Biological studies of interferon

Sensitivity of FCV to recombinant feline interferon (rFeIFN)

Feline calicivirus cause feline respiratory diseases, and inactivated and attenuated vaccines are available for its prevention. Moreover, the presence of vaccine breakdown strains (VBS) is problematic. In Japan, feline recombinant interferon (rFeIFN) has been used for its treatment. However the method of compare with each strains has not established. To examine the relationship between the breakdown vaccine strain and rFeIFN sensitivity, the sensitivity of 47 field isolates to rFeIFN was determined. The Log PDD(50) values were normally distributed within the range 1.1-3.7, with a mean value of 2.3 +/- 0.64. Since 68.3% of the PDD values fell in the range of the mean +/- standard deviation, the values in the range 1.7-2.9, the lower values, and the higher values were defined as representing moderate, low, and high sensitivity, respectively. Among the 15 vaccine breakdown strains, strain Fukuoka9 showed a low sensitivity, but strains ML89, T58, and N74 were highly sensitive, showing no association with vaccine breakdown. The amino acid sequence changes specific to the low rFeIFN-sensitive Fukuoka-9 strain were found, suggesting that these sites are involved in rFeIFN sensitivity.

Interference between viable strains of Newcastle disease virus

Durand, D. P. (University of Missouri, Columbia). Interference between viable strains of Newcastle disease virus. J. Bacteriol. 82:979-983. 1961.-Strains of Newcastle disease virus (NDV) which differed in their ability to produce plaques on monolayers of chicken embryo cells were studied during conditions of dual infection. Interference with NDV plaque formation by a nonplaque-forming NDV strain was observed. The primary mechanism involved with this type of interference appears to be due to the viable infectious virus, and is not associated with interferon production or the hemagglutinin of NDV.

Assay of interferon activity

At present there is a lack of standard criteria for the identification and evaluation of activity of antiviral compounds. Interferon was used to explore comparatively several laboratory methods. Interferon was produced in chick embryos and in chorioallantoic membranes suspended in vitro. Evaluation of interferon activity was performed by several methods: (i) percentage of inhibition of plaque-forming units; (ii) hemagglutinin reduction of challenge virus; (iii) titer of cytopathic effect of challenge virus; and (iv) plaque-inhibition test. The suggested methods for measurement are those which express the titer of challenge virus in plaque-forming units or in hemagglutinating units.

PRODUCTION OF AN INTERFERON BY L CELLS INFECTED WITH WESTERN EQUINE ENCEPHALOMYELITIS VIRUS

Lockart, Royce Z., Jr. (The University of Texas, Austin). Production of an interferon by L cells infected with Western equine encephalomyelitis virus. J. Bacteriol. 85:556-566. 1963.-Two strains of Western equine encephalomyelitis virus (WEE), WEE (L+) and WEE (L-), which differed with respect to their cytopathogenicity for L cells were isolated. Both strains reproduced in L cells, and both induced the production of an interferon distinct from virus particles. L-cell monolayers were protected from degeneration by prior addition of interferon. By use of the absence of cytopathic effects (CPE) as an end point, interferon content was assayed. Monolayers failing to show CPE consistently produced less than 2% as much virus as control monolayers, indicating that virus synthesis was also inhibited. The use of this assay method was facilitated by the use of horse serum that appeared to contain antibodies against WEE and that permitted interferon to act selectively in the presence of active virus. It was found that interferon was produced during the time in which active virus was produced, and not significantly later. No interferon could be found in fluids from cells treated with inactive virus, although these are known to act as interfering agents. Interferon production was inhibited by pretreatment of L cells with sufficient amounts of interferon. It is concluded that interferon production is closely connected with WEE virus synthesis in L cells. The question is raised as to whether interferon need be a necessary intermediate for interference in L cells.

CIRCULATING INTERFERON IN MICE AFTER INTRAVENOUS INJECTION OF VIRUS

Circulating interferon was detectable in mouse serum within 1 hour after the intravenous injection of various types of virus and it reached maximum levels in about 4 hours. Rapidly produced interferon may play a role in the pathogenesis of viral infection and in viral interference.

INTERFERON PRODUCTION AND SENSITIVITY OF SEMLIKI FOREST VIRUS VARIANTS

Semliki Forest virus was passaged 10 times in series in calf kindly cells, starting with virus passaged in the mouse brain (MB virus). A variant was obtained (termed CK virus). The two viruses were antigenically indistinguishable. When grown on L cells, CK virus formed smaller plaques than MB virus. In parallel growth curve studies in calf kidney cells, a small inoculum of CK virus grew more rapidly and to a higher final titre than a comparable inoculum of MB virus, and usually stimulated production of less interferon. Pre-treatment of cells with calf interferon reduced the growth of both viruses, but especially that of MB virus. The results are considered in relation to the phenomenon of virus adaptation. It is suggested that such differences between the two variants in their relative sensitivity to and production of interferon could have played a part in the emergence of CK virus as the predominant type during serial passages in calf cells.

