Primate Monocytes - CD14, CD16 - Ziegler-Heitbrock

Lipopolysaccharide engineering in Neisseria meningitidis: Structural analysis of different pentaacyl lipid A mutants and comparison of their modified agonist properties.

Abstract

Engineering the lipopolysaccharide (LPS) biosynthetic pathway offers the potential to obtain modified derivatives with optimized adjuvant properties. Neisseria meningitidis strain H44/76 was modified by expression of the pagL gene encoding lipid A 3-O-deacylase from Bordetella bronchiseptica and by inactivation of the lgtB gene encoding the terminal oligosaccharide galactosyltransferase. Mass spectrometry analysis of purified mutant LPS was used for detailed compositional analysis of all present molecular species. This determined that the modified LPS was mainly pentaacylated, demonstrating high efficiency of conversion from the hexaacyl to the 3-O-deacylated form by heterologous PagL expression. MS analyses provided also evidence for expression of only one major oligosaccharide glycoform, which lacked the terminal galactose residue as expected from inactivation of the lgtB gene. The immunomodulatory properties of PagL-deacylated LPS were compared to another pentaacyl form obtained from an lpxL1- mutant, which lacks the 2 secondary acyl chain. While both LPS mutants displayed impaired capacity to induce production of the pro-inflammatory cytokine IL-6 in the monocytic cell line Mono Mac 6, induction of the TRIF-dependent chemokine IP-10 was largely retained only for the lgtB-pagL+ mutant. Removal of remaining hexaacyl species exclusively present in lgtB-pagL+ LPS demonstrated that these minor species potentiate but do not determine the activity of this LPS. These results are the first to indicate qualitatively different response of human innate cells to pentaacyl lpxL1- and pagL+ LPS and show the importance of detailed structure-function analysis when working with modified lipid A structures. The pagL+ LPS has significant potential as immune modulator in humans.