Almost all animals use mucus to protect tissues exposed to the environment. For example, our stomach is lined with mucus to protect it from digestive acids. Mucus surfaces are also barriers that animals use to defend themselves against infections and prevent microorganisms from entering the body. But until recently, scientists had thought that these immune defenses were completely inert.
An artist’s conception of so-called bacteriophages attacking bacteria.
In a new groundbreaking study led by CIFAR Senior Fellow Forest Rohwer (San Diego State University), a team of researchers looked closely at mucus from animals, including humans, and found that it is filled with bacteria-killing viruses called bacteriophages that infect and kill incoming bacteria. The study is the first to show that viruses are an active player in an animal’s immune response. The findings were published in the Proceedings of the National Academy of Sciences.
The researchers collected mucus from humans, sea anemones, fish, corals and mice, and found that mucus layers had more bacteriophages and fewer bacteria than other areas in the organism. Further experimentation in the lab with mucus-producing human cell lines showed that adding viruses to the mixture reduced the number of E. Coli bacteria by more than 10,000 times. The viruses were able to stay in the mucus—instead of just diffusing through—by anchoring themselves to sugar molecules.
The study reveals a never-before-seen relationship between animals and viruses in which the viruses help protect its host from bacterial infection. This relationship likely acts at all mucus surfaces and has been evolving since animals first started producing mucus.
In the future, the team hopes to better understand the evolutionary dynamics in mucus and also what happens inside an organism. One of the long-term goals is to understand the exact role that mucus-based viruses play in protecting us from bacterial infection. Who would have thought that our bodies might be a battle-ground between viruses and bacteria?