Ken Cadwell, an immunologist at New York University, accidentally discovered the first clues about viruses’ healing qualities, while studying the microbiome — the host of 100 trillion microbes living in our bodies.
“Viruses have gotten a bad rap,” Cadwell said. “They don’t always cause disease.”
One of the main functions of the microbiome is ensuring that the intestines develop normally. A healthy gastrointestinal tract (gut) is lined with a dense mat of finger-like projections called villi.
Scientists study mice to better understand the microbiome. When scientists raised germ-free mice in sterile cages, their intestinal villi turned out sparse and thin.
The mice’s gut lining also failed to develop a normal supply of immune cells, which fight off pathogens — diseases-producing agents. As a result, the mice became vulnerable to injuries and infections.
In order for the gut to develop healthily, a complex chemical conversation must take place between the microbiome and host cells. Genetic mutations can disrupt the harmony between the microbiome and host cells, which causes immune cells in the gut to attack needed bacteria as if they were pathogens. Several experiments suggest that illnesses such as inflammatory bowel disease may be the cause of disunity between microbes and their hosts.
Cadwell set up experiments to understand exactly how the discord happens. He and his colleagues examined mice’s cells and guts, after purposefully mutating their genetics to increase the chance of developing inflammatory bowel disease.
In the middle of Cadwell’s research he moved the mice to a new lab and something strange happened — the mice were cured.
Cadwell figured out that the first lab contained a virus called murine norovirus, but the new one was virus-free. Murine norovirus is similar to the human strain that causes vomiting and diarrhea. The virus is actually harmless in healthy mice, but Cadwell said it induced inflammatory bowel disease in the genetically-mutated mice.
Cadwell was surprised by how the virus mirrored the microbiome and wondered if the virus had a beneficial purpose. So, he set up a new lab where he infected germ-free mice with murine norovirus and the mice developed fairly healthy intestines and an immune system.
“It’s just one virus, but it’s doing many of the things that an entire community of bacteria is doing,” Cadwell said.
The experiments were recently published in Nature.
Cadwell does not predict pills full of viruses will be prescribed to treat illnesses, but he wants to figure out the molecular tricks that the viruses are using to improve the health of their hosts.
Scientists who were not involved in the study think Cadwell and his colleagues are on to something.
“They did a very good job of starting to crack that nut,” Julie K. Pfeiffer, a virologist at University of Texas Southwestern Medical Center, said about viruses’ potential benefits.
David T. Pride, a microbiologist at the University of California, San Diego, said the new study will lead other researchers to try to find similar results in humans.
“The hunt for natural viruses that are beneficial to our immune systems has officially begun,” he said.