Studies in the in vivo expression of the influenza resistance gene Mx by in-situ hybridisation

Regulation of Interferon-stimulated Gene (ISG)12, ISG15, and MX1 and MX2 by Conceptus Interferons (IFNTs) in Bovine Uterine Epithelial Cells

Various endometrial genes in ruminant ungulates are regulated by conceptus interferon tau (IFNT). However, the effect of each IFNT isoform has not been carefully evaluated. In this study, the effects of 2 IFNT isoforms, paralogs found in utero, and interferon alpha (IFNA) on uterine epithelial and Mardin-Darby bovine kidney (MDBK) cells were evaluated. Expression vectors of the bovine interferon (bIFNT) genes bIFNT1, bIFNTc1, and bIFNA were constructed, and recombinant bIFNs (rbIFNs) were produced by 293 cells. Bovine uterine epithelial or MDBK cells were cultured in the presence or absence of increasing concentrations of each rbIFN for 24, 48, or 72 h. Transcript levels of the IFN-stimulated genes (ISGs) ISG12, ISG15, MX1, and MX2 were analyzed using quantitative reverse transcription-polymerase chain reaction. These messenger RNAs were up-regulated by rbIFN in a time- and concentration-dependent manner. In the epithelial cells, the ISG12 transcript level increased at 48 h after rbIFN treatment but slightly decreased at 72 h, whereas the transcript level of ISG15 increased at 24 h and was maintained through 72 h. Expressions of MX1 and MX2 increased at 72 h after rbIFN treatment. MX1 expression increased in all treatment groups, but MX2 increased only by bIFNTc1. In MDBK cells, the expression of ISG12 was increased by bIFNT1 and bIFNTc1 after 24 and 72 h; however, it was unchanged by rbIFNA. ISG15 increased following the same pattern as that seen in uterine epithelial cells, and MX1 showed a similar expression pattern. MX2 expression was increased by bIFNTc1 treatment in uterine epithelial cells, and its expression was increased by both bIFNT1 and bIFNTc1 in MDBK cells. These results show that epithelial and MDBK cell responses to IFNs differ, suggesting that IFNs possess common functions, but may have acquired different functions following gene duplication.

Insight into alternative approaches for control of avian influenza in poultry, with emphasis on highly pathogenic H5N1

Highly pathogenic avian influenza virus (HPAIV) of subtype H5N1 causes a devastating disease in poultry but when it accidentally infects humans it can cause death. Therefore, decrease the incidence of H5N1 in humans needs to focus on prevention and control of poultry infections. Conventional control strategies in poultry based on surveillance, stamping out, movement restriction and enforcement of biosecurity measures did not prevent the virus spreading, particularly in developing countries. Several challenges limit efficiency of the vaccines to prevent outbreaks of HPAIV H5N1 in endemic countries. Alternative and complementary approaches to reduce the current burden of H5N1 epidemics in poultry should be encouraged. The use of antiviral chemotherapy and natural compounds, avian-cytokines, RNA interference, genetic breeding and/or development of transgenic poultry warrant further evaluation as integrated intervention strategies for control of HPAIV H5N1 in poultry.

Inhibition of interferon induction and action by the nairovirus Nairobi sheep disease virus/Ganjam virus

The Nairoviruses are an important group of tick-borne viruses that includes pathogens of man (Crimean Congo hemorrhagic fever virus) and livestock animals (Dugbe virus, Nairobi sheep disease virus (NSDV)). NSDV is found in large parts of East Africa and the Indian subcontinent (where it is known as Ganjam virus). We have investigated the ability of NSDV to antagonise the induction and actions of interferon. Both pathogenic and apathogenic isolates could actively inhibit the induction of type 1 interferon, and also blocked the signalling pathways of both type 1 and type 2 interferons. Using transient expression of viral proteins or sections of viral proteins, these activities all mapped to the ovarian tumour-like protease domain (OTU) found in the viral RNA polymerase. Virus infection, or expression of this OTU domain in transfected cells, led to a great reduction in the incorporation of ubiquitin or ISG15 protein into host cell proteins. Point mutations in the OTU that inhibited the protease activity also prevented it from antagonising interferon induction and action. Interestingly, a mutation at a peripheral site, which had little apparent effect on the ability of the OTU to inhibit ubiquitination and ISG15ylation, removed the ability of the OTU to block the induction of type 1 and the action of type 2 interferons, but had a lesser effect on the ability to block type 1 interferon action, suggesting that targets other than ubiquitin and ISG15 may be involved in the actions of the viral OTU.

