AN INHIBITOR OF VIRAL ACTIVITY APPEARING IN INFECTED CELL CULTURES

Proteolysis of MDA5 and IPS-1 is not required for inhibition of the type I IFN response by poliovirus

BACKGROUND

The type I interferon (IFN) response is a critical component of the innate immune response to infection by RNA viruses and is initiated via recognition of viral nucleic acids by RIG-like receptors (RLR). Engagement of these receptors in the cytoplasm initiates a signal transduction pathway leading to activation of the transcription factors NF-κB, ATF-2 and IRF-3 that coordinately upregulate transcription of type I IFN genes, such as that encoding IFN-β. In this study the impact of poliovirus infection on the type I interferon response has been examined.

METHODS

The type I IFN response was assessed by measuring IFN-β mRNA levels using qRT-PCR and normalizing to levels of β-actin mRNA. The status of host factors involved in activation of the type I IFN response was examined by immunoblot, immunofluorescence microcopy and qRT-PCR.

RESULTS

The results show that poliovirus infection results in induction of very low levels of IFN-β mRNA despite clear activation of NF-κB and ATF-2. In contrast, analysis of IRF-3 revealed no transcriptional induction of an IRF-3-responsive promoter or homodimerization of IRF-3 indicating it is not activated in poliovirus-infected cells. Exposure of poliovirus-infected cells to poly(I:C) results in lower levels of IFN-β mRNA synthesis and IRF-3 activation compared to mock-infected cells. Analysis of MDA-5 and IPS-1 revealed that these components of the RLR pathway were largely intact at times when the type I IFN response was suppressed.

CONCLUSIONS

Collectively, these results demonstrate that poliovirus infection actively suppresses the host type I interferon response by blocking activation of IRF-3 and suggests that this is not mediated by cleavage of MDA-5 or IPS-1.

Plaque Development and Induction of Interferon Synthesis by RMC Poliovirus

Johnson, Terry C. (University of Minnesota, Minneapolis), and Leroy C. McLaren. Plaque development and induction of interferon synthesis by RMC poliovirus. J. Bacteriol. 90:565-570. 1965.-Plaque development by RMC poliovirus on human amnion cell monolayers was investigated with regard to autointerference and to the effect of acid-agar overlay on plaquing efficiency. The virus was inhibited by acid-agar overlay, thereby exhibiting the d(-) marker typical of attenuated poliovirus strains. In addition, a lack of RMC poliovirus plaque development on HeLa cell monolayers was shown to be the result of an agar inhibitor which could be removed by NaCl extraction. By use of a simplified plaque reduction assay, it was shown that interferon production was responsible for the autointerference phenomenon. Interferon synthesis did not correlate with the ages in vitro of human amnion cell cultures. Fibroblasts originating from the chorionic membrane produced negligible amounts of the inhibitor. Interferon synthesis by human amnion cells infected with RMC poliovirus was inhibited by actinomycin D. The addition of guanidine hydrochloride to infected cultures immediately after RMC poliovirus adsorption markedly inhibited interferon synthesis, although after 2 hr (postadsorption) guanidine had no effect on interferon production.

Antiviral susceptibility of Herpes simplex viruses and its clinical correlates: a single center's experience

The in vitro susceptibility to acyclovir of 204 herpes simplex virus isolates from 165 immunocompromised patients treated at our hospital was determined by the cytopathic effect reduction assay. Approximately 95% of herpes simplex virus 1 and 73% of herpes simplex virus 2 isolates were inhibited by acyclovir at concentrations of <2 microgram/mL. From 8 patients (5%), an isolate with low susceptibility to acyclovir (50% inhibitory dose, >3 microgram/mL) was recovered. Medical records of 83 patients were reviewed. Lesions resolved in most of the patients, independent of treatment. Treatment failures were not always associated with isolation of an in vitro-resistant virus. On the contrary, when a virus with low susceptibility to acyclovir was isolated, resolution of the lesion was the rule. In 9 of 10 patients with subsequent recurrent episodes of disease, the susceptibility of the viruses isolated was similar to that of the first episode. Routine susceptibility testing in our geographic area is not encouraged because of the low incidence of acyclovir-resistant herpes simplex viruses.

