For the first time, scientists have recorded high-resolution footage of influenza viruses entering living human cells. This achievement was made possible by a new microscopy method developed by researchers from Switzerland and Japan.
The research team, led by Yohei Yamauchi, Professor of Molecular Medicine at ETH Zurich, used a technique called virus-view dual confocal and AFM (ViViD-AFM). This method combines atomic force microscopy with fluorescence microscopy, allowing scientists to observe in detail how the flu virus interacts with the surface of human cells grown in Petri dishes.
Unlike previous techniques such as electron microscopy—which destroys cells and only provides static images—or traditional fluorescence microscopy that lacks spatial detail, ViViD-AFM makes it possible to track live interactions between viruses and cells.
The researchers found that human cells are not passive during infection. Instead, they attempt to capture the influenza virus. "Of course, our cells gain no advantage from a viral infection or from actively participating in the process. The dynamic interplay takes place because the viruses commandeer an everyday cellular uptake mechanism that is essential for the cells," said Yamauchi. He explained that this same mechanism is normally used by cells to absorb important substances like hormones or iron.
The study revealed that when an influenza virus attaches itself to a cell's membrane receptors, the cell forms a pocket at that site using clathrin proteins. The pocket then grows around the virus until it is enclosed in a vesicle and transported inside the cell.
Researchers also noted that these wavelike movements on the cell membrane intensify if the virus moves away from its surface. "Accordingly, the researchers have been able to show that the cell actively promotes virus uptake on various levels. In this way, the cell actively recruits functionally important clathrin proteins to where the virus is located," according to their findings.
The new imaging technique could be valuable for testing antiviral drugs in real time within cell cultures and may also be used to study other viruses or vaccines.
