The mouse interleukin 1 receptor antagonist protein: gene structure and regulation in vitro

Yersinia pestis activates both IL-1β and IL-1 receptor antagonist to modulate lung inflammation during pneumonic plague

Pneumonic plague is the most rapid and lethal form of Yersinia pestis infection. Increasing evidence suggests that Y. pestis employs multiple levels of innate immune evasion and/or suppression to produce an early “pre-inflammatory” phase of pulmonary infection, after which the disease is highly inflammatory in the lung and 100% fatal. In this study, we show that IL-1β/IL-18 cytokine activation occurs early after bacteria enter the lung, and this activation eventually contributes to pulmonary inflammation and pathology during the later stages of infection. However, the inflammatory effects of IL-1β/IL-1-receptor ligation are not observed during this first stage of pneumonic plague. We show that Y. pestis also activates the induction of IL-1 receptor antagonist (IL-1RA), and this activation likely contributes to the ability of Y. pestis to establish the initial pre-inflammatory phase of disease.

Inhalation of respiratory droplets containing Yersinia pestis results in a rapidly developing and lethal pneumonia. Interestingly, early interactions between Y. pestis and host cells in the lung contribute to significant immune evasion, but also ultimately result in severe innate immune activation. Our results demonstrate that Y. pestis activates pro-inflammatory cytokines IL-1β and IL-18 in the lung early during infection. However, there is very little early pulmonary inflammation while Y. pestis continues to multiply in the lung compartment. We show that the host protein IL-1RA is activated concurrently with IL-1β, attenuating early immune activation by this cytokine. We propose that this allows the organism to replicate to high titers, eventually triggering a vigorous inflammatory response and facilitating aerosol transmission. Therefore, evaluating early host activation of IL-1RA by Y. pestis may provide therapeutic targets against pneumonic plague.

Exacerbation of granuloma formation in IL-1 receptor antagonist-deficient mice with impaired dendritic cell maturation associated with Th2 cytokine production

Dendritic cell (DC) maturation at the site of inflammation and migration into draining lymph nodes is fundamental to initiate Ag-specific immune responses. Although several proinflammatory cytokines, including IL-1, are known to promote DC maturation in vitro, their contributions to DC activation and migration within peripheral inflamed tissue compartments are not yet fully understood. We show here that endogenous IL-1 receptor antagonist (IL-1ra) controls the activation state of liver-recruited DCs and their migration in a Propionibacterium acnes-induced murine granulomatous liver disease model. After P. acnes treatment, formation of portal tract-associated lymphoid tissue was conversely impaired in IL-1ra-deficient mice. IL-1ra-deficient mice developed hepatic granulomas within 3 days after P. acnes administration and showed a more pronounced granuloma formation than wild-type mice. Although sinusoidal granulomas contained numerous CD11c+ DCs at day 7, expressions of CCR7, IL-12p40 by these DCs were dramatically decreased in IL-1ra-deficient mice, suggesting aberrant DC maturation and sinusoid portal migration in the absence of endogenous IL-1ra. This was accompanied with enhanced intrahepatic Th2 cytokine production and severe hepatocellular damage. Thus, hepatocyte-derived IL-1ra may control optimal activation and migration of inflammatory DCs within the liver and thereby determine the local immune responses in granulomatous liver disease.

Genetic alterations of IL-1 receptor antagonist in mice affect plasma cholesterol level and foam cell lesion size

Inflammatory cytokines have been linked to atherosclerosis by using cell culture models and acute inflammation in animals. The goal of this study was to examine lipoprotein levels and early atherosclerosis in chronic animal models of altered IL-1 physiology by using mice with deficient or excess IL-1 receptor antagonist (IL-1ra). IL-1ra knockout C57BL/6J mice fed a cholesterol/cholate diet for 3 mo had a 3-fold decrease in non-high-density lipoprotein cholesterol and a trend toward increased foam-cell lesion area compared to wild-type littermate controls. IL-1ra transgenic/low-density lipoprotein receptor (LDLR) knockout mice fed a cholesterol-saturated fat diet for 10 wk showed a 40% increase in non-high-density lipoprotein cholesterol, consistent with the IL-1ra knockout data, although there was no change in lesion size. When these IL1-ra overexpressing transgenic mice on the LDLR knockout background were fed a high-cholesterol/high-fat diet containing cholate, however, a statistically significant 40% decrease in lesion area was observed compared to LDLR knockout mice lacking the transgene. By immunohistochemistry, IL-1ra was present in C57BL/6J and LDLR knockout aortae, absent in IL-1ra knockout aortae, and present at high levels in LDLR knockout/IL-1ra transgene aortae. In summary, IL-1ra tended to increase plasma lipoprotein levels and, when fed a cholate-containing diet, decrease foam-cell lesion size. These data demonstrate that in selected models of murine atherosclerosis, chronic IL-1ra depletion or overexpression has potentially important effects on lipoprotein metabolism and foam-cell lesion development.

