Scientists watch flu virus enter living human cells ^{CEFR B1}

For the first time, researchers watched in high resolution how influenza viruses enter living human cells. Teams from Switzerland and Japan developed a microscopy method called virus-view dual confocal and AFM (ViViD-AFM). The method combines atomic force microscopy (AFM) with fluorescence microscopy, giving finer spatial detail than fluorescence alone and avoiding the cell destruction caused by electron microscopy. Yohei Yamauchi at ETH Zurich led the study.

The observations show that cells are not passive during infection. Influenza viruses attach to molecules on the cell surface and move until they find a spot with many receptors close together, which becomes an efficient entry point. The virus then uses the cell's normal uptake mechanism that brings in substances such as hormones, cholesterol or iron.

When receptors detect a virus, the membrane forms a pocket shaped and stabilised by clathrin. The pocket grows, envelops the virus and becomes a vesicle that the cell carries inside. Inside the cell the vesicle coating dissolves and the virus is released. The technique is suitable for testing potential drugs in cell culture in real time and could also study other viruses or vaccines. The research appears in PNAS.