Different mechanisms for alpha and beta interferon induction

Beta interferon regulation of glucose metabolism is PI3K/Akt dependent and important for antiviral activity against coxsackievirus B3

An effective type I interferon (IFN)-mediated immune response requires the rapid expression of antiviral proteins that are necessary to inhibit viral replication and virus spread. We provide evidence that IFN-β regulates metabolic events important for the induction of a rapid antiviral response: IFN-β decreases the phosphorylation of AMP-activated protein kinase (AMPK), coincident with an increase in intracellular ATP. Our studies reveal a biphasic IFN-β-inducible uptake of glucose by cells, mediated by phosphatidylinositol 3-kinase (PI3K)/Akt, and IFN-β-inducible regulation of GLUT4 translocation to the cell surface. Additionally, we provide evidence that IFN-β-regulated glycolytic metabolism is important for the acute induction of an antiviral response during infection with coxsackievirus B3 (CVB3). Last, we demonstrate that the antidiabetic drug metformin enhances the antiviral potency of IFN-β against CVB3 both in vitro and in vivo. Taken together, these findings highlight an important role for IFN-β in modulating glucose metabolism during a virus infection and suggest that the use of metformin in combination with IFN-β during acute virus infection may result in enhanced antiviral responses.

IMPORTANCE

Type I interferons (IFN) are critical effectors of an antiviral response. These studies describe for the first time a role for IFN-β in regulating metabolism--glucose uptake and ATP production--to meet the energy requirements of a robust cellular antiviral response. Our data suggest that IFN-β regulates glucose metabolism mediated by signaling effectors similarly to activation by insulin. Interference with IFN-β-inducible glucose metabolism diminishes the antiviral response, whereas treatment with metformin, a drug that increases insulin sensitivity, enhances the antiviral potency of IFN-β.

Coronavirus pseudoparticles formed with recombinant M and E proteins induce alpha interferon synthesis by leukocytes

Transmissible gastroenteritis virus (TGEV), an enteric coronavirus of swine, is a potent inducer of alpha interferon (IFN-alpha) both in vivo and in vitro. Incubation of peripheral blood mononuclear cells with noninfectious viral material such as inactivated virions or fixed, infected cells leads to early and strong IFN-alpha synthesis. Previous studies have shown that antibodies against the virus membrane glycoprotein M blocked the IFN induction and that two viruses with a mutated protein exhibited a decreased interferogenic activity, thus arguing for a direct involvement of M protein in this phenomenon. In this study, the IFN-alpha-inducing activity of recombinant M protein expressed in the absence or presence of other TGEV structural proteins was examined. Fixed cells coexpressing M together with at least the minor structural protein E were found to induce IFN-alpha almost as efficiently as TGEV-infected cells. Pseudoparticles resembling authentic virions were released in the culture medium of cells coexpressing M and E proteins. The interferogenic activity of purified pseudoparticles was shown to be comparable to that of TGEV virions, thus establishing that neither ribonucleoprotein nor spikes are required for IFN induction. The replacement of the externally exposed, N-terminal domain of M with that of bovine coronavirus (BCV) led to the production of chimeric particles with no major change in interferogenicity, although the structures of the TGEV and BCV ectodomains markedly differ. Moreover, BCV pseudoparticles also exhibited interferogenic activity. Together these observations suggest that the ability of coronavirus particles to induce IFN-alpha is more likely to involve a specific, multimeric structure than a definite sequence motif.

In vivo study of interferon-alpha-secreting cells in pig foetal lymphohaematopoietic organs following in utero TGEV coronavirus injection