Acute systemic inflammation up-regulates secretory sphingomyelinase in vivo: a possible link between inflammatory cytokines and atherogenesis

Inflammation plays a critical role in atherogenesis, yet the mediators linking inflammation to specific atherogenic processes remain to be elucidated. One such mediator may be secretory sphingomyelinase (S-SMase), a product of the acid sphingomyelinase gene. The secretion of S-SMase by cultured endothelial cells is induced by inflammatory cytokines, and in vivo data have implicated S-SMase in subendothelial lipoprotein aggregation, macrophage foam cell formation, and possibly other atherogenic processes. Thus, the goal of this study was to seek evidence for S-SMase regulation in vivo during a physiologically relevant inflammatory response. First, wild-type mice were injected with saline or lipopolysaccharide (LPS) as a model of acute systemic inflammation. Serum S-SMase activity 3 h postinjection was increased 2- to 2.5-fold by LPS (P < 0.01). To determine the role of IL-1 in the LPS response, we used IL-1 converting enzyme knockout mice, which exhibit deficient IL-1 bioactivity. The level of serum S-SMase activity in LPS-injected IL-1 converting enzyme knockout mice was approximately 35% less than that in identically treated wild-type mice (P < 0.01). In LPS-injected IL-1-receptor antagonist knockout mice, which have an enhanced response to IL-1, serum S-SMase activity was increased 1. 8-fold compared with LPS-injected wild-type mice (P < 0.01). Finally, when wild-type mice were injected directly with IL-1beta, tumor necrosis factor alpha, or both, serum S-SMase activity increased 1. 6-, 2.3-, and 2.9-fold, respectively (P < 0.01). These data show regulation of S-SMase activity in vivo and they raise the possibility that local stimulation of S-SMase may contribute to the effects of inflammatory cytokines in atherosclerosis.

Arterial inflammation in mice lacking the interleukin 1 receptor antagonist gene

Branch points and flexures in the high pressure arterial system have long been recognized as sites of unusually high turbulence and consequent stress in humans are foci for atherosclerotic lesions. We show that mice that are homozygous for a null mutation in the gene encoding an endogenous antiinflammatory cytokine, interleukin 1 receptor antagonist (IL-1ra), develop lethal arterial inflammation involving branch points and flexures of the aorta and its primary and secondary branches. We observe massive transmural infiltration of neutrophils, macrophages, and CD4(+) T cells. Animals appear to die from vessel wall collapse, stenosis, and organ infarction or from hemorrhage from ruptured aneurysms. Heterozygotes do not die from arteritis within a year of birth but do develop small lesions, which suggests that a reduced level of IL-1ra is insufficient to fully control inflammation in arteries. Our results demonstrate a surprisingly specific role for IL-1ra in the control of spontaneous inflammation in constitutively stressed artery walls, suggesting that expression of IL-1 is likely to have a significant role in signaling artery wall damage.

The human intracellular interleukin 1 receptor antagonist promoter appropriately regulates gene expression in keratinocytes and gastrointestinal epithelial cells in vivo

The 4555-bp promoter fragment for intracellular interleukin 1 receptor antagonist (4555-bp icIL-1Ra) has recently been demonstrated to regulate gene expression in a cell-type specific manner in vitro in transient transfection studies. To examine the activity of this promoter in vivo, transgenic mice possessing the 4555-bp promoter coupled to the E. coli lacZ reporter gene were created. Expression of endogenous icIL-1Ra and E. coli lacZ mRNA were examined in different tissues by RT-PCR, RNase protection assay and in situ hybridization. In transgenic mice both endogenous icIL-1Ra and E. coli lacZ were co-expressed by keratinocytes and by epithelial cells in different organs of the digestive system. The transgene was also expressed in the brain in four out of five lines, whereas endogenous icIL-1Ra was not detected in this organ. In contrast, only icIL-1Ra mRNA, but not E. coli lacZ mRNA, was detected in lipopolysaccharide (LPS)-stimulated resident peritoneal macrophages from icIL-1Ra promoter transgenic mice. These results indicate that a 4555-bp promoter fragment of human icIL-1Ra appropriately regulates gene transcription in keratinocytes and gastrointestinal epithelial cells in vivo. However, other as yet unidentified regulatory regions influence icIL-1Ra gene expression in macrophages following LPS stimulation.

