Time-lapse in vivo dynamics of human corneal immune cells reveals a density-diffusivity relationship

We used time-lapse in vivo confocal microscopy (IVCM) combined with random walk modelling to investigate the homeostatic migratory dynamics of naïve dendritiform cells in human cornea. Specifically, we asked whether diffusion coefficient (D), which quantifies the tissue area a cell surveys over time, varies with local cell density and morphological parameters.

Two-dimensional time-lapse IVCM imaging was obtained from the subbasal nerve plexus at the corneal whorl of 55 healthy young adults. Dendritiform cells without visible dendrites were tracked at approximately 5-min intervals across three time points. Cell trajectories were analysed using mean square displacement to calculate displacement metrics and D. Relationships between D, local cell density and morphological features (area, length, circularity) were assessed.

Trajectories from 134 cells demonstrated isotropic, undirected migration consistent with a stochastic random walk. The median of D was 3.05 μm²/min (IQR: 0.81-7.78), while mean displacement and trajectory speeds were 0.93 ± 0.71 μm/min and 1.39 ± 0.69 μm/min, respectively. D showed a significant positive association with local cell density (rho = 0.33, p = 0.013).

This study provides in vivo real-time evidence that dendritiform cells in the healthy human cornea migrate randomly with a directional bias. Unexpectedly, higher local cell density was associated with greater D, contradicting the classical point that crowding constrains motility. These density-enhanced dispersal patterns suggest that corneal immune cells coordinate immune surveillance, even in the absence of inflammatory cues.