IL-6 and prostaglandin-E2 (PGE2), and activated nuclear factor kappaB (NF-kappaB) and the mitogen-activated protein kinases (MAPKs) p38, and extracellular signal-regulated protein kinase (ERK1/2), but not c-Jun N-terminal kinase (JNK) in microglial cultures. In comparison, IL-1beta induced the release of PGE2, IL-6 and activated NF-kappaB, p38, JNK and ERK1/2 in mixed glial cultures, but failed to induce any of these responses in microglial cell cultures. IL-1beta also failed to affect LPS-primed microglial cells. Interestingly, a neutralizing antibody to IL-1RII significantly increased the concentration of IL-1beta in the medium of LPS-treated microglia and exacerbated the IL-1beta-induced IL-6 release in mixed glia, providing the first evidence that microglial IL-1RII regulates IL-1beta actions by binding excess levels of this cytokine during brain inflammation.

Role of interleukin (IL)-1 type 1 receptor in mycobacterial infection

It is important to gain a better understanding of IL-1-mediated signaling events in mycobacterial infection. In order to clarify the role of IL-1 receptor type 1 (IL-1 R1) in IL-1 R1, knockout (KO) mice were infected with either Mycobacterium tuberculosis H37Rv or Kurono strain by the respiratory route, and their ability to control mycobacterial growth, pulmonary granuloma formation, and cytokine mRNA expression was investigated. IL-1 R1 KO mice developed significantly larger (P< 0.01) granulomatous lesions with neutrophil infiltration in their lungs than wild-type mice did after infection with the M. tuberculosis Kurono strain. The number of mycobacterial colonies in lungs and spleen increased from five weeks post-infection. Interferon-y production by spleen cells was low in IL-1 R1 KO mice. It is concluded that the IL-1 R1 is essential for IL-1-mediated signaling events in mycobacterial infection.

TNF-alpha compensates for the impaired host defense of IL-1 type I receptor-deficient mice during pneumococcal pneumonia

To determine the role of IL-1 in the host defense against pneumonia, IL-1R type I-deficient (IL-1R(-/-)) and wild-type (Wt) mice were intranasally inoculated with Streptococcus pneumoniae. Pneumonia resulted in elevated IL-1alpha and IL-1beta mRNA and protein levels in the lungs. Survival rates did not differ between IL-1R(-/-) and Wt mice after inoculation with 5 x 10(4) or 2 x 10(5) CFU. At early time points (24 and 48 h) IL-1R(-/-) mice had 2-log more S. pneumoniae CFU in lungs than Wt mice; at 72 h bacterial outgrowth in lungs was similar in both groups. Upon histopathologic examination IL-1R(-/-) mice displayed a reduced capacity to form inflammatory infiltrates at 24 h after the induction of pneumonia. IL-1R(-/-) mice also had significantly less granulocyte influx in bronchoalveolar lavage fluid at 24 h after inoculation. Since TNF is known to enhance host defense during pneumonia, we determined the role of endogenous TNF in the early impairment and subsequent recovery of defense mechanisms in IL-1R(-/-) mice. All IL-1R(-/-) mice treated with anti-TNF rapidly died (no survivors (of 14 mice) after 4 days), while 10-day survival in IL-1R(-/-) mice (control Ab), Wt mice (anti-TNF), and Wt mice (control Ab) was 7 of 13, 3 of 14, and 12 of 13, respectively. These data suggest that TNF is more important for host defense against pneumococcal pneumonia than IL-1, and that the impaired early host defense in IL-1R(-/-) mice is compensated for by TNF at a later phase.

