Vesicular stomatitis virus plaque production in monolayer cultures with liquid overlay medium: description and adaptation to a one-day, human interferon-plaque

Structural basis for inhibition of the drug efflux pump NorA from Staphylococcus aureus

Membrane protein efflux pumps confer antibiotic resistance by extruding structurally distinct compounds and lowering their intracellular concentration. Yet, there are no clinically approved drugs to inhibit efflux pumps, which would potentiate the efficacy of existing antibiotics rendered ineffective by drug efflux. Here we identified synthetic antigen-binding fragments (Fabs) that inhibit the quinolone transporter NorA from methicillin-resistant Staphylococcus aureus (MRSA). Structures of two NorA-Fab complexes determined using cryo-electron microscopy reveal a Fab loop deeply inserted in the substrate-binding pocket of NorA. An arginine residue on this loop interacts with two neighboring aspartate and glutamate residues essential for NorA-mediated antibiotic resistance in MRSA. Peptide mimics of the Fab loop inhibit NorA with submicromolar potency and ablate MRSA growth in combination with the antibiotic norfloxacin. These findings establish a class of peptide inhibitors that block antibiotic efflux in MRSA by targeting indispensable residues in NorA without the need for membrane permeability.

A direct high-throughput in Cell-ELISA for measuring infectivity of cytopathic and non-cytopathic bovine viral diarrhoea virus strains applied to the assessment of antiviral activity

Low-cost high-throughput methods applicable to any virus strain are required for screening antiviral compounds against multiple field strains. Colorimetric cell-viability assays are used for this purpose as long as the viruses are cytopathic (CP) in cell culture. However, bovine viral diarrhoea virus (BVDV) strains circulating in the field are mostly non-cytopathic (NCP). An In Cell-ELISA aimed to measure viral infectivity by detecting a conserved protein produced during viral replication (non-structural protein 3, "NS3") was developed. The ELISA is performed without harvesting the cells, directly on the 96-wells culture plate. NS3 In Cell-ELISA was tested for its ability to assess BVDV-specific antiviral activity of recombinant bovine type I and III IFNs. Results correlated to those measured by qRT-PCR and virus titration. NS3 In Cell-ELISA was also efficient in estimating the IC50 of two compounds with different antiviral activity. Estimation of the 50% inhibition dose of each IFN using six BVDV strains of different biotype and genotype showed that CP strains were more susceptible to both IFNs than NCP, while type 2 NCP viruses were more sensitive to IFN-I. The In Cell-ELISA format using a detector antibody against a conserved non-structural protein can be potentially applied to accurately measure infectivity of any viral strain.

Human keratinocytes and epidermoid carcinoma cell lines produce a cytokine with interleukin 3-like activity

Keratinocytes are capable of releasing distinct immunomodulating cytokines such as epidermal cell-derived thymocyte activating factor (ETAF) and an epidermal cell-derived natural killer cell augmenting factor (ENKAF). The present study was performed to determine whether human keratinocytes also may secrete an interleukin 3 (IL-3)-like mediator and thereby participate in the regulation of mast cell activity in the skin. Supernatants of freshly isolated human epidermal cells (EC) and malignant keratinocyte cell lines (A 431, SCC) were tested for their capacity to induce the proliferation of IL-3-dependent cell lines 32 DCL and FDCP. Human epidermal cell interleukin 3 (EC IL-3) is spontaneously released by freshly isolated EC, A 431, and squamous cell carcinoma (SCC) cells. However, both normal EC and A 431 cells produced increased levels of EC IL-3 activity when cultured in the presence of different stimulants, such as phorbol myristate acetate and lipopolysaccharide. The EC IL-3 activity was not inhibited when treated with a monoclonal anti-IL-1 or anti-IL-2-antibody. Biochemical characterization showed that human EC IL-3 has a molecular weight of 17K, elutes of DEAE-ion exchange high-performance liquid chromatography (HPLC) as one major peak at 0.36 M NaCl, and upon HPLC-chromatofocusing exhibits 3 isoelectric points of 7.8, 7.5, and 5.6. Upon reversed-phase HPLC, EC IL-3 activity eluted at about 100% acetonitrile. When highly purified EC IL-3 was labeled with 125I and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, a single homogeneous band exhibiting a molecular weight of 17K was seen, which correlated with the IL-3 activity and was free of ETAF/IL-1, IL-2, and interferon activity. These data indicate that human EC synthesize an IL-3-like cytokine which is distinct from ETAF/IL-1, IL-2, and interferon and thereby may participate in the regulation of mast cell activity during inflammatory and fibrotic, as well as hypersensitivity reactions.

