&Bullet; physics 14, p88
A new model shows that the properties of waves generated in a cell signaling process depend heavily on whether the cells are viewed as discrete units or as a collective mass.
Cut your finger and thousands of white blood cells called neutrophils swarm into the wound to fight bacteria. Fascinated by microscopic images of this migration, Paul Dieterle and Ariel Amir from Harvard University set out to better understand the process. Your previous model and that of others assumed that the cells behave as a continuum. Now the duo have explored how their model’s predictions change if the cells are instead treated as separate entities  . You find that the dynamics of the system can change significantly, resulting in unexpected behavior.
It is believed that neutrophils communicate with each other by releasing diffusible molecules that move as a wave through the surrounding fluid. While most models treat these waves as collective emanations, Dieterle and Amir consider waves generated by a population of discrete cells. The emission begins with a cell emitting a diffusible molecule. After a certain time, these molecules reach a neighboring cell, causing it to emit the same molecules. The process then repeats and builds up a wave of molecules that moves through the liquid.
The duo note that the speed of the wave depends on a number of parameters, including the cell density and the dimensions of the system. For example, they find that in a sparsely populated 1D system, in which cells react to molecular concentrations above a threshold, the waves move more slowly than predicted by continuum models. By increasing the cell density, the speed disparity disappears. Waves also move more slowly in 2D, but the disparity remains, while in 3D the opposite occurs – the wave speed is the same as the continuum speed for sparsely arranged cells and becomes slower with increasing density.
Katherine Wright is assistant editor of physics.
- P. Dieterle and A. Amir, “Diffusive wave dynamics beyond the continuum limit”, Phys. Rev. E104, 014406 (2021).