Deacylation of purified lipopolysaccharides by cellular and extracellular components of a sterile rabbit peritoneal inflammatory exudate

The extent to which the mammalian host is capable of enzymatic degradation and detoxification of bacterial lipopolysaccharides (LPS) is still unknown. Partial deacylation of LPS by the enzyme acyloxyacyl hydrolase (AOAH) prov ides such a mechanism, but its participation in the disposal of LPS under p hysiological conditions has not been established. In this study, deacylatio n of isolated radiolabeled LPS by both cellular and extracellular component s of a sterile inflammatory peritoneal exudate elicited in rabbits was exam ined ex vivo. AOAH-like activity, tested under artificial conditions (pH 5. 4, 0.1% Triton X-100), was evident in all components of the exudate (mononu clear cells [MNC] > polymorphonuclear leukocytes [PMN] > inflammatory [asci tic] fluid [AF]). Under more physiological conditions, in a defined medium containing purified LPS-binding protein, the LPS-deacylating activity of MN C greatly exceeded that of PMN. In AF, MNC (but not PMN) also produced rapi d and extensive CD14-dependent LPS deacylation. Under these conditions, alm ost all MNC-associated LPS underwent deacylation within 1 h, a rate greatly exceeding that previously found in any cell type. The remaining extracellu lar LPS was more slowly subject to CD14-independent deacylation in AF. Quan titative analysis showed a comparable release of laurate and myristate but no release of 3-hydroxymyristate, consistent with an AOAH-like activity. Th ese findings suggest a major role for CD14(+) MNC and a secondary role for AP in the deacylation of cell-free LPS at extravascular inflammatory sites.