Deacylation of lipopolysaccharide in whole Escherichia coli during destruction by cellular and extracellular components of a rabbit peritoneal inflammatory exudate

Deacylation of purified lipopolysaccharides (LPS) markedly reduces its toxi city toward mammals, However, the biological significance of LPS deacylatio n during infection of the mammalian host is uncertain, particularly because the ability of acyloxyacyl hydrolase, the leukocyte enzyme that deacylates purified LPS, to attack LPS residing in the bacterial cell envelope has no t been established, We recently showed that the cellular and extracellular components of a rabbit sterile inflammatory exudate are capable of extensiv e and selective removal of secondary acyl chains from purified LPS, We now report that LPS as a constituent of the bacterial envelope is also subject to deacylation in the same inflammatory setting, Using Escherichia coli LCD 25, a strain that exclusively incorporates radiolabeled acetate into fatty acids, we quantitated LPS deacylation as the loss of radiolabeled secondary (laurate and myristate) and primary fatty acids (5-hydroxymyristate) from the LPS backbone. Isolated mononuclear cells and neutrophils removed 50% an d 20-30%, respectively, of the secondary acyl chains of the LPS of ingested whole bacteria. When bacteria were killed extracellularly during incubatio n with ascitic fluid, no LPS deacylation occurred, In this setting, the add ition of neutrophils had no effect, but addition of mononuclear cells resul ted in removal of >40% of the secondary acyl chains by 20 h, Deacylation of LPS was always restricted to the secondary acyl chains. Thus, in an inflam matory exudate, primarily in mononuclear phagocytes, the LPS in whole bacte ria undergoes substantial and selective acyloxyacyl hydrolase-like deacylat ion, both after phagocytosis of intact bacteria and after uptake of LPS she d from extracellularly killed bacteria, This study demonstrates for the fir st time that the destruction of Gram-negative bacteria by a mammalian host is not restricted to degradation of phospholipids, protein, and RNA, but al so includes extensive deacylation of the envelope LPS.