Changing viral susceptibility of a human cell line in continuous cultivation. I. Production of infective virus in a variant of the Chang conjunctival cell following infection with swine or N-WS influenza viruses

Vaccine based on antibody-dependent cell-mediated cytotoxicity epitope on the H1N1 influenza virus increases mortality in vaccinated mice

Antibody-dependent cell-mediated cytotoxicity bridges humoral immunity and cellular immunity. Thus vaccine candidates which can elicit both broadly neutralizing antibodies and potent antibody-dependent cell-mediated cytotoxicity (ADCC) are recommended. Previously, a panel of functional epitopes that can elicit ADCC effects is isolated and characterized on the H1N1 Influenza Virus. Based on these identified epitopes, an epitope vaccine against H1N1 infection has been designed. The serum of vaccine immunized mice show potent ADCC activities in comparison with vector control group and HA ecto domain vaccinated group. However, the release of IL-6 and TNFα is higher in lung of epitope vaccine immunized mice. The viral load is also higher in epitope vaccine immunized mice. In addition, the epitope vaccine immunized mice showed lower survive rate than both empty vector immunized mice and HA ectodomain immunized mice. Passive transfer of serum from epitope vaccine immunized mice to healthy adult mice can decrease the survival rate of recipients after viral challenge. Our data suggested that ADCC epitope based vaccine has a mortality promoting effect rather than protective effect after H1N1 viral challenge. This result provides indications in future vaccine design with a consideration of balancing humoral immune response and cellular immune response.

Short Tandem Repeat (STR) Profiles of Commonly Used Human Ocular Surface Cell Lines

PURPOSE

The purpose of this study is to establish the short tandem repeat (STR) profiles of several human cell lines commonly used in ocular surface research.

MATERIALS AND METHODS

Independently DNA was extracted from multiple passages of three human corneal epithelial cell lines, two human conjunctival epithelial cell lines and one meibomian gland cell line, from different laboratories actively involved in ocular surface research. The samples were then subjected to STR analysis on a fee-for-service basis in an academic setting and the data compared against that in available databases.

RESULTS

The STR profiles for the human corneal epithelial cells were different among the three cell lines studied and for each line the profiles were identical across the samples provided by three laboratories. Profiles for the human conjunctival epithelial cells were different among the two cell lines studied. Profiles for the meibomian gland cell line were identical across the samples provided by three laboratories. No samples were contaminated by elements of other cell lines such as HeLa.

CONCLUSIONS

This comprehensive study provides verification of STR profiles for commonly used human ocular surface cell lines that can now be used as a reference by others in the field to authenticate the cell lines in use in their own laboratories.

In vitro alternatives to the use of animals in ocular toxicology testing

Chemical substances, including household products, industrial chemicals, and cosmetics, must be tested for ocular toxicity or irritancy so that the public can be assured of their safety or warned of dangers associated with their use. The in vivo Draize test is the standard method used to meet this requirement; however, this test is coming under increasing criticism on scientific and ethical grounds. This has led to the development of a large number of proposed in vitro tests, some of which are routinely used to screen chemicals in toxicology laboratories. This review addresses regulations governing ocular irritancy testing and the current status of the movement toward use of alternative methods. Such methods include the use of cultured cells, hen's eggs, isolated animal eyes and corneas, human corneal epithelial cell lines, and the recently developed in vitro corneal equivalent models. The protocols for these methods are outlined, and their endpoints are described with respect to prediction of in vivo responses. The tests are evaluated in the context of the outcomes of validation studies and acceptance by regulatory agencies. While several of these tests yield useful information concerning ocular irritancy, to date, no in vitro alternative test has been validated as a replacement for the Draize test. If the goal of replacing the in vivo test while protecting the public from chemical eye injury is to be achieved, further development and improvement of alternative tests, as well as establishment of a human ocular toxicity data base, are required.

Pre-clinical investigation of the efficacy of an artificial tear solution containing hydroxypropyl-guar as a gelling agent

PURPOSE

Pre-clinical studies of a new artificial tear product (Systane Lubricating Eye Drops Alcon Laboratories, Inc., Fort Worth, TX) containing the novel gelling agent hydroxypropyl-guar (HP-guar) and two demulcents, polyethylene glycol 400 (PEG) and propylene glycol (PG) were conducted to determine the ability of the product to protect ocular surface epithelial cells from desiccation in vivo and in vitro, and to promote recovery of the damaged corneal epithelial barrier in vivo. Other leading artificial tear products were also evaluated as comparators to determine the relative effectiveness of different polymer systems.