Differentiation of closely related cells by a variant of poliovirus, type 2, MEF1 strain

By application of a variant of poliovirus, Type 2, MEF₁ strain, as a selective agent it was possible to distinguish among stable parent strains of epithelial cells and their clonal derivatives by their differential morphologic response to infection. The variant of poliovirus grew in a number of cell strains without induction of observable cytopathogenic changes. Other strains of cells reacted to viral infection by manifesting partial or complete degeneration. Parent HeLa cells and virus underwent simultaneous serial propagation in the absence of homotypic antiserum to virus. The stability of the virus-cell relationship was established by results from replicate experiments conducted over a period of years. Some cell strains of common origin maintained in different laboratories did not react similarly to the cytopathogenic effect of virus. Representative experiments revealed that the morphologic response of HeLa cells to MEF virus infection was not influenced by the presence or absence of pleuropneumonia-like organisms. The differential morphologic response of cells to infection was confirmed by efficiency-of-plating experiments which revealed differences in the capacity of MEF virus to form plaques in the test cell strains. Serial passages of MEF virus in cell strains demonstrated differences in their selection for cytopathogenic "mutants" of virus.

The role of interferon in vaccinia virus infection of mouse embryo tissue culture

The production of an interferon-like substance by vaccinia virus is described. The physical properties of vaccinia interferon are shown to be similar to those of previously reported interferons. Data defining the role of vaccinia interferon in cell resistance and in establishment and maintenance of a carrier culture are presented. Elimination of virus from an infected culture is demonstrated and the role of interferon in the recovery process is considered.

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.

Modulation of interferon-gamma receptor during human T lymphocyte alloactivation

Previous work has shown that neutralization of physiologically secreted interferon(IFN)-gamma or blockade of its receptor during T lymphocyte activation inhibits both proliferation and cytotoxic T lymphocyte generation, suggesting that IFN-gamma plays a crucial role in T lymphocyte induction and differentiation. In this study, the kinetics of the surface expression of the 90-kDa IFN-gamma receptor (IFN-gamma R) was followed during human mixed lymphocyte reaction (MLR) to alloantigens. IFN-gamma R mRNA is constitutively expressed on resting peripheral blood lymphocytes emerging from nylon wood column (NW-PBL) and its expression increases two- to threefold on alloactivated NW-PBL. IFN-gamma R protein is poorly expressed on the membrane of resting CD3+ cells, but up-modulates after 3-day MLR and sharply down-modulates at day 6. Both the p55 and the p75 chains of interleukin-2 receptor (IL-2R) were shown to up-modulate in parallel with IFN-gamma R, whereas they were still highly expressed at day 6. After alloactivation, IFN-gamma and IL-2 secretion starts at 24 h, peaks at day 3 and decreases just when IFN-gamma R and IL-2R begin to up-modulate. Proliferation peaks at day 6. Lastly, stimulation with distinct cell populations showed that the intensity of lymphocyte proliferation, IFN-gamma R membrane up-modulation, and IFN-gamma and IL-2 secretion are regulated in a parallel manner, thus suggesting that they are interrelated. Taken as whole these results demonstrate that increased expression of IFN-gamma R on T lymphocytes can be a critical event during their activation, and strongly support the hypothesis that IFN-gamma/IFN-gamma R interaction provides a signal for its progression.

Increased projection of MHC and tumor antigens in murine B16-BL6 melanoma induced by hydrostatic pressure and chemical crosslinking

The B16-BL6 melanoma, like most spontaneously arising tumors, is poorly immunogenic and expresses low levels of major histocompatibility complex (MHC) antigens. Treatment of cells of this tumor in vitro by hydrostatic pressure in the presence of adenosine 2',3'-dialdehyde (oxAdo), a membrane-impermeant crosslinker, caused elevated projection of MHC and a specific tumor antigen as demonstrated by flow-cytometric analysis. Maximum projection of both the MHC and the tumor antigens could be reached by application of 1200 atm for 15 min in the presence of 20 mM oxAdo. It is not yet clear whether this passive increase in availability of antigens on the cell surface originated from a dormant pool of antigens in the plasma membrane or from pressure-induced fusion of antigen-rich intracellular organelles (e.g. the endoplasmic reticulum). The immunogenic properties of the antigen-enriched B16-BL6 cells are described in the following paper.

