  Immune cells have evolved to recognize and eliminate pathogens, and the
efficiency of this process can be measured in a Petri dish. Yet, even if the
cells are time-lapse recorded and tracked with high resolution, it is difficult
to judge whether the immune cells find their targets by mere chance, or if they
approach them in a goal-directed way, perhaps using remote sensing mechanisms
such as chemotaxis. To answer this question, we assign to each step of an
immune cell a 'p-value', the probability that a move, at least as
target-directed as observed, can be explained with target-independent migration
behavior. The resulting distribution of p-values is compared to the
distribution of a reference system with randomized target positions. By using
simulated data, based on various chemotactic search mechanisms, we demonstrate
that our method can reliably distinguish between blind migration and
target-directed 'hunting' behavior.