Cloning and characterizing of the ovine MX1 gene promoter/enhancer region

Ovine MX1 (MX1) is expressed in the uterus during the estrous cycle and is strongly up-regulated during early pregnancy in the uterus and peripheral blood leukocytes. In this study we cloned the MX1 gene promoter/enhancer, and tested its response to interferon tau (IFN-tau). To address the role of IFN tau in regulating MX1 expression, serial deletion mutants were prepared along with a clone that contained a full-length promoter including the two proximal ISREs but lacking an intronic ISRE site. Promoter deletions showed the two proximal ISRE sites, but not the intronic ISRE site, were required for maximal response to IFN tau. Interestingly, MX1 promoter deletion mutants revealed the presence of distal positive (-920 to -715) and negative (-715 to -437) regulatory regions. Identifying positive and negative regulatory regions in MX1 promoter will help define the complex regulation of MX1 during early pregnancy in ruminants.

Genetic immunity and influenza pandemics

In addition to the great number of publications focused on the leading role of virus mutations and reassortment in the origin of pandemic influenza, general opinion emphasizes the victim side of the epidemic process. Based on the analysis and integration of relevant ecological, epidemiological, clinical, genetic and experimental data, the present article is focused on the evolution of 'virus - victim' ecological systems resulting in the formation of innate (i.e. genetic, constitutional) immunity in the involved species and populations. This kind of immunity functions today as the greatest natural barrier to the pandemic spread of influenza among humans and ecologically related kinds of animals. Global influenza pandemics can arise when the worldwide population contains at least a minimum number of people susceptible to a known or mutant influenza virus. Special attention is paid in this article to individual tests for the presence of this barrier, including the implications of specific findings for public health policy. Such tests could be based on in vitro observation of the action of relevant virus strains on primary cell cultures or on their cellular or molecular components extracted from individuals. The resources of the Human Genome Project should also be utilized.

Expression of the type I interferon receptor and the interferon-induced Mx protein in human endometrium during the menstrual cycle

OBJECTIVE

To investigate the expression of the type I interferon receptor (IFNAR) and interferon-induced Mx protein (Mx) in normal human endometrium throughout the menstrual cycle.

DESIGN

Prospective study.

SETTING

Medical university in Japan.

PATIENT(S)

Thirty-seven normal endometrial tissues from fertile women who had undergone hysterectomies for reasons other than endometrial disease.

INTERVENTION(S)

IFNAR-1, IFNAR-2, MxA, and MxB gene expression was analyzed by reverse transcription-real-time quantitative polymerase chain reaction. Moreover, localization of IFNAR-1 and IFNAR-2 were studied by immunohistochemistry.

MAIN OUTCOME MEASURE(S)

Expression of IFNAR-1, IFNAR-2, MxA, and MxB.

RESULT(S)

Expression of IFNAR-2 gene was significantly increased in the menstrual and midsecretory phase as compared with in the proliferative phase. Immunohistochemistry for IFNAR-1 and IFNAR-2 revealed weak staining of glandular epithelium and weak staining of stromal cells during the proliferative phase. However, an intense immunohistochemical staining of IFNAR-2 was observed on the surface and basement membrane of glands in the secretory phase. There was no statistical difference between MxA and MxB gene expression throughout the menstrual cycle.

CONCLUSION(S)

Our results suggest that IFNAR and Mx are expressed in the human endometrium and that the expression of IFNAR is cyclically changed during the menstrual cycle.

Expression of the uterine Mx protein in cyclic and pregnant cows, gilts, and mares

