Adhesion of leukocytes on a fibrinogen-coated surface in static conditions: experimentation and modelization.

The adhesion of polymorphonuclear leukocytes (PMNs) on the vascular endothe lium is a complex process that occurs during different biological and patho logical events and involves numerous molecules. The adhesion cascade is ind uced after PMN stimulation by various molecular or cellular signals. Fibrin ogen is one of the substrates for CD11b/CD18 beta 2-integrins expressed at the PMN surface; fibrinogen-neutrophil binding is induced by inflammatory r eactions. In order to understand this process, we have carried out studies on the bas is of preliminary experiments on red blood cells and synthetic particles. T he modelization of quiescent PMNs adhesion on a fibrinogen substrate was in vestigated with a sedimentation cell chamber. Two different physiological c onditions were tested: the activated state of PMN by a synthetic pro-inflam matory activator (FMLP). The activated state of PMNs was both quantified by flow cytometry and controlled by fluorescence microscopy. The results suggest that quiescent neutrophils deposit in accordance with t he ballistic deposition model. This random adsorption model differs from ra ndom sequential adsorption (RSA) in that the cells arriving at the surface are able to roll along cells previously adsorbed introducing the notion of gravitational attraction of cells. The preliminary results obtained with stimulated PMN do not allow to choose between one of this two deposition models. Nevertheless, the qualitative a nd quantitative effects of FMLP on neutrophils were demonstrated by modific ations of adhesion molecules expression.