Kinematic analysis of chemotaxis of fresh and stored neutrophils

When neutrophils are isolated from the circulation the first function to begin to deteriorate is chemotaxis. To characterize the loss of chemotaxis that occurs during storage, a computer-assisted video motion analysis of neutrophils responding to formyl-methionyl-leucyl-phenylalanine (FMLP) was used in an agarose assay. The chemotactic speed, velocity, and orientation angle were measured, and a persistence of locomotion index (velocity/speed) and chemotropic index (cosine of the orientation angle) were calculated for fresh neutrophils and neutrophils stored in plasma at 20 to 22 degrees C for 24 hours. The data reveal that: (1) the frequency distribution of speed for individual stored cells had a different shape than that of fresh cells owing to a subpopulation of stored cells (approximately 35 percent) which migrated at a slower mean speed; (2) the frequency distribution of orientation for fresh cells is not normally distributed and contains a subpopulation (approximately nine percent of the total) of cells which orient at random in a gradient; (3) the precision of orientation of the majority of stored cells is comparable to that of fresh cells, but approximately 35 percent of the stored cells orient at random in a chemoattractant gradient; (4) neither the persistence index nor the orientation of both fresh and stored cells were correlated with speed; (5) the chemotropic index and persistence index are correlated, and this correlation is not altered by storage suggesting that stored cells which show decreased persistence also show a decreased chemotropic index. It is proposed that neutrophils respond to a gradient of fMLP with either fast, persistent, accurately oriented locomotion or slower, less persistent, randomly oriented locomotion. In addition to those neutrophils which do not migrate in response to fMLP, it is proposed that there are two subpopulations of motile neutrophils. Storage at 20 to 22 degrees C induces shifts between these three modes of behavior.