Biochemical mechanisms that interact with membrane-associated IL-1 RII (60-kDa decoy) receptors in populations of adherent macrophages and vascular endothelium

The aim of this investigation was to identify the potential biochemical mechanisms that alter the integrity of membrane-associated IL-1 RII (decoy) receptor complexes expressed by populations of adherent macrophages and vascular endothelium. The initial research strategy utilized to achieve this objective involved delineating the ability of macrophage activation or exposure of macrophages and vascular endothelium to a spectrum of enzyme proteases to influence the expression of membrane-associated IL-1 RII (decoy) or generate soluble fragments of this receptor complex. Results from these investigations revealed that stimulated macrophages displayed proportional increases in both the expression of membrane-associated IL-1 RII (decoy) and release of soluble receptor fragments. Exposure of macrophages and vascular endothelium to the reference proteases discovered the ability of cathepsin-D to biochemically deplete membrane-associated IL-1 RII (decoy) in addition to generating soluble fragments of this receptor complex. Complementary investigations isolated a carboxyl/aspartate protease from activated macrophages utilizing pepstatin-A affinity chromatography. Exposure of vascular endothelium to pepstatin-A binding proteins resulted in a detectable depletion of membrane-associated IL-1 RII (decoy) and generation of soluble receptor fragments. Evaluation of pepstatin-A binding proteins by SDS-PAGE identified a primary protein fraction with a molecular mass of 47-52 kDa that closely correlates with the known molecular size of leukocyte cathepsin-D fractions. Macrophage pepstatin-A binding protein fractions evaluated by nondenaturing haemoglobin-substrate PAGE (Hb-PAGE) analysis detected a lucent proteolytic band at 47-52 kDa. Macrophage pepstatin-A binding proteins also hydrolyzed a synthetic enzyme-specific substrate that selectively recognizes cathepsin-D biochemical activity. In conclusion, the leukocyte carboxyl/aspartate protease cathepsin-D can biochemically alter the integrity and generate soluble fragments of membrane-associated IL-1 RII (60-kDa decoy) receptor complexes expressed by macrophages and vascular endothelium.

Involvement of the acute phase protein alpha 1-acid glycoprotein in nonspecific resistance to a lethal gram-negative infection

Resistance to gram-negative infection can be induced by pretreating animals with several agents such as turpentine and interleukin (IL)-1. Because these agents are powerful inducers of acute phase proteins, we wondered whether these proteins, more particularly alpha(1)-acid glycoprotein (alpha(1)-AGP), are involved in nonspecific resistance to infection. Turpentine and IL-1 protect completely against a lethal challenge of Klebsiella pneumoniae when given 48 and 12-48 h before the challenge, respectively. alpha(1)-AGP induction in the serum reached peak values 48 h after turpentine and 12-48 h after IL-1 injection. Administration of alpha(1)-AGP, 2 h before a challenge of K. pneumoniae, significantly increased the survival. Numbers of bacteria cultured from blood and organs were significantly lower in mice pretreated with a protective dose of turpentine, IL-1, or alpha(1)-AGP. These data suggest that alpha(1)-AGP is a possible mediator in turpentine- or IL-1-induced protection because time points of maximal induction of alpha(1)-AGP by turpentine or IL-1 and of optimal protection by alpha(1)-AGP coincide. Transgenic overexpression of rat alpha(1)-AGP protected mice from a K. pneumoniae infection. Bacterial counts in blood and organs were significantly lower in transgenic mice, and only in control mice were large necrotic areas, apoptosis, and blood clots observed in the spleen. Our data suggest that alpha(1)-AGP prevents gram-negative infections and may be an essential component in nonspecific resistance to infection.

