Cellular augmentation of polymorphonuclear leukocyte chemotaxis.

The density of neutrophils influences the number of cells that will respond to a chemoattractant, endotoxin-activated serium. When fewer than 3 x 10(5) polymorphonuclear leukocytes (PMN) were placed in the top compartment of a modified Boyden chemotaxis chamber, the cellular response was weak. Complete membrane penetration by activated neutrophils rarely was observed. When this number of PMN was exceeded, however, both the number of cells and the percentage of neutrophils responding to the leukoattractant increased. The density of cells required for effective chemotactic response to occur was such that intimate cell-to-cell contact was suggested. This indicated that PMN exerted a kinetic influence upon one another. Extracts of disrupted PMN induced an otherwise insufficient number of neutrophils to respond to the chemotactic stimulus. The active component was isolated in the cytoplasmic fraction (postcentrifugation, 100,000 x g, 60 min) of PMN, but was not present in other subcellular fractions. This cytoplasmic augmentor of chemotaxis (CACh) increased random mobility of neutrophils, but was not, itself, a chemotactic factor. These findings suggest that PMN cooperate in their response to a leukotactic stimulus.