INTERACTIONS OF ETHER-DISRUPTED INFLUENZA A2 VIRUS WITH ERYTHROCYTES, INHIBITORS, AND ANTIBODIES

Evaluation of different inactivation methods for high and low pathogenic avian influenza viruses in egg-fluids for antigen preparation

In view of the emerging avian influenza (AI) viruses, it is important to study the susceptibility of AI viruses to inactivating agents for preparation of antigens and inactivated vaccines. The available information on susceptibility of both the high and low pathogenic AI viruses to different inactivating agents is inadequate and ambiguous. It has been shown that different subtypes of influenza viruses require different physical and chemical conditions for inactivation of infectivity. The present study was undertaken to evaluate the use of beta-propiolactone (BPL), formalin and ether for inactivation and its impact on antigenicity of AI viruses. A total of nine high and low pathogenic AI viruses belonging to four influenza A subtypes were included in the study. The H5N1 viruses were from the clades 2.2, 2.3.2.1 and 2.3.4. The H9N2 virus included in the study was of the G1 genotype, while the H11N1 and H4N6 viruses were from the Eurasian lineage. The viruses were treated with BPL, formalin and with ether. The confirmation of virus inactivation was performed by two serial passages of inactivated viruses in embryonated chicken eggs. The infectivity of all tested AI viruses was eliminated using 0.1% BPL and 0.1% formalin. Ether eliminated infectivity of all tested low pathogenic AI viruses; however, ether with 0.2% or 0.5% Tween-20 was required for inactivation of the highly pathogenic AI H5N1 viruses. Treatment with BPL, ether and formalin retained virus hemagglutination (HA) titers. Interestingly ether treatment resulted in significant rise in HA titers (P<0.05) of all tested AI viruses. This data demonstrated the utility of BPL, formalin and ether for the inactivation of infectivity of AI viruses used in the study for the preparation of inactivated virus antigens for research and diagnosis of AI.

Antigenic analysis of H2 influenza virus haemagglutinin with monoclonal antibodies

Antigenic analysis of human and avian H2 influenza virus was carried out with monoclonal antibodies to the HA molecules of H2 influenza viruses isolated in the early stage of an H2 pandemic. The study revealed antigenic differences between inhibitor sensitive (Japan+/57, RI+57) and inhibitor resistant strains (Japan-/57, Ri-/57). This indicates that the receptor-binding specificity of the haemagglutinin can markedly influence the antigenic analysis obtained with monoclonal antibodies in HI test. Minor antigenic differences (microheterogeneity) could be detected between different H2 influenza viruses isolated in 1957. Minor antigenic variation continued in the H2 viruses until 1961, but significant antigenic drift occurred in 1962 so that viruses isolated after that date reacted with few monoclonal antibodies. Analysis of avian H2 influenza viruses suggested antigenic differences between the different avian H2 haemagglutinin, but no correlation between the year of isolation and the progressive antigenic drift similar to that seen in the human strains was found.

Characterization of H2 influenza virus hemagglutinin with monoclonal antibodies: influence of receptor specificity

Antigenic analysis of human and avian H2 influenza viruses were done with monoclonal antibodies to the HA molecules in hemagglutination inhibition (HI) assays. These studies revealed that the receptor-binding specificity of the hemagglutinin can markedly influence the antigenic analysis obtained with monoclonal antibodies in HI tests. Influenza viruses that are sensitive or resistant to inhibition by horse serum inhibitors showed marked differences in their reactivity with monoclonal antibodies to the hemagglutinin. This was apparent with the A/RI/5+/57 and A/RI/5-/57 strains of H2N2 viruses isolated by Choppin and Tamm (1960a), half of the panel of different monoclonal antibodies failed to inhibit hemagglutination of the RI/5- variant, whereas all of the 18 monoclonal antibodies inhibited RI/5+. These findings have important implications in the antigenic analysis of influenza viruses where HI assays are conventionally used to determine the extent of antigenic drift in nature. Antigenic differences were detectable between different human H2 influenza virus isolates from 1957 that were sensitive to inhibition by horse serum, indicating that minor antigenic variation occurs within the first year of appearance of the new subtype. Minor antigenic variation continued in the H2 viruses until 1961, but by 1962 antigenically distinguishable variants that could be discriminated with both monoclonal antibodies and postinfection ferret antisera predominated. Analysis of avian H2 influenza viruses with a panel of monoclonal antibodies indicated that antigenic variation occurs and that multiple different variants cocirculate in the population. There was no progressive antigenic change in the avian H2 influenza viruses with time, as was found with the human H2N2 strains. Topographical mapping of the H2 hemagglutinin by selection of antigenic variants with monoclonal antibodies and analysis of their reactivity patterns by HI showed overlap between the epitopes examined. These results may reflect restriction in the antibody repertoire of the mice used in preparation of the monoclonal antibodies or that the H2 hemagglutinin does not have such discrete nonoverlapping antigenic regions found in the early H3 influenza virus.

