Common bacteria manipulate the immune system to infect us

Researchers from The University of Queensland (UQ) have identified how a common bacteria can manipulate the human immune system during respiratory infections and cause persistent illness.

Researchers, led by Professor Ulrike Kappler from the University of Queensland's School of Chemical and Molecular Biosciences, studied the mechanisms of virulence of Haemophilus influenzae, a bacterium that plays an important role in exacerbating respiratory infections.

Laboratory studies conducted by the team on human respiratory epithelium grown in the lab showed how infection with Haemophilus influenzae can induce tolerance and suppress immune responses.

Professor Kappler said bacteria have a unique ability to "talk" to the immune system and deactivate it, convincing it that there is no threat.

The researchers prepared human nasal tissue in the lab, cultured it to resemble the surfaces of the human respiratory tract, and then monitored changes in gene expression over the course of a 14-day "infection."

They found very limited production of inflammatory molecules over time, which are normally produced within hours of bacteria infecting human cells.

“We then applied both live and dead Haemophilus influenzae, and showed that the dead bacteria caused rapid production of inflammation makers, while the live bacteria prevented this. This proves that bacteria can effectively reduce the human immune response,” said Professor Kappler.

Co-author and paediatric respiratory physician Professor Peter Sly from the University of Queensland's School of Medicine said the findings show how Haemophilus influenzae can cause chronic infections, living primarily in the cells that line the surface of the respiratory tract.

“This is a rare behavior that many other bacteria don’t have,” Sly said. “If local immunity is reduced, for example during a viral infection, the bacteria may be able to take over and cause a more serious infection.”

The findings could help fuel future research to develop new treatments to prevent these infections by helping the immune system recognize and kill them.

“We will look at ways to develop treatments that boost the immune system’s ability to detect and eliminate the pathogen before it can cause further damage,” said Professor Kappler.

The results of the study were published in the journal PLOS Pathogens.