METHODS

Damage due to desiccation was assessed by measuring corneal uptake of methylene blue compared to untreated corneas. Corneas of anesthetized rabbits were treated with the new artificial tear product and subjected to desiccation by holding the eyelids open for 2 hours with a speculum. Control eyes were subjected to desiccation without application of a tear formulation. To measure recovery of the corneal epithelium from damage, corneas of anethesthetized rabbits were exposed to 0.01% benzalkonium chloride (BAC) for 5 minutes to increase epithelial permeability. The corneas were exposed to the new artificial tear for 1.5 hours followed by measurement of uptake of 5,6 carboxyfluorescein (CF). In the desiccation and CF uptake experiments, the new tear product was also compared to a tear product formulation without HP-guar and to a commercially available artificial tear containing carboxymethyl cellulose (CMC) and Purite. In a third set of experiments, immortalized human corneal epithelial cells and Chang conjunctival cells in culture were exposed to the PEG/PG/HP-guar tear product, the control formulation without HP-guar, a tear formulation preserved with BAC, or the artificial tear containing CMC/Purite for 15min. The tear formulation was removed and the cells were exposed to desiccating conditions in a laboratory safety hood for 10 or 30min. Cell viability was determined using the MTT assay.

RESULTS

The in vivo desiccation model, showed that the new tear product, Systane, offered complete protection of the cornea from desiccation (methylene blue uptake not different than naïve control). Following exposure to 0.01% BAC, the new artificial tear product also provided an environment in which the corneal epithelium recovered completely from damage (CF uptake not different than normal, untreated cornea). This level of protection was not observed when corneas were treated with other formulations. Results from the in vitro desiccation procedure indicated that viability of corneal epithelial and Chang cells treated with the PEG/PG/HP-guar product was significantly greater than viability of cells treated with the tear product without HP-guar or the tear products containing BAC or CMC/Purite.

CONCLUSIONS

The tear product containing HP-guar, PEG 400 and propylene glycol satisfies several pre-clinical criteria for an appropriate artificial tear formulation. It gives long-term desiccation protection of the intact cornea and also epithelial cells in culture and has no apparent deleterious affects on cells. It also provides conditions in which a damaged corneal epithelium can recover normal barrier function. The combination of ingredients in the formulation appears to provide an effective mucomimetic artificial tear product. These pre-clinical data suggest that the product will be effective in providing superior relief for the dry eye sufferer.

Release of complement regulatory proteins from ocular surface cells in infections

PURPOSE

The decay accelerating factor (DAF or CD55) and the membrane inhibitor of reactive lysis (MIRL or CD59), two complement regulatory proteins that protect self cells from autologous complement-mediated injury, are attached to corneal and cqonjunctival epithelial cells by glycosylphos-phatidylinositol (GPI) anchors. We sought to 1) determine the frequency with which bacteria recovered from patients with infections of the eye elaborate factors that can remove these surface proteins from ocular cells, 2) determine the spectrum of bacteria from other sites that have similar effects, and 3) establish the time interval required for reconstitution of the two regulators.

METHODS

Culture supernatants of 18 ocular isolates [P. aeruginosa (n = 3), S. marcescens (n = 1), S. epidermidis (n = 9), and S. aureus (n = 5)], and > 100 other clinical specimens isolated in the hospital's microbiology laboratory [P. mirabilis (n = 1), S. aureus (n = 65), S. epidermidis (n = 24), B. cereus (n = 12), H. influenzae (n = 15), and Enterobacter sp. (n = 21)] were incubated at 37 degrees C for various times with conjunctival epithelial cells, conjunctival fibroblasts or HeLa cells and the release of DAF and CD59 proteins from the surfaces of the cells analyzed by 2-site immunoradiometric assays and by Western blotting. The kinetics of recovery of DAF and CD59 expression on the cells was measured by flow cytometry.

RESULTS

DAF and/or CD59 release from the cell monolayers varied from < 5% to > 99% at as much as a 1:81 dilution of the supernatant from some bacteria. On conjunctival epithelial cells, more than 8 hr was required for 44% recovery of DAF expression and for 50% recovery of CD59 expression.

CONCLUSIONS

Bacteria produce phospholipases and/or other enzymes which can efficiently remove DAF and CD59 from ocular cell surfaces. This phenomenon may correlate with their in vivo pathogenicity.

