ACTIVE MOTION OF POLYMORPHONUCLEAR LEUKOCYTES IN RESPONSE TO CHEMOATTRACTANT IN A MICROPIPETTE

A novel experimental method of producing and observing the active moti on of polymorphonuclear leukocytes (PMNs) using a micropipette techniq ue has been recently developed (Usami et al., 1992). The present paper develops a quantitative theory for the chemoattractant gradients and cell locomotion observed in these experiments. In previous experimenta l methods (e.g., the Boyden chamber, the Zygmond chamber and the Dunn chamber) for study chemotaxis of leukocytes, fibroblasts, and PMNs, th e exact nature of the concentration gradient of the chemoattractant is unknown. The cells may themselves modify the local gradient of the ch emoattractant. In experiments using the micropipette, an internal sour ce of chemoattractant provides well-defined boundary and initial condi tions which allow the computation of the chemoattractant concentration gradient during the active locomotion of the PMNs. Since the cell com pletely fills the pipette lumen, convection is limited to the motion o f the cells themselves. In coordinates moving with cell, it is assumed that diffusion is the only mechanism of mass transport of the chemoat tractant (fMLP). Computations of the fMLP concentration during locomot ion of the cell were carried out for a range of rates of fMLP binding by the receptors expressed on the front face of the cell membrane. The results show that the front face of the cell is subjected to increasi ng fMLP concentration during the cell motion. The sequence of events i nvolve receptor binding of fMLP, signal transduction, polymerization o f the cell cytoskeleton at the membrane of the front face, spatially d ependent adhesion to the pipette wall, and localized contraction of th e cytoskeleton. This sequence of events leads to the steady locomotion of the leukocytes in the micropipette. The computation of the distrib ution of the fMLP concentration during cell locomotion with constant v elocity in micropipette experiments shows that the cell is exposed to increasing concentration of fMLP. This suggests that chemotaxis maybe induced by temporal gradient of an attractant.