Dynamic Traction Forces of Human Neutrophil Adhesion

Abstract

The focus of our presentation will be the mechanics of human neutrophil adhesion and the associated role of the cell cytoskeleton during this process. The principle tool we employ to measure adhesive forces is microfabricated-Post-Array-Detectors (mPADs). We achieve high spatial and temporal resolution of neutrophil adhesion to arrays of sub-micron diameter vertical pillars functionalized with the adhesive ligand fibronectin (FN). Additionally, we will present adherent cell profiles (vertical contours) of neutrophils on pillars via confocal microscopy. The adhesion event is stimulated by haptokinetic interaction with FN alone, consistent with our previous work on continuous fields of FN (Henry et al. 2014. Integr Biol. 6:348). Our preliminary data shows the adhesion event is initially a fast (38 ± 8 s, mean ± sd, n = 7 cells) protrusive front that spreads radially outwards with an average per-pillar force of 32 ± 17 pN (mean ± sd, n = 7 cells). Over the next 2-5 min the cell transitions from a protrusive phenotype to a contractile phenotype with the peripheral pillars being deflected inwards towards the cell center and having an average per-pillar force of −43 ± 26 pN (mean ± sd, n = 7 cells). Pillar behavior can be dichotomized according to the position of the pillar relative to the cell's geometric centroid. Peripheral pillars (those residing at the edge of the cell footprint) are highly contractile and persistent in their contractility, core pillars are less so. Pretreatment of quiescent neutrophils with a variety of small molecule inhibitors of the cell cytoskeleton alter the long-time (i.e. minutes) contractile phase of adhesion but have little effect on the short-time (i.e. seconds) protrusive signature. A notable exception is pretreatment with Jasplakinolide which rigidifies the quiescent cortical actin shell and abrogates adhesion completely.