Modulation of the acute phase response by altered expression of the IL-1 type 1 receptor or IL-1ra

A complete understanding of the role for endogenously produced interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-alpha), and IL-1 receptor antagonist (IL-1ra) in the acute phase response to inflammation remains unknown. In the present studies, knockout mice lacking either a functional IL-1 type I receptor (IL-1RI(-/-)), a TNF type I receptor (TNFR-I(-/-)), or both IL-1 type I and TNF type I receptors (IL-1RI(-/-)/TNFR-I(-/-)) received a turpentine abscess. Additional mice deficient in IL-1ra protein (IL-1ra(-/-)) or overexpressing IL-1ra protein (IL-1ra(tg)) were similarly treated. After a turpentine abscess, IL-1 receptor knockout mice exhibited an attenuated inflammatory response compared with wild-type or animals lacking a functional TNFR-I. Mice overexpressing IL-1ra also had an attenuated hepatic acute phase protein response, whereas IL-1ra knockout mice had a significantly greater hepatic acute phase response. We conclude that the inflammatory response to a turpentine abscess is the result of a balance between IL-1ra expression and IL-1 binding to its type I receptor. Endogenously produced IL-1ra plays a central role in mitigating the magnitude of the IL-1-mediated inflammatory response and, ultimately, the outcome to a turpentine abscess.

Hemolytically active (acylated) alpha-hemolysin elicits interleukin-1beta (IL-1beta) but augments the lethality of Escherichia coli by an IL-1- and tumor necrosis factor-independent mechanism

Many pathogenic Escherichia coli produce the toxin alpha-hemolysin (Hly), and lipopolysaccharide (LPS), interleukin-1 (IL-1), and tumor necrosis factor (TNF) have all been recognized as important effector molecules during infections by gram-negative organisms. Despite the characterization of many in vitro effects of hemolysin, no direct relationship has been established between hemolysin, LPS, proinflammatory cytokine production, and E. coli-induced mortality. Previously, we have shown in vivo that hemolysin elicits a distinct IL-1alpha spike by 4 h into a lethal hemolytic E. coli infection. Using three transformed E. coli strains, WAF108, WAF270, and WAH540 (which produce no Hly [Hlynull], acylated Hly [Hlyactive], or nonacylated Hly [Hlyinactive], respectively), we sought to determine the specific roles of hemolysin acylation, LPS, IL-1, and TNF in mediating the lethality of E. coli infection in mice. WAF270 was 100% lethal in BALB/c, C3H/HeJ, and C57BL/6 mice; in mice pretreated with antibody to the type 1 IL-1 receptor; in type 1 IL-1 receptor-deficient mice; and in dual (type 1 IL-1 receptor-type 1 TNF receptor)-deficient mice at doses which were nonlethal (0%) with both WAF108 and WAH540. At lethal doses, WAF270 killed by 6 +/- 2.3 h while WAF108 and WAH540 killed at 36 +/- 9.4 and 36 +/- 13.8 h, respectively. These differences in mortality were not due to IL-1 or TNF release, and the enhanced expression of LPS, which corresponded to Hly expression, was not likely the primary factor causing mortality. We demonstrate that bacterial fatty acid acylation of hemolysin is required in order for it to elicit IL-1 release by monocytes and to confer its virulence on E. coli.

Brain cytokine mRNAs in anorectic rats bearing prostate adenocarcinoma tumor cells

Cancer is consistently associated with anorexia. The Lobund-Wistar rat model of prostate cancer exhibits clinical manifestations (including anorexia) that resemble many aspects of the human disease. Cytokines are proposed to be involved in cancer-associated anorexia. Here we investigated mRNA profiles of feeding-modulatory cytokines and neuropeptides in specific brain regions of anorectic Lobund-Wistar rats bearing prostate adenocarcinoma tumor cells. Interleukin (IL)-1beta system components (ligand, signaling receptor, receptor accessory proteins, receptor antagonist), tumor necrosis factor-alpha, transforming growth factor-beta1, glycoprotein 130 (IL-6 receptor signal transducer), proopiomelanocortin (POMC, opioid peptide precursor), and neuropeptide Y (NPY) mRNAs were analyzed with sensitive and specific RNase protection assays. The same brain region sample was assayed for all components. The data show that early anorexia in tumor-bearing rats was associated with an upregulation of IL-1beta mRNA in the brain regions examined (cerebellum, cortex, and hypothalamus). IL-1 receptor antagonist (IL-1Ra) mRNA and IL-1 receptor type I mRNA levels were also significantly increased in the cortex and hypothalamus. All other cytokine components, POMC, or NPY mRNA levels were not significantly different between tumor-bearing and pair-fed (control) rats. IL-1beta mRNA and IL-1Ra mRNA were also significantly upregulated in the spleen of tumor-bearing rats. These data suggest that 1) IL-1beta mRNA upregulation in the brain may be relevant to the anorexia exhibited by the tumor-bearing Lobund-Wistar rat and 2) in vivo characterization of cytokine components in discrete brain regions during cancer is necessary to understand underlying molecular mechanisms responsible for cancer-associated neurological manifestations.

