A new study has found a novel way in which certain bacteria are recognised and trigger our immune system.
Dr Norihito Kawasaki has led a group of researchers investigating the role of molecules called lipopolysaccharides. These molecules are found on the outer surface of a large group of bacteria, where they play a key role in protecting the bacteria. But they also give away their identity to molecules that play a role in our immune defence.
Now, in a paper published in the Journal of Biological Chemistry, the researchers have uncovered new details about how this recognition happens, and how this information is relayed to the immune system so that it can coordinate a response.
Lipopolysaccharides, as their name suggests are made up of a fatty lipid section attached to a sugary polysaccharide part. Whilst the lipid part is relatively similar between different bacteria, the polysaccharide is highly variable. Lipopolysaccharides (LPS) have been recognised for their role in triggering immune response, but this new research adds to our understanding of how this happens and helps explain how we react to infection by certain bacteria.
Using a combination of techniques involving isolated immune cells, the researchers showed that the polysaccharide part of the LPS can be recognised by proteins from the host called lectins. Lectins are proteins that bind to specific polysaccharides, and play important roles in a number of different processes, including in modulating the immune system.
“This helps us understand what happens when bacterial infections occur, and how our bodies fight against infection” said Dr Kawasaki.
Specific lectins bind to the LPS, and this leads to an enhanced immune response over that which is seen when there is no connection between lectins and the LPS polysaccharide. This brings a level of specificity to the response based on the sugar chemistry displayed on the bacteria’s surface proteins.
As well as helping us understand these fundamental infection processes, the new insights into these mechanisms might help in the design of vaccine adjuvants that increase the efficacy of vaccinations.
The Institute of Food Research is strategically funded by the Biotechnology and Biological Sciences Research Council (BBSRC), who funded the research along with a Marie-Curie Incoming Fellowship award from the EU 7th Framework Programme to Dr Kawasaki.
Wittmann, A., Lamprinaki, D., Bowles, K.M., Katzenellenbogen, E., Knirel, Y.A., Whitfield, C., Nishimura, T., Matsumoto, N., Yamamoto, K., Iwakura, Y., Saijo, S., and Kawasaki, N. Dectin-2 Recognises Mannosylated O-antigens of Human Opportunistic Pathogens and Augments Lipopolysaccharide Activation of Myeloid Cells, Journal of Biological Chemistry doi: 10.1074/jbc.M116.741256