Effect of endotoxin on cells and on their response to infection by polioviruses

Murphy, W. H. (The University of Michigan, Ann Arbor) and C. Wisner. Effect of endotoxin on cells and on their response to infection by polioviruses. J. Bacteriol. 83:649-662. 1962.-The effect of lipopolysaccharide on HeLa-S3, HeLa-Gey, Chang-liver, Maben, and L strain mouse fibroblasts was studied. The liminal dose of endotoxin for the human epithelial cell strains was approximately 250 mug/ml, and their order of sensitivity to endotoxin was: Chang-liver, HeLa-Gey, HeLa-S3, and Maben, the latter being the most resistant. Endotoxin at concentrations exceeding 100 mug/ml was cytotoxic to the L strain of mouse fibroblasts and caused them to markedly agglutinate. Cytotoxic response of cells to endotoxin was not characterized by cell lysis, but by distinctive nuclear changes. In an attempt to demonstrate the metabolic induction of the latent infection of cell cultures by a noncytopathic variant of poliovirus, endotoxin was added at maximal subliminal concentration to cell cultures totally, partially, or fully susceptible to virus. Endotoxin caused a slight but consistent accelerative cytopathic response of cells to infection by cytopathic poliovirus, but failed to induce cytopathic response to infection by submoderate (noncytopathic) poliovirus. Although endotoxin slightly suppressed yields of poliovirus from cells, it did not affect the plating efficiency of virus on cell monolayers.

Adenovirus-mediated gene transfer to the ocular surface epithelium

Gene transfer to the ocular surface epithelium is of potential therapeutic value. It was determined whether a reporter gene can be introduced into the ocular surface epithelium in vitro (human cell lines), ex vivo (human tissues), and in vivo (rats) by treating with a recombinant, replication-deficient, adenovirus type 5. Human and conjunctival cell lines were cultured with various multiplicities of infection (MOI; 3.2x10(-5)-5x10(-1)) of adenovirus vector (Ad5:Adex1CAlacZ) containing the reporter gene lacZ (1.3-2.0x10(4) PFU ml-1). The ex vivo study used human corneal and conjunctival tissues obtained from an eye bank and during surgery. Non-specific upregulation of inflammatory cytokines of conjunctival epithelium infected by Ad5 was assayed and its suppression by steroids. For the in vivo study, Ad5 (5x10(5) PFU, 5-10 microliter) was applied to the eyes of 8-12-week-old cotton rats, which were enucleated 24 and 48 hr later. The maximum lacZ expression in vitro was demonstrated in the corneal epithelial cell line at 7 days (1x10(-1) MOI) and conjunctival epithelial cell line at 2 days (4x10(-4) MOI). Furthermore, lacZ was also expressed in the superficial corneal and conjunctival epithelium in the ex vivo study. IL-6, IL-8, and ICAM-1 expression from conjunctival epithelium by Ad5 was significantly inhibited by treatment with betamethasone (BM). For the in vivo study, only the conjunctival epithelium demonstrated beta-Gal activity at 24 and 48 hr after application. These data indicate that adenovirus vector is capable of directly delivering gene to the corneal and conjunctival epithelium, suggesting a variety of possible gene therapy uses. The concomitant application of steroid eye drops may avoid inflammation.

Comparative studies of the isozymes of lactic dehydrogenase in rabbit and man. Observations during development and in tissue culture

During development of rabbit tissues, characteristic sequential alterations in the LDH isozyme pattern occur, and consist for liver and muscle in loss of the most rapidly migrating anodal bands, and increased activity in the cathodal bands and slower migrating anodal bands. In heart the reverse changes were observed. Comparison of the isozyme patterns observed in various fetal and adult human tissues suggests that these same sequential alterations probably occur. A species-specific isozyme pattern is obtained in long term culture of rabbit, chick, and human cells. The alterations in tissue culture are characterized by a gradual redistribution of total LDH activity in which there is decreased intensity of rapidly migrating anodal bands. These sequential alterations are independent of the organ of origin. The number of bands observed in the starch gel is partly dependent upon the total activities applied. Isozymes may provide a convenient method for determining the species of origin of cell lines in common use and for investigating the effects of various alterations in the in vitro environment on cells grown in tissue culture.

Isolation of influenza A and B viruses in HeLa cells

The HeLa cell line which is one of the most popular cell lines was shown to be suitable for isolation of types A (H3N2) and B influenza viruses from throat washings of patients. Sixty-nine and 67 out of 147 throat washings taken from patients during the period from January to April 1994, were positive for influenza A virus in HeLa cells and MDCK cells respectively. Seven out of 10 throat washings taken between January and March, 1993, were positive for influenza B virus in MDCK. Of these 7, 4 were also positive for HeLa cells.