Antigenic properties of the envelope of influenza virus rendered soluble by surfactant-solvent systems

Dissociating chemical treatments employing surfactant-solvent systems were applied to purified influenza A and B viruses to obtain viral preparations possessing a significantly higher or lower haemagglutinating activity than the intact virus. All preparations, whether with high or low haemagglutinating activity, with the exception of envelope protein solubilized by Triton X-100, were significantly lacking in the ability to excite the formation of haemagglutination-inhibiting and virus-neutralizing antibodies in inoculated ferrets. In contrast to other treatments, Triton X-100 treatment of virus significantly enhanced the antigenicity of viral protein as judged by virus neutralization and haemagglutination inhibition tests. Yet the haemagglutinating activity of the envelope protein solubilized with Triton X-100 was about 1% that of the intact virus. Results suggest that the correlation assumed to exist between the haemagglutinating activity of influenza virus and its ability to excite the formation of humoral antibodies is coincidental. Another important point is that the specific antigenicity of viral protein may be lost or enhanced owing to effects, other than solubilization, by surface-active agents.

Degradation of influenza virus by non-ionic detergent

Preparations of influenza virus A0 PR8/34 and A2 Malaysia/68 have been studied in the electron microscope. They were similar in appearance to preparations made by others. Each preparation was degraded by Triton N 101. The process of degradation appeared to be different from that observed using ether and, by inference, a number of other agents.

Soluble antigens obtained from influenza virus by treatment with non-ionic detergent

Highly purified influenza virus was degraded using anionic and non-ionic detergents. Best results were obtained using the non-ionic detergent Triton N 101. Tests showed that virus extracts contained neuraminidase and a substance that reacted specifically with rabbit antibody to virus haemagglutinin (specific serum blocking substance). Haemagglutination-inhibiting antibody was produced when virus extracts were inoculated into guinea-pigs. Immunodiffusion tests showed that extracts were complex. Host-specific material was regularly found. Under appropriate conditions S-antigen was detected as a single line pattern component. Two or more virus-specific materials were also present. One of these was probably neuraminidase and the other the specific serum blocking substance.

Effect of polymerized orosomucoid on some strains of influenza virus

1. Polymers of orosomucoid were produced in two molecular shapes, filamentous (;chain') and spherical (;ball'), by heating the sodium salt of the monomer in either water or high concentrations of sodium chloride. An ;intermediate' state containing both shapes in various proportions was found in preparations obtained by polymerizing orosomucoid in intermediate concentrations of sodium chloride. 2. The filamentous form of polymer was found to inhibit strongly the haemagglutination of some (;sensitive') strains but not of other (;insensitive') strains of influenza virus; the ;intermediate' form feebly inhibited haemagglutination by ;sensitive' strains. 3. The filamentous form agglutinated both ;sensitive' and ;insensitive' strains of virus; the other forms of polymer did not. It also inhibited multiplication of both ;sensitive' and ;insensitive' strains when inoculated into embryonated and de-embryonated eggs. 4. The ;intermediate' and spherical forms of the polymer had no effect on the virus multiplication. 5. Polymers of orosomucoid from which neuraminic acid had been split off had no detectable effect on influenza viruses.

Automated procedure for measuring antigenicity of extracted and intact influenza virus

An automated serum-blocking (S-B) technique was developed in an attempt to find an in vitro test for the determination of the antigenicity of extracted influenza vaccines. The S-B test depends on the ability of an antigen to combine with (or block) specific (in this case, hemagglutination-inhibiting) antibodies. After mixing the test virus with a constant amount of specific antiserum and hemagglutinating virus in an Auto Analyzer, chicken erythrocytes were pumped into the system and the mixture was incubated by passing through coils. The hemagglutinated cells were removed and the residual cells were lysed. The optical density was read and recorded automatically. The S-B test was much more reproducible than the chicken cell agglutination (CCA) test. There was good correlation between the S-B and CCA titers of intact influenza virus, but not of ether-extracted influenza virus. The CCA titer of influenza strains of type A was reduced significantly during ether-extraction. The S-B titers indicated that there was no significant loss in specific antigenicity when influenza strains of types A and B were extracted with ether and Tween-80 according to the described procedure. The S-B test seemed to be a true measurement of the total antigens present in influenza vaccines.

