Analysis of the Migration of Neutrophil-Like Cells under a pH Gradient using a Microfluidic Device

Neutrophils are known to accumulate in an acidified inflammatory microenvironment, but the effects of environmental factors on neutrophils are not fully understood. Here, we investigated the response of neutrophil-like differentiated human promyelocytic leukemia cells (HL-60) to pH changes. A previously developed microfluidic device that enables control of the oxygen concentration was used to control the pH in a microenvironment. The CO
2
concentration in the cell culture medium was controlled by gas exchange between the media and gas channels, thereby establishing certain pH gradients based on chemical equilibrium. The device enabled the generation of a pH 8.5 to 7.1 gradient when gas mixtures of 1% and 50% CO
2
were supplied to the left and right gas channels, respectively. Neutrophil-like differentiated HL-60 cells were then seeded into the media channels to observe their cellular dynamics under the pH gradient. Quantitative evaluation showed that cell migration was suppressed in the low-pH (high CO
2
concentration) region compared to the high-pH (low CO
2
concentration) region, whereas no clear chemotactic migration in response to pH was observed.