Pregnancy and interferon-tau (IFN tau) upregulate uterine Mx gene expression in ewes; however, the only known role for Mx is in the immune response to viral infection. We hypothesize that Mx functions as a conceptus-induced component of the anti-luteolytic mechanism and/or regulator of endometrial secretion or uterine remodeling during early pregnancy. This study was conducted to determine the effects of early pregnancy on uterine Mx expression in domestic farm species with varied mechanisms of pregnancy recognition. Endometrium from cows, gilts, and mares was collected during the first 20 d of the estrous cycle or pregnancy, and total messenger RNA (mRNA) and protein were analyzed for steady-state levels of Mx mRNA and protein. Northern blot analysis of Mx mRNA detected an approximately 2.5 Kb of mRNA in endometrium from each species. In pregnant cows, steady-state levels of Mx mRNA increased 10-fold (P < 0.05) above levels observed in cyclic cows by d 15 to 18. In cyclic gilts, slot blot analysis indicated that endometrial Mx mRNA levels did not change between d 5 and 18 of the cycle. However, in pregnant gilts, Mx levels tended (P = 0.06) to be elevated two-fold on d 16 only, and in situ hybridization indicated that this increase occurred in the stroma. In mares, Mx mRNA was low, but detectable, and did not change between ovulation (d 0) and d 20, regardless of reproductive status. Western blot analysis revealed multiple immunoreactive Mx protein bands in each species. One band was specific to pregnancy in cows. As in ewes, in situ hybridization analysis indicated that Mx mRNA was strongly expressed in the luminal epithelium, stroma, and myometrium by d 18 in cows. However, on d 14 in gilts, Mx was expressed primarily in the stroma, and on d 14 in mares, low levels of Mx expression were confined largely to the luminal epithelium. The uteruses of cows, gilts, and mares express Mx, and expression is upregulated during pregnancy in cows and gilts--animals whose conceptuses secrete interferons during early pregnancy, but that possess different mechanisms for pregnancy recognition.

Molecular cloning of the pufferfish (Takifugu rubripes) Mx gene and functional characterization of its promoter

Mx proteins are members of a family of interferon-inducible genes that are expressed by cells in response to viral infection. They are important determinants of innate immunity against viral infection in vertebrates. We cloned the pufferfish ( Takifugu rubripes) Mx gene and sequenced 80 kb from the Mx locus. The Fugu Mx gene spans 3.4 kb from the transcription start site to the polyadenylation signal, and is made up of 12 exons and 11 introns. The protein sequence encoded by the Fugu Mx gene is 77%, 48%, and 51% identical to that of trout Mx1, chicken Mx, and mouse Mx1 genes, respectively. The Fugu Mx gene is expressed in a variety of tissues, with high expression detected in the heart, gill, kidney, intestine, and brain. Analysis of the 5'-flanking sequence of the gene showed the presence of two interferon-stimulated response elements (ISRE) at positions -51 to 38 and -97 to 85, relative to the transcription start site. The Fugu Mx promoter was inducible by human IFN-beta in the human hepatoma (Huh7) cells and by polyinosinic: polycytidilic acid in the top minnow hepatoma (PLHC-1) cells. Deletion analysis of the promoter showed that both ISREs contributed to inducibility. These results demonstrate that the molecular mechanisms involved in Mx gene regulation are conserved between fish and mammals.

Effect of poly I:C on the expression of Mx proteins and resistance against infection by infectious salmon anaemia virus in Atlantic salmon

Mx proteins are induced by type I interferons (IFN alpha and beta) in mice and humans and inhibit the replication of orthomyxoviruses and some other single-stranded RNA viruses. Recently, Mx genes have been cloned from Atlantic salmon. Mx transcripts were shown to be induced in head-kidney, liver and gills of the fish by the synthetic double-stranded RNA polyinosinic polycytidylic acid (poly I:C). In the present work we have studied expression of Mx protein in organs of Atlantic salmon treated with poly I:C. A quantitative immunoblot method was established to monitor expression of Mx protein and to compare relative amounts of Mx protein in different organs. Treatment of Atlantic salmon with poly I:C increased the relative amount of Mx protein in liver, stomach, hindgut, head-kidney and spleen. In gills the levels of Mx protein were similar in control fish and poly I:C treated fish. Immunohistochemistry of tissue sections from liver, head-kidney and gills from poly I:C treated fish was in accordance with the immunoblotting data and showed staining for Mx protein in several different cell types. Classification of infectious salmon anaemia virus as an orthomyxovirus makes it a putative target for Atlantic salmon Mx protein. Atlantic salmon treated with poly I:C showed reduced cumulative mortality compared to the control fish when challenged with infectious salmon anaemia virus (ISAV) by intraperitoneal injection. This demonstrates that poly I:C has some protective effect against ISAV in vivo.