I wish to thank Mr H. Moores and Mr R. Sims for skilful technical assistance.

Poxvirus pathogenesis

Poxviruses are a highly successful family of pathogens, with variola virus, the causative agent of smallpox, being the most notable member. Poxviruses are unique among animal viruses in several respects. First, owing to the cytoplasmic site of virus replication, the virus encodes many enzymes required either for macromolecular precursor pool regulation or for biosynthetic processes. Second, these viruses have a very complex morphogenesis, which involves the de novo synthesis of virus-specific membranes and inclusion bodies. Third, and perhaps most surprising of all, the genomes of these viruses encode many proteins which interact with host processes at both the cellular and systemic levels. For example, a viral homolog of epidermal growth factor is active in vaccinia virus infections of cultured cells, rabbits, and mice. At least five virus proteins with homology to the serine protease inhibitor family have been identified and one, a 38-kDa protein encoded by cowpox virus, is thought to block a host pathway for generating a chemotactic substance. Finally, a protein which has homology with complement components interferes with the activation of the classical complement pathway. Poxviruses infect their hosts by all possible routes: through the skin by mechanical means (e.g., molluscum contagiosum infections of humans), via the respiratory tract (e.g., variola virus infections of humans), or by the oral route (e.g., ectromelia virus infection of the mouse). Poxvirus infections, in general, are acute, with no strong evidence for latent, persistent, or chronic infections. They can be localized or systemic. Ectromelia virus infection of the laboratory mouse can be systemic but inapparent with no mortality and little morbidity, or highly lethal with death in 10 days. On the other hand, molluscum contagiosum virus replicates only in the stratum spinosum of the human epidermis, with little or no involvement of the dermis, and does not spread systemically from the site of infection. The host response to infection is progressive and multifactorial. Early in the infection process, interferons, the alternative pathway of complement activation, inflammatory cells, and natural killer cells may contribute to slowing the spread of the infection. The cell-mediated response involving learned cytotoxic T lymphocytes and delayed-type hypersensitivity components appears to be the most important in recovery from infection. A significant role for specific antiviral antibody and antibody-dependent cell-mediated cytotoxicity has yet to be demonstrated in recovery from a primary infection, but these responses are thought to be important in preventing reinfection.

Protective effect of recombinant murine interferon beta against mouse hepatitis virus infection

Recombinant murine interferon beta (rMuIFN-beta) protected susceptible C57BL/6 mice against lethal mouse hepatitis virus (MHV) infection. rMuIFN-beta was life saving if it was given intraperitoneally beginning 21 h before infection and daily thereafter for 9 days, and lengthened the survival time if given from 3 h after infection. rMuIFN-beta treatment beginning 24 h after infection was ineffective. The survival rate was dose-dependent, and the 50% effective dose of rMuIFN-beta for survival was 1780 IU per day. rMuIFN-beta pretreatment inhibited virus growth completely in the brain and moderately in the liver and spleen and prevented severe hepatic lesions. rMuIFN-beta also protected beige mice and cyclophosphamide-treated mice against MHV infection, suggesting that activation of natural killer cells or T-cells by rMuIFN-beta is not critical for protection.

Inactivation by polymyxin B of the endotoxin-mediated interferon production in the rabbit

Polymyxin B (PB) completely or at least significantly inhibited the capacity of Shigella dysenteriae 1 cells and the lipopolysaccharide (LPS) and lipid A (LA) subunits of several bacterial endotoxins to induce interferon (IFN) in rabbits. Animals injected with LPS inactivated by PB to the point of not inducing detectable IFN levels did not develop hyporesponsiveness to secondary IFN induction by a homologous inducer. It was concluded that PB inhibits the IFN-inducing capacity of endotoxin and its subunits as a consequence of binding to the LA-moiety of LPS. The results confirmed the exclusive role of LA as the only IFN-inducing component of Gram-negative bacterial endotoxin.

Comparison of three bioassays for rat interferon

Compared to the well-characterized murine and human interferons, few studies have been conducted on rat interferons. In the present study, we compared three rat interferon bioassays: a plaque-reduction method, a hemagglutination yield-reduction method, and a method involving reduction in viral cytopathic effect. These methods were evaluated in order to better assay rat interferons and thus facilitate investigations to determine the antiviral, antitumor, and immunoregulatory role of interferon in existing rat model systems. Each method has certain desirable characteristics; the choice of bioassay depends on the specific application required. Overall, the reduction in viral cytopathic effect bioassay combines most of the desired features of a rat interferon bioassay including sensitivity, precision, convenience, rapidity, and economy.