Unusual monocyte-lymphocyte interactions determine the specificity of the immune-specific interferon response induced by Newcastle disease and herpes simplex viruses

Virus-induced immune-specific interferon (IS-IFN) is produced by previously sensitized peripheral blood mononuclear leukocytes (PBML) three to five days after they are placed in tissue culture. This IS-IFN is readily identified on the basis of its time of production and its synergistic composition of alpha and gamma interferons. The current studies demonstrate that circulating monocytes control the specificity and magnitude of the IS-IFN response. No IS-IFN is produced by PBML that are heavily depleted of monocytes. Immune-specific IFN production is enhanced in PBML cultures that are partially depleted of monocytes. Partial monocyte depletion permits virus to induce the production of IS-IFN by unsensitized PBML.

Immunostimulatory function of herpes simplex virus isolates from patients with frequent herpes labialis and a deficiency in immune-specific interferon production

Approximately 30% of persons with frequent episodes of herpes labialis are deficient in the production of HSV-induced immune-specific interferon (IFN) (Green, 1985). Herpes simplex virus (HSV) strains isolated from persons who make immune-specific IFN and from persons who do not make it were examined for their immunostimulatory capabilities. HSV isolated from the primary oral lesions of two patients deficient in immune-specific IFN production, one person with an intact immune-specific IFN response, HSV types 1 and 2 laboratory strains, and Newcastle disease virus (NDV) were added to cultures of peripheral blood mononuclear cells (PBML) from HSV seropositive donors. All HSV-isolates induced comparable titers of immune-specific IFN. These studies suggest that failure of some patients to develop an immune-specific IFN response is determined by the host, not the virus.

Immune-specific interferon production by peripheral blood mononuclear leukocytes from patients with primary and recurrent oro-labial herpes simplex virus infections

Immune-specific IFN (IFN) is produced by the peripheral blood mononuclear leukocytes (PBML) of greater than 95% of HSV-seropositive humans with infrequent recurrences of herpes labialis [Green, Yeh, and Overall, 1981]. However, herpes virus-induced immune-specific IFN was produced by PBML from only 33 of 48 (68.8%) persons with frequent recurrences (2-12 episodes a year). Two of eight subjects with primary herpes gingivostomatitis also failed to produce immune-specific IFN during either the acute or convalescent phases of their initial HSV infection. These data suggest that some persons have a defective immune-specific IFN response that exists from the time of their primary oro-labial HSV type 1 infection. This defect may predispose to a higher frequency of disease in some individuals.

Convenient assay for interferons

A convenient assay for interferons based on reduction of cytopathic effect was developed. The number of manipulations and the lengths of the various incubation steps were reduced to a minimum. The assay is simple to perform and can be completed within 16 h. Moreover, it can be used with various types of cells and a variety of viruses.

Rapid, quantitative, semiautomated assay for virus-induced and immune human interferons

An improved human interferon (IF) assay is described. This procedure is based on the ability of encephalomyocarditis virus to replicate in WISH cell microcultures with the production of discrete plaques in the presence of a liquid tissue culture medium. Performance of 50% plaque reduction endpoint assays in micro-culture required only 0.1 ml of specimen for determinations using duplicate dilutions beginning at 1:3. Semiautomated equipment facilitated simultaneous in situ dilution and distribution of multiple IF samples in cultures containing preformed WISH cell monolayers. An incubation period of 5 to 6 h was adequate for development of maximal antiviral activity by both virus- and immune-induced IF. Sensitivity of the encephalomyocarditis microplaque reduction assay was comparable to that of other commonly used techniques. The method is rapid, can be completed within 30 h from the beginning of the IF assay, and is able to accommodate as many as 40 to 50 samples at a single time. Encephalomyocarditis microplaque reduction is suitable for the quantitation of IF as an antiviral agent or a lymphokine.

