Interrelationships of Interferon and Immunity During Viral Infections

Interferon is one determinant of host resistance. The immune responses, cellular or humoral, are other components. Cell-mediated responses appear to be involved in host resistance to certain viral infections, particularly the herpesvirus group and vaccinia virus. It is suggested that immune and interferon responses may complement one another and contribute to host resistance. The relative importance of each component depends upon the virus-host interaction. Finally, evidence has been presented which suggests that production of interferon as a result of antigen-sensitized cell interaction may further link these two components of the host response.     

Interferon: Effects On The Immune Response And The Mechanism Of Activation Of The Cellular Respons

Abstract

The discovery of interferon in 1957 by Drs. Alick Isaacs and Jean Lindenmann led to major revisions in the concepts of man's defenses against viral infections. Interferons are well known as inhibitors of virus replication. This inhibition is accomplished by acting on the host cell rather than on the virus (Figure 1). The proposed biological mediator of the antiviral action of interferon is not interferon, but an antiviral protein, which is produced by a cell after that cell has come into contact with interferon.     

Isolation of highly fusogenic variants of simian virus 5 from persistently infected cells that produce and respond to interferon.

A series of experiments were undertaken to examine how interferon and neutralizing antibodies influence the ability of simian virus 5 (SV5) (strain W3) to establish and maintain persistent infections in murine cells. In contrast to the rapid decline in SV5 protein synthesis observed in murine BALB/c fibroblasts (BF cells), which produce and respond to interferon, between 24 and 48 h postinfection there was no inhibition of virus protein synthesis in MSFI- cells, skin fibroblasts derived from alpha/beta-interferon receptor knockout BALB/c mice. Furthermore, the addition of anti-interferon antibodies to the culture medium of infected BF cells significantly reduced the observed decline in virus protein synthesis. Following infection of untreated BF cells, the majority replicated virus but survived the infection and eventually cleared the virus after 8 to 15 days. However, not all the cells were cured, and the cultures became persistently infected. Upon passage of persistently infected cultures, the virus fluxed between active and repressed states as a consequence of interferon production. This resulted in a balance being reached in which only 5 to 20% of the cells were infected at any one time. After 30 passages of the persistently infected cells, highly fusogenic virus variants arose (one of which was isolated and termed W3-f). W3-f remained as sensitive to interferon as the parental W3 isolate but, in the absence of interferon, spread much more rapidly than the parental W3 strain through BF cell monolayers. Sequence analysis revealed no deduced amino acid differences between the F proteins of W3 and W3-f. BF cell cultures persistently infected with W3-f were rapidly cleared of virus by the addition of virus-neutralizing antibodies to the culture medium. In contrast, neutralizing antibodies had little effect on the numbers of cells persistently infected with W3 over several passages. These results suggest that the ability of paramyxoviruses to cause cell-cell fusion may be selected for in vivo as a consequence of their adaptation to the interferon response rather than their need to escape from neutralizing antibodies. The significance of these observations with regard to persistent parainfluenza virus infections in vivo is further discussed.     

Interferon: effects on the immune response and the mechanism of activation of the cellular response.

The discovery of interferon in 1957 by Drs. Isaacs and Lindenmann led to major revisions in the concepts of man's defenses against viral infections. There are at least two types of interferon. Along with their antiviral properties, they have recently been shown to exert a suppressive effect on the humoral and cellular immune response; they affect both B and T lymphocytes. A variety of substances, including virus, polyribonucleotides, and mitogens for T lymphocytes, are good interferon inducers. T lymphocytes seem to be necessary for these inducers to exert their immunosuppressive effects. The immunosuppressive effects of interferon inducers suggests that interferons may be mediators of suppressor T lymphocyte effects. In the virus system, interferon does not exert its antiviral effects by direct action on the virus, but rather derepresses a cell gene that results in the production of an antiviral protein. This antiviral protein is probably the mediator of inhibition of virus replication. This is a complex sequence of events that results in the interaction of interferon with the cell membrane and the resulting production of the antiviral state in the cell. This review will examine the various steps of this involved process.     

Comparative study of rabies virus persistence in human and hamster cell lines.

Persistent infections by rabies virus in BHK-21/13S and HEp-2 cells were studied comparatively. No evidence of interferon production, selection of virus-resistant cells, or integration of the viral genome could be found. Persisting viruses replicated efficiently at 34, 36, and 40 degrees C. Both persistently infected cultures released defective interfering virus particles. A cyclical pattern of infection, which was not characteristic of the persistently infected HEp-2 system, was observed in persistently infected BHK cultures. The virus from persistently infected BHK cultures lost its virulence for mice, whereas the virus from persistently infected HEp-2 cultures retained mouse-killing capacity for more than 3 years.     