Conditional disruption of the peroxisome proliferator-activated receptor gamma gene in mice results in lowered expression of ABCA1, ABCG1, and apoE in macrophages and reduced cholesterol efflux

Disruption of the peroxisome proliferator-activated receptor gamma (PPAR gamma) gene causes embryonic lethality due to placental dysfunction. To circumvent this, a PPAR gamma conditional gene knockout mouse was produced by using the Cre-loxP system. The targeted allele, containing loxP sites flanking exon 2 of the PPAR gamma gene, was crossed into a transgenic mouse line expressing Cre recombinase under the control of the alpha/beta interferon-inducible (MX) promoter. Induction of the MX promoter by pIpC resulted in nearly complete deletion of the targeted exon, a corresponding loss of full-length PPAR gamma mRNA transcript and protein, and marked reductions in basal and troglitazone-stimulated expression of the genes encoding lipoprotein lipase, CD36, LXR alpha, and ABCG1 in thioglycolate-elicited peritoneal macrophages. Reductions in the basal levels of apolipoprotein E (apoE) mRNA in macrophages and apoE protein in total plasma and high-density lipoprotein (HDL) were also observed in pIpC-treated PPAR gamma-MXCre(+) mice. Basal cholesterol efflux from cholesterol-loaded macrophages to HDL was significantly reduced after disruption of the PPAR gamma gene. Troglitazone selectively inhibited ABCA1 expression (while rosiglitazone, ciglitazone, and pioglitazone had little effect) and cholesterol efflux in both PPAR gamma-deficient and control macrophages, indicating that this drug can exert paradoxical effects on cholesterol homeostasis that are independent of PPAR gamma. Together, these data indicate that PPAR gamma plays a critical role in the regulation of cholesterol homeostasis by controlling the expression of a network of genes that mediate cholesterol efflux from cells and its transport in plasma.

Interferon-inducible Mx proteins in fish

Mx proteins are members of a family of interferon-inducible genes expressed when cells are treated with double-stranded RNA or virus infection. These proteins are important components of the antiviral response and form the first line of the body's defense against virus infections. The exact mechanism of action for these proteins has not been discovered, but mice missing the Mx genes are extremely sensitive to influenza virus infection. Mammals have between two and three Mx genes whose functions may vary with regard to the inhibition of a specific virus, cellular localization, and activity. The cDNA of three rainbow trout Mx proteins has been cloned and a comparison of their sequences with that of avian and mammalian species reveals striking conservation of domains. They all maintain the tripartite ATP/GTP binding domain and the dynamin family signature in the amino terminal half of the protein. In the carboxyl terminal half of the Mx proteins are the localization signals and the leucine zipper motifs which account for the trimerization of Mx in the cell. Like the rat and human Mx proteins, the different trout Mx proteins exhibit distinctly different immunohistochemical staining patterns in cells transfected with plasmids expressing RBTMx1, RBTMx2, or RBTMx3. To date, the antiviral function of the trout Mx proteins has not been satisfactorily established.

Effects of the estrous cycle and early pregnancy on uterine expression of Mx protein in sheep (Ovis aries)

Conceptuses of ruminant ungulates produce large amounts of a type I interferon, interferon-tau (IFNtau), which is the signal for maternal recognition of pregnancy. Induction of cellular Mx proteins is an important component of the response to type I interferon in the immune system, but Mx regulation and function have not been studied in the uterus. This study examined temporal and spatial alterations in ovine uterine Mx expression during the cycle and early pregnancy using immunohistochemistry, in situ hybridization, and Northern and slot-blot analysis. Sheep uterine endometrium expressed a single approximately 2.5-kilobase Mx mRNA transcript that was detectable at all stages of the estrous cycle and early pregnancy examined. In cyclic ewes, mRNA abundance in endometrium increased from Day 1 to peak levels at Day 13 and then declined to Day 15. In pregnant ewes, steady-state levels of Mx mRNA were first detected above the level in cyclic ewes at Day 13 postmating, were greater than 10-fold higher at Day 15, and remained elevated at Day 19. Expression of Mx mRNA in the myometrium did not change during the estrous cycle but increased approximately 23-fold between Days 11 and 15 of pregnancy. Immunohistochemical and in situ hybridization analysis revealed a similar temporal pattern of Mx expression. In cyclic ewes, Mx protein and mRNA were initially localized to the luminal epithelium at Days 1 and 3, increased from Days 5 to 13, especially in the shallow uterine glands, and then declined at Day 15. Pregnancy resulted in up-regulation of Mx expression in the luminal and glandular epithelium, stroma, and myometrium. Punctate Mx immunostaining and Mx mRNA concentrations were greatest when progesterone production was maximal during the estrous cycle and were strongly up-regulated by the conceptus across the entire uterine wall. It is suggested that a cascade of induction of Mx gene expression proceeds from the luminal epithelium to the outer longitudinal myometrium and that transcriptional activation of the promoter may involve both soluble cytokines (i.e., IFNtau) and steroid hormones (i.e., progesterone).

