Stimulatory effect on acetyltransferase activity by endotoxin-activated serum.

Endotoxin-activated serum, but not endotoxin or serum alone, had a stimulatory effect on acetyltransferase activity (AT) of neutrophils, which is a key enzyme in biosynthesis of platelet-activating factor. The AT stimulatory factor in endotoxin-activated serum was heat-stable, undialysable, and its activity was linear to that of endotoxin between 0.05-5μg/ml. Zymosan-activated serum, which is known to contain a substantial amount of C5a, induced superoxide anion production and degranulation of neutrophils, but did not elevate the AT level of neutrophils. On the other hand, endotoxin-activated serum did not induce superoxide anion production or degranulation. These findings provided evidence against the role of C5a in induction of AT. Sephadex G-200 gel chromatograhy and protein A affinity chromatograhy suggest that modified IgG molecules play a role in elevating the AT level of neutrophils.