Aldose reductase regulates TNF-alpha-induced cell signaling and apoptosis in vascular endothelial cells

TNF-alpha, generated during the systemic inflammatory response, triggers a wide range of biological activities that mediate the neurologic manifestations associated with cancer and infection. Since this cytokine regulates ion channels in vitro (especially Kv1.3 and Kir2.1), we aimed to study Kv1.3 and Kir2.1 expression in brain in response to in vivo systemic inflammation. Cancer-induced cachexia and LPS administration increased plasma TNF-alpha. Kv1.3 and Kir2.1 expression was impaired in brain during cancer cachexia. However, LPS treatment induced Kv1.3 and downregulated Kir2.1 expression, and TNF-alpha administration mimicked these results. Experiments using TNF-alpha double receptor knockout mice demonstrated that the systemic inflammatory response mediates K(+) channel regulation in brain via TNF-alpha-dependent and -independent redundant pathways. In summary, distinct neurological alterations associated with systemic inflammation may result from the interaction of various cytokine pathways tuning ion channel expression in response to neurophysiological and neuroimmunological processes.     

Effect of catecholamines on intracellular cytokine synthesis in human monocytes.

Proinflammatory cytokines produced by monocytes, like Interleukin-6 (IL-6), Interleukin-8 (IL-8), and tumor necrosis factor (TNF-alpha) are known for their pivotal role in the initiation of the inflammatory response following cardiopulmonary bypass (CPB). Catecholamines like epinephrine (Epi) and norepinephrine (Nor) are often necessary to stabilize the cardiac function in the early postoperative period and may influence the cytokine expression in monocytes. In this study we investigated the effects of Epi and Nor on IL-6, IL-8 and TNF-alpha expression in human monocytes stimulated with lipopolysaccharide (LPS) in whole blood, analyzed intracellularly by flow cytometry. Kinetics of intracellular proinflammatory cytokine production and LPS ED(50) were obtained. To simulate different stages of inflammation in vivo, varying concentrations of LPS (0.2 ng/ml, 1 ng/ml and 10 ng/ml) were used for stimulation. After a stimulation with LPS TNF-alpha was the first produced cytokine, followed by IL-8 and IL-6. All cytokines peaked from 3 h to 6 h. Epi and Nor had comparable effects on the expression of IL-6, IL-8 and TNF-a in monocytes. Both inhibited IL-6 and TNF-alpha expression in a concentration dependent manner whereas IL-8 expression remained unchanged. We conclude that monocytes are targets for Epi and Nor concerning their cytokine expression. The inhibiting effects of Nor and Epi were almost identical for all cytokines. Cytokine expression was affected most at low LPS concentrations.     

Inhalative vs. systemic IL-10 administration: Differences in the systemic inflammatory response and end-organ inflammation following hemorrhagic shock

Interleukin-10 is known to modulate the systemic inflammatory response after trauma. This study investigates differences in the systemic and end-organ inflammation in animals treated with either inhalative or systemic IL-10 after experimental hemorrhagic shock (HS). Pressure controlled HS was performed in C57/BL6 mice for 1.5h (6 animals per group). Inhalative or systemic recombinant mouse IL-10 (50μg/kg dissolved in 50μl PBS) was administered after resuscitation. Animals were sacrificed after 4.5 or 22.5h of recovery. Serum levels of IL-6, IL-10, KC, MCP-1, and LBP were determined by ELISA. Pulmonary and liver inflammation was analyzed by standardized Myeloperoxidase (MPO) kits. Systemic and inhalative IL-10 administration affected the systemic inflammatory response as well as end-organ inflammation differently. Differences were obvious in the early (6h) but not later (24h) inflammatory phase. Systemic IL-10 application was associated with a decreased systemic inflammatory response as well as hepatic inflammation, whereas nebulized IL-10 solely reduced the pulmonary inflammation. Our study demonstrates that systemic and nebulized IL-10 administration differentially influenced the systemic cytokine response and end-organ inflammation. Early pulmonary but not hepatic protection appears to be possible by inhalative IL-10 application. Further studies are necessary to assess exact pathways.     

