Longevity Briefs: Scientists Can Now Image Flu Virus Infections In Real-Time

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Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

Why is this research important: Influenza (flu) infections cause around 400 000 human deaths every year, and while seasonal flu vaccines work, their effectiveness drops in subsequent years as the virus mutates. Antiviral drugs, meanwhile, only work if administered during a narrow window of time, and also promote the evolution of drug resistant viruses. Despite being one of the most common viral infections in humans, there are still large gaps in our understanding when it comes to how influenza infections progress and spread. Plugging these gaps can help scientists to improve the vaccine and to treat infections more effectively.

What did the researchers do: In this study, researchers set out to engineer an influenza A virus (the type of influenza virus that can cause global pandemics) so that its presence in infected mice could be tracked in real time. They planned to do this by inserting a gene coding for a bioluminescent protein into the virus’s genome, so that cells infected by the virus would produce light. Previous attempts had been made to do this, but had reduced the ability of the modified viruses to cause disease, making them less useful for research purposes.

In the present study, researchers tried introducing genetic code for two types of bioluminescent reporter: NanoLuc, a bioluminescent enzyme similar to those used previously but with much higher luminescence, and HiBiT. HiBiT is a small protein that isn’t bioluminescent by itself, but combines with a larger protein called LgBiT to produce a bioluminescent protein. The small size of the HiBiT gene made it less likely to interfere with the virus’s replication, while the larger LgBiT could be introduced via an injection into the mice.

Key takeaway(s) from this research: In mice infected with influenza A viruses containing the genetic code for NanoLuc protein, the researchers were able to image viral infections in the respiratory tract by measuring bioluminescence. Bioluminescence correlated with viral dose, body weight change and prognosis, suggesting that this tool can be used to monitor the clinical progression of the infection. Importantly, the modified virus didn’t show any reductions in its ability to cause disease, and the doses required for luminescence to be detected were not lethal to the mice.

Images showing luminescence over 9 days post-infection in mice given various doses of modified influenza A virus. PFU (along the left) is a measure of viral dose.
Real-time tracking of bioluminescent influenza A virus infection in mice

Mice infected with HiBiT viruses, on the other hand, didn’t produce any luminescence. The researchers suggest the reason for this is probably that the injected LgBiT (necessary for producing bioluminescence by combining with HiBiT) didn’t reach the cells of the respiratory tract in sufficient concentrations. To fix this problem in the future, mice could be genetically modified so that their cells produced LgBiT, removing the need for an injection.

The ability to track influenza infections in real-time is likely to prove very useful for studying the effectiveness of new vaccines and antiviral drugs in animal models. It may also save the lives of many animals, as studying the progression of a viral infection usually requires multiple mice to be sacrificed at different stages of the disease.