The neurobiology of human immunodeficiency virus infections

A variety of diseases of the central and peripheral nervous systems evolves during the course of human immunodeficiency virus (HIV) infections. Most are not related to documented opportunistic infections and may be the direct result of HIV infections, as large proportions of healthy and ill HIV-infected persons show evidence of nervous system infection. These diseases occur at different times during the infection and have diverse inflammatory, demyelinating, or degenerative pathological features that suggest different pathogenetic mechanisms. The route and determinants of HIV invasion of the nervous system are unknown. Within the brain, viral antigen and RNA are found predominantly in macrophages, but the reason why profound dementia and cortical atrophy result from this infection remains a mystery. By analogy to other lentivirus infections, particularly visna virus in sheep, neuropathological changes may be mediated by cytokines. Other possible pathogenetic mechanisms include toxicity of viral polypeptides, transactivation of viral or cellular genes, autoimmunity, or other opportunistic infections. Clarification of the pathogenesis of HIV-related diseases is critical to the design of rational therapies.     

Mink parvoviruses and interferons: in vitro studies.

Although interferons can inhibit the replication of a number of viruses, little is known about their ability to inhibit parvovirus replication. Therefore, in vitro experiments were done to determine if Aleutian disease virus and mink enteritis virus, two autonomously replicating mink parvoviruses, induced interferon, were sensitive to the effects of interferon, or inhibited the production of interferon. The results indicated that these parvoviruses neither induced nor were sensitive to the effects of interferon. Furthermore, preexisting parvovirus infections did not inhibit poly(I).poly(C)-induced interferon production. This independence from the interferon system may, therefore, be a general property of the autonomously replicating parvoviruses.     

Methamphetamine Reduces Human Influenza A Virus Replication

Methamphetamine (meth) is a highly addictive psychostimulant that is among the most widely abused illicit drugs, with an estimated over 35 million users in the world. Several lines of evidence suggest that chronic meth abuse is a major factor for increased risk of infections with human immunodeficiency virus and possibly other pathogens, due to its immunosuppressive property. Influenza A virus infections frequently cause epidemics and pandemics of respiratory diseases among human populations. However, little is known about whether meth has the ability to enhance influenza A virus replication, thus increasing severity of influenza illness in meth abusers. Herein, we investigated the effects of meth on influenza A virus replication in human lung epithelial A549 cells. The cells were exposed to meth and infected with human influenza A/WSN/33 (H1N1) virus. The viral progenies were titrated by plaque assays, and the expression of viral proteins and cellular proteins involved in interferon responses was examined by Western blotting and immunofluorescence staining. We report the first evidence that meth significantly reduces, rather than increases, virus propagation and the susceptibility to influenza infection in the human lung epithelial cell line, consistent with a decrease in viral protein synthesis. These effects were apparently not caused by meth’s effects on enhancing virus-induced interferon responses in the host cells, reducing viral biological activities, or reducing cell viability. Our results suggest that meth might not be a great risk factor for influenza A virus infection among meth abusers. Although the underlying mechanism responsible for the action of meth on attenuating virus replication requires further investigation, these findings prompt the study to examine whether other structurally similar compounds could be used as anti-influenza agents.     

Resistance to Alpha/Beta Interferons Correlates with the Epizootic and Virulence Potential of Venezuelan Equine Encephalitis Viruses and Is Determined by the 5′ Noncoding Region and Glycoproteins

We compared the alpha/beta interferon (IFN-α/β) sensitivities of the TC-83 vaccine strain and 24 enzootic and epizootic Venezuelan equine encephalitis (VEE) isolates. The IFN-resistant or -sensitive phenotype correlated well with epizootic or enzootic potential. IFN-α/β resistance of Trinidad donkey (TRD) virus correlated with virulence determinants in the 5′ noncoding region and glycoproteins. Infection of mice lacking a functional IFN system with the IFN-sensitive TC-83 virus resulted in disease equivalent to that produced by the virulent, IFN-resistant TRD virus, further demonstrating that IFN resistance contributes to VEE virus virulence and is a biological marker of epizootic potential.     