Non-infectious UV-inactivated transmissible gastroenteritis virus (TGEV) was previously shown to induce interferon alpha (IFN alpha) secretion following in vitro incubation with blood mononuclear cells. In this study, pig foetuses at different stages of gestation were injected in utero with (a) partially UV-inactivated wild TGEV or (b) fully UV-inactivated wild or dm49-4 mutant TGEV coronavirus. Nucleated cells from foetal liver, bone marrow, spleen and blood were isolated 10 or 20 h after injection and assayed ex vivo for IFN alpha secretion by ELISPOT and ELISA techniques. The administration of TGEV induced IFN alpha-secreting cells in foetal lymphohaematopoietic organs at mid-gestation. In contrast, IFN alpha was not detected in control sham-operated foetuses. A specific point mutation in the amino acid sequence of the viral membrane glycoprotein M of TGEV mutant dm49-4 was associated with lower or absent IFN alpha in utero inducibility by mutant virus as compared with wild virus. Flow cytometry analysis did not show differences in leukocyte surface marker expression between control and TGEV- or between dm49-4 and wild virus-treated foetus cells, with the exception of a reduction in percentages of polymorphonuclear cells in TGEV-treated lymphohaematopoietic tissues, which is probably due to IFN alpha secretion. The present data provided in vivo evidence of IFN alpha secretion at the cell level in foetal lymphohaematopoietic organs. Such IFN alpha-secreting cells in lymphohaematopoietic tissues may be the source of IFN alpha detected during foetal infections.

Stimulation of natural interferon-alpha/beta-producing cells by Staphylococcus aureus

Human peripheral blood mononuclear cells (PBMCs) produced high levels of antiviral activity, as determined by bioassay, when stimulated by Staphylococcus aureus Cowan I (SAC) and E. coli. Specific immunoassays demonstrated the presence of both IFN-alpha and gamma and, for SAC, also low levels of IFN-beta. The frequencies of SAC-induced IF N-alpha-producing cells (IPCs) were up to 1-2 per 10(3) PBMCs. These IPCs expressed the HLA-DR and CD4 antigens but not CD3, CD14, or CD19, thus resembling the natural IFN-alpha-producing cells (NIPC). The SAC was more efficient as IFN inducer when heat killed than when streptomycin inhibited. The SAC was inhibitory to virally induced IFN-alpha responses, in particular when streptomycin inhibited. Both pronase treatment and mechanical disruption of SAC cells abolished their capacity to induce IFN-alpha production. Staphylococcal strains lacking or expressing low levels of protein A (SpA) showed a decreased ability to induce IFN-alpha production. However, purified SpA did not itself induce IFN-alpha. Possibly, SpA together with other bacterial surface proteins is important for the capacity of SAC to induce IFN-alpha production in NIPC.

Ontogeny of interferon alpha secreting cells in the porcine fetal hematopoietic organs

We examined the ontogeny of IFN-alpha Secreting Cells (IFN-alpha SC) in different hematopoietic organs and blood of porcine fetuses at different stages of gestation. Cells were induced to produce IFN-alpha by incubation with the coronavirus TGEV and IFN-alpha SC were detected by ELISPOT. A striking finding was that IFN-alpha SC could be detected in the fetal liver as early as at 26 days of gestation, i.e., during the first quarter of gestation, a period at which T-cell markers could not be detected by flow cytometry. In addition, IFN-alpha SC could be detected in the cord blood, the spleen and the bone marrow of fetuses at later stages of gestation. These data indicate that IFN-alpha SC appear very early during the ontogeny of the immune system, long before the development of the specific immune system, and may therefore represent an early antiviral defence mechanism. IFN-alpha SC were found to be associated with hematopoietic organs, which argues for their hematopoietic lineage.

The leukocyte function-associated antigen-1 (LFA-1) is involved in the interferon-alpha response induced by herpes simplex virus in blood leukocytes

The role of the leukocyte function-associated antigen-1 (LFA-1) family of integrins (beta 2 integrins) in the interferon-alpha (IFN-alpha) response was examined, using human peripheral blood mononuclear cells (PBMCs) stimulated in vitro by glutaraldehyde-fixed Herpes simplex virus-infected WISH amnion cells. Monoclonal antibodies (mAbs) to the beta 2 chain (CD18) and to the alpha chain of LFA-1 (CD11a) reduced the number of IFN-alpha-producing cells (IPCs) by 30-50%, but mAbs to CD11b or c caused no inhibition. The IB4 mAb to CD18 was inhibitory when added during the first 2 h of the IFN-alpha response, but did not alter its kinetic. In contrast, the IB4 prevented the early enhancement of the IFN-alpha response caused by addition of interleukin-3 (IL-3) or granulocyte-macrophage colony-stimulating factor (GM-CSF). However, a delayed down-regulation of the IPC response occurred in such PBMC cultures, and a paradoxical increase in the total production of IFN-alpha. The results suggest that LFA-1 (CD11a/CD18) participates in the early phase of the IFN-alpha response and may be activated by cytokines such as IL-3 and GM-CSF.

