BIOPHYSICAL ASPECTS OF HUMAN NEUTROPHIL MOTILITY

Neutrophils play an important role in the vertebrate immune system and are activated by chemoattractants released at injury sites, Upon stim ulation, neutrophils change their shape from spherical to elongated (' 'polarized''), They migrate up chemotactic gradients to infection sour ces where they kill invading microbes, Migration is essential for neut rophil function, It is characterized by the constant remodeling of cel lular shape and protrusions, Cell protrusions can be separated into th in, veil-like lamellipods and pseudopods, which give the cell a polari zed morphology. Neutrophils respond periodically to the environment, T heir motile behavior oscillates at high and low frequencies, The high- frequency component (similar to 8 sec) parallels oscillations in cytos keletal actin polymerization and is also evident in other neutrophil r esponses, The low-frequency period (similar to 1 min) is also apparent in force production, velocity and directional changes of crawling neu trophils. Thus, we propose a model in which the fundamental neutrophil motor is an oscillator, represented by shape changes with fast and sl ow cyclic behavior, The 8-sec shape oscillations are superimposed on t he polarized cell and may reflect the driving force as the neutrophil glides on a substratum, Then, approximately every 1 min, the cell paus es and determines its next locomotory direction.