Interferon Production by Nonviral Stimuli of Microbial Origin

An increasing number of nonviral materials of microbial origin has been reported to stimulate the production of interferon in cell cultures and (or) in animals. These materials include (a) gram-negative bacteria or the endotoxins prepared from their cell walls, (b) other microorganisms such as Rickettsiae, Bedsoniae, Protozoa, and (c) fungal products such as a mannan from Candida and various antibiotics which act as protein synthesis inhibitors, e.g., glutarimide antibiotics and tenuazonic acid. A summary is presented of the current state of knowledge about interferon production in animals by the most thoroughly studied nonviral substance of microbial origin, bacterial endotoxin. Further evidence is presented which clearly distinguishes the "endotoxin-type" of interferon response in animals from the response seen after the injection of virus. The data suggest that the release of preformed interferon from the tissues occurs in animals injected with endotoxin. On the other hand, interferon produced in response to the injection of virus is newly synthesized protein. While the exact chemical structure of the component of bacterial endotoxin responsible for interferon release has not yet been elucidated, it is clear that the lipid portion of the lipopolysaccharide, rather than the O-specific polysaccharide side chains or the core polysaccharide, is the active moiety.     

Persistent virus infection inhibits type I interferon production by plasmacytoid dendritic cells to facilitate opportunistic infections

Emerging studies indicate an association between virus-induced impairment in type I interferon (IFN-I) production and enhanced susceptibility to opportunistic infections, which represent a major health problem. Here, we provide in vivo evidence that lymphocytic choriomeningitis virus (LCMV) infection of its natural murine host dramatically diminishes the unique capacity of plasmacytoid dendritic cells (pDCs) to secrete high levels of systemic IFN-I. While both acute and persistent LCMV infections suppress pDC IFN-I response, only the persistent virus induces a long-lasting diversion of this innate immune pathway. The consequent reduction in IFN-I production serves to impair natural killer cell responses in LCMV-infected mice challenged subsequently with murine cytomegalovirus (MCMV) as an opportunistic pathogen. This innate defect also compromises the host's ability to counteract early MCMV spread. These findings provide a mechanistic explanation for the occurrence of opportunistic infections following viral insults and have important implications for treating such medical complications.     

Molecular structure of human fibroblast and leukocyte interferons: probe by lectin and hydrophobic chromatography.

Structural differences between human leukocyte virus-induced interferon and human fibroblast polyinosinic-polycytidylic acid (rIn-rCn)-induced interferon have been noted in previous studies. This study reports the behavior of human leukocyte and fibroblast interferon, induced by virus and by rIn-rCn, in several lectin and hydrophobic chromatographic systems. Differences in both glycosylation and in hydrophobicity of human leukocyte and fibroblast interferons are documented. Human fibroblast interferon is a glycoprotein, whereas our evidence suggests that human leukocyte interferon probably is not. Also, fibroblast interferon is more hydrophobic than leukocyte interferon, as probed on several hydrophobic adsorbents. The possible relationships of these differences to each other and to antigenic variations are discussed. Generally, the differences appear to be attributable to the cell type in which the interferon was induced. However, our results suggest that at least subtle differences in the processing of the induction signal (virus or rIn-rCn) within the same cell type may occur, slightly altering some structural features.     

BVDV and innate immunity.

Infection with bovine viral diarrhea virus (BVDV) is prevalent in the cattle population worldwide. The virus exists in two biotypes, cytopathic and non-cytopathic, depending on the effect of the viruses on cultured cells. BVDV may cause transient and persistent infections which differ fundamentally in the host's antiviral immune response. Transient infection may be due to both cytopathic and non-cytopathic biotypes of BVDV and leads to a specific immune response. In contrast, only non-cytopathic BVD viruses can establish persistent infection as a result of infection of the embryo early in its development. Persistent infection is characterized by immunotolerance specific for the infecting viral strain. In this paper we discuss the role of innate immune responses in the two types of infection. In general, both transient and persistent infections are associated with an increased frequency of secondary infections. Associated with the increased risk of such infections are, among others, impaired bacteria killing and decreased chemotaxis. Interestingly, non-cytopathic BVDV fails to induce interferon type I in cultured bovine macrophages whereas cytopathic biotypes readily trigger this response. Cells infected with non-cytopathic BVDV are also resistant to induction of interferon by double stranded RNA, a potent interferon inducer signalling the presence of viral replication in the cell. Thus, non-cytopathic BVDV may dispose of a mechanism suppressing a key element of the antiviral defence of the innate immune system. Since interferon is also important in the activation of the adaptive immune response, suppression of this signal may be essential for the establishment of persistent infection and immunotolerance.     