A new method evaluating quantitative time-dependent cytotoxicity of ophthalmic solutions in cell culture. Beta-adrenergic blocking agents

A new method of evaluating quantitative cytotoxicity in cell culture was demonstrated using Chang's cultured human conjunctival cells. Time-dependent cytotoxicity of some beta-adrenergic blocking agents was shown and expressed by exposure time, causing 50% cell damage (50% cell damage time CDT50). Pure timolol maleate maleate of 0.25% and 0.5% concentration caused no cytotoxicity within a 64-min exposure. Pure befunolol hydrochloride of 0.25%, 0.5% and 1% inhibited 10%-30% of cell growth at 64-min exposure. Pure bupranolol of 0.125%, 0.25%, 0.5% and 1% showed evident cytotoxicity and CDT50 at 66 min 48 s, 38 min 54 s, 3 min 46 s and 1 min 18 s, respectively. Commercial preparations, which contained benzalkonium chloride as a preservative, indicated more rapid cytotoxicity. Timolol preparations of 0.25% and 0.5% showed CDT50 at 48.1 s and 2 min 4 s, respectively. Befunolol preparations of 0.25%, 0.5% and 1% showed CTD50 at 43.4% s, 4 min 38 s and 58 s, respectively, Bupranolol preparations of 0.125%, 0.25%, 0.5% and 1% demonstrated CDT50 at 1 min 11 s, 3 min 24 s, 22.3 s and 13.7 s, respectively.

Faecal adenoviruses from Glasgow babies. Studies on culture and identity

Attempts were made to isolate viruses from babies' stools that contained adenoviruses detected by electron microscopy. One hundred and fifty-nine specimens from 71 children were studied and adenoviruses of established serotypes were isolated from 81 stools. Serial stool samples containing adenovirus particles were obtained from 35 children, and prolonged shedding of recognized serotypes was common. Simultaneous and sequential infections by different serotypes were also observed. Thirty-six children shed adenoviruses that could not be isolated using cell cultures normally used to detect adenoviruses, and nine of these children also shed adenoviruses of established serotypes. Passage in Chang conjunctival cell culture allowed characterization of fastidious adenoviruses from 14 children as members of a previously unrecognized serotype.

Analysis of nuclear accumulation of influenza NP antigen in von Magnus virus-infected cells

When 1-5C-4 cells were infected with von Magnus virus derived from influenza A/RI/5+ virus by successive undiluted passages in chick embryos, virus-specific proteins were synthesized but production of infectious virus was inhibited. In these cells the synthesis of viral RNA was suppressed and the nucleoprotein (NP) antigen was found predominantly in the nucleus in contrast to standard virus-infected cells in which the antigen was distributed throughout the whole cell. The intracellular location and migration of NP were determined by isotope labeling and sucrose gradient centrifugation of subcellular fractions. In standard virus-infected cell NP polypeptide was present predominantly in the cytoplasm in the form of viral ribonucleoprotein (RNP) and intranuclear RNP was detected in reduced amounts. In contrast, in von Magnus virus-infected cells NP polypeptide was present predominantly in the nucleus in a nonassembled, soluble from and the amount of cytoplasmic RNP was considerably reduced. After short-pulse labeling NP was detected exclusively in the cytoplasm in a soluble form and after a chase a large proportion of such soluble NP was seen in the nucleus. It is suggested that a large proportion of the NP synthesized in von Magnus virus-infected cells in not assembled into cytoplasmic RNP because of the lack of available RNA and the NP migrated into the nucleus and remained there.

In vitro growth of some fastidious adenoviruses from stool specimens

Sixty-seven stool specimens from 51 children, positive for adenoviruses by electron microscopy and negative for growth in human-embryo kidney cells, were tested for growth in Chang conjunctiva cells. Twenty-eight specimens caused a cytopathic effect over more than one passage in these cultures, and several adenovirus strains grew better at 33 degree C than at 37 degree C. Most of the culture-positive specimens also induced the development of adenovirus antigens in KB cells detectable by a group-specific indirect immunofluorescence test. Twenty-four of the 25 fastidious strains tested were antigenically related and were distinct from the established serotypes commonly isolated from stools.

