Scientists have, for the first time, captured real-time footage of influenza viruses “surfing” their way into human cells, a breakthrough that could reshape understanding of how flu infections begin. The discovery comes from a Swiss–Japanese research team that developed a high-precision imaging technique capable of tracking the virus at the exact moment it breaches a living cell.
As winter brings the familiar symptoms of fever, body aches and runny noses, the study sheds new light on how influenza viruses invade the body. These viruses typically enter through respiratory droplets and target susceptible cells, but until now, the critical moments of the virus’s entry had never been observed with such clarity.
Led by Yohei Yamauchi, Professor of Molecular Medicine at ETH Zurich, the team used a custom-built microscopy system to zoom in on the surface of living human cells grown in a petri dish. The approach allowed researchers to film the very instant an influenza virus attaches itself and is drawn inside. What they observed surprised them: the cell does not simply wait passively for the virus. In fact, it seems to reach out.
“Infection is like a dance between virus and cell,” Yamauchi said. The virus may be the invader, but the cell’s own intake machinery unintentionally helps it along.
A surfing virus and an active cell
Before entering, the flu virus latches onto specific molecules on the cell’s membrane and glides across the surface, almost like surfing, until it reaches an area densely packed with receptors. These clustered sites provide the smoothest entry point.
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Once the virus binds there, the cell begins shaping a small pit beneath it. A protein called clathrin strengthens and deepens this indentation. As the pocket expands, it envelopes the virus, forming a vesicle that the cell pulls inward. Once inside, the outer coating dissolves, and the virus is set free to begin infection.
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This process taps into a normal cellular system that the cell relies on to absorb essential substances such as hormones, iron and cholesterol – a system the virus cleverly hijacks.
Why scientists couldn’t see this before
Earlier imaging methods fell short. Electron microscopy required destroying cells to obtain images, capturing only frozen snapshots of the infection. Fluorescence microscopy allowed live imaging but lacked the resolution to reveal fine surface movements.
To overcome these limitations, the researchers combined atomic force microscopy (AFM) with fluorescence imaging, creating a technique they call ViViD-AFM (virus-view dual confocal and AFM). This hybrid method produces high-resolution, real-time images of the virus interacting with the cell membrane.
With ViViD-AFM, the team found that the cell actively takes part in the virus’s entry. It summons clathrin to the attachment site and even pushes its membrane upward toward the virus. These movements intensify if the virus drifts, almost as if the cell is trying to capture it.
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Because ViViD-AFM allows scientists to watch infection unfold live, it provides a powerful tool for testing antiviral drugs at the cellular level. Researchers said the method can also be used to study other viruses or even vaccine particles, offering unprecedented insight into how they interact with human cells in real time.
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