Treatment of anti-recombinant interferon-alpha 2 antibody positive CML patients with natural interferon-alpha

Of 38 patients with a Philadelphia-chromosome positive chronic myeloid leukaemia treated with recombinant interferon alpha (rIFN-alpha) 2a or 2b and monitored for emergence of IFN-antibodies in their sera 11 patients developed rIFN-alpha 2 binding and 10 rIFN-alpha 2 neutralizing antibodies. rIFN-alpha neutralizing antibody positive patients experienced significantly (P less than 0.025) more clinical relapses (6/10) than IFN-antibody negative patients (6/28) during continuous IFN-therapy. Furthermore, IFN-antibody-positive patients with titre above 400 INU/ml were more likely to relapse under rIFN-alpha-therapy than IFN-antibody-negative patients with titre below 400 INU/ml (P less than 0.05). Seven rIFN-antibody-positive patients experiencing a clinical relapse or a primary non-responsiveness were treated with two- to three-fold increased doses of rIFN-alpha 2. Only one of these seven patients developed a partial haematological remission upon intensification of the rIFN-alpha 2 therapy. Consecutively, the six patients failing high dose rIFN-alpha treatment were switched to a natural IFN-alpha preparation (3 x 9 x 10(6) I.U. weekly s.c.). Under such treatment two of the six patients achieved a long-lasting complete, one a partial haematological remission. In high-titred IFN-antibody positive patients significantly altered serum-IFN-titre and minimal IFN-inducible Mx-homologue concentrations were measured; in contrast, nIFN-alpha induced normal IFN-titre and dose-equivalent Mx-homologue amounts in these patients. The data prove that high-titred rIFN-alpha neutralizing antibodies abrogate the biological action of rIFN-alpha, but not of nIFN-alpha in vivo and explains why nIFN-alpha can be effective in the anti rIFN-alpha 2 positive patients.

The human intracellular Mx-homologous protein is specifically induced by type I interferons

The murine Mx-1 protein is one of the best biochemically and functionally characterized interferon (IFN)-induced proteins that is necessary, and sufficient, for providing resistance to murine cells against viral influenza infection. Recently an intracellular human protein homologous to the murine Mx-1 protein has been identified by means of a specific monoclonal antibody. The restricted induction of this intracellular protein in human mononuclear cells (MNC) by various cytokines was investigated. MNC from 26 of 28 healthy people and 35 of 36 cancer patients before IFN-alpha therapy had no detectable Mx-homologous protein. Incubation of human MNC with IFN-alpha and IFN-beta for 24 h at different concentrations led to a dose-dependent induction of the Mx-homologous protein. All IFN-alpha or IFN-beta preparations tested were equally effective in eliciting this intracellular protein. IFN-gamma induced only 1% of the Mx amount elicited by type-1 IFN compared on a weight basis. Neither interleukin (IL) 1 nor IL3, IL4, IL5, IL6, tumor necrosis factor-alpha/beta, granulocyte colony-stimulating factor (CSF) or granulocyte macrophage-CSF at any of the concentrations tested were capable of eliciting any detectable amount of the Mx homolog, while IL2 was a poor Mx-homologous protein inducer. In the presence of high-titered IFN-alpha antisera both IL2 and IFN-gamma were unable to stimulate this protein, proving that IFN-gamma and IL2 indirectly induce the Mx homolog via IFN-alpha. Therefore, the human Mx-homologous protein is a strictly by type I IFN-regulated protein in human peripheral blood lymphocytes.

Recombinant human interferon (IFN) alpha-2b in chronic myelogenous leukaemia: dose dependency of response and frequency of neutralizing anti-interferon antibodies

Twenty-seven patients with Philadelphia chromosome positive chronic myelogenous leukaemia in the chronic phase were treated with low doses of recombinant interferon (IFN) alpha-2b. Ten patients entered a complete and six a partial haematologic remission with a median duration of 5.8 and 9.1 months respectively. Five minor cytogenetic responses were observed. These results are inferior compared to other studies with higher interferon-doses. Fever was an acute side effect after injection of IFN, limb pains and fatigue occurred protractedly. Haematologic side effects, nonspecific EEG changes, weight loss, and development of pulmonary infiltrates were observed in later periods of the treatment. Eight patients developed neutralizing anti-IFN antibodies after 4.2-20.4 months (median 12.8 months). Anti-IFN antibodies were associated with relapse or refractoriness to IFN treatment: five out of nine patients with rising WBC after initial fall had antibodies, while four did not. Two out of four patients with primary non-response had IFN-antibodies. These results may indicate a serious problem in the long-term treatment of CML with recombinant interferon.