Zinc deficiency enhances interleukin-1alpha-induced metallothionein-1 expression in rats

This study investigated whether interleukin-1alpha-induced metallothionein gene expression is affected by zinc deficiency. Weaning male rats were fed a zinc-deficient (ZD) diet (2 mg zinc/kg) or a zinc-supplemented diet [50.8 mg zinc/kg; controls for the diet included pair-fed (PF) and ad libitum consumption groups (AL)] for 4 wk. All rats except those that served as controls for interleukin-1alpha administration, (injected with vehicle and killed at 0 h) were then injected subcutaneously with interleukin-1alpha (2 x 10(7) units/kg body wt) and killed at 3, 6, 12, 24 and 72 h after the injection. Compared with AL and/or PF rats, zinc depletion significantly reduced zinc concentrations in plasma and liver but not in kidney or intestine, and significantly reduced hepatic, renal, and intestinal metallothionein-1 mRNA levels analyzed by competitive reverse transcription-polymerase chain reaction (RT-PCR). Interleukin-1alpha injection reduced plasma zinc concentration and enhanced liver zinc concentration, but did not affect zinc levels in kidney or intestine. Metallothionein-1 mRNA was significantly elevated by interleukin-1alpha in liver, kidney and intestine of all groups; the levels in liver and kidney of ZD rats 6 h after the injection were significantly higher than those of AL or PF rats. Liver metallothionein protein levels were enhanced after interleukin-1alpha injection in both AL and ZD rats. Semiquantitative RT-PCR revealed significantly higher hepatic levels of interleukin-1 receptor type-I mRNA in ZD rats than in AL and PF rats but no differences in renal or intestinal tissues among groups before interleukin-1alpha challenge. In conclusion, zinc deficiency induces upregulation of metallothionein-1 gene expression in response to interleukin-1alpha challenge in rats.

Leptin produces anorexia and weight loss without inducing an acute phase response or protein wasting

The ob gene product leptin is known to produce anorexia and loss of body fat when chronically administered to both lean and genetically obese mice. The current study was undertaken to examine whether administration of recombinant leptin in quantities sufficient to produce decreases in food intake and body weight and alterations in body composition would elicit either an hepatic acute phase protein response or preferential loss of carcass lean tissue. Mice were administered increasing quantities of recombinant human leptin or human tumor necrosis factor-alpha as a positive control. Although leptin (at 10 mg/kg body wt) produced significant anorexia and weight loss (both P < 0.05), human leptin administration did not appear to induce an hepatic acute phase protein response in either lean or genetically obese mice, as determined by protein synthetic rates in the liver or changes in the plasma concentration of the murine acute phase protein reactants, amyloid A, amyloid P, or seromucoid (alpha1-acid glycoprotein). In addition, human leptin administration did not induce a loss of fat-free dry mass (protein) in lean or obese animals. The findings suggest that at doses adequate to alter food intake and body weight leptin is not a significant inducer of the hepatic acute phase response nor does leptin promote the preferential loss of somatic protein characteristic of a chronic inflammatory process.

