Cell Polarity : An Examination of Its Behavioral Expression and Its Consequences for Polymorphonuclear Leukocyte Chemotaxis

Locomoting polymorphonuclear leukocytes (PMNs) exhibit a morphological polarity . We demonstrate that they also exhibit a behavioral polarity in their responsiveness to chemotactic factor stimulation . This is demonstrated by (a) the pattern of their locomotion in a homogeneous concentration of chemotactic factors, (b) their responses to increases in the homogeneous concentration of chemotactic factors, and (c) their responses to changes in the direction of a chemotactic gradient . The behavioral polarity is not a function of the rate of locomotion or the particular stimulant used to orient the cells, but may reflect an asymmetric distribution of chemotactic receptors or the motile machinery . The polar behavior affects the chemotactic ability of PMNs . The data are discussed in relation to possible mechanisms of sensing a chemotactic gradient . Locomoting polymorphonuclear leukocytes (PMNs) have a morphological polarity, with a thin, granule-free pseudopod at the front and a uropod or tail at the rear . Such polarity could merely represent the current direction of locomotion by the cell and not affect the ability of the cell to respond to new stimuli . This would mean that the PMN would be equally capable of extending a new pseudopod in any direction at any time . Alternatively, the morphological polarity could correlate with a structural polarity that biases subsequent responses of the cell. Thus, the cell would also exhibit a behavioral polarity . The extreme of this situation would be analogous to a car with no reverse gear : it can turn but only moves forward and keeps a fixed polarity . The extent to which the PMN behavior is amorphous or linked to the morphological polarity is important for our understanding of several processes . A polarity that biases behavior would affect the way cells align themselves along a new chemotactic gradient and would affect the interpretation of experiments examining the mechanism by which cells detect a gradient . A behavioral polarity could also stabilize the cell orientation in a constant gradient and therefore serve to effectively amplify the directional signal . Finally, as we begin to study the mechanisms of cell locomotion on a molecular level, an understanding of the cell's behavior will be useful . For example, if a cell is functionally polarized, it may not be TIIE JOURNAL OF CELL BIOLOGY " VOLUME 89 JUNE 1981 585-592 © The Rockefeller University Press 0021-9525/81/06/0585/08 $1 . 00 necessary to search for a difference in some mediator of the motility (e .g., pH or calcium ion concentration) between the front and the back of a cell, because the same signal placed in different environments could result in diverse responses, such as extension at the front of a cell and contraction at the rear and along the sides. Previous studies have shown that PMNs locomoting in a homogeneous solution tend to persist in a given direction, making turns of small angles, usually <900 (2, 14, 25) . Other cells, including fibroblasts and slime molds, also show persistence in their direction of locomotion (1, 10, 16) . We now report on an examination of the effect of polarity on PMN responses to chemotactic factors . Using a number of different tests, we find that the front of a locomoting cell is more responsive to stimulation by chemotactic factors than the tail . This asymmetry in responsiveness correlates with the morphological polarity and not with the dynamic features of the locomotion, e.g . , the rate of locomotion . Neither the morphological nor the behavioral polarity is dependent upon the presence of microtubules . MATERIALS AND METHODS