Site-specific modulation of LPS-induced fever and interleukin-1 beta expression in rats by interleukin-10

Bacterial lipopolysaccharide (LPS) induces fever that is mediated by pyrogenic cytokines such as interleukin (IL)-1 beta. We hypothesized that the anti-inflammatory cytokine IL-10 modulates the febrile response to LPS by suppressing the production of pyrogenic cytokines. In rats, intravenous but not intracerebroventricular infusion of IL-10 was found to attenuate fever induced by peripheral administration of LPS (10 microg/kg iv). IL-10 also suppressed LPS-induced IL-1 beta production in peripheral tissues and in the brain stem. In contrast, central administration of IL-10 attenuated the febrile response to central LPS (60 ng/rat icv) and decreased IL-1 beta production in the hypothalamus and brain stem but not in peripheral tissues and plasma. Furthermore, intravenous LPS upregulated expression of IL-10 receptor (IL-10R1) mRNA in the liver, whereas intracerebroventricular LPS enhanced IL-10R1 mRNA in the hypothalamus. We conclude that IL-10 modulates the febrile response by acting in the periphery or in the brain dependent on the primary site of inflammation and that its mechanism of action most likely involves inhibition of local IL-1 beta production.     

Human immunodeficiency virus type 1 infection increases the in vivo capacity of peripheral monocytes to cross the blood-brain barrier into the brain and the in vivo sensitivity of the blood-brain barrier to disruption by lipopolysaccharide

Human immunodeficiency virus type 1 (HIV-1), introduced into the brain by HIV-1-infected monocytes which migrate across the blood-brain barrier (BBB), infects resident macrophages and microglia and initiates a process that causes HIV-1-associated neurocognitive disorders. The mechanism by which HIV-1 infection circumvents the BBB-restricted passage of systemic leukocytes into the brain and disrupts the integrity of the BBB is not known. Circulating lipopolysaccharide (LPS), which can compromise the integrity of the BBB, is significantly increased in HIV-1-infected individuals. We hypothesized that HIV-1 infection increases monocyte capacity to migrate across the BBB, which is further facilitated by a compromise of BBB integrity mediated by the increased systemic LPS levels present in HIV-1-infected individuals. To investigate this possibility, we examined the in vivo BBB migration of monocytes derived from our novel mouse model, JR-CSF/EYFP mice, which are transgenic for both a long terminal repeat-regulated full-length infectious HIV-1 provirus and ROSA-26-regulated enhanced yellow fluorescent protein. We demonstrated that JR-CSF/EYFP mouse monocytes displayed an increased capacity to enter the brain by crossing either an intact BBB or a BBB whose integrity was partially compromised by systemic LPS. We also demonstrated that the JR-CSF mouse BBB was more susceptible to disruption by systemic LPS than the control wild-type mouse BBB. These results demonstrated that HIV-1 infection increased the ability of monocytes to enter the brain and increased the sensitivity of the BBB to disruption by systemic LPS, which is elevated in HIV-1-infected individuals. These mice represent a new in vivo system for studying the mechanism by which HIV-1-infected monocytes migrate into the brain.     

Endotoxin tolerance: regulation of cytokine production and cellular changes in response to endotoxin application in cancer patients.