Blockade of brain type II interleukin-1 receptors potentiates IL1beta-induced anorexia in mice

Interleukin-1beta (IL1beta) peripheral activities are mediated by type I IL1 receptors (IL1RI), whereas type II IL1 receptors (IL1RII) act as 'decoy' targets. To study the functionality of IL1RII in the brain, mice were treated with an intracerebroventricular injection of a neutralising MoAb directed against IL1RII (4E2, 1 microg) followed by recombinant rat IL1beta at a dose (2 ng) that produced a moderate but significant decrease of food intake 1 h 30 min after injection. The administration of 4E2 to IL-1beta treated mice significantly potentiated IL1beta-induced decrease in food intake without altering hypothermia. The effects of IL1beta were abrogated in the positive control group treated with IL1ra (2 microg, i.c.v). These results suggest that brain IL1RII down-regulate the effects of IL1beta on its cell targets in the brain.

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.

Brain type I but not type II IL-1 receptors mediate the effects of IL-1 beta on behavior in mice

In the immune system, interleukin (IL)-1 beta effects are mediated by the type I IL-1 receptors (IL-1RI), whereas the type II IL-1 receptors (IL-1RII) act as inhibitory receptors. IL-1RI and IL-1RII are also present in the brain. To study their functionality in the brain, mice were centrally treated with neutralizing monoclonal antibody (MAb) directed against IL-1RI (35F5, 1 microgram) or against IL-1RII (4E2, 2 micrograms) and were centrally injected with recombinant rat IL-1 beta at a dose (2 ng) that decreased social exploration. Only 35F5 was effective in abrogating the behavioral effect of IL-1 beta. Moreover, 4E2 (1 microgram i.c.v.) did not potentiate the behavioral response to a subthreshold dose of IL-1 beta (1 ng i.c.v.). To examine the ability of brain IL-1RI to mediate the effects of endogenous IL-1 beta, mice were centrally treated with 35F5 (4 micrograms) and peripherally injected with IL-1 beta (1 microgram). Like IL-1 receptor antagonist (4 micrograms i.c.v.), 35F5 abrogated the effects of IL-1 beta. These results suggest that brain IL-1RI mediates the behavioral effects of IL-1 beta in mice.

Gene transfer with IL-4 and IL-13 improves survival in lethal endotoxemia in the mouse and ameliorates peritoneal macrophages immune competence

Systemic anti-cytokine therapies have been unsuccessful in preventing mortality from gram-negative bacteremia in humans partly because of the failure to neutralize pro-inflammatory cytokines at sites of exaggerated production. In an attempt to deliver anti-inflammatory cytokines to organs directly, gene transfer was employed. Thirty-six BALB/c mice were injected intraperitoneally with cationic liposomes containing plasmids encoding the human interleukin-4 (hIL-4) or IL-13 gene. Both, hIL-4 and hIL-13 mRNA were detected by reverse transcription-polymerase chain reaction analysis in the liver and the spleen of the animals. Fourty-eight hours after the in vivo gene transfer, these 36 mice and 18 mock-transfected mice, were challenged with a lethal dose of E. coli lipopolysaccharide with D-galactosamine (D-GalN). Gene transfer with hIL-4 reduced the serum tumor necrosis factor (TNF)-alpha production in response to endotoxin/D-GalN by 80% from 113.1 pg/ml in mock-transfected animals to 22.2 pg/ml (p < 0.05); human IL-13 gene transfer reduced serum TNF-alpha levels by 90% (113.1 pg/ml to 11.6 pg/ml; p < 0.05). Survival was improved from 20% to over 83% in both treatment groups (p < 0.001). Our data demonstrate a potent in vivo anti-inflammatory action of both IL-4 and IL-13. In addition, the immune functions of peritoneal macrophages are significantly ameliorated in both treatment groups, with IL-13 demonstrating better macrophage immune modulation than IL-4 (p < 0.05).