Enrichment of coronavirus-induced interferon-producing blood leukocytes increases the interferon yield per cell: a study with pig leukocytes

Porcine peripheral blood mononuclear cells, which secrete IFN alpha in response to a coronavirus, transmissible gastroenteritis virus, were detected by a filter immunoplaque assay (ELISPOT). IFN alpha-producing cells (IPC), which are present at a low frequency in the blood, could be enriched up to 100-fold by sequential depletion of plastic-adherent cells and cell fractionation on metrizamide density gradients. IPC were present in the non-adherent low-density cell subpopulation. Cell selection experiments using antibody (Ab)-coated immunomagnetic beads revealed that porcine IPC could be positively selected by anti-CD4 or -SLA-class-II Ab, but not by anti-CD2 or -CD8 Ab. The estimated IFN yield per IPC was found to increase when IPC were assayed at higher concentrations. These data suggest that IPC represent a unique and distinct cell population in the blood, which could secrete higher amounts of IFN following its accumulation at a site of viral infection.

Interferon-alpha (IFN-alpha) production by human intestinal mononuclear cells. Response to virus in control subjects and in Crohn's disease

The virus induced production of interferon alpha by human intestinal lamina propria mononuclear cells was investigated. Intestinal and autologous peripheral cells from control subjects and patients with Crohn's disease were cultured in vitro with and without stimulation with the Newcastle disease virus. Interferon alpha was measured and characterised in the culture supernatants after 12 hours and the kinetics of production was evaluated over the following four days of culture. No detectable interferon alpha was found in cultures of unstimulated intestinal and autologous peripheral mononuclear cells from controls and Crohn's disease whereas interferon alpha was released in all cultures stimulated with the virus. In all 12 hours experiments in both groups, virus stimulated intestinal mononuclear cells yielded significantly less interferon alpha than the autologous peripheral cells. The kinetics experiments showed that control intestinal mononuclear cells appeared to be poorly responsive to virus stimulation showing a release of interferon alpha significantly lower than that of the autologous peripheral cells. The interferon alpha release at day 4 by control cells (either intestinal or peripheral) did not differ from that measured after the first 12 hours. In contrast, the interferon alpha produced by Crohn's disease cells progressively increased during the culture period and the amount of interferon alpha measured at day 4 was significantly higher than that released at 12 hours. These data suggest that normal human intestinal mononuclear cells are down regulated in their capability of producing interferon alpha and that in Crohn's disease their activation for this function is enhanced. These data also suggest that in Crohn's disease intestinal mononuclear cells exhibit a transient hyporesponsiveness to in vitro stimulation possibly related to massive in vivo exposure to interferon alpha inducers.

Molecular cloning of a gene encoding porcine interferon-beta

A gene encoding the porcine interferon-beta (poIFN-beta) was cloned from a genomic library. The sequence of a potential intronless coding region as well as 1,265 bp of the 5'- and 277 bp of the 3'-flanking regions is presented. The gene is predicted to encode a mature protein of 165 amino acids and a signal peptide of 21 amino acids. This probable poIFN-beta shows high homology (63%) with human (hu) IFN-beta at the amino acid level, but less with porcine (po) IFN-alpha 1 (32%). It contains three cysteines and three potential N-glycosylation sites. A region of the 5' flank (-116 to -159) of the gene is homologous to the IFN gene regulatory element (IRE) of the huIFN-beta gene which mediates virus inducibility. Southern blot analysis indicates that the poIFN-beta gene is present as a single copy in the porcine genome. Its expression in porcine peripheral blood leukocytes stimulated in vitro by pseudorabies virus (PRV) was demonstrated at the RNA level both by Northern blot analysis and by in situ hybridization. The latter approach in addition detected only about one IFN-beta mRNA-containing cell per 2,000 PRV-stimulated porcine leukocytes, a frequency in the same range as that for leukocytes containing IFN-alpha mRNA.