An immunoenzyme quantitative assay for the antiviral effect of interferons

A technique is described for measurement of the antiviral activity of interferon by an immunoenzymatic assay for viral proteins. Cells treated by tested samples of interferon (IFN) are infected with vesicular stomatitis virus (VSV) and following the development of viral cytopathy are lysed by the addition of deoxycholate and then transferred into ELISA microplates. The viral proteins bind effectively to the microplates proportionally to their level in the culture and may be measured by incubating the plates sequentially with (1) rabbit antiserum against VSV, (2) a conjugate of alkaline phosphatase either to protein A or to an antibody against rabbit IgG and (3) p-nitrophenylphosphate. This procedure may be further simplified by using antibodies against VSV to which alkaline phosphatase has been directly conjugated. We found this immunoenzyme assay to be superior to the 'cytopathic effect inhibition' assay in precision and sensitivity and in being independent of the effectiveness of viral cytopathy.

A study showing a high degree of interlaboratory variation in the assay of human interferon

Identical human fibroblast interferon samples were assayed in four different laboratories, in all of which the international reference standards were used. Up to tenfold differences in titer were observed between the laboratories. Differences of this magnitude make meaningful comparisons of clinical and other interferon studies difficult and clearly indicate the need for an internationally accepted standardized interferon assay system.

Activation of macrophages for microbicidal and tumoricidal effector functions by soluble factors from EL-4, a continuous T cell line

Macrophages treated with culture fluids from EL-4 cells, a continuous T cell line, were activated to kill mKSA-TU-5 fibrosarcoma cells, amastigotes of Leishmania tropica, and schistosomula of Schistosoma mansoni. Active EL-4 factors eluted from Sephadex G-100 in two distinct regions: molecular weight 45,000 (activities induced killing of unrelated intracellular and extracellular targets) and molecular weight 23,000 (activities induced killing of extracellular targets only). These results confirm heterogeneity among activation signals for the induction of macrophage microbicidal and tumoricidal activities. Factors that induced cytocidal activity against extracellular tumor cells and schistosomula were distinct from those that induced destruction of intracellular amastigotes.

Antitumour activity of endotoxin, concanavalin A and poly I: C and their ability to elicit tumour necrosis factor, cytostatic factors, and interferon in vivo

Concanavalin A, endotoxin, poly I: C, and tumour necrosis serum (TNS) were compared for antitumour activity against Meth A sarcoma transplanted in syngeneic BALB/c mice and their capacity to induce tumour necrosis factor (TNF), heat-stable cytostatic factors, and heat-labile interferon in the blood of normal and Corynebacterium parvum-pretreated mice. All the agents induced hyperemia and inhibition of mitosis at 4 h, and by 24 h many tumours had a dark necrotic centre. Subsequent tumour growth was inhibited and in some of the treated mice tumours regressed completely. Poly A: U and normal mouse serum did not induce regression and their effects were less marked in all other respects, suggesting that these events may be linked. The necrotizing effects of concanavalin A and poly I: C are unlikely to be mediated by TNF, because neither agent could mimic endotoxin in eliciting RNase-resistant necrotizing and regressing activity in the serum of mice pretreated with C. parvum. Poly I: C did not induce strong cytostatic activity in the sera of C. parvum-treated mice, and for this and other reasons these factors are unlikely to be responsible for the observed effects. Concanavalin A, endotoxin, and poly I: C induced high levels of serum interferon but purified interferon had only weak antitumour activity in the Meth A system, suggesting that interferon may not be the mediator. From these and other data it is concluded that there is no clear relationship between the capacity of the agents to induce tumour necrosis and their capacity to elicit TNF, cytostatic factors, and interferon.

Effects of various coryneforms on mononuclear phagocyte system function and on production of tumour necrosis factor in mice

Vaccines of 6 strains of the genera Corynebacterium and Propionibacterium were tested for induction of hepatosplenomegaly and stimulation of clearance of injected colloidal carbon and viable Listeria monocytogenes. These effects were compared with the ability of these strains to support the endotoxin-induced liberation of tumour necrosis factor, interferon and heat-stable cytostatic factors in mouse circulation. Five strains caused good stimulation of macrophage functions and induced high levels of all factors. One strain was nearly lacking in macrophage stimulatory capacity and also failed to support factor production. These data are discussed in relation to the production mechanisms of the factors.

