Ayooshi Mitra, Amity University Kolkata
Meningitis is an inflammatory condition that affects the membranes that surround the brain and spinal cord. Viruses, bacteria, fungi, and parasites can all cause it. Bacterial meningitis is one of the most serious types, and it is a leading cause of death and disability in children all over the world. Several bacteria can cause the infection, including the respiratory pathogens Streptococcus pneumoniae and Haemophilus influenzae, which are responsible for approximately 200,000 meningitis-related deaths each year. These two bacteria frequently live in healthy people’s noses and throats without causing illness. They can spread into the bloodstream and cause invasive diseases in some cases, but the reasons for this are largely unknown.
A group of researchers at Sweden’s Karolinska Institutet discovered a mechanism to escape the immune system through meningitis-creating bacteria. In laboratory tests, they discovered that Streptococcus pneumoniae and Haemophilus influenzae respond to rising temperatures by producing defences that keep them alive. The researchers believe that this discovery will help us better understand the mechanisms that these bacteria use to evade our normal immune defences and will be an important piece of the puzzle in determining what turns this normally harmless bacterium into a lethal killer.
The researchers set out to investigate the relationship between temperature changes and the survival of these bacteria in a laboratory setting in this study. Another recent discovery linked the temperature sensing abilities of the bacterium N. meningitides to invasive meningococcal disease prompted the experiments. Elevated temperatures and fever are signs of infection, and they typically boost our immune system’s ability to fight illness. In this study, however, the researchers discovered that when exposed to higher temperatures, both S. pneumoniae, and H. influenzae activated stronger immune defences. They accomplished this via mechanisms involving four distinct RNA thermosensors (RNATs), which are temperature-sensitive non-coding RNA molecules. The RNATs helped generate considerably larger protective capsules as well as binding Factor H immune-modulatory proteins to prevent bacteria from attacking the immune system.
The study’s findings suggest that temperature sensing RNATs provide an extra layer of defence that aids bacteria in colonizing their natural habitat in the nose and throat. Interestingly, the researchers discovered that these RNATs have no sequence similarity, but all retain the same thermosetting ability, implying that these RNATs evolved independently to sense the same temperature cue in the nasopharynx to avoid immune killing. The researchers feel that further research in this field is needed to determine what causes these pathogens to breach the mucous membrane and enter the bloodstream and then the brain, and future research involving an in vivo infection model is needed to characterize the role of these RNATs during colonization and invasion. This research was published in the journal “PLoS Pathogens”.
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Source:
Eichner H, Karlsson J, Spelmink L, Pathak A, Sham L-T, Henriques-Normark B, et al. (2021) RNA thermosensors facilitate Streptococcus pneumoniae and Haemophilus influenzae immune evasion. PLoSPathog 17(4): e1009513. https://doi.org/10.1371/journal.ppat.1009513
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