Uptake and deacylation of bacterial lipopolysaccharides by macrophages from normal and endotoxin-hyporesponsive mice

Abstract

Macrophages are thought to play a central role in the responses of animals to gram-negative bacterial lipopolysaccharides (LPS). Since nothing is known about the metabolism of LPS by these cells, we studied the uptake and deacylation of radiolabeled LPS by thioglycolate-elicited peritoneal macrophages from normal (C3H/HeN) and LPS-hyporesponsive (C3H/HeJ) mice. Macrophages from both kinds of mice took up and deacylated LPS that were added to the culture medium. Opsonization of the LPS with anti-LPS immunoglobulin G antibodies greatly increased LPS uptake; the opsonized LPS also underwent deacylation at rates that were directly related to the amount of cell-associated LPS. An analysis of the fatty acid composition of the cell-associated LPS indicated that the cells have one or more acyloxyacyl hydrolases that remove the non-hydroxylated fatty acids that are normally substituted to the hydroxyl groups of (glucosamine-linked) 3-hydroxytetradecanoate residues in lipid A; we also found evidence for deacylation of 3-hydroxytetradecanoate from the glucosamine backbone. LPS deacylation by macrophages from C3H/HeN and C3H/HeJ mice was qualitatively and quantitatively similar. Nonopsonized LPS are able to stimulate LPS-responsive cells; in these studies we established that animal cells can deacylate nonopsonized LPS, thus raising the possibility that LPS metabolism may play a role in modulating cellular stimulation.