Concentration gradients in the under-agarose chemotaxis assay system with attractant surface adsorption

To evaluate directional locomotion or chemotaxis of polymorphonuclear leukocytes (PMNL), assay conditions need to be understood quantitatively. The characteristics of the gradient of a chemoattractant in an assay system depend on, for example, the geometry of the system and the diffusion coefficient of the attractant, but since PMNL are able to respond to surface-bound attractants, surface adsorption of the attractant might also be a factor of importance. We have solved the diffusion equation to characterize the gradients present in the under-agarose assay system, when surface adsorption of the chemoattractant is taken into account. Application of the theory to experimental data shows that surface adsorption is important for the cellular response to the chemotactic factor generated from normal human serum, but not for the response to the chemotactic peptide fMLP.