Correlation between speed and turning naturally arises for sparsely sampled cell movements.

Mechanisms regulating cell movement are not fully understood. One feature of cell movement that determines how far cells displace from an initial position is persistence, the ability to perform movements in a direction similar to the previous movement direction. Persistence is thus determined by turning angles between two sequential displacements and can be characterized by an average turning angle or persistence time. Recent studies documenting T cell movement in zebrafish found that a cell's average speed and turning are negatively correlated, suggesting a fundamental cell-intrinsic program whereby cells with a lower turning ability are intrinsically faster. In this paper we confirm existence of the correlation between turning and speed for six different datasets on 3D movement of CD8 T cells in murine lymph nodes (LNs) or liver. By simulating correlated or persistent random walks (PRWs) using two different frameworks we show that the negative correlation between speed and turning naturally arises when cell trajectories are sub-sampled, i.e., when the frequency of sampling is lower than frequency at which cells make movements. This effect is strongest when the sampling frequency is on the order of magnitude with the typical cell persistence time and when cells vary in persistence time. The effect arises due to sensitivity of estimated cell speeds to the frequency of imaging. Interestingly, by using estimated persistence times for cells in two of our datasets and simulating cell movements using the OU process we could partially reproduce the experimentally observed correlation between turning and speed without a cell-intrinsic program linking the two processes. Our results thus suggest that sub-sampling may contribute to (and perhaps fully explains) the observed correlation between speed and turning at least for some cell trajectory data and emphasize the role of sampling frequency in inference of critical cellular parameters of cell motility such as speeds.