Endotoxin (lipopolysaccharide, LPS) has the property of inducing tolerance to its own biological effects. This phenomenon has been extensively studied in animal models but only few studies exist on the regulation in humans. Here we describe experiments designed to determine the cytokine regulation and cellular changes in humans during induction of LPS tolerance after repeated LPS injections. Intravenous administration of purified LPS Salmonella abortus equi to cancer patients induces high amounts of circulating tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), interleukin-8 (IL-8), granulocyte colony-stimulating factor (G-CSF), and macrophage colony-stimulating factor (M-CSF). Repeated injections of LPS at daily intervals resulted in a marked downregulation of the cytokine response and in the case of TNF-alpha, IL-8, G-CSF, and M-CSF the cytokine response was reduced to baseline levels. In contrast, significant increases in serum IL-6 were detected up to day 5 of repeated LPS injections. Hematological changes included transient decreases in WBCs affecting granulocytes, monocytes, and lymphocytes, followed by a marked granulocytosis. The drop in WBCs remained unaltered throughout the 5 day course of repeated LPS injections whereas the granulocyte overshoot recovery diminished gradually. When PBMCs of the cancer patients were restimulated ex vivo a marked enhancement of the capacity to produce TNF-alpha, IL-113, and IL-6 occurred, which is in contrast to the decreasing TNF-alpha serum levels obtained in vivo. In parallel, a shift in monocyte subpopulations from CD14+/CD16- to CD14+/CD16+ cells was observed. The data provide evidence that different mechanisms are implicated in the cytokine downregulation following repeated LPS injections to cancer patients. Furthermore, PBMCs from LPS tolerant patients do not demonstrate a reduction in their capacity to produce cytokines.     

IL-8 in septic shock, endotoxemia, and after IL-1 administration

Much effort has been directed toward elucidating the host response to sepsis and inflammation, resulting in the definition of a cascade of endogenous mediators that direct metabolic and immunological responses. Here we report that IL-8, a novel cytokine produced by a variety of cells in vitro in response to stimulation with bacterial LPS and the proinflammatory cytokines, appears in the circulation of primates in vivo during septic shock, sublethal endotoxemia, and after the administration of IL-1 alpha. The magnitude of the IL-8 response correlates with the severity of the insult, and levels of IL-8 peak relatively late, after those of TNF-alpha and IL-1 beta, and simultaneously with those of IL-6. IL-8 has been primarily defined as a selective activator and chemoattractant of neutrophils, and we demonstrate that after LPS or IL-1 alpha infusion, circulating neutrophil numbers rapidly recover from an initial neutropenia while IL-8 concentrations are maximal, supporting the hypothesis that IL-8 influences circulating leukocyte populations in vivo. We conclude that IL-8 is another participant in the cytokine cascade elicited by sepsis and inflammation and, as such, may play a significant role in host defense and disease.     

Maternal LPS induces cytokines in the amniotic fluid and corticotropin releasing hormone in the fetal rat brain

Perinatal infections are a risk factor for fetal neurological pathologies, including cerebral palsy and schizophrenia. Cytokines that are produced as part of the inflammatory response are proposed to partially mediate the neurological injury. This study investigated the effects of intraperitoneal injections of lipopolysaccharide (LPS) to pregnant rats on the production of cytokines and stress markers in the fetal environment. Gestation day 18 pregnant rats were treated with LPS (100 microg/kg body wt i.p.), and maternal serum, amniotic fluid, placenta, chorioamnion, and fetal brain were harvested at 1, 6, 12, and 24 h posttreatment to assay for LPS-induced changes in cytokine protein (ELISA) and mRNA (real-time RT-PCR) levels. We observed induction of proinflammatory cytokines interleukin (IL)-1 beta, IL-6, and tumor necrosis factor-alpha (TNF-alpha) as well as the anti-inflammatory cytokine IL-10 in the maternal serum within 6 h of LPS exposure. Similarly, proinflammatory cytokines were induced in the amniotic fluid in response to LPS; however, no significant induction of IL-10 was observed in the amniotic fluid. LPS-induced mRNA changes included upregulation of the stress-related peptide corticotropin-releasing factor in the fetal whole brain, TNF-alpha, IL-6, and IL-10 in the chorioamnion, and TNF-alpha, IL-1 beta, and IL-6 in the placenta. These findings suggest that maternal infections may lead to an unbalanced inflammatory reaction in the fetal environment that activates the fetal stress axis.     