Adherence of Yersinia enterocolitica to mammalian epithelial cell lines

Yersinia enterocolitica RIMD 2501003 grown at 25 C avidly adhered to various kinds of cultured epithelial cell lines (HeLa, FL, Y-1 adrenal, human intestine, human conjunctiva) but the bacteria grown at 37 C did not adhere. This phenomenon paralleled the temperature-dependent motility of the bacteria. To clarify the adherence mechanism, we obtained two kinds of mutants, an immobile mutant and a nonadherent mutant, by treatment with N-methyl-N'-nitro-N-nitrosoguanidine. The immobile mutant did not move on soft agar but retained the capacity to adhere to cultured epithelial cells when grown at 25 C. The nonadherent mutant did not adhere to cultured epithelial cells but retained the ability to move on soft agar when grown at 25 C. When the bacteria were killed by heat, ultraviolet light irradiation or formaldehyde they lost their capacity to adhere to the cultured epithelial cells. Antiserum against Y. enterocolitica RIMD 2501003 grown at 25 C was absorbed with the bacteria grown at 37 C, with the bacteria grown at 25 C, with the nonadherent mutant grown at 25 C and with the bacteria killed by various means. Only the antiserum absorbed with bacteria grown at 37 C inhibited the adherence of bacteria. These data indicate that motility does not correlate with adherence of Y. enterocolitica. It appears that the adherence factor involves both a temperature-dependent surface factor and a factor synthesized de novo during the interaction of susceptible cells with the bacteria.

Recent contributions of molecular biology to the clinical virology of myxoviruses

Recent advances in the clinical virology of influenza are based on non-pragmatically oriented research on the genetics and biochemistry of the influenza virus. Antigenically hybrid recombinant viruses can be tailored to provide monospecific reagents for serological studies. Basic research on viral structure and the mechanism of viral replication has directly influenced the establishment of a cell culture system suitable for the isolation of most influenza viruses. Identification of viral genotype by RNA gel electrophoresis and mapping of oligonucleotides of viral RNA has already facilitated epidemiologic investigations. The clinical virologist of the future must have an understanding of the potential limitations of these techniques for specific strain identification.

Analysis of nuclear accumulation of influenza nucleoprotein antigen in the presence of p-fluorophenylalanine

When p-fluorophenylalanine (FPA) was added to influenza virus RI/5+-infected cells 4 hr after infection, virus-specific proteins were synthesized but infectious progeny virus was not produced. In these cells, synthesis of viral RNA was strongly inhibited and nucleoprotein (NP) antigen was found predominantly in the nucleus in contrast to untreated cells in which NP antigen was distributed throughout the whole cell. The intracellular location and migration of NP were examined by isotope labeling followed by fractionation of infected cells. In untreated cells, a large portion of the NP was present in the cytoplasm and most of it was detected in the form of ribonucleoprotein (RNP). In contrast, in FPA-treated cells little viral RNP was detectable and NP was present predominantly in the nucleus in a nonassembled, soluble form. When FPA was removed from the culture, synthesis of viral RNA was soon restored and a large amount of viral RNP appeared in the cytoplasm; this was followed by the production of infectious virus. The results of the experiments suggest that the NP synthesized in the presence of FPA is not assembled into viral RNP because of the lack of available RNA, and such NP migrates readily into the nucleus and accumulates there.

Influenza B virus genome: assignment of viral polypeptides to RNA segments

It was shown that all eight RNA segments of influenza B viruses are most likely monocistronic and code for eight virus-specific polypeptides. A genetic map of the influenza B virus genome was established, and six polypeptides (P1 protein, nucleoprotein, hemagglutinin, neuraminidase, M protein, and nonstructural protein) were unambiguously assigned to specific RNA segments. Molecular weight estimates of the eight individual genes are obtained by using the glyoxal method. These results suggest that each influenza B virus RNA segment has a greater molecular weight than the influenza A virus RNA segment which codes for the analogous gene product.

Genetic dimorphism in influenza viruses: characterization of stably associated hemagglutinin mutants differing in antigenicity and biological properties

