MODELING THE REVERSIBLE KINETICS OF NEUTROPHIL AGGREGATION UNDER HYDRODYNAMIC SHEAR

Neutrophil emigration into inflamed tissue is mediated by beta(2)-inte grin and L-selectin adhesion receptors, Homotypic neutrophil aggregati on is also dependent on these molecules, and it provides a model syste m in which to study adhesion dynamics. In the current study we formula ted a mathematical model for cellular aggregation in a linear shear fi eld based on Smoluchowski's two-body collision theory, Neutrophil susp ensions activated with chemotactic stimulus and sheared in a cone-plat e viscometer rapidly aggregate, Over a range of shear rates (400-800 s (-1)), similar to 90% of the single cells were recruited into aggregat es ranging from doublets to groupings larger than sextuplets, The adhe sion efficiency fit to these kinetics reached maximum levels of >70%. Formed aggregates remained intact and resistant to shear up to 120 s, at which time they spontaneously dissociated back to singlets. The rat e of cell disaggregation was linearly proportional to the applied shea r rate, and it was similar to 60% lower for doublets as compared to la rger aggregates, By accounting for the time-dependent changes in adhes ion efficiency, disaggregation rate, and the effects of aggregate geom etry, we succeeded in predicting the reversible kinetics of aggregatio n over a wide range of shear rates and cell concentrations. The combin ation of viscometry with flow cytometry and mathematical analysis as p resented here represents a novel approach to differentiating between t he effects of hydrodynamics and the intrinsic biological processes tha t control cell adhesion.