Abstract

Ninety years after the discovery of the virus causing the influenza disease, this malady remains one of the biggest public health threats to mankind. Currently available drugs and vaccines only partially reduce deaths and hospitalizations. Some of the reasons for this disturbing situation stem from the sophistication of the viral machinery, but another reason is the lack of a complete understanding of the molecular and physiological basis of viral infections and host–pathogen interactions. Even the functions of the influenza proteins, their mechanisms of action and interaction with host proteins have not been fully revealed. These questions have traditionally been studied in mammalian animal models, mainly ferrets and mice (as well as pigs and non-human primates) and in cell lines. Although obviously relevant as models to humans, these experimental systems are very complex and are not conveniently accessible to various genetic, molecular and biochemical approaches. The fact that influenza remains an unsolved problem, in combination with the limitations of the conventional experimental models, motivated increasing attempts to use the power of other models, such as low eukaryotes, including invertebrate, and primary cell cultures. In this review, we summarized the efforts to study influenza in yeast, Drosophila, zebrafish and primary human tissue cultures and the major contributions these studies have made toward a better understanding of the disease. We feel that these models are still under-utilized and we highlight the unique potential each model has for better comprehending virus–host interactions and viral protein function.

Highlights

  • When the influenza polymerase acid subunit (PA)-X protein was expressed in yeast, 29 unintended mutations appeared in PA-X. 24 of the PA-X mutants seem relevant to mammalian systems as they caused a reduced antiviral shutoff activity when tested in mammalian cells [131]

  • normal human bronchial epithelial (NHBE) cells may provide further knowledge to influenza tropism, the host susceptibility to complications and response to the virus in the lower respiratory tract. To validate these cells as a model for influenza, NHBE cells were compared with Madin-Darby Canine Kidney (MDCK) cells and NHBE cells were found to have better correlative data in terms of replication abilities of live attenuated viruses isolated from different strains [54]

  • It may seem not relevant on a first glance, when studying aspects of influenza infection in yeast, Drosophila and zebrafish provide knowledge and a conceptual understanding that could not have been obtained in other experimental systems

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Summary

Introduction

As influenza is able to infect a variety of hosts, this increases the chance of mutation and genetic changes in the virus [6] Another reason could stem from the fact that we still do not fully understand critical steps in the infection cycle and have not thoroughly unraveled the function and mechanisms of action of several of the influenza viral proteins. The fact that after 90 years of massive efforts, there is still no efficient therapy or comprehensive vaccination, combined with the many questions regarding influenza pathology that are still open, has motivated investigators to try new, in some cases seemingly irrelevant, experimental models Models such as single-cell organisms (yeast), or invertebrates, such as Drosophila melanogaster (Drosophila) and aquatic vertebrates, such as zebrafish, appear to be not legitimate for studying a human-infecting virus. The purpose of this review is to draw attention to the emerging ‘alternative models’ and discuss the benefits one could extract from them for better comprehending the intricacies of the influenza virus and developing tools for devising novel anti-influenza therapies

The Life Cycle of the Influenza Virus
The Disease of Influenza and Available Therapies
Traditional Models to Study Influenza
Cell Lines
HEK293 and Vero Cells
Animal Models
Ferrets
Drosophila Melanogaster
Application of the Drosophila System for the Study of Viruses
Drosophila and Influenza Virus Infection
Zebrafish
Primary Human Tissue Culture
Conclusions and Future Directions
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