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 of 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.

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