Effects of vagus nerve stimulation and vagotomy on systemic and pulmonary inflammation in a two-hit model in rats

Pulmonary inflammation contributes to ventilator-induced lung injury. Sepsis-induced pulmonary inflammation (first hit) may be potentiated by mechanical ventilation (MV, second hit). Electrical stimulation of the vagus nerve has been shown to attenuate inflammation in various animal models through the cholinergic anti-inflammatory pathway. We determined the effects of vagotomy (VGX) and vagus nerve stimulation (VNS) on systemic and pulmonary inflammation in a two-hit model. Male Sprague-Dawley rats were i.v. administered lipopolysaccharide (LPS) and subsequently underwent VGX, VNS or a sham operation. 1 hour following LPS, MV with low (8 mL/kg) or moderate (15 mL/kg) tidal volumes was initiated, or animals were left breathing spontaneously (SP). After 4 hours of MV or SP, rats were sacrificed. Cytokine and blood gas analysis was performed. MV with 15, but not 8 mL/kg, potentiated the LPS-induced pulmonary pro-inflammatory cytokine response (TNF-α, IL-6, KC: p<0.05 compared to LPS-SP), but did not affect systemic inflammation or impair oxygenation. VGX enhanced the LPS-induced pulmonary, but not systemic pro-inflammatory cytokine response in spontaneously breathing, but not in MV animals (TNF-α, IL-6, KC: p<0.05 compared to SHAM), and resulted in decreased pO(2) (p<0.05 compared to sham-operated animals). VNS did not affect any of the studied parameters in both SP and MV animals. In conclusion, MV with moderate tidal volumes potentiates the pulmonary inflammatory response elicited by systemic LPS administration. No beneficial effects of vagus nerve stimulation performed following LPS administration were found. These results questions the clinical applicability of stimulation of the cholinergic anti-inflammatory pathway in systemically inflamed patients admitted to the ICU where MV is initiated.     

Endogenous brain IL-1 mediates LPS-induced anorexia and hypothalamic cytokine expression

The present study was designed to determine the role of endogenous brain interleukin (IL)-1 in the anorexic response to lipopolysaccharide (LPS). Intraperitoneal administration of LPS (5-10 microgram/mouse) induced a dramatic, but transient, decrease in food intake, associated with an enhanced expression of proinflammatory cytokine mRNA (IL-1beta, IL-6, and tumor necrosis factor-alpha) in the hypothalamus. This dose of LPS also increased plasma levels of IL-1beta. Intracerebroventricular pretreatment with IL-1 receptor antagonist (4 microgram/mouse) attenuated LPS-induced depression of food intake and totally blocked the LPS-induced enhanced expression of proinflammatory cytokine mRNA measured in the hypothalamus 1 h after treatment. In contrast, LPS-induced increases in plasma levels of IL-1beta were not altered. These findings indicate that endogenous brain IL-1 plays a pivotal role in the development of the hypothalamic cytokine response to a systemic inflammatory stimulus.     

Lipopolysaccharide-Activated Microglia Induce Dysfunction of the Blood–Brain Barrier in Rat Microvascular Endothelial Cells Co-Cultured with Microglia

The blood–brain barrier (BBB) is formed by brain capillary endothelial cells, astrocytes, pericytes, microglia, and neurons. BBB disruption under pathological conditions such as neurodegenerative disease and inflammation is observed in parallel with microglial activation. To test whether activation of microglia is linked to BBB dysfunction, we evaluated the effect of lipopolysaccharide (LPS) on BBB functions in an in vitro co-culture system with rat brain microvascular endothelial cells (RBEC) and microglia. When LPS was added for 6 h to the abluminal side of RBEC/microglia co-culture at a concentration showing no effects on the RBEC monolayer, transendothelial electrical resistance was decreased and permeability to sodium-fluorescein was increased in RBEC. Immunofluorescence staining for tight junction proteins demonstrated that zonula occludens-1-, claudin-5-, and occludin-like immunoreactivities at the intercellular borders of RBEC were fragmented in the presence of LPS-activated microglia. These functional changes induced by LPS-activated microglia were blocked by the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, diphenyleneiodonium chloride. The present findings suggest that LPS activates microglia to induce dysfunction of the BBB by producing reactive oxygen species through NADPH oxidase.     