Influenza virus recombinant X-53 produced for use in the 1976 National Immunization Program for swine influenza was found to comprise two types of virions differing in their antigenic, replicative, and plaque-forming characteristics. One type, characteristic of X-53 and designated "L," was relatively low-yielding in chicken embryos, produced small clear plaques in Madin-Darby dog kidney cells, and was selectively inhibited by heterotypic antibody to the A/sw/Cam/39 strain of swine influenza virus. The other, X-53a or "H," was high-yielding in chicken embryos, produced large turbid plaques in dog kidney cells, and was not inhibited by concentrations of A/sw/Cam/39 antisera inhibitory to X-53. It was shown that A/NJ/11/76 (HswN1) virus, from which X-53 was derived, and five other swine influenza virus isolates from humans and pigs were dimorphic mixtures of the two types of virus. Segregation of the hemagglutinin genes of L and H variants by further recombination demonstrated that their different properties were pleiotropic phenotypes of mutation in the hemagglutinin gene. Under selective conditions suppressive to the L mutant, mutation of cloned L to H virus was observed. This observation, as well as the apparent ubiquity of the two mutants in nature, suggests that this is another example of viral dimorphism-the stable association of two allelic mutants. Of special significance is the indication that antigenic variants may be selected by selection for properties other than antigenicity, and therefore may represent mutants with pathogenic effects determined by factors other than lesser modulation by host antibody.

Genetics of resistance of animals to viruses: I. Introduction and studies in mice

Inherited resistance to animal viruses may be conveniently classified into three types: monogenetic, following simple mendelian ratios; polygenetic; and cytoplasmic. A virus is a unique cellular parasite, dependent upon the host for reproduction and nourishment in a variety of different ways. Since, as with the other types of parasites, the host and the parasite have necessarily evolved together. It is a distortion to consider the resistance of the host, without considering the evolutionary steps in the development of this extreme form of parasitism; therefore, this chapter reviews some of the ideas put forward about host-agent interactions in plants as well as in animals. The importance of genes in regulating the resistance to disease, including parasites and parasitoids, is apparent if the disease is considered to be an important evolutionary force. The selective effects of viruses have not yet been adequately studied. Continued attempts to find a correlation between the different blood groups and differing severity of smallpox infection clearly searched for selective forces, but the results were inconclusive. Most of the knowledge of genetic resistance to virus disease rests on the study of resistance to selected agents in various inbred strains of mice and chickens, rather than on any knowledge of the effects of genetic resistance in a natural heterozygous population. The increasing frequency, however, with which genetic resistance is found, is in itself an evidence that these genes are important in natural outbred populations. In addition, there are increasing numbers of virus diseases, in which the viral agent seems to be inherited in a mendelian fashion.

Intracellular development of membrane protein of influenza virus

The intracellular development of membrane protein (MP) of influenza A virus was investigated by immunofluorescent staining. Monospecific antiserum was prepared by immunizing rabbits with MP eluted from SDS-polyacrylamide gels of SDS-disrupted NWS virions. In the productive infection in clone 1-5C-4 cells, MP antigen was first detected over the whole cell at 4 hr after infection, concomitantly with the appearance of hemagglutinin (HA) antigen in the cytoplasm, and bright nuclear fluorescence was then observed. Nucleoprotein (NP) antigen was detected in the nucleus prior to the appearance of fluorescence of MP antigen and thereafter the cytoplasmic fluorescence developed. Late in infection, all of these three antigens were observed predominantly in the cytoplasm with stronger fluorescence at the cell surface. Essentially similar findings were obtained in the abortive infections in L cells and BHK cells. The above results suggest that the membrane protein of influenza A virus is present in the nucleus as well as in the cytoplasm of infected cells.

Mapping of the influenza virus genome: identification of the hemagglutinin and the neuraminidase genes

Polyacrylamide gel electrophoresis of the RNA of influenza A/PR/8/34 (H0N1) and A/Hong Kong/8/68 (H3N2) viruses and recombinant viruses derived from them revealed that each contains eight RNA segments, the fourth of which codes for hemagglutinin. (The largest RNA of the segmented genome is counted as band 1.) The neuraminidase gene was identified as the sixth segment in the RNA pattern of influenza A/PR8 virus and as the fifth segment of A/Hong Kong virus. The molecular weights of the RNAs for the hemagglutinin and the neuraminidase genes lie in the range of 600,000-700,000.

Quantitative assessment of hemadsorption by myxoviruses: virus hemadsorption assay

The standardization and quantitative evaluation of an assay for myxoviruses, based on the enumeration of individual infected clone 1-5C-4 cells manifesting hemadsorption within 24 h of infection, are described. Hemadsorption was detectable earlier than immunofluorescence in infected cells or hemagglutinins in culture medium. The relationship between virus concentration and cells exhibiting hemadsorption was linear. The assay was highly precise, sensitive, and reproducible.

