Human Neutrophils Under Mechanical Stress

Abstract

White blood cells play an important role in blood flow dynamics in the microcirculation because of their large volume and low deformability (Bagge et al. 1980). Among them, the neutrophil is of special interest, for it can activate and change its mechanical properties in seconds (Evans et al. 1993). Early studies of the mechanical properties of the passive neutrophil (Bagge et al. 1977) suggest that it behaves as a simple viscoelastic solid (represented as elastic and viscous elements in series with another elastic element). This model, known as the “standard solid model” (Schmidt-Schönbein et al. 1981), is based on small deformation experiments in which the viscosity and the two elasticities are considered as bulk properties of the cytoplasm. The results from large deformation experiments, however, cannot be explained by this model. Evans and Kukan (1984) proposed a model where the elastic resistance of the cell comes from a thin domain close to the cell surface (the “cortex”), while the cytoplasm interior is a liquid rather than a solid. According to this model there are two parameters: the cortical tension and the apparent cytoplasmic viscosity, which are sufficient for characterizing the rheology of the neutrophil.