Cellular cooperation in polymorphonuclear leukocyte chemotaxis: augmentation by neutrophil cytoplasm

The number of polymorphonuclear leukocytes (PMN) responding to a chemotactic stimulus is influenced by the cell density. Evidence is presented that the cytoplasmic fraction of PMN augments the response of neutrophils to endotoxin-activated serum but the activator of chemotaxis (CACh) in cytosol is not chemotactic itself. This cytoplasmic neutrophil cytosol is not present in nuclear, microsomal or large granular fractions. Preliminary characterization studies suggest that CACh is nondialyzable, has a molecular weight of less than that of albumin, is heat stable (56 degrees C for 30 min) but is destroyed by trypsin. Studies on intracellular concentrations of cAMP and cGMP following incubation of PMN with various subcellular fractions suggest that CACh causes the loss of intracellular cAMP, a finding which could account for its chemokinetic action. As expected, the lysosomal fraction of PMN was chemotactic and reduced the net negative surface charge of neutrophils. CACh, however, was neither chemotactic nor did it alter the charge density on PMN surfaces. These studies provide evidence for cellular cooperation in the initial phases of the chemotactic response. The clustering of PMN along endothelial surfaces could provide the necessary local cell density for this augmented response to take place.