Our cells may get a health benefit when they engulf bacteria-killing viruses. Understanding the role of these viruses, known as phages, in our bodies is important, as they are increasingly used in some parts of the world as an alternative to antibiotics amid the resistance crisis.
“We know that broadly phage therapy is safe,” says Jeremy Barr at Monash University in Australia. But cells trap phages, which are abundant in the human body, as they internalise liquid from their surroundings and scientists don’t know the full extent of how this impacts cells, he says.
To learn more, Barr and his colleagues exposed human and other mammalian cells to phages, namely the well-studied T4 phage, in a laboratory. Staining the phage’s DNA allowed them to see when the cells had engulfed the virus.
The researchers wanted to know whether taking up the phage triggered any inflammation within the cells. They found that no immune responses were turned on after the cells took up the bacteria-killing viruses.
This suggests that phages could treat bacterial infections that cause inflammation without making symptoms worse, says Sabrina Green at KU Leuven in Belgium.
In another part of the experiment, the team explored how engulfing a phage might change processes within a cell. After analysing 2000 proteins that govern cellular functions in lung and kidney cells, the researchers focused on two signalling pathways that were consistently altered.
After the cells engulf the virus, one pathway boosts cell growth, survival and proliferation, while the other temporarily stalls the cell cycle just before a cell replicates its DNA. Cells might scavenge resources from the virus for their own growth during this stalling, says Barr.
“It is very likely phage-mammalian cell interactions are taking place all the time in our bodies, without any dramatic consequences,” says Mikael Skurnik at the University of Helsinki in Finland. This reinforces his confidence that phage therapies are safe, he says.
According to Barr, cells engulfing phages may mean that fewer phages are available in the body to attack bacteria when used therapeutically. But Green says that might not be an issue because phages propagate and replenish their numbers as they target bacteria.
Future studies could look at many different types of phages rather than just focusing on T4, says Green.