Cell attachment and penetration by influenza virus

Attachment and penetration of influenza virus into clone 1-5C-4 cells were quantitatively determined by the immunofluorescent cell-counting assay. Aided by centrifugal force, more than 95% of virus inocula of five representative influenza virus strains (A(0)/PR8, A(1)/Ann Arbor, A(2)/Japan, B/Lee, B/Great Lakes) were attached to cells at a linear rate within 10 min, in contrast to approximately 35% after stationary incubation at 35 C for 2 h. By the former procedure, a proportionality between the number of infected cells and volume of inoculum was revealed which was not evident when stationary incubation was employed. Maximal binding of virus to cells occurred at 0.2 M NaCl. The salt requirement, added to evidence of pH dependence and temperature independence, indicated that the initial virus-cell union involved electrostatic forces. Virus penetration into cells, measured by the insensitivity of virus-cell complexes to antiviral serum, was linear and complete within 15 min at 35 C for all five virus strains tested. Maximal virus penetration occurred at 0.1 to 0.2 M NaCl; the process was pH- and temperature-dependent. Both virus attachment and penetration processes were partially inhibited in the presence of diethylaminoethyl-dextran.

Developmental sequence and intracellular sites of synthesis of three structural protein antigens of influenza A2 virus

Specific antisera for hemagglutinin (HA) and neuraminidase antigens of influenza A(2) virus (A(2)E) were produced through the segregation of the two proteins in reciprocal viral recombinants of A(2)E and A(0)e viruses. Gamma globulin fractions of these specific antisera and of antiserum specific for the nucleoprotein (NP) antigen of A(0)e virus were conjugated with fluorescein isothiocyanate and employed to follow the synthesis of the three structural proteins in clone 1-5C-4 human aneuploid cells, with parallel measurement of serological and biological activity of the antigens by other techniques. In this system, NP antigen appeared first (at 3 hr) in the cell nucleus, whereas HA and neuraminidase appeared coincidentally, at 4 hr after infection, in the cytoplasm. The initial detectability of biological or complement-fixing activity of the proteins coincided with their demonstrability as stainable antigens. Late in infection, all three antigens were detected at the cell surface. Antibody specific for HA partially blocked the intracellular staining of neuraminidase and inhibited the enzymatic activity of both extracted and intact extracellular virus. These observations suggest the close intracytoplasmic proximity of the two envelope antigens and perhaps their initial association in a larger protein.

Independent variation in nature of hemagglutinin and neuraminidase antigens of influenza virus: distinctiveness of hemagglutinin antigen of Hong Kong-68 virus

Antigenic variations of the two virus-coded surface proteins of influenza virus-hemagglutinin and neuraminidase-were examined in seven strains of influenza A(2) virus (including the Hong Kong/68 strain) isolated from 1957 to 1968. Changes in the two antigens were found to occur independently in nature, resulting in new viruses which differ from older strains more with respect to one antigen than the other. The Hong Kong/68 strain is markedly different from previous A(2) strains in its hemagglutinin antigen but possesses neuraminidase indistinguishable antigenically from that of recent strains. Immunization experiments in mice provided evidence that only the neuraminidase component of an earlier A(2) strain provided protection against Hong Kong virus challenge. Segregation of hemagglutinin and neuraminidase antigens through recombination of each of the seven strains of influenza A(2) virus with A(0)/NWS virus made it possible to investigate antigenic variation of the two dissociated surface proteins independently in a common plaque assay system. Comparison of these hybrid viruses with the parent A(2) strains provided evidence that all the cross-reactivity of the Hong Kong strain with previous A(2) viruses is explicable on the basis of its similar neuraminidase component. It is proposed that the taxonomy of influenza A viruses must take into account differences in neuraminidase as well as hemagglutinin antigens.

Protective effects of specific immunity to viral neuraminidase on influenza virus infection of mice

Antibody specific for viral neuraminidase can be demonstrated in mice following (i) pulmonary infection with influenza virus, (ii) immunization with ultraviolet-in-activated influenza virus, (iii) immunization with isolated neuraminidase of influenza A(2) virus, and (iv) passive immunization with sera of rabbits immunized with isolated A(2) neuraminidase. Neuraminidase antibody produced by any of these methods exerts a profound inhibiting effect on virus replication in the lungs of mice challenged with strains of virus having homologous neuraminidase protein, even in the absence of hemagglutinating inhibiting antibody to the challenge virus, and results in markedly decreased pulmonary virus titers and diminished lung lesions. These observations suggest that antineuraminidase immunity may play a significant role in the protection against influenza virus challenge observed in mice after infection or artificial immunization.