Developmental expression and 5' end cDNA cloning of the porcine 2x and 2b myosin heavy chain genes

Muscle research on farm animals suffers from a lack of basic molecular probes and immunochemical reagents. To complete the cloning of a comprehensive range of isoform-specific postnatal myosin heavy chain (MyHC) probes from the pig, we report here on the 5 '-end cDNA isolation, identification, and in vivo characterization of the porcine equivalent of the 2x (fast oxidative-glycolytic) and 2b (fast glycolytic) MyHC isoforms. Comparative analyses of primary nucleotide and deduced amino acid sequences of the porcine slow, 2a, 2x, and 2b cDNAs showed that the 2x and 2b isoforms were most homologous with each other and the slow isoform was the least similar. At or just after birth, at least 3 postnatal muscle fiber types (slow/beta, 2a, and 2x) were present. MyHC 2x expressing fibers were arranged distinctively as large outer rings, each surrounding an inner ring of 2a fibers, which in turn circumscribed one or more central slow fibers. Subsequently, different muscles expressed at different times the MyHC 2b isoform such that by 10 weeks, 2b fibers became the most dominant fiber type, in size and number in nearly all muscles examined except for its notable absence in the soleus muscle. Co-expression of two or more MyHC isoforms within the same fiber was not a feature of porcine muscles unlike that observed in rat and human muscles. For the first time, porcine muscle fibers can now be classified into 4 adult phenotypes (slow/beta 2a, 2x, and 2b) according to the expression of specific MyHC isoforms.

Inducible gene targeting in mice

A method of gene targeting that allows the inducible inactivation of a target gene in mice is presented. The method uses an interferon-responsive promoter to control the expression of Cre recombinase. Here, Cre was used to delete a segment of the DNA polymerase beta gene flanked by IoxP recombinase recognition sites. Deletion was complete in liver and nearly complete in lymphocytes within a few days, whereas partial deletion was obtained in other tissues. This method can be used for the inducible inactivation of any other gene in vivo.

Molecular characterization of a developmentally regulated porcine skeletal myosin heavy chain gene and its 5′ regulatory region

Members of the myosin heavy chain (MyHC) gene family show developmental stage- and spatial-specificity of expression. We report on the characterization and identification of a porcine skeletal fast MyHC gene, including its corresponding 5′ end cDNA and 5′ regulatory region. This MyHC isoform was found exclusively in skeletal muscles from about the last quarter of gestation through to adulthood. Expression of this isoform was higher postnatally and its spatial distribution resembled a rosette cluster; each with a ring of fast fibres surrounding a central slow fibre. This rosette pattern was absent in the adult diaphragm but about 20% of the fibres continued to express this MyHC isoform. Further in vivo expression studies, in a variety of morphologically and functionally diverse muscles, showed that this particular skeletal MyHC isoform was expressed in fast oxidative-glycolytic fibres, suggesting that it was the equivalent of the fast IIA isoform. Two domains in the upstream regulatory region were found to confer differentiation-specific expression on C2 myotubes (−1007 to -828 and -455 to -101), based on in vitro transient expression assays using the chloramphenicol acetyltransferase (CAT) reporter gene. Interestingly, for high levels of CAT expression to occur, a 3′ region, extending from the transcriptional start site to part. of intron 2, must be present in all the DNA constructs used.

In vivo expression and molecular characterization of the porcine slow-myosin heavy chain

We report on the molecular characterization of the porcine slow-myosin heavy chain (HC) beta gene and the isolation of its 5′ end cDNA. In vivo expression study, by in situ hybridization and histochemistry, revealed a highly regular rosette pattern of fiber arrangement, with a slow fiber occupying the central core, in all the skeletal muscles examined. This feature can be advantageous in the distinction of primary and secondary fibers in myogenic lineage studies. In the neonatal heart, beta isoform expression is diffuse, with higher expression occurring in the ventricle than in the atrium. Transient transfection assays showed the porcine promoter functions in a muscle- and differentiation stage-specific manner. In the 5′ regulatory region are several putative positive and negative regulatory elements, including a positive and a negative element in close proximity to each other in intron 1.