Single amino acid changes in the viral glycoprotein M affect induction of alpha interferon by the coronavirus transmissible gastroenteritis virus

Transmissible gastroenteritis virus, an enteropathogenic coronavirus of swine, is a potent inducer of alpha interferon (IFN-alpha) both in vitro and in vivo. Previous studies have shown that virus-infected fixed cells or viral suspensions were able to induce an early and strong IFN-alpha synthesis by naive lymphocytes. Two monoclonal antibodies directed against the viral membrane glycoprotein M (29,000; formerly E1) were found to markedly inhibit virus-induced IFN production, thus assigning to M protein a potential effector role in this phenomenon (B. Charley and H. Laude, J. Virol. 62:8-11, 1988). The present report describes the selection and characterization of a collection of 125 mutant viruses which escaped complement-mediated neutralization by two IFN induction-blocking anti-M protein monoclonal antibodies. Two of these mutants, designated H92 and dm49-4, were found to exhibit a markedly reduced interferogenic activity. IFN synthesis by lymphocytes incubated with purified suspensions of these mutants was 30- to 300-fold lower than that of the parental virus. The transcription of IFN-alpha genes following induction by each mutant was decreased proportionally, as evidenced by Northern (RNA) blot analysis. The sequence of the M gene of 20 complement-mediated neutralization-resistant mutants, including the 2 defective mutants, was determined by direct sequencing of genome RNA. Thirteen distinct amino acid changes were predicted, all located at positions 6 to 22 from the N terminus of the mature M protein and within the putative ectodomain of the molecule. Two substitutions, Thr-17 to Ile and Ser-19 to Pro, were assumed to generate the defective phenotypes of mutants dm49-4 and H92, respectively. The alteration of an Asn-Ser-Thr sequence in dm49-4 virus led to the synthesis of an M protein devoid of a glycan side chain, which suggests a possible involvement of this structure in IFN induction. Overall, these data supported the view that an interferogenic determinant resides in the N-terminal, exposed part of the molecule and provided further evidence for the direct role of M protein in the induction of IFN-alpha by transmissible gastroenteritis virus. The acronym VIP (viral interferogenic protein) is proposed as a designation for this particular class of proteins.

[Value of interferon alpha determination in the diagnosis of meningoencephalitis presumed to be of viral origin]

Quantitative determination of alpha interferon (IFN) is used as an early marker in viral encephalitis. IFN is detected during 10 days following the onset of clinical symptoms. In 26 patients (11 children from 1 day to 6 year old and 15 adults from 17 to 70 year old) with central nervous system disorders (15 meningo-encephalitis, 5 meningitis, 1 myelitis, 1 polyradiculoneuritis, 1 dementia, 1 epilepsy and 2 other), alpha IFN is quantified using a cytopathic effect inhibition assay of VSV on MDBK cells. The mean value of alpha IFN is 80 UI/ml (range from 0 to 512 UI/ml). Virus involved are herpes virus in 38.5% of cases (10/26) and 66% of viral meningoencephalitis (8/12), H.I.V. in 3 cases, VZV in 2 and measles virus in 1 case. Viral aetiology is suspected in six other patients. The results show the importance of early determination of alpha IFN (immediately after the first symptoms and on the first admission to the hospital) in sera and cerebrospinal fluids (CSF) simultaneously with viral culture and antibody research. The presence of alpha IFN only in CSF and a higher titre of alpha IFN in CSF than in serum are important data to distinguish primitive acute necrotizing encephalitis from post eruptive or post infectious perivenous encephalitis. In herpes virus infections with specific treatment all the patients recover. However to prevent brain damage in survivors the treatment should be established as soon as possible.

