The way signals from infectious bacteria gain entry into the cytoplasm of host cells to activate disease-fighting inflammasomes has been discovered by researchers.

‘Understanding how inflammasomes sense bacterial invaders may reveal new ways to control the onset of these diseases.’

“Researchers have known for some time that bacterial ligands or signals must gain entry into the cytoplasm of cells to activate inflammasomes. However, the mechanism by which these signals are liberated and presented to disease-fighting inflammasome sensors has not been clear,” said Kanneganti. 




In the past 15 years, around five different types of pathogen-fighting inflammasomes have been identified in cells. In the current study, the scientists looked at how different bacteria triggered defense responses in bone marrow-derived macrophages in mice. The scientists revealed that IRGB10 is essential for the activation of two inflammasomes.
When cells were exposed to the pathogen Francisella novicida, the AIM2 inflammasome, a sensor that detects DNA from invading bacteria, was activated. F. novicida is a highly infectious pathogen that causes rabbit fever, a potentially fatal disease in humans. When cells were confronted with another pathogen, Escherichia coli, the lipopolysaccharide-sensing NLRP3 inflammasome was “kick started” into action.
E. coli is a commonly found bacterium and certain strains may cause food poisoning. The involvement of different inflammasomes shows that the body is poised to act quickly to the presence of a range of pathogens and sensor molecules like DNA or sugars that are liberated as the invading bacteria are broken down.
Joint first authors on the paper were Si Ming Man and Rajendra Karki, both postdoctoral research associates at St. Jude. “When IRGB10 islocalized to the bacterial cell membrane it starts the process of breaking down the bacterial invader. This liberates DNA or lipopolysaccharide from the pathogens, which eventually reaches and triggers action from the inflammasomes,” said Man. Added Karki: “We think IRGB10 proteins serve as a “lethal hit” to damage cytosolic bacteria in macrophages.”
Advertisement
Since the authors had observed similar distributions for guanylate-binding proteins, another group of antimicrobial proteins, they wondered if the two types of proteins worked together. Further experiments confirmed that the recruitment of IRGB10 to the bacterial cell membrane depended on the activity of these guanylate-binding proteins.
Advertisement
In time, the study of the body’s quick-reaction immune system could help scientists find new ways to design drugs or vaccines to combat bacterial infections. Unusual changes in the activity of inflammasomes have also been linked to different types of autoimmune and inflammatory diseases. Understanding how inflammasomes sense bacterial invaders may reveal new ways to control the onset of these diseases.
Source-Newswise