Bold opening: Flu viruses don’t just attack quietly—they choreograph a living, microscopic dance on the surface of our cells, and scientists are finally watching it in real time.
As winter returns, so does the flu, brought by influenza viruses that enter the body through droplets and target vulnerable cells. A joint research team from Switzerland and Japan has taken an exceptionally close look at how this virus behaves. Using a self-designed microscopy approach, researchers can zoom in on the outer surface of human cells in a petri dish and observe, live and in high detail, the moment an influenza virus infiltrates a living cell.
Led by Yohei Yamauchi, a Professor of Molecular Medicine at ETH Zurich, the team made an unexpected discovery: the cells aren’t passive bystanders as the virus approaches. Instead, they seem to actively engage, almost as if assisting the virus. “The infection of our body cells is like a dance between virus and cell,” says Yamauchi.
Viral Surfing on the Cell Surface
Even though infection doesn’t benefit the cell, the interaction appears dynamic because the virus exploits a routine cellular uptake system that cells rely on for essential substances. This system normally ferries nutrients such as hormones, cholesterol, and iron into the cell.
To start infection, the influenza virus binds to specific molecules on the cell surface. The process resembles surfing along the membrane. The virus glides across the surface, attaching to one molecule after another until it reaches a region rich in receptors. A patch with many receptors side by side provides the most efficient entry route.
When the cell’s receptors sense the virus’s attachment, the membrane begins to indent at that spot. A structural protein called clathrin shapes and supports this deepening pocket. As the pocket grows, it wraps around the virus to form a vesicle. The cell then pulls this vesicle inward, the coat dissolves, and the virus is released inside.
Why Earlier Microscopy Fell Short
Past attempts to capture this pivotal moment relied on electron microscopy, which requires destroying cells to obtain an image, yielding only static snapshots. Fluorescence microscopy, while capable of live imaging, lacks high spatial resolution.
ViViD-AFM Sheds Light on Viral Entry
The new method, which combines atomic force microscopy (AFM) with fluorescence microscopy, is called virus-view dual confocal and AFM (ViViD-AFM). This hybrid approach enables tracking of the virus’s fine-scale movements as it enters the cell.
Using ViViD-AFM, the researchers showed that cells assist the virus at multiple stages of entry. They recruit crucial clathrin proteins to the attachment site, and the membrane at that location pushes upward, appearing to seize the virus. These membrane movements intensify if the virus attempts to drift away from the surface.
Implications for Antiviral Research
Because ViViD-AFM lets scientists observe infection as it happens, it provides a powerful platform to test antiviral drug candidates directly in cell cultures. The team notes that this technique could also be applied to studying other viruses or even vaccines, offering researchers real-time insight into how these particles interact with cells.
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