Transformation of a novel direct-repeat repressor element into a promoter and enhancer by multimerisation

Studies on the regulation of interferon (IFN) responsive genes have mainly been centred on the highly conserved IFN stimulated responsive elements (ISREs) which can mediate type I and II IFN inducibility. To date little is known about other functional cis-acting regulatory motifs in IFN responsive genes. We report here on the identification of a repressor element in the human MxA gene defined to a 19 base pair (bp) region which houses a 9 bp direct repeat. DNA-specific protein binding on this element is not affected by IFN treatment and is distinct from ISRE binding proteins. Remarkably, contrary to expectations, when the repressor element is multimerised and spliced, in either orientation, to a reporter gene it behaves like a functional, constitutive promoter. Positioning the multimerised element in front of the SV40 enhancerless promoter also led to enhanced expression. The same protein(s) seem to bind to both the single repressor element and its multimerised form. This discovery of phenotypic reversal on a repressor element via multimerisation may have important implications in vivo.

A whole blood immunoassay for the interferon-inducible human Mx protein

Mx protein, an intracellular protein induced by type I interferons (IFNs), is useful as a marker for the IFN-induced state. It is detectable, for example, in leukocytes of patients undergoing IFN-alpha treatment as well as in patients suffering from viral or autoimmune diseases. For immunizations and standardizations, recombinant human MxA protein was expressed in Escherichia coli and purified from inclusion bodies by several steps of chromatography. Two monoclonal antibodies against nonoverlapping epitopes and specific for human Mx protein were selected to establish a simple two-site immunometric enzyme assay. In addition, a monoclonal antibody also reacting with Mx proteins of other species was identified. Prior to assay, whole blood samples were lysed with a nonionic detergent. The sample was incubated on wells coated with a first monoclonal antibody (1304.5.32) together with a second biotinylated monoclonal (1302.34.16), which, after washing, was revealed by an avidin-alkaline phosphatase system. Limit of detection was 5 ng/ml. In two-thirds of normal blood samples (n = 87), Mx protein levels were below 5 ng/ml; 25 samples (29%) had Mx levels between 5 and 50 ng/ml; and 4 samples (5%) were above 50 ng/ml. No Mx was found in plasma, and the mononuclear cell fraction accounted for the bulk of Mx in blood. In vitro, as determined by flow cytometry, monocytes and lymphocytes accumulated Mx protein for 24 h with similar kinetics and remained at plateau levels for more than 70 h. Monocytes contained around eight times more Mx than lymphocytes. The immunoassay was also suitable for detecting Mx after IFN induction in heparinized blood.

Strong expression of foreign genes following direct injection into fish muscle

We report here for the first time direct injection of genes into fish muscle in vivo. Plasmids used contain either SV40 early promoter, rabbit beta-cardiac myosin heavy chain promoter, human MxA promoter or an artificial promoter, fused to a chloramphenicol acetyltransferase (CAT) or beta-galactosidase reporter gene. CAT assays revealed that most gene constructs were highly expressed. Histochemical analysis showed that beta-galactosidase was strongly expressed at the site of injection within muscle fibres. This method provides an excellent system for testing expression of gene constructs, including those of mammalian origin, in fish muscle in vivo and has the potential for fish vaccination.

Molecular and functional analysis of the virus- and interferon-inducible human MxA promoter

The virus- and interferon-inducible human MxA (IFI-78k) gene is a homologue of the murine influenza resistance gene Mx1. Three overlapping human cosmid clones covering most of the gene including its promoter region were isolated. Sequencing the 5' MxA cDNA derived by RT-PCR (reverse transcriptase-polymerase chain reaction) confirmed the most 5' putative transcriptional start site. The MxA promoter does not contain a TATA or CCAAT box but has three Interferon Stimulated Response Element (ISRE) motifs. Strong induction with type I interferons was demonstrated with a fragment containing only two ISREs in human L132 cells. This induced expression was not adversely affected by 2-aminopurine. However, the promoter showed constitutive expression in transiently or stably transfected murine LM cells.