NEUTROPHIL ACTIVATION ASSOCIATED WITH INCREASED NEUTROPHIL ACYLOXYACYL HYDROLASE ACTIVITY DURING INFLAMMATION IN CATTLE

: Acyloxyacyl hydrolase (AOAH) is a lysosomal enzyme found in neutrophils and macrophages that acts to partially deacylate the lipid-A component of the endotoxin of gram-negative bacteria rendering it less toxic, yet maintaining much of its immunostimulatory potential. We have found that the activity of neutrophil AOAH per cell increased during localized inflammation. The purpose of this study was to determine the mechanism(s) responsible for these increases in neutrophil AOAH activity. Because changes in neutrophil maturity commonly are associated with inflammation, intravascular infusion of purified gram-negative bacterial lipopolysaccharide and SC injection of bovine recombinant granulocyte colony-stimulating factor was used to induce large numbers of circulating immature neutrophils. Immature neutrophils were found to have AOAH activity equal to that of mature cells; however, when neutrophils were stimulated in vitro with known activators, AOAH activity of activated cells was more than that of unstimulated cells. The increase in AOAH activity was inversely related to prestimulation activity. Increases in AOAH activity after neutrophil activation were not a result of de novo synthesis of the enzyme, because cycloheximide did not prevent activation-induced increases in activity.