Assaying macrophage chemotaxis using fluid‐walled microfluidics

While many tools exist to study immune-cell chemotaxis in vitro, current methods often lack desirable features. Using fluid-walled microfluidics, circuits are built around primary murine macrophages deposited in pre-defined patterns on Petri dishes or microplates. Concentration gradients of complement component 5a (C5a) are established in flow-free or flowing environments, image cell migration, and relate cell directionality and velocity to calculated local C5a concentrations. In flow-free circuits built around patterned macrophages, only cells nearest the C5a source migrate regardless of local attractant concentration. Conversely, in flowing circuits free from intercellular signaling and attractant degradation, only cells distant from the source migrate. In both systems, cells respond to lower C5a concentrations than previously reported (≈0.1 pM). Finally, macrophages follow instantly-shifted gradients better than slowly-shifting ones, suggesting that migration depends on both spatial and temporal responses to concentration.