Toll-Like Receptor 4-MD-2 Complex Mediates the Signal Transduction Induced by Flavolipin, an Amino Acid-Containing Lipid Unique toFlavobacterium meningosepticum

Abstract

Flavolipin, an amino acid-containing lipid isolated from Flavobacterium meningosepticum, induces many immune responses. It has been shown that flavolipin does not induce an immune response of macrophages derived from C3H/HeJ mice, which possess a point mutation in Toll-like receptor 4 (TLR4). To determine whether TLR4 or the molecular complex of TLR4 and TLR4 association molecule MD-2 mediates the flavolipin signal, flavolipin responsiveness was examined by measuring NF-κB activation in Ba/F3 cells and Ba/F3 transfectants expressing TLR4 or both TLR4 and MD-2. Flavolipin-induced NF-κB activation was detected in the cells expressing both TLR4 and MD-2, but not in the other cells. Expression of CD14 in the transfectant expressing both TLR4 and MD-2 increased the sensitivity to flavolipin. Furthermore, flavolipin stereoisomers were chemically synthesized, and their abilities to induce NF-κB activation were examined. (R)-Flavolipin, in which the configuration of the lipid moiety is R, induced NF-κB activation via the TLR4-MD-2 complex, but (S)-flavolipin did not. In this study, we demonstrated the involvement of TLR4-MD-2 and CD14 in flavolipin signaling and the importance of the (R)-configuration of the flavolipin lipid moiety for the induction of an immune response via TLR4-MD-2.

Critical residues involved in Toll-like receptor 4 activation by cationic lipid nanocarriers are not located at the lipopolysaccharide-binding interface

“…This implies that different anchoring points can lead to dimerization and foresees other possible ways of TLR4 activation that have not been explored until now. It is likely that, in the future, other microbial or endogenous TLR4 stimulators (like amino acid-containing lipid present in many Gram-negative bacteria [ 38 , 39 ], but also gangliosides [ 40 ] or ceramides [ 41 , 42 ], which all share common structural features with diC14-amidine) will be demonstrated to be able to activate TLR4 through interaction with the TLR4 dimerization interface, expanding the possible ligands of TLR4 to non-MD-2-binding lipids. Finally, this new recognition interface might also be involved in the recognition of nanoparticles by the innate immune system.…”

Branched Fatty Acyl Esters of Hydroxyl Fatty Acids (FAHFAs), Appealing Beneficial Endogenous Fat against Obesity and Type‐2 Diabetes

“…Gomi et al. showed that the ( R )‐configuration of the lipid moiety in flavolipin is essential for induction of the signals mediated by the TLR4‐MD‐2 complex while the ( S )‐enantiomer did not induce any activation.…”

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“…A Ba/F3 cell line introduced with p55Igluc was established previously (26) and was named Ba/luc here. Ba/F3 cell lines were maintained as described previously (25).…”