Infective substructures of Sendai virus from infected Ehrlich ascites tumor cells

Increase of infectivity for embryonated eggs was observed in Ehrlich ascites tumor cells after intraperitoneal inoculation of Sendai virus into tumor-bearing mice. Virus-induced actinomycin-resistant ribonucleic acid consisting of 14S, 18S, 22S, 35S, and 48S was synthesized, and S antigen was produced in infected cells. The infectivity was suggested to be due to viral ribonucleoprotein for the following reasons: (i) the infectivity was unaffected by V antiserum but was abolished by whole hyperimmune serum, (ii) the infectivity was resistant to ribonuclease, (iii) virus particles were found neither in cells nor on red blood cell stroma treated with cellular extracts, (iv) structures similar to Sendai virus ribonucleoprotein with a maximal length of 10,500 A were observed in cellular extracts.

Envelope protein of influenza virus. I. Hemagglutinating activity of reassociated subunits

The hemagglutinating properties of influenza virus envelope protein, prepared by reassociation of polypeptide subunits, have been defined and compared with those of virus and ether-split hemagglutinin. In general, the characteristics of the intact and ether-split virus were found to be similar, whereas those of the envelope protein were distinctly different. The use of chicken, pigeon, and guinea pig erythrocytes both at 23 and 4 C disclosed that the hemagglutinating titers of envelope protein preparations were particularly dependent on the system employed. Under optimal conditions, with guinea pig cells at 4 C, the titers of envelope protein preparations were equivalent to those of the original virus concentrates. The hemagglutinating activity of envelope protein was particularly sensitive to elevated temperature, concentrated urea, sulfhydryl-reducing reagents, and tryptic digestion at high salt concentrations. In all these respects, the intact virus was more resistant than the envelope protein. Interpretation of the data indicates that the hemagglutinin is stabilized when associated with the lipid micelle at the surface of the virus.

Studies on pneumonia virus of mice (PVM) in cell culture. I. Replication in baby hamster kidney cells and properties of the virus

Pneumonia virus of mice (PVM) has been serially propagated in a line of baby hamster kidney (BHK21) cells. A maximum titer of 6.3 x 10(6) TCID(50) per ml was obtained, and there was little variation in yield on serial passage. PVM grown in BHK21 cells was antigenically similar to virus obtained from the mouse lung, but was somewhat less virulent for the mouse after 10 serial passages in these cells. Virus produced by BHK21 cells agglutinated mouse erythrocytes without prior heating or other treatment. Sedimentation of PVM in the ultracentrifuge or precipitation by ammonium sulfate resulted in a loss in infectivity but an increase in hemagglutinating activity, presumably due to disruption of the virus particle. In a potassium tartrate density gradient, the major portion of infective virus sedimented at a density of approximately 1.15, and noninfective hemagglutinin, at a density of approximately 1.13. Stock virus preparations appear to contain a large amount of noninfective hemagglutinin. The replication of PVM was not inhibited by 5-fluoro-2'-deoxyuridine, 5-bromo-2'-deoxyuridine, or 5-iodo-2'-deoxyuridine. Infected cells contained eosinophilic cytoplasmic inclusions which showed the acridine orange staining characteristic of single-stranded RNA. Foci of viral antigen were observed in the cytoplasm of infected cells by fluorescent antibody staining. The results suggest that PVM is an RNA virus that replicates in the cytoplasm.

Characterization of a low molecular weight antigenic protein from the envelope of influenza virus

Eckert, Edward A. (The University of Michigan, Ann Arbor). Characterization of a low molecular weight antigenic protein from the envelope of influenza virus. J. Bacteriol. 92:1430-1434. 1966.-An antigenic protein from the lipid-extracted residue of influenza virus strain PR8 was solubilized with urea-dithiothreitol (DTT). The protein subunits had a sedimentation coefficient of 2S in urea-DTT and reassociated to a 4S state on dialysis. This form of the envelope protein did not agglutinate erythrocytes, but reacted with strain-specific antisera in the complement-fixation and blocking-antigen tests.