Bacterial DNA or oligonucleotides containing unmethylated CpG motifs can minimize lipopolysaccharide-induced inflammation in the lower respiratory tract through an IL-12-dependent pathway.

To determine whether the systemic immune activation by CpG DNA could alter airway inflammation, we pretreated mice with either i.v. bacterial DNA (bDNA) or oligonucleotides with or without CpG motifs, exposed these mice to LPS by inhalation, and measured the inflammatory response systemically and in the lung immediately following LPS inhalation. Compared with non-CpG oligonucleotides, i. v. treatment with CpG oligonucleotides resulted in higher systemic concentrations of polymorphonuclear leukocytes, IL-10, and IL-12, but significantly reduced the concentration of total cells, polymorphonuclear leukocytes, TNF-alpha, and macrophage inflammatory protein-2 in the lavage fluid following LPS inhalation. The immunoprotective effect of CpG-containing oligonucleotides was dose-dependent and was most pronounced in mice pretreated between 2 and 4 h before the inhalation challenge, corresponding to the peak levels of serum cytokines. bDNA resulted in a similar immunoprotective effect, and methylation of the CpG motifs abolished the protective effect of CpG oligonucleotides. The protective effect of CpG oligonucleotides was observed in mice with either a disrupted IL-10 or IFN-gamma gene, but release of cytokines in the lung was increased, especially in the mice lacking IFN-gamma. In contrast, CpG DNA did not protect mice with a disrupted IL-12 gene against the LPS-induced cellular influx, even though CpG DNA reduced the release of TNF-alpha and macrophage inflammatory protein-2 in the lung. These findings indicate that CpG-containing oligonucleotides or bDNA are protected against LPS-induced cellular airway inflammation through an IL-12-dependent pathway, and that the pulmonary cytokine and cellular changes appear to be regulated independently.     

Interleukin-1beta and tumor necrosis factor-alpha mediation of endotoxin action on growth hormone

In humans and sheep, endotoxin (LPS) administration results in increased growth hormone (GH) concentrations. To determine the role of cytokines in the effect of LPS on GH, sheep were challenged with IL-1beta or TNF-alpha. GH data were compared with results with LH, where the major effects of LPS are known to act via the hypothalamus. Intracerebroventricular (icv) administration of IL-1beta or TNF-alpha did not alter plasma concentrations of GH. Endotoxin was then administered intravenously (iv) in combination with icv injection of IL-1 receptor antagonist (IL-1RA), TNF antagonist (sTNF-R1), or saline. Administration of LPS increased GH (P < 0.0001), although coadministration of IL-1ra or sTNF-R1 icv did not alter GH response to LPS. In contrast, plasma concentrations of LH were profoundly inhibited by icv administration of either cytokine (P < 0.03), but the LH response to LPS was not altered by cytokine antagonists. Intravenous administration of either IL-1beta or TNF-alpha increased plasma concentrations of GH (P < 0.0001). Administration of IL-1RA and sTNF-R1 iv prevented LPS-induced increases in GH. Although LH was suppressed by high iv doses of IL-1beta (P = 0.0063), the antagonists did not alter the LH response to LPS. To determine whether LPS might directly activate GH release, confocal microscopy revealed colocalization of CD14, the LPS receptor, with GH and, to a lesser extent, LH and some prolactin (PRL)-containing cells, but not ACTH or TSH. These data are consistent with the effects of LPS on GH secretion originating through peripheral cytokine presentation to the pituitary, as well as a potential to act directly on selective populations of pituitary cells via CD14.     

