Scientists at Vanderbilt University have developed a miniature device that is capable of monitoring large numbers of individual living cells and their biochemical state in real time without significantly affecting their function.
Scientists have been trying to develop systems for single-cell analysis for a number of years. Because of the difficulty of keeping normal cells alive, they have been forced to use cells that have been genetically altered so they can be cultured indefinitely. Although the alteration “immortalizes” the cells, it also significantly limits their usefulness. The MTN is the first system that can monitor biochemical changes in large numbers of normal or primary cells at the single-cell level for prolonged periods, Unutmaz says.
The new device consists of a series of hair-sized channels molded in a special kind of plastic that is glued onto the bottom of a glass microscope coverslip. A shoebox-sized pump pushes fluid (normally the media used to culture cells) through one channel that opens up into a chamber filled with hundreds of tiny, three-sided wells small enough to trap individual cells. When cells are injected upstream, they are passively trapped in the wells and are held there solely by the fluid flowing out even smaller holes in the well bottoms. By precisely controlling the flow rate, the researchers can keep normal cells alive for longer than 24 hours.
The researchers monitor the cells with a digital camera attached to a standard microscope, typically snapping images every 30 seconds. They have written software that allows them to analyze the movements and reactions of individual cells. They can record various cell behaviors by injecting different fluorescent dyes into the cells. For example, when naive T-cells are primed for an immune response, the concentration of calcium ion in their cytoplasm jumps up. So, when the cytoplasm contains a dye that fluoresces when it comes into contact with calcium, it glows brightly enough to be easily detected.
The surprise discovery of paracrine signaling was made by graduate student Shannon Faley, now a postdoctoral research associate at the University of Glasgow, Scotland. She filled up a nanophysiometer chamber with naive human T-cells and then added mature dendritic cells. She was looking for evidence of T-cell activation when the T-cells and dendritic cells were trapped in the same well and came into contact. This contact is part of the process that allows dendritic cells to convey information about potentially infectious invaders to the naive T-cells, which can then begin dividing to produce an army of effector T-cells custom-designed to attack the invaders.
Faley saw what she was looking for, but she also noticed something unexpected: some T-cells that were trapped in wells downstream of those with dendritic cells, which had never been in direct contact with them, were also lighting up. “My reaction when I saw them was, ‘What in the world is going on?’” she says.
“When she saw this, Shannon did a very clever thing,” says Wikswo. “She took one chamber and filled it with dendritic cells and took a second chamber and filled it with T-cells. Then she hooked the second chamber downstream of the first.” When she did so, the T-cells in the second chamber immediately began lighting up, demonstrating that the mature dendritic cells were releasing a chemical factor that activates naive T-cells without coming into contact.
Press release: New nano device detects immune system cell signaling…
Images: Top: Photo of the nanophysiometer Side: Illustration depicts two multi-trap nanophysiometers connected in series.