Some recombinant human cytokines stimulate glycosaminoglycan synthesis in human synovial fibroblast cultures and inhibit it in human articular cartilage cultures

Recombinant human cytokines were compared for their effects on glycosaminoglycan (GAG) synthesis in human synovial fibroblast cultures and human articular cartilage explant cultures. In fibroblast cultures, recombinant human interleukin-1 alpha (rHuIL-1 alpha), rHuIL-1 beta, and recombinant human tumor necrosis factor alpha (rHuTNF alpha) stimulated hyaluronic acid (HA) production and, to a lesser extent, sulfated GAG production, while recombinant human gamma-interferon did not have a significant effect. Half-maximal stimulation of HA by rHuIL-1 beta was 0.14 pM, while stimulation for rHuIL-1 alpha and rHuTNF alpha was 1.6 pM and 32 pM, respectively. Indomethacin (10 micrograms/ml) had no influence on HA stimulation by cytokines, while hydrocortisone (2-10 micrograms/ml) caused a significant reduction. In articular cartilage cultures, the cytokines inhibited production of sulfated GAGs. The activity of rHuIL-1 beta was greater than that of rHuIL-1 alpha (half-maximal inhibition at 0.71 pM and 4.7 pM, respectively) and both were considerably more active than rHuTNF alpha; gamma-interferon again had no significant effect. Neither indomethacin nor hydrocortisone influenced cytokine-induced inhibition by either rHuIL-1 preparation. These studies indicate that cytokines released during an inflammatory process may affect GAG synthesis in human joint tissues and may have opposite effects on GAG synthesis in different types of connective tissues.

Presence of interferon and anti-interferon in patients with systemic lupus erythematosus

Sera from 61 patients with systemic lupus erythematosus (SLE) were serially screened over a period of at least 2 years for IFN and anti-IFN antibodies. IFN concentrations were measured both with a cytopathic effect assay and a more sensitive radioimmunoassay. Of the patients 15% (9/61) had IFN in their serum at one or more occasions as measured in the bioassay (greater than or equal to 6 IU/ml); employing a RIA (greater than or equal to 1 IU/ml) 28% (17/61) of the patients studied were positive for IFN-alpha. Fifteen patients had a measurable interferonemia over 2-16 months; only two patients had detectable IFN in their serum at only one occasion. In five patients, hourly and daily variations of the IFN titer as measured by RIA were found to amount to less than 80%. The IFN activity found in these sera was characterized as IFN-alpha by means of acid stability, cross-reactivity on heterologous cells, trypsin sensitivity, and neutralization by homologous and heterologous antisera. IFN antibodies were quantified with a neutralization bioassay, an ELISA, and a radioimmunoassay. Of the 61 patients 5% (3) possessed high titers of anti-IFN antibodies which persisted over 2 years. The IFN-alpha antibody positive patients had an inactive form of the disease over years without visceral involvement but decreased serum complement levels (C4, C3, CH50) and repeated episodes of Quincke-like edema.

Induction of human gamma interferon by Sarcophaga peregrina humoral lectin

Humoral lectin isolated from the hemolymph of injured Sarcophaga peregrina (flesh-fly) larvae was found to activate human peripheral blood cells to produce interferon activity. This interferon was inactivated by dialysis against a solution of pH 2.0 and by heat treatment at 56 degrees C for 30 min, indicating that it was a gamma interferon. The role of this lectin in the defence mechanism is discussed from the viewpoint of comparative immunology.

Interferon-mediated inhibition of virus penetration

Pretreatment of mouse L cells with mouse interferon (IFN) inhibits the penetration of vesicular stomatitis virus without affecting viral adsorption. The inhibition of virus uptake by IFN is dose dependent and, at the highest dose tested (1,000 units/ml), reaches 65%; 24 hr of treatment with IFN are required for maximal effect. A similar inhibition of uptake of virus occurs in human diploid fibroblasts and primary chicken embryo fibroblasts treated with homologous IFN. No significant inhibition occurs when cells are treated with heterologous IFN. These results document a previously unrecognized antiviral effect of IFN--namely, inhibition at the level of viral uptake.

Expression of the human fibroblast interferon gene in Escherichia coli

We applied the method of Guarente et al. [Guarente, L., Lauer, G., Roberts, T.M. & Ptashne, M. (1980) Cell 20, 543-553] to construct plasmids that direct expression in Escherichia coli of the human fibroblast interferon (F-IF) gene. Two plasmids were recovered. One directs efficient synthesis of a protein whose primary sequence is that of pre-F-IF and the other, that of mature F-IF. Extracts of bacteria synthesizing mature F-IF display antiviral activity characteristic of human F-IF. This activity is lower than that expected from the differential rate of synthesis of the protein. We have detected no such activity in extracts of bacteria synthesizing pre-F-IF.