Changes in the mechanical and adhesive behaviour of human neutrophils on cooling in vitro

Changes in the rheological properties of neutrophils may influence flow in microvessels that are cooled below normal body temperature. We investigated the effects of temperature on the mechanical and adhesive properties of hu man neutrophils by measuring transit times for individual cells flowing thr ough 8-mum-pores in filters, and adhesion to P-selectin for cells perfused over a monolayer of activated platelets. Pore transit time increased as tem perature was decreased from 37 degreesC to 0 degreesC. Upon rapid cooling, there was an instantaneous increase attributable to changes in aqueous visc osity. Interestingly, at 10 degreesC specifically, there was an additional increase in transit time, which was abolished by the inhibitor of actin pol ymerization, cytochalasin B. This meant that by 15 min, transit time at 10 degreesC was greater than at 0 degreesC. Most adherent cells on P-selectin were rolling, rather than stationary, at 10, 26 or 37 degreesC. The velocit y of rolling slowed with decreasing temperature. The total number of adhere nt cells decreased with increasing wall shear rate, but for a given shear r ate there was relatively little effect of temperature on attachment. Howeve r, when adhesion at 10, 26 or 37 degreesC was compared at equal shear stres s (taking into account fluid viscosity), adhesion was greatest at 10 degree sC. Measurements of immunofluorescence showed that exposure to 10 degreesC gradually increased expression of beta2-integrin CD11b/CD18, but this did n ot cause transformation to stationary adhesion with time in the flow assay. Thus, neutrophils show an anomalous rheological response around 10 degrees C, which may impair local microcirculation in the cold. On rewarming, "acti vated" cells might inhibit recovery or become released into the systemic ci rculation.