Scientists watch flu virus enter living human cells ^{CEFR B2}

Researchers have recorded, in living human cells, the detailed process by which influenza viruses enter cells. Teams from Switzerland and Japan, led by Yohei Yamauchi at ETH Zurich, developed a new imaging approach called virus-view dual confocal and AFM (ViViD-AFM). This method combines atomic force microscopy (AFM) with fluorescence microscopy to provide higher spatial detail than fluorescence alone while avoiding the damage caused by electron microscopy.

The study shows that cells actively participate in the entry process rather than remaining passive. Influenza viruses first attach to molecules on the cell surface and then move across the membrane until they encounter a region where many receptor molecules sit close together; that clustered site forms an efficient entry point. The virus hijacks the cell’s ordinary uptake pathway, which normally brings vital substances such as hormones, cholesterol or iron into the cell.

• The membrane forms a depression or pocket at the receptor site.
• Clathrin proteins shape and stabilise this pocket as it grows.
• The pocket envelops the virus and becomes a vesicle that enters the cell.

Because ViViD-AFM records these events in living cells, the researchers could follow dynamic behaviours: the cell recruits clathrin to the virus site, the surface bulges to hold the virus, and wavelike membrane movements increase if the virus moves away. The technique offers new options for antiviral research, including testing the effect of potential drugs in cell culture in real time, and it could also be applied to study other viruses or vaccines. The research appears in PNAS.