Effect of temperature on tether extraction, surface protrusion, and cortical tension of human neutrophils

Neutrophil rolling on endothelial cells, the initial stage of its migrational journey to a site of inflammation, is facilitated by tether extraction and surface protrusion. Both phenomena have been studied extensively at room temperature, which is considerably lower than human body temperature. It is known that temperature greatly affects cellular mechanical properties such as viscosity. Therefore, we carried out tether extraction, surface protrusion, and cortical tension experiments at 37°C with the micropipette aspiration technique. The experimental temperature was elevated using a custom-designed microscope chamber for the micropipette aspiration technique. To evaluate the constant temperature assumption in our experiments, the temperature distribution in the whole chamber was computed with finite element simulation. Our simulation results showed that temperature variation around the location where our experiments were performed was less than 0.2°C. For tether extraction at 37°C, the threshold force required to pull a tether (40 pN) was not statistically different from the value at room temperature (51 pN), whereas the effective viscosity (0.75 pN·s/μm) decreased significantly from the value at room temperature (1.5 pN·s/μm). Surface protrusion, which was modeled as a linear deformation, had a slightly smaller spring constant at 37°C (40 pN/μm) than it did at room temperature (56 pN/μm). However, the cortical tension at 37°C (5.7 ± 2.2 pN/μm) was substantially smaller than that at room temperature (23 ± 8 pN/μm). These data clearly suggest that neutrophils roll differently at body temperature than they do at room temperature by having distinct mechanical responses to shear stress of blood flow.