Lipopolysaccharide-Induced Striatal Nitrosative Stress and Impaired Social Recognition Memory Are Not Magnified by Paraquat Coexposure

Systemic inflammation triggered by lipopolysaccharide (LPS) administration disrupts blood–brain barrier (BBB) homeostasis in animal models. This event leads to increased susceptibility of several encephalic structures to potential neurotoxicants present in the bloodstream. In this study, we investigated the effects of alternate intraperitoneal injections of LPS on BBB permeability, social recognition memory and biochemical parameters in the striatum 24 h and 60 days after treatments. In addition, we investigated whether the exposure to a moderate neurotoxic dose of the herbicide paraquat could potentiate LPS-induced neurotoxicity. LPS administration caused a transient disruption of BBB integrity, evidenced by increased levels of exogenously administered sodium fluorescein in the striatum. Also, LPS exposure caused delayed impairment in social recognition memory (evaluated at day 38 after treatments) and increase in the striatal levels of 3-nitrotyrosine. These events were observed in the absence of significant changes in motor coordination and in the levels of tyrosine hydroxylase (TH) in the striatum and substantia nigra. PQ exposure, which caused a long-lasting decrease of striatal mitochondrial complex I activity, did not modify LPS-induced behavioral and striatal biochemical changes. The results indicate that systemic administration of LPS causes delayed social recognition memory deficit and striatal nitrosative stress in adult mice and that the coexposure to a moderately toxic dose of PQ did not magnify these events. In addition, PQ-induced inhibition of striatal mitochondrial complex I was also not magnified by LPS exposure, indicating the absence of synergic neurotoxic effects of LPS and PQ in this experimental model.

     

Interleukin-6 and interleukin-15 are selectively regulated by lipopolysaccharide and interferon-gamma in primary pig adipocytes

3T3-L1 adipocytes express the lipopolysaccharide (LPS) receptor and respond to direct stimulation with the antigen by increasing the expression of inflammatory mediators. Activation of this receptor by its ligand in the macrophage causes the activation and translocation of nuclear factor-kappaB (NF-kappaB) to the nucleus where it regulates the expression of proinflammatory cytokines and other target genes. We investigated whether LPS could stimulate NF-kappaB translocation in primary pig adipocytes and regulate the expression and secretion of TNF-alpha and IL-6. LPS clearly induced the nuclear translocation of NF-kappaB and also upregulated (P < 0.05) the mRNA expression and secretion of IL-6 into the culture medium. An induction of TNF-alpha expression by LPS was not detected, but with extended incubation (8 h), there was a modest increase (P < 0.09) in the media concentration of this cytokine. Inhibition of either ERK1/2, PKC, or the inhibitory G protein (Gi) with U-0126, bisindolylmaleimide HCl, and pertussis toxin, respectively, blocked (P < 0.05) the increase in IL-6 expression caused by LPS. Because LPS administration in vivo increases circulating concentrations of IFN-gamma, and because this cytokine also regulates multiple immune modulators in the adipocyte, we also determined whether IFN-gamma regulates cytokine expression in primary adipocytes. Although the expression of IL-6 and TNF-alpha was unresponsive to IFN-gamma, the expression of IL-15 was markedly upregulated (P < 0.01). Furthermore, the induction of IL-15 expression by IFN-gamma was blocked by inhibition of PKC. These data indicate that NF-kappaB is responsive to LPS in the adipocyte and also identify key mediators of LPS-induced IL-6 expression. In addition, we provide novel evidence that IFN-gamma targets the adipocyte to induce IL-15 expression, thus indicating a possible role for the adipocyte in the regulation of T-cell function and muscle metabolism during the innate immune response.     