Genetic Variability of Hepatitis C Virus (HCV) 5’ Untranslated Region in HIV/HCV Coinfected Patients Treated with Pegylated Interferon and Ribavirin

Association between hepatitis C virus (HCV) quasispecies and treatment outcome among patients with chronic hepatitis C has been the subject of many studies. However, these studies focused mainly on viral variable regions (E1 and E2) and usually did not include human immunodeficiency virus (HIV)-positive patients. The aim of the present study was to analyze heterogeneity of the 5''untranslated region (5''UTR) in HCV/HIV coinfected patients treated with interferon and ribavirin. The HCV 5’UTR was amplified from serum and peripheral blood mononuclear cells (PBMC) samples in 37 HCV/HIV coinfected patients treated for chronic hepatitis C. Samples were collected right before treatment, and at 2, 4, 6, 8, 12, 20, 24, 36, 44, 48, 60, and 72 weeks. Heterogeneity of the 5''UTR was analyzed by single strand conformational polymorphism (SSCP), cloning and sequencing. Sustained virological response (SVR) was achieved in 46% of analyzed HCV/HIV co-infected patients. Stable SSCP band pattern was observed in 22 patients (62.9%) and SVR rate among these patients was 23%. Decline in the number of bands and/or shift in band positions were found in 6 patients (17.1%), 5 (83%) of whom achieved SVR (p=0.009). A novel viral genotype was identified in all but one of these patients. In 5 of these 6 patients a new genotype was dominant. 5''UTR heterogeneity may correlate with interferon and ribavirin treatment outcome. In the analyzed group of HCV/HIV coinfected patients, viral quasispecies stability during treatment favored viral persistence, whereas decrease in the number of variants and/or emergence of new variants was associated with SVR. Among injection drug users (IDU) patients, a new genotype may become dominant during treatment, probably due to the presence of mixed infections with various strains, which have different susceptibility to treatment.     

The Cytotoxic T-Cell Response to Herpes Simplex Virus Type 1 Infection of C57BL/6 Mice Is Almost Entirely Directed against a Single Immunodominant Determinant

Many virus infections give rise to surprisingly limited T-cell responses directed to very few immunodominant determinants. We have been examining the cytotoxic T-lymphocyte (CTL) response to herpes simplex virus type 1 (HSV-1) infection. Previous studies have identified the glycoprotein B-derived peptide from residues 498 to 505 (gB(498-505)) as one of at least three determinants recognized by HSV-1-specific CTLs isolated from C57BL/6 mice. We had previously found that in vitro-derived CTLs directed to gB(498-505) show a characteristic pattern of T-cell receptor (TCR) usage, with 60% of gB(498-505)-specific CD8(+) T cells expressing BV10(+) TCR beta chains and a further 20% expressing BV8S1. In this report, we confirm that this TCR V-region bias is also reflected in the ex vivo response to HSV-1 infection. A high proportion of activated CD8(+) draining lymph node cells were found to express these dominant V regions, suggesting that a substantial number of in vivo responding T cells were directed to this one viral determinant. The use of an HSV-1 deletion mutant lacking the gB(498-505) determinant in combination with accurate intracellular gamma interferon staining allowed us to quantify the extent of gB-specific T-cell dominance. Together, these results suggested that between 70 and 90% of all CD8(+) HSV-1-specific T cells target gB(498-505). While deletion of this determinant resulted in an attenuated CD8(+) T-cell response, it also permitted the emergence of one or more previously unidentified cryptic specificities. Overall, HSV-1 infection of C57BL/6 mice results in an extremely focused pattern of CD8(+) T-cell selection in terms of target specificity and TCR expression.     

The inhibition of endotoxin-induced local inflammation by LDH virus or LDH virus-infected tumors is mediated by interferon

The footpad swelling reaction induced by local injection of S. marcescens lipopolysaccharide was found to be inhibited in mice given a transplantable tumor (TA3) or cell-free ascitic fluid from tumor-bearing mice. The tumor was shown to contain LDH virus, which is known to cause inapparent persistent infections in mice. Monoclonal antibodies directed against protein VP3 of the LDH virus could partially abrogate the anti-inflammatory effect of the TA3-ascitic fluid, and, conversely, the anti-inflammatory effect could be obtained by LDH virus isolated from the tumor and reproduced by serial passage of cell-free fluids. Inhibition of the footpad reaction was seen in the acute but not in the chronic phase of LDH virus infection, suggesting that the anti-inflammatory effect might be due to endogenous interferon (IFN) which, similarly, was only detectable in the acute phase. Newcastle disease virus, another potent interferon inducer, had a similar inhibitory effect on the footpad reactivity. Moreover, the inhibitory effect of LDH virus infection could partially be abrogated by administration of a polyclonal antibody directed against murine IFN-alpha,beta. Finally, passively administered natural murine IFN-alpha,beta or recombinant murine IFN-alpha 1 (but not recombinant murine IFN-beta) was found to cause inhibition of the footpad reaction. Since Gram-negative bacteria and their lipopolysaccharides have the ability to induce a systemic interferon response, our findings suggest that this interferon may play a modulatory role in local inflammation caused by these bacteria. Our findings also open a new perspective for interferon therapy of certain inflammatory reactions to bacterial infections.