Recombination of influenza A viruses of human and animal origin

Simultaneous infection of the allantoic sac of the chick embryo with influenza A/equine 1/56 and any of three recombinants derived from human influenza viruses produced stable hybrids with antigens from each parent strain. These hybrids contain the hemagglutinin protein of the equine virus and the neuraminidase of the human strains. The experiments demonstrate genetic homology of human and equine influenza A viruses and suggest the possibility of their recombination in nature.

Replication and plaque assay of influenza virus in an established line of canine kidney cells

A plaque assay system has been developed for types A and B influenza viruses in an established line of canine kidney cells (MDCK-USD). In addition to a homogeneous susceptible cell, consistent plaque production depends on the use of highly purified agar (Agarose). This quantitative system was used to determine the rate of adsorption, synthesis, and thermal inactivation of influenza viruses, as well as to determine a dose response curve. Plaque assays on the MDCK-USD line and the parent MDCK line showed that the latter was more sensitive to A/Swine and A(2)/Japan 305 viruses. Titration of standard virus pools in embryonated eggs and MDCK-USD indicated that the cell culture system was as sensitive as the in ovo assay.

Antiviral activity of antiserum specific for an influenza virus neuraminidase

Antiserum specific for influenza A(2) neuraminidase was produced by immunization of rabbits with the purified enzyme which had been isolated by electrophoresis from the proteins of a detergent-disrupted A(0)A(2) influenza virus recombinant [X-7 (F1)]. This recombinant contained hemagglutinin of the A(0) subtype and A(2) neuraminidase. Antiserum to the isolated A(2) neuraminidase did not react in any of four serological tests with A(0) or A(2) subtype viruses that lacked the A(2) enzyme. In contrast, the antiserum inhibited the neuraminidase activity only of wild-type and recombinant viruses containing the A(2) enzyme, regardless of the nature of their hemagglutinin proteins. The antiserum caused hemagglutination-inhibition of some, but not all, viruses bearing the A(2) enzyme, and it reduced the plaque size or plaque number of all viruses tested that contained A(2) neuraminidase. In the chick embryo and in cell culture, low dilutions of antiserum reduced the yield of virus. True neutralization of virus in the chick embryo did not occur. We conclude that an antiserum specific for A(2) neuraminidase influenced the yield and release of virus from influenza virus-infected cells.

Virological, immunochemical, and cytochemical studies of four HeLa cell lines infected with two strains of influenza virus

The production of infectious virus, hemagglutinin, and viral (V) antigens and the changes in ribonucleoprotein (RNP) and lipoprotein metabolism have been studied in four sublines of HeLa cells infected with the PR8 and a PR8 recombinant strain of influenza virus. Much greater amounts of infectious virus and much less hemagglutinin were produced by the PR8 recombinant than by PR8 virus in all four cell lines. Different amounts of infectious virus per infected cell were produced by the recombinant in the four cell lines, whereas very little infectious virus was produced by the PR8 strain in any of the HeLa cells. In all cell lines infected with both strains of virus, "soluble" (S) antigen appeared early in the nucleolus. In cells infected with PR8 recombinant, S antigen subsequently filled the nucleus and later appeared in the cytoplasm. In most cells infected with PR8 virus, nuclear S antigen did not fuse to fill the nucleus, and S antigen was not detected in the cytoplasm. V antigen was observed in the cytoplasm of cells when diffuse nuclear S antigen had formed. The earliest and most frequent change in the RNP of the infected cells was a decrease in stainable RNP spherules (nucleolini) in the nucleolus. This was followed, in a smaller proportion of cells, by the appearance of nuclear and cytoplasmic inclusions containing RNP. There was a characteristic difference in the morphology of the cytoplasmic inclusions produced by the two strains of virus, but the same types of inclusions were observed in all four HeLa lines. A significant increase in lipoprotein was observed only in association with the cytoplasmic inclusions produced by PR8 recombinant virus. There was a striking difference in the proportion of cells with cytochemical changes in RNP in the four cell lines. A significant cytopathic effect (CPE) was observed only in three virus-cell systems in which a high proportion of cells exhibited changes in nucleolinar RNP. It is suggested that disappearance of RNP in the nucleolini may be an indication of shutdown of host ribonucleic acid synthesis and that this in turn results in a CPE. Virus infection resulted in a C-mitotic block that was followed by karyorrhexis. Infection of the cell did not always result in the production of infectious virus, in changes in the RNP of the nucleolini, in the development of nuclear or cytoplasmic RNP inclusions, or in CPE. The results suggest that production of infectious virus, shutdown of cellular RNP synthesis with accompanying CPE, and the formation of inclusions appear to be independent events.