Improved conditions for the production and detection of interferon from guinea pig embryo cells

Primary guinea pig embryo (GPE) fibroblasts were assessed as potential sources of guinea pig interferon (IFN). GPE cells proved to be excellent in vitro producers of guinea pig IFN, although the actual amounts produced were only detectable when sample irradiation under ultraviolet light (to inactivate inducing viruses) was substituted for overnight sample treatment at pH 2. Thus, the rapid spontaneous inactivation of large proportion of the antiviral activity after overnight exposure to 4 degrees C, regardless of pH, was avoided. IFN was induced using Newcastle disease virus (NDV), Sindbis virus, and a genetic variant of vesicular stomatitis virus, VSV T1026R1. Each virus exhibited different dose response kinetics, with VSV T1026R1 proving the most efficient inducer of the three. Optimal IFN production depended largely on virus multiplicity and cell age. All the antiviral activity produced by GPE fibroblasts had the classical properties of species specificity, susceptibility to trypsin, and a broad range of antiviral activity.

Regulation of murine macrophage Ia antigen expression by a lymphokine with immune interferon activity

A culture supernatant of concanavalin A-activated spleen cells (Con A supernatant) induced murine macrophages to express Ia antigens in vitro. Biochemical characterization of the Con A supernatant indicated that the macrophage Ia antigen regulatory activity shares molecular weight, pI, and hydrophobic and affinity characteristics with immune interferon (IFN-gamma). Antiserum to mouse IFN-gamma neutralized both the macrophage Ia antigen regulatory and IFN-gamma bioactivities of the Con A supernatant. Furthermore, both partially purified murine IFN-gamma (10(7) U/mg protein sp act) and IFN-containing culture supernatants of the murine BFS T cell line-induced macrophage Ia antigen expression in vitro. Culture supernatants containing colony-stimulating factor, interleukin 1, interleukin 2, macrophage migration inhibitory factor, and a macrophage-activating activity that were distinct from IFN-gamma did not induce macrophage Ia antigen expression. Taken together, the data indicate that the in vitro expression of Ia antigens on macrophages is regulated by an activity that has the characteristics of interferon.

Production of immune interferon by an interleukin 2-independent murine T cell line

An interleukin 2-independent murine T cell line (BFS) was isolated that produced immune interferon after stimulation with phorbol 12-myristate 13-acetate. The BFS cell line did not produce detectable levels of interleukin 1, interleukin 2, B cell growth factor, macrophage-granulocyte colony-stimulating factor, macrophage-activating factor, or T cell replacing factor. Maximal interferon was induced 48 hr after stimulation with phorbol myristate acetate at 10-100 ng/ml. Production of interferon by phorbol myristate acetate-stimulated BFS cell cultures was synergistically increased by the addition of EL4 thymoma cell culture supernatants. BFS-derived interferon activity was sensitive to pH 2 treatment and was neutralized with antiserum to immune interferon but was resistant to heating at 56 degrees C and to treatment with antiserum to type I interferon. In addition, the interferon activity was sensitive to trypsin but resistant to RNase. BFS-derived interferon had an apparent molecular weight of 48,000 and a pI of 5.5-6.0. Each of these properties is consistent with the conclusion that the BFS cell line produces immune interferon after stimulation with phorbol myristate acetate.

Radioactive human lymphoblastoid interferon. One-step purification, regulation of heterogeneous species production and its use for radioimmunoassay

Human lymphoblastoid interferon (alpha type), labeled with [3H]leucine added to virus-induced Namalwa cells, was purified quantitatively and in one step from the culture fluid by immune precipitation. The material showed, upon polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, only four radioactive bands with molecular weights ranging from 17000 to 21000, which coincided well with interferon activity. They coincided also with the four interferon protein bands in the electropherogram of unlabeled interferon purified by a different method. The purity of the labeled interferon was ascertained also by polyacrylamide gel electrophoresis in the absence of dodecyl sulfate. Pulse-labeling of interferon with [3H]leucine for 1 h at various times after induction indicated that the cells always synthesized and secreted the four interferon species in parallel during the interferon production period. Competitive radioimmunoassay for human interferon alpha was achieved by the use of purified radioactive interferon, anti-(interferon alpha) serum, and bacterial adsorbent. The immune precipitation of the labeled interferon was inhibited by unlabeled interferon alpha, and 100 international reference units of interferon alpha could be measured in this way.