The essential role of the intestinal microbiota in facilitating acute inflammatory responses

The restoration of blood flow, i.e., reperfusion, is the treatment of choice to save viable tissue following acute ischemia of a vascular territory. Nevertheless, reperfusion can be accompanied by significant inflammatory events that limit the beneficial effects of blood flow restoration. To evaluate the potential role of the intestinal microbiota in facilitating the development of tissue injury and systemic inflammation, germ-free and conventional mice were compared in their ability to respond to ischemia and reperfusion injury. In conventional mice, there was marked local (intestine) and remote (lung) edema formation, neutrophil influx, hemorrhage, and production of TNF-alpha, KC, MIP-2, and MCP-1. Moreover, there was an increase in the concentration of serum TNF-alpha and 100% lethality. In germ-free mice, there was no local, remote, or systemic inflammatory response or lethality after intestinal ischemia and reperfusion and, in contrast to conventional mice, germ-free animals produced greater amounts of IL-10. Similar results were obtained after administration of LPS, i.e., little production of TNF-alpha or lethality and production of IL-10 after LPS in germ-free mice. Blockade of IL-10 with Abs induced marked inflammation and lethality in germ-free mice after ischemia and reperfusion or LPS administration, demonstrating that the ability of these mice to produce IL-10 was largely responsible for their "no inflammation" phenotype. This was consistent with the prevention of reperfusion-associated injury by the exogenous administration of IL-10 to conventional mice. Thus, the lack of intestinal microbiota is accompanied by a state of active IL-10-mediated inflammatory hyporesponsiveness.     

Lipopolysaccharide induces rapid production of IL-10 by monocytes in the presence of apoptotic neutrophils

There is growing evidence that apoptotic neutrophils have an active role to play in the regulation and resolution of inflammation following phagocytosis by macrophages and dendritic cells. However, their influence on activated blood monocytes, freshly recruited to sites of inflammation, has not been defined. In this work, we examined the effect of apoptotic neutrophils on cytokine production by LPS-activated monocytes. Monocytes stimulated with LPS in the presence of apoptotic neutrophils for 18 h elicited an immunosuppressive cytokine response, with enhanced IL-10 and TGF-beta production and only minimal TNF-alpha and IL-1beta cytokine production. Time-kinetic studies demonstrated that IL-10 production was markedly accelerated in the presence of apoptotic neutrophils, whereas there was a sustained reduction in the production of TNF-alpha and IL-1beta. This suppression of proinflammatory production was not reversible by depletion of IL-10 or TGF-beta or by addition of exogenous IFN-gamma. It was demonstrated, using Transwell experiments, that monocyte-apoptotic cell contact was required for induction of the immunosuppressive monocyte response. The response of monocytes contrasted with that of human monocyte-derived macrophages in which there was a reduction in IL-10 production. We conclude from these data that interaction between activated monocytes and apoptotic neutrophils creates a unique response, which changes an activated monocyte from being a promoter of the inflammatory cascade into a cell primed to deactivate itself and other cells.     

Colonic production and expression of IL-4, IL-6, and IL-10 in neonatal suckling rats after LPS challenge

It has been demonstrated that the neonatal suckling rat is more susceptible to endotoxin [lipopolysaccharide (LPS)]-induced colonic damage compared with weaned littermates. There is evidence to suggest that differences in the production of certain cytokines, including interleukin (IL)-4, IL-6, and IL-10, are associated with intestinal inflammation in children. We have examined the production, localization, and mRNA detection of these cytokines in suckling and weaned rat colons after bacterial LPS challenge. Suckling (10 day old) and weaned (25 day old) rats were injected with LPS (3 mg/kg ip). Colon samples were taken up to 4 h after treatment, and cytokines were measured by ELISA. LPS-induced cytokine levels were significantly different in suckling rats compared with weaned rats. Cytokine localization to the colonic mucosa was evident in suckling rats up to 4 h after LPS administration but was not consistently seen in weaned rats. The mRNA for cytokines examined were detected by RT-PCR in suckling but not in weaned rat colons after LPS treatment. Induction of neutropenia via anti-neutrophil serum (ANS) administration did not affect cytokine mRNA detection in neonates after LPS treatment. Weaned animals displayed positive detection of all cytokines examined after ANS. Therefore, we have shown that the suckling rat displays a different production and expression of colonic IL-4, IL-6, and IL-10 compared with weaned littermates after LPS challenge. Furthermore, neutrophils may be implicated in colonic cytokine expression after LPS challenge in rats.