Secretory interleukin-1 receptor antagonist gene expression requires both a PU.1 and a novel composite NF-kappaB/PU.1/ GA-binding protein binding site

The human secretory interleukin-1 receptor antagonist (secretory IL-1Ra) gene is controlled through three lipopolysaccharide (LPS)-responsive promoter elements, one of which was identified as an NF-kappaB binding site. Sequence analysis of the secretory IL-1Ra promoter identified a potential PU.1 binding site located between positions -80 and -90 on the complementary strand overlapping the NF-kappaB site. Gel shift analysis using this potential binding site with nuclear extracts from RAW 264.7 macrophages demonstrated the formation of three complexes, one LPS-inducible and two constitutive. The inducible factor was identified as NF-kappaB, and the constitutive factors were identified as PU.1 and GA-binding protein. Site-directed mutagenesis of the -93 to -79 promoter region demonstrated that mutation of either the NF-kappaB 5'-half site or the PU.1/GA-binding protein half-site alone did not significantly decrease LPS responsiveness. However, a mutation that disrupted the binding of all three factors resulted in a 50% decrease in LPS responsiveness. A second PU.1 binding site centered at -230 was identified by gel shift and supershift assays. Mutation of the core GGAA region resulted in a 50% decrease in LPS-responsive promoter activity. Mutation of both the distal and proximal LPS response elements led to an almost complete loss of responsiveness. These data therefore suggest that the regulation of IL-1Ra gene expression is a complex event involving the interactions of three different transcription factors with a single cis-acting element and that the two PU.1 binding sites are the major response elements for LPS-induced IL-1Ra gene expression.

Interleukin-1 receptor antagonist: role in biology

The interleukin-1 receptor antagonist (IL-1Ra) is a member of the IL-1 family that binds to IL-1 receptors but does not induce any intracellular response. Two structural variants of IL-1Ra have previously been described: a 17-kDa form that is secreted from monocytes, macrophages, neutrophils, and other cells (sIL-1Ra) and an 18-kDa form that remains in the cytoplasm of keratinocytes and other epithelial cells, monocytes, and fibroblasts (icIL-1Ra). An additional 16-kDa intracellular isoform of IL-1Ra has recently been described in neutrophils, monocytes, and hepatic cells. Both of the major isoforms of IL-1Ra are transcribed from the same gene through the use of alternative first exons. The two promoters regulating transcription of the secreted and intracellular forms have been cloned, and some of the functional cis-acting DNA regions have been characterized. The production of IL-1Ra is stimulated by many substances including adherent IgG, other cytokines, and bacterial or viral components. The tissue distribution of IL-1Ra in mice indicates that sIL-1Ra is found predominantly in peripheral blood cells, lungs, spleen, and liver, while icIL-1Ra is found in large amounts in skin. Studies in transgenic and knockout mice indicate that IL-1Ra is important in host defense against endotoxin-induced injury. IL-1Ra is produced by hepatic cells with the characteristics of an acute phase protein. Endogenous IL-1Ra is produced in numerous experimental animal models of disease as well as in human autoimmune and chronic inflammatory diseases. The use of neutralizing anti-IL-1Ra antibodies has demonstrated that endogenous IL-1Ra is an important natural antiinflammatory protein in arthritis, colitis, and granulomatous pulmonary disease. Treatment of human diseases with recombinant human IL-1Ra showed an absence of benefit in sepsis syndrome. However, patients with rheumatoid arthritis treated with IL-1Ra for six months exhibited improvements in clinical parameters and in radiographic evidence of joint damage.

