Plasma lipopolysaccharide-deacylating activity (acyloxyacyl hydrolase) increases after lipopolysaccharide administration to rabbits.

Acyloxyacyl hydrolase (AOAH) is a leukocyte enzyme that removes secondary (acyloxyacyl-linked) acyl chains from the lipid A moiety of bacterial lipopolysaccharides (LPS). We now report that the same enzymatic activity is present in normal rabbit plasma and that its activity can be greatly increased by LPS challenge. Intravenous administration of LPS to rabbits resulted in a rapid increase (peaking at 90 minutes, with a mean peak increase of 16-fold) of plasma AOAH activity; the activity then slowly decreased to baseline levels over 24 hours. The plasma AOAH is probably derived, at least in part, from circulating leukocytes, since (a) the AOAH response was significantly diminished in leukopenic rabbits, and (b) incubation of blood or isolated leukocytes with LPS in vitro resulted in increased extracellular AOAH activity. These results indicate that AOAH can appear extracellularly, in plasma, as part of the early response to intravenous LPS challenge. The cellular source(s) and biological role of the plasma enzyme remain to be determined.