| Research Abstract |
Bacterial cell wall components have been known as potent immunostimulator for animals. In this research, we investigated to understand the recognition mechanism of the immunostimulation based on the chemical structure of the bacterial cell wall components such as muramyldipeptide (MDP) of peptidoglycan, and lipid A, a glycolipid part of lipopolisaccharide, which we had revealed as the minimal active components for the immunostimulation.
Since the discovery of MDP as the active component, the receptor of MDP have been investigated by many researchers, and we found that N0D2, which was found in animal cells by Inohara at University of Michigan, is the receptor for MDR We demonstrated with synthetic compounds that N0D2 also recognizes the bigger structure having MDP with tetrasaccharide or octasaccharide and it leads to activate the immune system. We also found NODI, which is in cytoplasm of animal cells, is the receptor of peptides containing diaminopimeric acid, a component of gram-negative bacterial peptidoglycan. On the other hand, it was shown that TLR2, a receptor on membrane of animal immune cells, recognizes the peptidoglycan partial structures modified with hydrophobic group.
Lipopolysaccharide and its active moiety lipid A had known as the ligand of TLR4. In order to understand the activation mechanism, we investigated the role of MD2, which is a protein coupled with TLR4, as the collaboration with Miyake at the University of Tokyo, and found TLR4-MD2 complex is a real functional receptor of lipopolysaccharide and lipid A. We also synthesized a series of lipid A analogues that show antagonistic or endotoxic activity, and tried to analyze the structural characteristic of the endotoxic and antagonistic activity with the molecular modeling calculation and observation of the bioactivity.
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