By passing a suspension of polymorphonuclear leucocytes through a parallel-plate chamber their adhesiveness can be assessed by scoring the number of cells trapped on the lower plate, and the fluid shear stress can be defined for a given flow rate. Since the adhesiveness of the cell at the instant of collision must exceed the distractive shear if the cell is to stop, the kinetics of cell accumulation provide a measure of the adhesiveness of the leucocytes and the adhesive interaction can be quantified. This measure of adhesion does not suffer from the complication that the force required to remove the cells from the surface will be greater if the cells have the opportunity to spread before the distractive force is applied. The assay is described in detail and the results of modifying the surface of the flow chamber and altering the composition of the suspension medium are used to illustrate the method. Plasma proteins generally seemed to reduce the adhesiveness of neutrophil leucocytes, whether they were present as a coat of adsorbed protein or in the suspension medium during perfusion. Neutrophil leucocytes, unless suspended in relatively high concentrations of plasma, were considerably more adhesive than other cells that have been tested in this assay system.

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