The induction of interferon-alpha and interferon-beta mRNA in human natural interferon-producing blood leukocytes requires de novo protein synthesis

The induction of interferon-alpha (IFN-alpha) and IFN-beta mRNA in natural IFN producing (NIP) cells in cultures of human peripheral blood mononuclear cells (PBMCs), stimulated by glutaraldehyde-fixed Herpes simplex virus type 1 (HSV)-infected WISH cells, was studied. The protein synthesis inhibitor cycloheximide (CHX) totally prevented the appearance of both IFN-alpha and IFN-beta mRNA, also in cultures supplemented with a conditioned medium (CM) assumed to contain soluble factors necessary for the IFN induction. However, when PBMCs were preincubated for 4 h in medium supplemented with fetal bovine serum (FBS) with or without addition of CM, the subsequent induction of IFN-alpha/beta mRNA became partially resistant to CHX. In serum-free medium containing interleukin-3 (IL-3) or granulocyte-macrophage colony-stimulating factor (GM-CSF), the early induction of IFN-alpha mRNA became resistant to CHX, and, in contrast to FBS and CM supplemented medium, this was observed also without a preincubation of the PBMCs. In contrast, IL-1, IL-2, IL-4, IL-6, tumor necrosis factor-alpha (TNF-alpha), IFN-alpha, or IFN-gamma had no such effects. Our results suggests that de novo synthesis of proteins normally is required for the induction of IFN-alpha/beta mRNA. Such proteins might be cytokines, possibly CSFs, which in turn also may require protein synthesis for their actions. In contrast, the actual triggering signal provided by the HSV-inducer is independent of protein synthesis.

Interferons and the colony-stimulating factors IL-3 and GM-CSF enhance the IFN-alpha response in human blood leucocytes induced by herpes simplex virus

Human peripheral blood mononuclear cells (PBMC) were stimulated to produce interferon-alpha (IFN-alpha) by glutaraldehyde-fixed Herpes simplex virus type 1 (HSV)-infected WISH amnion cells in vitro. Different cytokines were included during the stimulation and tested for their ability to enhance the IFN-alpha response which occurs in the natural IFN-alpha producing (NIP) leucocytes. The total production of IFN-alpha and the numbers of IFN-alpha producing cells (IPCs) were increased by interleukin-3 (IL-3) or granulocyte-macrophage colony-stimulating factor (GM-CSF). Their most marked effect was to reduce the time required for induction of the IPC by the HSV-infected cells, thereby causing both an earlier peak of IPC numbers and secretion of IFN-alpha. Addition of IFN-alpha 2b did not alter the kinetics of the IFN-alpha response in the same way as the two CSFs, but instead generally increased the IPC numbers and the production of IFN-alpha. The IL-3 and GM-CSF, especially in combination with IFN-alpha, had the most pronounced enhancing effects on IPC numbers when PBMC were induced at low cell concentrations. The cytokines IL-1, IL-2, IL-4, IL-6 or tumour necrosis factor-alpha (TNF-alpha) had no detectable effects on the IFN-alpha response. The results suggest that cytokines such as the CSFs and IFNs may be involved in the regulation of NIP cell functions.

Glycosylation is required for coronavirus TGEV to induce an efficient production of IFN alpha by blood mononuclear cells

Porcine peripheral blood mononuclear cells (PBMC) are induced to produce interferon alpha (IFN alpha) following in vitro exposure to coronavirus TGEV (transmissible gastroenteritis virus)-infected glutaraldehyde-fixed cell monolayers or to TGEV virions. In the present report, we examined the possibility that glycosylation of viral proteins could play a major role in interactions with PBMC leading to the production of IFN alpha. Con A pretreatment of TGEV-infected cell monolayers before fixation with glutaraldehyde and exposure to PBMC caused a dose-dependent inhibition of IFN alpha induction, implying that masking of carbohydrates at the surface of infected cells lowered IFN-alpha-induction. Similarly, inhibition of N-linked glycosylation by tunicamycin during viral infection of cell monolayers altered their ability to induce IFN alpha. In addition, complete cleavage of 'complex type' oligosaccharides by peptide-N-glycohydrolase F lowered the capacity of TGEV virions to induce IFN alpha. Thus, these findings strongly suggest that glycosylation of the viral proteins, and more precisely the presence of complex-type oligosaccharides, is an important requirement for a completely efficient interaction with PBMC leading to the production of IFN-alpha.