Immune interferon in the circulation of patients with autoimmune disease

The observation that type II, or immune, interferon could be produced by peripheral-blood leukocytes in vitro on an immune-specific basis suggested that it also might be produced in vivo in various autoimmune disorders. We found immune interferon in the serums of patients with systemic lupus erythematosus, rheumatoid arthritis, scleroderma and Sjögren's syndrome. Among 28 patients with systemic lupus erythematosus, 71 per cent of those with active and 21 per cent of those with inactive disease showed interferon in their serums. Serial serum samples showed a good correlation between interferon titers and disease activity. Moreover, interferon titers correlated positively with antibodies to DNA and negatively with serum levels of the third component of complement. It is possible that the production of interferon may contribute to immunologic aberrations in auto-immune diseases and also protect the already compromised host from viral infections.

Effect of interferon, elevated temperature, and cell type on replication of acute hemorrhagic conjunctivitis viruses

Five strains of enterovirus type 70 (E 70) and four of coxsackievirus type A 24 (CA 24) were studied for their sensitivity to interferon (IF), ability to induce IF, replication at various temperatures, and adaptability to human and mouse cell cultures. We found that isolates ranged from 0.01 to 16 times as sensitive to fibroblast IF as vesicular stomatitis virus, depending upon the cell type used and the multiplicity of infection. Most of the isolates induced no detectable IF; however, when induction occurred the titers were relatively low (5 to 300 U). Only E 70 virus isolates were adaptable to growth in L-cells. Replication of all viruses was inhibited approximately 90% at 37 to 39 degrees C depending upon the cell type. These results and the accessibility of the eye to application of IF and/or heat suggests the possibility of their use for treatment. The adaptation of certain E 70 viruses to mouse L-cells opens the possibility of development of a mouse model infection.

Variables affecting viral plaque formation in microculture plaque assays using homologous antibody in a liquid overlay

A liquid antibody microculture plaque assay and the variables that govern its effectiveness are described. The assay is based on the principle that low concentrations of homologous antibody can inhibit secondary plaque formation without inhibiting formation of primary plaques. Thus, clear plaques that followed a linear dose response were produced. The assay was found to be more rapid, less cumbersome, and less expensive than assays using agar overlays and larger tissue culture plates. It was reproducible, quantitative, and had about the same sensitivity as the agar overlay technique in measuring infectious coxsackievirus type B-3. It was more sensitive in assaying adenovirus type 3 and Western equine encephalomyelitis, vesicular stomatitis, Semliki forest, Sendai, Sindbis, and Newcastle disease viruses than were liquid, carboxymethylcellulose, and methylcellulose microculture plaque assays. The variables influencing sensitivity and accuracy, as determined by using coxsackievirus type B-3, were: (i) the inoculum volume of virus; (ii) the incubation period of virus; and (iii) the incubation temperature.

Enhancement of IgE-mediated histamine release from human basophils by viruses: role of interferon

Human leukocytes maintained in culture are induced to release histamine when exposed to ragweed antigen E or anti-IgE. Leukocyte cultures incubated with virus (i.e. HSV-1, Influenza A, and Adeno-1) but not exposed to ragweed antigen E or anti-IgE fail to release histamine. If, however, leukocyte cultures are first exposed to virus and then to ragweed antigen E or anti-IgE, significant enhancement of histamine release occurs. Both infectious and inactivated virus enhance histamine release and the degree of enhancement is related to the concentration of virus and the length of the incubation. Tissue culture fluid harvested 8 h after exposure of leukocytes to virus contains a soluble factor which is capable of enhancing histamine release when added to fresh leukocyte cultures. This factor has all the properties of interferon including species specificity and cannot be dissociated from the antiviral activity of interferon. Moreover, both known inducers of interferon (poly I:poly C) and standard preparations of interferon are capable of enhancing histamine release. The enhancement of histamine release by interferon represents a new biological role for interferon.