Dual role of the immune response in street rabiesvirus infection of mice

The cellular and humoral immune responses of mice to footpad injection of salivary gland suspensions of street rabiesvirus were investigated. Suppression of these responses with cyclophosphamide both increased the overall mortality rate from (50 to 100%) and delayed onset of disease signs and death for 1 to 2 weeks. Despite the absence of disease signs in these immunosuppressed animals, virus was present in the central nervous system, as shown by fluorescent-antibody staining of corneal epithelium. The onset of paralysis after limited immunosuppression was temporally related to a return to immune responsiveness, and passive transfer of homologous immune serum to infected immunosuppressed animals brought about their early paralysis and death. These findings indicate the importance of the immune response in the pathogenesis of street rabiesvirus infection.

Endotoxin-induced release of tumour necrosis factor and interferon in vivo is inhibited by prior adrenoceptor blockade

The effect of alpha- and beta-adrenoceptor blocking agents on endotoxin-induced release of tumour necrosis factor (TNF), and of interferon in the circulation of Corynebacterium parvum-treated mice was the subject of this study. TNF was quantified after injection of TNF containing heated serum (TNS) into Meth A sarcoma-bearing mice by determining colour, extent, and incidence of haemorrhagic necrosis. The release of TNF was weakly inhibited by the competitive alpha-blocker phentolamine and the beta-blocker propranolol. The non-competitive alpha-blocker phenoxybenzamine inhibited to a higher degree. Endotoxin-induced elicitation of growth-inhibiting principles into TNS was antagonized by propranolol and phenoxybenzamine. Administration of adrenaline before endotoxin inhibited the elicitation of TNF and growth-inhibitory activities, which indicates tachyphylaxis. The release of interferon was effectively inhibited by both alpha-adrenoceptor blockers but not by propranolol. The interferon was heat-labile. The results indicate that endotoxin-induced TNF and interferon are separate factors, elicited in different ways. As both alpha-blockers do not only inhibit reactions at the alpha-adrenergic receptor but also reactions at the serotonin receptor and in the case of phenoxybenzamine also at the choline receptor, it is suggested that endotoxin-induced release of the anti-tumour factors is controlled by reactions mediated by one or more of these receptors. It is suggested that the inhibition of TNF release by propranolol may be due to the membrane-stabilizing activity of this agent.

Interferon assay

Interferon was discovered by virologists and its activity is defined in virological terms. In spite of the more recent discovery of a multitude of non-antiviral effects its activity is best assayed in terms of the antiviral effect at least until immunoassays are developed to measure, specifically, the different types of interferon. From an overview of the qualities of the 3 major varieties of assay system it is suggested that for most immunological purposes a virus-plaque-reduction type of assay is likely to be the most suitable. Points of importance regarding reference standards, the choice of a cell/virus system, criteria for acceptance of a virus inhibitor as interferon and the handling and storage of interferon preparations are briefly reviewed.

Mouse model for abortive rabies infection of the central nervous system

When adult mice were injected by the footpad route with the attenuated rabies virus ERA/BHK, serum- and brain-associated antibody and interferon were produced, nonspecific cytotoxic cells and virus-specific cytolytic T cells in the spleen were activated, and a nonlethal infection of the central nervous system occurred. Cyclophosphamide treatment of these animals 1 day after virus infection suppressed antibody formation and induction of cytolytic T cells and resulted in a lethal infection. Virus injection into athymic mice also produced lethal infections. This indicated the importance of the T-cell response in survival but did not allow the response of cytolytic T cells to be distinguished from that of helper T cells. because cyclophosphamide has a longer-lasting effect on B cells than on T cells, the resulting mortality when virus is injected at intervals after cyclophosphamide treatment can be used to distinguish the importance of each of these cells in viral clearance. Although delay of rabies virus ERA/BHK injection until 3 days after cyclophosphamide treatment resulted in induction of a strong cytolytic T-cell response and reduced mortality, the mortality could be further reduced by delaying virus infection until the B-cell response had recovered. This indicated that both humoral and cellular immune components were vital for survival in this model.

The viral diseases of fish: a review through 1978. Part 1: Diseases of proven viral etiology

In this review, a survey is made of the published literature on the viral diseases of fish available up to and including the year 1978. It is divided into two main sections. Part 1 describes 11 diseases where a virus has been isolated and proven to be the causative agent. Part 2 discusses 16 diseases where there is reason to suspect viral etiology because of evidence deriving from electron microscopy or transmission experiments with bacteria-free filtrates of homogenates of diseased tissue, but where final proof of a causative relationship is lacking. The review attempts to provide the most significant information on the disease process itself, in most cases including external signs, fish species susceptible, pathology, geographic distribution, existence of carriers, methods of transmission, and control. It also gives the most recent and significant data concerning the nature of the causative virus, including its cultural, biological, and physicochemical properties, where such information is available.