Generalized Lévy walks and the role of chemokines in migration of effector CD8(+) T cells

Chemokines play a central role in regulating processes essential to the immune function of T cells(1-3), such as their migration within lymphoid tissues and targeting of pathogens in sites of inflammation. Here we track T cells using multi-photon microscopy to demonstrate that the chemokine CXCL10 enhances the ability of CD8(+) T cells to control the pathogen T. gondii in the brains of chronically infected mice. This chemokine boosts T cell function in two different ways: it maintains the effector T cell population in the brain and speeds up the average migration speed without changing the nature of the walk statistics. Remarkably, these statistics are not Brownian; rather, CD8(+) T cell motility in the brain is well described by a generalized Lévy walk. According to our model, this surprising feature enables T cells to find rare targets with more than an order of magnitude more efficiency than Brownian random walkers. Thus, CD8(+) T cell behavior is similar to Lévy strategies reported in organisms ranging from mussels to marine predators and monkeys(4-10), and CXCL10 aids T cells in shortening the average time to find rare targets.