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Influenza Virus Reassortment Is Enhanced by Semi-infectious Particles but Can Be Suppressed by Defective Interfering Particles.

Fonville JM, Marshall N, Tao H, Steel J, Lowen AC - PLoS Pathog. (2015)

Bottom Line: Computational results predicted enhanced reassortment at a given % infection or multiplicity of infection with increasing semi-infectious particle content.As expected, the introduction of semi-infectious particles with UV-induced lesions enhanced reassortment.These data indicate that semi-infectious particles increase the rate of reassortment and may therefore accelerate adaptive evolution of IAV.

View Article: PubMed Central - PubMed

Affiliation: Center for Pathogen Evolution, Department of Zoology, University of Cambridge, United Kingdom.

ABSTRACT
A high particle to infectivity ratio is a feature common to many RNA viruses, with ~90-99% of particles unable to initiate a productive infection under low multiplicity conditions. A recent publication by Brooke et al. revealed that, for influenza A virus (IAV), a proportion of these seemingly non-infectious particles are in fact semi-infectious. Semi-infectious (SI) particles deliver an incomplete set of viral genes to the cell, and therefore cannot support a full cycle of replication unless complemented through co-infection. In addition to SI particles, IAV populations often contain defective-interfering (DI) particles, which actively interfere with production of infectious progeny. With the aim of understanding the significance to viral evolution of these incomplete particles, we tested the hypothesis that SI and DI particles promote diversification through reassortment. Our approach combined computational simulations with experimental determination of infection, co-infection and reassortment levels following co-inoculation of cultured cells with two distinct influenza A/Panama/2007/99 (H3N2)-based viruses. Computational results predicted enhanced reassortment at a given % infection or multiplicity of infection with increasing semi-infectious particle content. Comparison of experimental data to the model indicated that the likelihood that a given segment is missing varies among the segments and that most particles fail to deliver ≥1 segment. To verify the prediction that SI particles augment reassortment, we performed co-infections using viruses exposed to low dose UV. As expected, the introduction of semi-infectious particles with UV-induced lesions enhanced reassortment. In contrast to SI particles, inclusion of DI particles in modeled virus populations could not account for observed reassortment outcomes. DI particles were furthermore found experimentally to suppress detectable reassortment, relative to that seen with standard virus stocks, most likely by interfering with production of infectious progeny from co-infected cells. These data indicate that semi-infectious particles increase the rate of reassortment and may therefore accelerate adaptive evolution of IAV.

No MeSH data available.


Related in: MedlinePlus

Results observed with UV treated Pan/99wt and Pan/99var viruses match simulated co-infections in which each virus carries an average of 2.0 UV hits per genome.Experimental data points obtained with UV treated virus stocks, plotted with open circles, are overlaid on a black line indicating the model’s predicted relationships for % HA positive cells vs. % dually HA positive cells (A) and % HA positive cells vs. % reassortment (B). Computational viruses carried an average of 2.0 UV hits per genome when PP settings found to best match the data obtained with untreated virus stocks were used (0.25, 0.5, 075, 0.75, 1, 1, 1, 1 for segments 1–8, respectively).
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ppat.1005204.g007: Results observed with UV treated Pan/99wt and Pan/99var viruses match simulated co-infections in which each virus carries an average of 2.0 UV hits per genome.Experimental data points obtained with UV treated virus stocks, plotted with open circles, are overlaid on a black line indicating the model’s predicted relationships for % HA positive cells vs. % dually HA positive cells (A) and % HA positive cells vs. % reassortment (B). Computational viruses carried an average of 2.0 UV hits per genome when PP settings found to best match the data obtained with untreated virus stocks were used (0.25, 0.5, 075, 0.75, 1, 1, 1, 1 for segments 1–8, respectively).

Mentions: We also assessed whether the increase in reassortment seen with UV treatment was quantitatively related to the observed difference in infectivity between UV treated and untreated virus stocks. Analysis of results with the UV treated virus stocks indicated that the levels of reassortment and co-infection observed best matched those predicted for a virus population that had suffered 2.0 hits per genome on average (Fig 7). Based on a Poisson distribution of UV hits per virus, this UV dose would be expected to reduce PFU titer by 7.4-fold. The observed knock-down in PFU titers with UV treatment was 11-fold. These results are comparable, particularly when one considers the typical range of error of a plaque assay (approximately 2-fold) [34], and therefore further support the validity of the model.


