Read any “secrets to a healthy gut” article or listen to Dr. Andrew Huberman‘s Podcasts on “Gut and Brain Health,” and you’ll learn all about the role of bacteria in the human microbiome. But here’s something no one talks about – viruses and gut health. So how does this unlikely duo work? Below, we reveal a new study suggesting that transplanting certain viruses could potentially treat Irritable Bowel Disease (IBD) and other intestinal disorders. Let’s dive in.
The Human Virome & Viral “Dark Matter”
The bacteria and fungi typically found in the gut microbiome are thought to play an essential role in intestinal diseases, such as IBD. In this condition, immune cells in the gut (the large intestine) overreact to a perceived threat to the body, leading to tissue damage and inflammation. Less well-known is that the human body also hosts different viruses, called the virome. So what’s the difference between bacteria and viruses? On a biological level, the key difference is that bacteria are free-living cells that can live inside or outside a body, while viruses are a non-living collection of molecules that need a host to survive, according to the Institute for Molecular Bioscience. Viruses are believed to be the most abundant biological commodities on the planet. And the human virome is similarly expansive, with significant variety. Recently, studies of the human virome have explained diversity at different body sites, the relationships to disease states, and how the human virome evolves during early life.
Regrettably, most data in a standard virome study remain unidentified despite this work, highlighting the importance of unexplored viral “dark matter.” Sounding like the title for a science fiction movie – viral dark matter is an unclassified group of viruses that can pose a significant obstacle for those in this research field. According to eLife Sciences, this problem led a group of scientists to attempt to classify some of the unknown viral sequences. They added the 2,500 newly characterized viral sequences to the publicly accessible GenBank database. Hopefully, the expanded databases will better equip scientists to explore the diversity of viruses and help detect disease-causing viruses in humans.
So what do scientists know? One notable finding is that the gastrointestinal tract is commonly the most abundant site of viral colonization. Research has also uncovered many changes in gut viruses in people with diseases like IBD. But whether these shifts contribute to inflammation or are a secondary effect caused by inflammation remains a mystery. Luckily, a research team led by Dr. Kate Jeffrey from Massachusetts General Hospital may have some answers. Their new study analyzed gut virome samples from people with Crohn’s disease or ulcerative colitis, the two types of IBD. Findings were published in Science Immunology.
New Study Findings
The research discovered that in human cell cultures, the viromes from people with IBD and those with healthier guts interacted differently with immune cells called macrophages (cells involved in the detection and destruction of bacteria and other harmful organisms). Viruses separated from healthy people dampened macrophages and the inflammatory response resulting from their activity. However, those from participants with IBD activated macrophages. Next, the team used cultures containing intestinal epithelial cells, the protective cells that line the gut. The viruses isolated from participants with IBD induced a greater breakdown of this protective layer when compared to those taken from participants with healthy guts.
Viruses from people with healthy guts were able to suppress inflammation when added to cultures containing viruses from people with IBD. The analysis found that people with IBD had many resident virus species not often found in people with healthy guts. To measure the relationship between the virome and inflammation in living tissues, the researchers transplanted viruses from people with IBD and those with healthy guts into mice. Mice given the healthy viruses showed no changes in gut health. However, mice given viruses from people with IBD experienced increased inflammation. In a mouse model of ulcerative colitis, transplanting viruses from people with healthy guts protected against inflammation and damage. In contrast, transplanting those from people with IBD worsened tissue damage.
“Our work provides a missing functional link that our collective virome is an important contributor to human health, but when perturbed does provoke inflammation in IBD and conceivably many other diseases,” says Dr. Kate Jeffrey to NIH Research Matters. More studies are needed to understand what viruses make up a healthy human virome. Transplanting such viruses into people with inflammatory gut diseases, like IBD, could serve as a potential treatment and hope for sufferers.
