Viral biodiversity and human health – the potential role of environmental bacteriophages in training the human immune system

Abstract

The biodiversity hypothesis suggests that exposure to microbial biodiversity has beneficial health effects such as reduced risk for allergies and various autoimmune diseases. However, these associations are not yet based on strong causal evidence—findings have been inconclusive and contradictory, and the potential mechanisms are unclear. Moreover, one key component and driver of biodiversity has not been properly considered: bacteriophages, that is, bacterial viruses. Bacteriophages can influence the bacterial biodiversity across diverse environments and represent the most abundant microorganisms on Earth. By piggybacking and killing the winner, phages lyse dominant bacterial host strains leading to a release of resources to the remaining community, thereby diminishing the risk of rare bacterial species going extinct. Such changes could have indirect effects with immune system through phage-mediated changes in bacterial community diversity and composition, which could shape the bacteriome-immune system interaction. Furthermore, bacteriophages could directly interact with the human immune system as phage particles and their components may trigger immune response and cause other reactions with human cells. We hence hypothesize that phages, through their influence on bacterial communities and their own direct effects, may influence the “training” of immune system. However, the direct causal evidence is still lacking, and thus more data is required to test this hypothesis.