Influenza Virus Reassortment Is Enhanced by Semi-infectious Particles but Can Be Suppressed by Defective Interfering Particles.

Fonville JM, Marshall N, Tao H, Steel J, Lowen AC - PLoS Pathog. (2015)

Results observed with UV treated Pan/99wt and Pan/99var viruses match simulated co-infections in which each virus carries an average of 2.0 UV hits per genome.Experimental data points obtained with UV treated virus stocks, plotted with open circles, are overlaid on a black line indicating the model’s predicted relationships for % HA positive cells vs. % dually HA positive cells (A) and % HA positive cells vs. % reassortment (B). Computational viruses carried an average of 2.0 UV hits per genome when PP settings found to best match the data obtained with untreated virus stocks were used (0.25, 0.5, 075, 0.75, 1, 1, 1, 1 for segments 1–8, respectively).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4595279&req=5

ppat.1005204.g007: Results observed with UV treated Pan/99wt and Pan/99var viruses match simulated co-infections in which each virus carries an average of 2.0 UV hits per genome.Experimental data points obtained with UV treated virus stocks, plotted with open circles, are overlaid on a black line indicating the model’s predicted relationships for % HA positive cells vs. % dually HA positive cells (A) and % HA positive cells vs. % reassortment (B). Computational viruses carried an average of 2.0 UV hits per genome when PP settings found to best match the data obtained with untreated virus stocks were used (0.25, 0.5, 075, 0.75, 1, 1, 1, 1 for segments 1–8, respectively).
Mentions: We also assessed whether the increase in reassortment seen with UV treatment was quantitatively related to the observed difference in infectivity between UV treated and untreated virus stocks. Analysis of results with the UV treated virus stocks indicated that the levels of reassortment and co-infection observed best matched those predicted for a virus population that had suffered 2.0 hits per genome on average (Fig 7). Based on a Poisson distribution of UV hits per virus, this UV dose would be expected to reduce PFU titer by 7.4-fold. The observed knock-down in PFU titers with UV treatment was 11-fold. These results are comparable, particularly when one considers the typical range of error of a plaque assay (approximately 2-fold) [34], and therefore further support the validity of the model.

Bottom Line: Computational results predicted enhanced reassortment at a given % infection or multiplicity of infection with increasing semi-infectious particle content.As expected, the introduction of semi-infectious particles with UV-induced lesions enhanced reassortment.These data indicate that semi-infectious particles increase the rate of reassortment and may therefore accelerate adaptive evolution of IAV.

View Article: PubMed Central - PubMed

Affiliation: Center for Pathogen Evolution, Department of Zoology, University of Cambridge, United Kingdom.

ABSTRACT
A high particle to infectivity ratio is a feature common to many RNA viruses, with ~90-99% of particles unable to initiate a productive infection under low multiplicity conditions. A recent publication by Brooke et al. revealed that, for influenza A virus (IAV), a proportion of these seemingly non-infectious particles are in fact semi-infectious. Semi-infectious (SI) particles deliver an incomplete set of viral genes to the cell, and therefore cannot support a full cycle of replication unless complemented through co-infection. In addition to SI particles, IAV populations often contain defective-interfering (DI) particles, which actively interfere with production of infectious progeny. With the aim of understanding the significance to viral evolution of these incomplete particles, we tested the hypothesis that SI and DI particles promote diversification through reassortment. Our approach combined computational simulations with experimental determination of infection, co-infection and reassortment levels following co-inoculation of cultured cells with two distinct influenza A/Panama/2007/99 (H3N2)-based viruses. Computational results predicted enhanced reassortment at a given % infection or multiplicity of infection with increasing semi-infectious particle content. Comparison of experimental data to the model indicated that the likelihood that a given segment is missing varies among the segments and that most particles fail to deliver ≥1 segment. To verify the prediction that SI particles augment reassortment, we performed co-infections using viruses exposed to low dose UV. As expected, the introduction of semi-infectious particles with UV-induced lesions enhanced reassortment. In contrast to SI particles, inclusion of DI particles in modeled virus populations could not account for observed reassortment outcomes. DI particles were furthermore found experimentally to suppress detectable reassortment, relative to that seen with standard virus stocks, most likely by interfering with production of infectious progeny from co-infected cells. These data indicate that semi-infectious particles increase the rate of reassortment and may therefore accelerate adaptive evolution of IAV.

No MeSH data available.


Related in: MedlinePlus