Preferential localization of systemically administered radiolabeled interleukin 1alpha in experimental inflammation in mice by binding to the type II receptor

Previously, we have shown that systemically administered radiolabeled interleukin 1alpha (IL-1alpha) accumulates preferentially in inflammatory foci in mice. Since inflammation is characterized by influx of leukocytes, which represent IL-1 receptor (IL-1R) positive cells, radiolabeled IL-1 may specifically localize in inflammation by binding to its receptors on infiltrated leukocytes. This hypothesis was tested in a series of studies in mice with acute focal inflammations. Evidence for specific IL-1-IL-1R interaction in induced inflammation was found: microscopic autoradiography revealed that 125I-IL-1alpha localized at the site of inflammatory cells with time; 125I-myoglobin, a similar-sized protein with no known interactions in vivo, was not retained in the inflammation. Furthermore, the uptake 125I-IL-1alpha in inflammatory tissue was significantly lower in neutropenic mice than in immunocompetent mice (0.05+/-0.004 vs. 0.65+/-0.06% ID/g at 48 h after injection, P < 0.0007). Moreover, the uptake of 125I-IL-1alpha at the inflammatory site could be blocked with the anti-IL-1R type II antibody 4E2. At 48 h after injection, the uptake with and without blocking the type II IL-1R was 0.13+/-0.01 and 0. 65+/-0.05% ID/g, respectively (P < 0.0001). These in vivo studies provide evidence that systemically administered radiolabeled IL-1alpha localizes in inflammatory tissue by specific receptor binding, predominantly by binding to the type II IL-1R.

Interleukin-1beta (IL-1beta)-induced modulation of the hypothalamic IL-1beta system, tumor necrosis factor-alpha, and transforming growth factor-beta1 mRNAs in obese (fa/fa) and lean (Fa/Fa) Zucker rats: implications to IL-1beta feedback systems and cytokine-cytokine interactions

Interleukin-1beta (IL-1beta) induces anorexia, fever, sleep changes, and neuroendocrine alterations when administered into the brain. Here, we investigated the regulation of the IL-1beta system (ligand, receptors, receptor accessory protein, and receptor antagonist), tumor necrosis factor-alpoha (TNF-alpha), transforming growth factor (TGF)-beta1, and TGF-alpha mRNAs in the hypothalamus of obese (fa/fa) and lean (Fa/Fa) Zucker rats in response to the intracerebroventricular microinfusion of IL-1beta (8.0 ng/24 hr for 72 hr, a dose that yields estimated pathophysiological concentrations in the cerebrospinal fluid). IL-1beta increased IL-1beta, IL-1 receptor types I and II (IL-1RI and IL-1RII), IL-1 receptor accessory protein soluble form (IL-1R AcP II), IL-1 receptor antagonist (IL-1Ra), TNF-alpha, and TGF-beta1 mRNAs in the hypothalamus from obese and lean rats. IL-1beta-induced IL-1beta system and ligand (IL-1beta, TNF-alpha, and TGF-beta1) mRNA profiles were highly intercorrelated in the same samples. Levels of membrane-bound IL-1R AcP and TGF-alpha mRNAs did not change. Heat-inactivated IL-1beta had no effect. The data suggest 1) the operation of an IL-1beta feedback system (IL-1beta/IL-1RI/IL-1R Acp II/IL-1RII/IL-1Ra) and 2) potential cytokine-cytokine interactions with positive (IL-1beta <--> TNF-alpha) and negative (TGF-beta1 --> IL-1beta/TNF-alpha) feedback. Dysregulation of the IL-1beta feedback system and the TGF-beta1/IL-1beta-TNF-alpha balance may have implications for neurological disorders associated with high levels of IL-1beta in the brain.

