Assaying how the success of phagocytosis depends on the mechanics of a large viscoelastic target

Abstract

The state of the art does not provide a method for determining how the success of phagocytosis depends on the mechanics of a target that is much larger than the phagocytosing cell. We have developed such a method. We vary the elastic moduli of millimeter-sized abiotic gels that contain fluorescent beads to act as tracers for phagocytosis. We isolate human neutrophils, expose them to gels for one hour, and then measure what percentage of neutrophils contain beads - this is our metric for successful phagocytosis. Both increased polymer concentration in agarose gels and increased crosslinking density in alginate gels are associated with decreased success of phagocytosis. When we plot the percentage of neutrophils containing beads as a function of the gel elastic modulus, we find that data from both alginate and agarose gels collapse onto the same curve. This demonstrates the utility of our method as a way of measuring how the viscoelastic mechanics of a large target impact the success of phagocytosis.