A new study shows that eukaryotic viruses can maintain both mucosal immunity and intestinal homeostasis in mice. If mice are infected with norovirus (MNV), it can have the same beneficial effect as intestinal bacterial colonization. Scientists have long known that RNA viruses can often be isolated in healthy infants and children and in patients recovering from acute gastroenteritis. Such viral infections are usually thought to be harmful to the organism. But the new findings disprove this hypothesis and suggest that these viruses may play a role similar to that of other microorganisms such as bacteria. Dr. Elizabeth and his colleagues from New York University School of Medicine published their findings online in the Nov. 19 issue of the journal Nature. The researchers used three groups of mice: germ-free mice without microbes, wild-type mice treated with a combination of antibiotic therapies, and mice whose intestinal tissues were damaged by treatment with sodium dextran sulfate. The innovation of this study was the discovery that gastrointestinal viruses can help maintain intestinal health as well as repair damaged intestines. Prior to this study, there were few studies involving viruses colonizing the intestine. The team infected germ-free and antibiotic-treated mice with MNV and found that viral infection repaired inflammation-induced intestinal tissue damage, restored intestinal cell counts, restored intestinal cell function, and restored intestinal tissue structure. These apparent results occurred at 2 weeks after MNV infection. MNV infection also helps to restore the immune system of the intestine. However, how the virus restores the immune system is unclear. The researchers found increased expression of type 1 interferon-related antiviral proteins, suggesting that the virus plays a key role in driving the immune response. The researchers also found that antibiotic-treated mice infected with MNV had doubled levels of T cells in their blood, and significant levels of antibodies were detected in both the intestines and blood of the mice. These events were consistent with a normal viral immune response. In conclusion the authors concluded that once antibiotic treatment eliminates intestinal bacteria, viral infection may contribute to the immune system of the intestine. MNV also improved survival in mice when antibiotic-treated mice received sodium dextran sulfate. ”We all know that people get viral and bacterial infections all the time, but they don’t get sick,” Dr. Ken, a senior researcher from New York University, said in a press release, “and now we’ll have scientific evidence that not all viral infections are harmful, and that it’s possible that they are also beneficial and healthy, just like bacteria.” He noted that the role of gut microbes in health and disease has received increasing attention. In the gastrointestinal tract, there are a variety of microorganisms, including bacteria, archaea, fungi, and viruses. These microbes have a variety of health benefits, including regulation of the immune system and prevention of inflammation. While the collection of microbes in the gastrointestinal tract is commonly referred to as the gut microbiome, the collection of viruses in the gastrointestinal tract is more specifically referred to as the gut virome. New findings suggest that the previously overlooked gut virome may be as important as the gut microbiome. The researchers focused on MNV as a result of their finding that chronic MNV infection protects those mice with inflammatory bowel disease. Next year, the group will experiment with other enteroviruses and their role in the microbiome. Drs. Yao Wang and Julie Zhu of the University of Texas Southwestern Medical Center at Dallas also published an editorial. The editorial states, “We believe that the symbiotic reciprocal relationship between the viral group and the host is an incredible advance.” Therefore, they speculate that mammalian intestinal viruses may one day act as probiotics. In addition to this, they mention a question of great relevance: “Do mammalian enteroviruses play a role in the normal intestinal environment?