Neutrophil chemotaxis in moving gradients of fMLP

In this study the fluid gradient chamber, a modified version of the Boyden chamber that enables mobile gradients, was used to study the migration of h uman granulocytes in gradients of fMLP, Temporal chemotactic gradients were created by moving density-stabilized spatial gradients at different veloci ties in relation to migrating cells. Random and directed cell migration was quantified by applying a theoretical population distribution model to expe rimental cell distributions obtained from cell counts at different depths i n the filters. Rates of random and directed migration generally increased w ith gradient velocity. At negative gradient velocities, i.e., when the grad ients were moved in a direction opposite to that of cell migration to decre ase fMLP concentration over time, random and directed migration was inhibit ed. At positive gradient velocities, migration rates were not significantly different from those seen in immobile gradients. The fact that the rate of directed migration was smaller at negative gradient velocities indicates t hat negative temporal gradients reduced the average speed and/or orientatio n of the chemotactically migrating cells. In immobile gradients, the cells generated a small concentration increase over time when they migrated in th e up-gradient direction. Consequently; a positive temporal gradient as perc eived by the cells may act as a positive feedback signal to maintain. chemo tactic migration.