Production of mice deficient in genes for interleukin (IL)-1alpha, IL-1beta, IL-1alpha/beta, and IL-1 receptor antagonist shows that IL-1beta is crucial in turpentine-induced fever development and glucocorticoid secretion

Interleukin (IL)-1 is a major mediator of inflammation and exerts pleiotropic effects on the neuro-immuno-endocrine system. To elucidate pathophysiological roles of IL-1, we have first produced IL-1alpha/beta doubly deficient (KO) mice together with mice deficient in either the IL-1alpha, IL-1beta, or IL-1 receptor antagonist (IL-1ra) genes. These mice were born healthy, and their growth was normal except for IL-1ra KO mice, which showed growth retardation after weaning. Fever development upon injection with turpentine was suppressed in IL-1beta as well as IL-1alpha/beta KO mice, but not in IL-1alpha KO mice, whereas IL-1ra KO mice showed an elevated response. At this time, expression of IL-1beta mRNA in the diencephalon decreased 1.5-fold in IL-1alpha KO mice, whereas expression of IL-1alpha mRNA decreased >30-fold in IL-1beta KO mice, suggesting mutual induction between IL-1alpha and IL-1beta. This mutual induction was also suggested in peritoneal macrophages stimulated with lipopolysaccharide in vitro. In IL-1beta KO mice treated with turpentine, the induction of cyclooxygenase-2 (EC 1.14.99.1) in the diencephalon was suppressed, whereas it was enhanced in IL-1ra KO mice. We also found that glucocorticoid induction 8 h after turpentine treatment was suppressed in IL-1beta but not IL-1alpha KO mice. These observations suggest that IL-1beta but not IL-1alpha is crucial in febrile and neuro-immuno-endocrine responses, and that this is because IL-1alpha expression in the brain is dependent on IL-1beta. The importance of IL-1ra both in normal physiology and under stress is also suggested.

Functions of interleukin 1 receptor antagonist in gene knockout and overproducing mice

Interleukin 1 receptor antagonist (IL-1ra) is a cytokine whose only known action is competitive inhibition of the binding of interleukin 1 (IL-1) to its receptor. To investigate the physiological roles of endogenously produced IL-1ra, we generated mice that either lack IL-1ra or overproduce it under control of the endogenous promoter. Mice lacking IL-1ra have decreased body mass compared with wild-type controls. They are more susceptible than controls to lethal endotoxemia but are less susceptible to infection with Listeria monocytogenes. Conversely, IL-1ra overproducers are protected from the lethal effects of endotoxin but are more susceptible to listeriosis. Serum levels of IL-1 following an endotoxin challenge are decreased in IL-1ra nulls and increased in IL-1ra overproducers in comparison to controls. These data demonstrate critical roles for endogenously produced IL-1ra in growth, responses to infection and inflammation, and regulation of cytokine expression.

Expression of interleukin 1 alpha, interleukin 1 beta and interleukin 1 receptor antagonist mRNA in mouse brain: regulation by bacterial lipopolysaccharide (LPS) treatment

Lipopolysaccharide (LPS) stimulation is known to induce interleukin-1 (IL-1) mRNA expression in various immune cell types. Since IL-1 synthesis has been suggested to occur locally in brain tissue, we investigated the expression of IL-1 (alpha and beta) and IL-1 receptor antagonist (IL-1ra) mRNAs in various structures of the central nervous system, as well as in the spleen, following intraperitoneal injection of LPS (100 micrograms/mouse). After RNA extraction and amplification by the reverse transcription-polymerase chain reaction (RT-PCR), the PCR products were separated on an agarose gel, transferred and hybridized with digoxigenin-labeled probes synthetized by nested PCR. Glyceraldehyde phosphate deshydrogenase mRNA was used as an internal control. Under basal conditions the expression of IL-1 alpha, IL-1 beta and IL-1ra mRNAs in the brain was extremely low for the three cytokines; in the spleen these mRNAs were clearly detectable. Following LPS stimulation, mRNAs were strongly increased in all the tested tissues (cortex, hippocampus, hypothalamus, cerebellum, pituitary and spleen). The kinetics of mRNAs expressions in the brain were similar for all the tested regions, with a maximum at 6 h and a decrease up to 24 h after LPS administration. In the spleen the maximum was observed as soon as 1 h following stimulation. In conclusion, peripheral LPS stimulation induces a strong and transient expression of IL-1 alpha and IL-1 beta mRNAs in the brain. IL-1ra mRNA is also stimulated by LPS in various regions of the brain.(ABSTRACT TRUNCATED AT 250 WORDS)