Next the researchers sought to pinpoint the exact movement patterns of individual T cells in living tissue from T. gondii-infected mice. This was possible with multi-photon imaging, a technique that relies on a refined yet powerful microscope that can display living tissues in three dimensions in real time. Using this approach, the team found that CXCL10 appeared to play a role in the speed at which T cells are able to search for and control infection.
To the extent that immunologists had considered T-cell movement patterns at all, many assumed that they moved in a highly directed fashion to find infected cells. But when the researchers analyzed the movement of T cells, they found their data did not match what would be expected: the T cells showed no directed motion.
That's where the statistical physics expertise of Liu and Banigan came in.
"We looked at a much more complete way to quantify these tracks and found that the standard model didn't fit at all," Liu said. "After some work we managed to find a model that did fit the tracks beautifully."
"The model that finally led us down the right path," Banigan said, "had a strong signature of something really interesting," a model known as a Lvy walk.
This "walk," or a mathematically characterized path, tends to have many short "steps" and occasional long "runs." The model was not fully consistent with the data, however.
"Rather, I had to look at variations on the Lvy walk model," Banigan said, because the researchers also observed that the T cells paused between steps and runs. Like the movements of the cells, the pauses were
|Contact: Katherine Unger Baillie|
University of Pennsylvania