A subpopulation analysis of f-MLP stimulated granulocytes migrating in filters

Leukocyte migration in vitro has been studied extensively during many years without providing satisfactory theoretical models for the different migratory behaviors (chemotaxis and chemokinesis) of leukocyte populations. The present study utilized the fluid gradient chamber, which is a new method to study leukocyte migration in filters. Human neutrophils were applied between two stacked filters and migrated in all directions under the influence of constant concentrations or chemotactic gradients of f-MLP, maintained in fluid phase density gradients. The distributions of the granulocytes over filter depth were fitted to theoretical functions composed by 1–3 Gaussian distributions, representing subpopulations. The results showed that the neutrophils migrated as two discrete subpopulations during chemokinetic stimulation (a constant concentration of f-MLP). One of the subpopulations showed less active and passive (slow sedimentation under the influence of gravity) translocation. The most mobile subpopulation was divided into two new subpopulations when exposed to chemotactic stimulation (concentration gradient of f-MLP), one of which responded chemotactically and one of which migrated in random directions. The properties of the different subpopulations where characterized in terms of diffusion coefficient (random migration), convection velocity (chemotactic migration) and sedimentation coefficient (passive translocation).