Cytokines and the hepatic acute phase response

The acute phase response is an orchestrated response to tissue injury, infection or inflammation. A prominent feature of this response is the induction of acute phase proteins, which are involved in the restoration of homeostasis. Cytokines are important mediators of the acute phase response. Uncontrolled and prolonged action of cytokines is potentially harmful, therefore mechanisms exist which limit the activity of cytokines; these include soluble cytokine receptors and receptor antagonists. The cytokine signal is transmitted into the cell via membrane-bound receptors. Different intracellular signalling pathways are activated by different cytokine-receptor interactions. Eventually, cytokine-inducible transcription factors interact with their response elements in the promotor region of acute phase genes and transcription is induced. Systemic inflammation results in a systemic acute phase response. However, local inflammatory or injurious processes in the liver may also induce an acute phase response, for example after partial hepatectomy and during hepatic fibrosis. The acute phase proteins induced in these conditions probably act to limit proteolytic and/or fibrogenic activity and tissue damage. The possible function of the acute phase protein alpha 2-macroglobulin in hepatic fibrosis is discussed in some detail.

HIV-1 gp120 modulates hypothalamic cytokine mRNAs in vivo: implications to cytokine feedback systems

HIV-1-derived envelope glycoprotein 120 (gp120) may play an important role in HIV-1 neuropathology. Gp120 may act through mediators including proinflammatory cytokines. Here, we investigated the regulation of the IL-1 beta system [IL-1 beta, IL-1 receptor type I (IL-1RI), IL-1 receptor antagonist (IL-1Ra), IL-1 receptor accessory proteins (IL-1R AcP I and II)], TNF-alpha, TGF-alpha, and TGF-beta 1 mRNAs in the hypothalamus of Wistar rats in response to the chronic intracerebroventricular (ICV) microinfusion (via osmotic minipumps) of HIV-1 gp120 (100, 500, and 1000 ng/24 h for 72 h). Gp120 increased IL-1 beta, IL-1Ra, TNF-alpha, and TGF-beta 1 mRNAs. Gp120-induced cytokine mRNA profiles were highly intercorrelated in the same samples. Levels of IL-1RI, IL-1R AcP I and II, and TGF-alpha did not change significantly, and levels of GAPDH mRNA were constant. The data suggest potential cytokine-cytokine interactions with positive (IL-1 beta<-->TNF-alpha) and negative (IL-1Ra-->IL-1 beta; TGF-beta 1-->IL-1 beta/TNF-alpha) feedback in gp120 action. A dysregulation of the balance between stimulatory and inhibitory cytokine mechanisms may participate in the initiation, propagation, and/or aggravation of HIV-1 neuropathology.

Interleukin-1 receptor type I mRNA levels in brain regions from male and female rats

Interleukin-1 (IL-1) induces a variety of neurological manifestations by direct action in the central nervous system (CNS). The IL-1 receptor type I (IL-1RI) mediates IL-1 signalling. In the present study, the steady-state content of IL-1RI mRNA was determined by a sensitive RNase protection assay in brain regions obtained from normal male and nonestrous female Wistar rats. The results show that brain regions differ in IL-1RI mRNA content. Highest levels of IL-1RI mRNA were detected in the male and female cerebral cortex. High levels of IL-1RI mRNA were also observed in the brain stem and its structures, and the cerebellum. Male and female rats exhibited similar differential profile of IL-1RI mRNA levels in the frontal cortex, hippocampus, hypothalamus, and cerebellum. The present data on brain distribution of IL-1RI mRNA levels suggest that distinct brain regions may depend differentially on the IL-1 system.

Molecular regulation of the brain interleukin-1 beta system in obese (fa/fa) and lean (Fa/Fa) Zucker rats

