Polymorphonuclear leucocyte chemotaxis: detection of the gradient and development of cell polarity.

The ability of polymorphonuclear leucocytes to respond to a chemical gradient has been examined by observing their behaviour in response to the peptide N-formylnorleucylleucylphenylalanine (f-NorleuLeuPhe). The cells appear to detect the direction of the chemical gradient by sensing differences in the number of their chemotactic receptors that are bound acroos their dimensions. When moving, a PMN has a polarized form with ruffles or pseudopods at the front and a knob-like tail at the rear. The potential for forming new pseudopods appears to exist in a gradient from anterior to posterior along the cell axis. Rapidly increasing the concentration of peptide can transiently induce the formation of ruffles over most of the cell surface except the tail. The presence of transient reversible responses to increases in the chemotactic factor suggests that with time the leucocyte adapts to the concentration of peptide to which it is exposed. A simple model which describes the cell polarity and adaptation is presented.