Eavesdropping on the immune system could provide vital clues to curing diseases, but homing in on the body’s various immune-cell signals has proved a difficult and daunting task. Some chemical messages – those that travel directly from cell to cell – are easy to pick up. Others, called paracrine signals because they travel between cells that have no direct contact, are produced in such small amounts and are so localized that detection has been nearly impossible.But thanks to a device called a multitrap nanophysiometer (MTN), detection of paracrine signals has gotten a lot easier. And it couldn’t have happened without some quick thinking by Shannon Faley, PhD candidate at Vanderbilt University in Nashville, Tenn.The multitrap nanophysiometer was developed at the Vanderbilt Institute for Integrative Biosystems Research and Education, part of Vanderbilt University in Nashville, Tenn. Courtesy of Vanderbilt Institute for Integrative Biosystems Research and Education.Now a postdoctoral researcher in the department of electronics and electrical engineering at the University of Glasgow in Scotland, Faley wasn’t even looking for paracrine signals; she was studying the direct interaction of T cells and dendritic cells (DCs) – the immune system’s soldiers and scouts, respectively. But when she noticed that they were interacting even when they weren’t in contact, her curiosity was piqued.“I was monitoring the fluorescence of T cells preloaded with a calcium-sensitive dye as they made contact with dendritic cells within the MTN,” she said. “This was a very basic experiment and was done more as a validation of our platform than [as a] search for some new piece of biological information.”Faley observed that, as expected, the T cells lit up when they came into contact with DCs, but others lit up with no direct contact. “I didn’t know what was going on, but I needed to find out if the calcium transients were caused by something I’d done incorrectly.”She quickly isolated the dendritic cells from the T cells, placing them into separate MTNs and connecting them with tubing, which allowed the effluent produced by cells in the first device to travel into the second device. “It turned out,” she said, “that mature DCs produce chemical signals which stimulate naive T cells without any contact.”Faley was unsure, at first, of the significance of her finding. “To me, this was very exciting,” she said, “although I wasn’t sure that anyone else would think so, as it’s well known that chemical signaling plays a very important role in immune response.”What she and her team found after studying the related literature was that the MTN itself, developed at the Vanderbilt Institute for Integrative Biosystems Research and Education, can play a key role in the investigation of all kinds of complex intercellular signals. They reported their findings in Lab on a Chip, Issue 10, 2008.The intricate system, which resembles a number of microscope slides stacked together, is made of a clear polymer containing microscopic traps, or wells, and channels; a pump forces liquid through the system to keep up to thousands of cells alive for study.“The trick is to trap large numbers of cells in separate regions of the device – so we can do lots of experiments in parallel,” said John P. Wikswo, professor of biomedical engineering, physics, molecular physiology and biophysics at Vanderbilt. “We keep them alive with a slow fluid flow. [The MTN is] almost like an artificial lymph node.”It allows for a more natural study environment than cell culture, Faley said. “The flow also allows us to inject various reagents – dyes, toxins, drugs, cellular products – and, because all of this takes place upon a microscope stage, we can observe the earliest cellular reactions,” she added. “The system is expandable so that there can be multiple devices used in tandem. It’s also designed to be flexible and allow incorporation of detection modalities in addition to optical microscopy.”“Our studies show that the MTN provides a means of studying intercellular communication while monitoring individual nonadherent cells in real time,” Faley said. “This information can’t be easily obtained using any other tool in a cell biologist’s toolbox.”