Infrequent but efficient interferon-alpha-producing human mononuclear leukocytes induced by herpes simplex virus in vitro studied by immuno-plaque and limiting dilution assays

Human blood mononuclear leukocytes (PBMCs) producing interferon-alpha (IFN-alpha) after stimulation by herpes simplex virus type 1 (HSV) in vitro were identified by a filter immuno-plaque assay. Individual IFN-alpha-producing cells (IPCs) yielded between 0.5 and 2 units IFN-alpha, sufficient to protect cultures of MDBK cells against a viral challenge. Therefore, their frequency could be determined by a limiting dilution assay as well as by an immuno-plaque assay. Similar estimates of between 2 and 55 IPCs per 10(4) PBMCs at the peak of the IFN-alpha response were obtained by the two methods. IPCs were first detected 3 h after stimulation by HSV; their number peaked at 8 h and then declined. IPC frequencies were influenced by the concentrations of HSV and PBMCs during induction, but the quantity of IFN-alpha produced per IPC was relatively constant. The relation between the numbers of IPCs and PBMCs was linear at high PBMC concentrations, whereas at low PBMC concentrations fewer IPCs than expected were detected. The response could be fully restored by adding a combination of filler cells (Namalwa or U937 cells) and conditioned medium from 6-h HSV-induced PBMC cultures. Our results suggest that HSV induces an IFN-alpha response in a relatively rare population of efficient IPCs by complex mechanisms, which may involve cell cooperation and/or production of soluble factors.

Differences in the mechanism of induction of interferon-alpha by herpes simplex virus and herpes simplex virus-infected cells

The cellular source of IFN alpha after induction with Herpes simplex virus type-1 (HSV) and HSV-infected fibroblasts was investigated by using human peripheral blood mononuclear cell (PBMC) populations, purified according to conventional procedures, and which included T- and B-lymphocytes as well as monocytes. It appears that the cells responding to HSV virions are monocytes, whereas the PBMC population induced by HSV-infected cells is represented by B-lymphocytes. Furthermore, by using monoclonal antibody (MoAb) to HLA class I and class II products, it appears that different membrane structures are involved in the induction of IFN by HSV virions, as opposed to HSV-infected cells. In fact, most anti-HLA class II MoAbs inhibit IFN induction by HSV-infected cells, and not IFN induction by HSV virions.

Induction of alpha interferon by transmissible gastroenteritis coronavirus: role of transmembrane glycoprotein E1

Epithelial cells infected with the coronavirus transmissible gastroenteritis virus (TGEV) and fixed by glutaraldehyde induced a high alpha interferon (IFN-alpha) production in nonimmune porcine as well as human or bovine peripheral blood mononuclear cells (PBMC). IFN-alpha was detected as early as 3 h after exposure of PBMC to infected cells and at producer/inducer cell ratios as low as 1/1. Two of four monoclonal antibodies directed against the viral transmembrane glycoprotein E1 could block the IFN-inducing capacity of both TGEV-infected cells and viral particles. On the other hand, IFN-alpha induction was not markedly affected by monoclonal antibodies directed against other E1 epitopes, against peplomer glycoprotein E2, or against nucleocapsid protein. Thus, these findings strongly imply that IFN induction by TGEV results from interactions between an outer membrane domain of E1 and the PBMC membrane.

Membrane interactions involved in the induction of interferon-alpha by Mycoplasma pneumoniae

Interferon (IFN) induction by Mycoplasma pneumoniae (MP) in human peripheral blood mononuclear cells (PBMC) has been studied. We show that IFN yields depend on the concentration of both lymphocytes and MP. The effective IFN inducer appears to be the mycoplasma membrane, and IFN production occurs without significant lymphocyte proliferation. Data obtained by both positive and negative selection experiments suggest that the PBMC subpopulation induced by MP is B lymphocyte, as opposed to the main subpopulation induced by NDV that is monocyte. Evidence is also provided suggesting that the membrane interaction between MP and the B cells is mediated by MHC Class II antigens.

Synthesis of intrathecal interferon in systemic lupus erythematosus with neurological complications

Intrathecal synthesis of interferon in the absence of viral or bacterial infection was detected during the occurrence of neurological complications in two patients with systemic lupus erythematosus. The interferons displayed characteristics similar to those observed in the sera of patients with the disease. No interferon inducing activity was detected in the cerebrospinal fluid or serum of the two patients. These observations support the hypothesis of a localised mechanism of interferon induction in systemic lupus erythematosus which includes the interaction of lymphocytes with damaged tissues.