Interleukin-1 beta (IL-1 beta) induces anorexia when administered acutely or chronically into the cerebrospinal fluid (CSF) at doses that yield estimated pathophysiological concentrations. Enhanced sensitivity to IL-1 beta-induced anorexia has been observed in animal models of obesity, including the obese (fa/fa) Zucker rat. Obesity is also associated with increased tumor necrosis factor-alpha mRNA expression in adipose tissue. This suggests that obese individuals may have dissimilar sensitivity to cytokine action and differential regulation of cytokine production. In this study, we investigated the regulation of the IL-1 beta system (IL-1 beta, IL-1 receptor type I (IL-1RI) and IL-1 receptor antagonist (IL-1Ra)) in the central nervous system (CNS) in response to the chronic intracerebroventricular (i.c.v.) microinfusion (via osmotic minipumps) of 8 ng IL-1 beta/24 h/72 h-a dose that yields estimated pathophysiological concentrations in the CSF. IL-1 beta, IL-1RI and IL-1Ra mRNAs were determined by sensitive RNase protection assays in brain target regions for IL-1 beta (cerebellum, parieto-frontal cortex, hippocampus, hypothalamus and midbrain). The results show that chronic i.c.v. microinfusion of IL-1 beta increased the IL-1 beta mRNA, IL-1R1 mRNA and IL-1Ra mRNA levels in the hypothalamus > cerebellum in both obese (fa/fa) and lean (Fa/Fa) Zucker rats. IL-1 beta mRNA levels also increased in the cortex, hippocampus and midbrain of obese (fa/fa) rats. The profiles of IL-1 beta mRNA, IL-1RI mRNA and IL-1Ra mRNA in the same hypothalamic samples obtained from obese or lean rats were highly intercorrelated. However, no significant differences in the level of IL-1 beta system mRNAs induction were observed in any brain region between obese and lean rats. On the other hand, levels of rat glyceraldehyde 3-phosphate dehydrogenase mRNA were fairly constant, and heat-inactivated IL-1 beta (8 ng/24 h/72 h) had no effect on IL-1 beta, IL-1RI and IL-1Ra mRNAs levels in any brain region. The data suggest: (1) the operation of an IL-1 beta feedback system (IL-1 beta/IL-1Ra/IL-1RI) in brain regions; (2) that enhanced sensitivity of obese rats to IL-1 beta-induced anorexia is not dependent on changes in the brain IL-1 beta system at the mRNA level; and (3) that the present novel approach can be used to investigate the molecular basis of cytokine action in the CNS.

Regulation of brain interleukin-1 beta (IL-1 beta) system mRNAs in response to pathophysiological concentrations of IL-1 beta in the cerebrospinal fluid

Interleukin-1 beta (IL-1 beta) is released during pathophysiological processes. IL-1 beta induces neurological manifestations when administered into the cerebrospinal fluid (CSF) at pathophysiological concentrations detected during central nervous system (CNS) infections and other neurological disorders. In the present study, we investigated the regulation of the IL-1 beta system in the CNS in response to the chronic intracerebroventricular (icv) microinfusion of IL-1 beta at estimated pathophysiological concentrations in the CSF. IL-1 receptor type I (IL-1RI), IL-1 receptor antagonist (IL-1Ra), and IL-1 beta mRNAs were determined by sensitive RNase protection assays in brain target regions for IL-1 beta (cerebellum, parieto-frontal cortex, hippocampus, and midbrain). The results show that chronic icy microinfusion of IL-1 beta induced significant anorexia, increased the cerebellar IL-1RI mRNA content, increased IL-1Ra and IL-1 beta mRNAs levels in the cerebellum > midbrain > cortex > hippocampus, and induced profiles of IL-1RI mRNA, IL-1Ra mRNA, and IL-1 beta mRNA that were highly intercorrelated. On the other hand, levels of rat glyceraldehyde 3-phosphate dehydrogenase mRNA and 18S rRNA were fairly constant, and heat-inactivated IL-1 beta had no effect on food intake or on IL-1RI, IL-1Ra, and IL-1 beta mRNAs levels in any brain region. The data suggest the operation of an IL-1 beta feedback system (IL-1 beta/ IL-1Ra/IL-1RI) in brain regions. Dysregulation of the CNS IL-1 beta feedback system may have pathophysiological significance. This may be reflected, for example, in the pathogenicity and severity of neurological diseases, such as CNS infections.