Study authors include, from left: Miriam Merad, MD, PhD; graduate student Aleksey Chudnovskiy; and Veronika Kana, postdoctoral fellow, MD, PhD.
The discovery of a novel type of microbe found in laboratory mice at the Icahn School of Medicine at Mount Sinai has shed new light on the existence of similar organisms in humans, which may help boost the immune system and protect against food-borne toxins, such as salmonella.
Scientists led by Miriam Merad, MD, PhD, Director of the Immunology Institute at the Icahn School of Medicine, described the discovery of the mouse microbe—called Tritrichomonas musculis (T. mu)—in the October 6, 2016, issue of Cell. Their findings suggest that a previously unknown set of single-cell organisms, or protists, which belong to a different biological classification than bacteria, live in the guts of mice and influence their immune system.
The significance of the Mount Sinai study was featured in a subsequent blog by Francis S. Collins, MD, PhD, Director of the National Institutes of Health, who commented: “Recently, we humans have started to pay a lot more attention to the legions of bacteria that live on and in our bodies because of research that’s shown us the many important roles they play in everything, from how we efficiently metabolize food to how well we fend off disease. As it turns out, bacteria may not be the only interior bugs with the power to influence our biology positively.”
Prior to the new findings, scientists considered protists similar to T. mu to be disease-carrying parasites. In fact, T. mu seemed to increase the number of tumors in mice with a genetic susceptibility for colon cancer and it increased weight loss and tissue damage in mice with preexisting inflammatory disease. But, the inflammation caused by a rapid increase in immune cells—dendritic and T cells—brought about by T. mu, led to beneficial results for mice, overall.
“Protists probably aren’t all bad when it comes to our health,” according to Dr. Collins. “As in the laboratory mice, they may afford us with extra immune protection, which could be especially beneficial for those living in parts of the world where infectious disease is an ever-present threat.”
Mount Sinai’s scientific team also included investigators from the National Institute of Allergy and Infectious Diseases, and Universidad del Rosario, Bogotá, Colombia. The study found that humans from around the world harbor a related microbe, Dientamoeba fragilis (D. fragilis). This protist—taken from the fecal samples from people in South America, Africa, Europe, and Asia—has been associated with irritable bowel syndrome, but its effects are not completely clear.
The scientists theorized that the absence of this microbe could also explain why some people are more susceptible to certain infections than others. In recent years, advances in DNA sequencing technologies have enabled scientists to identify and study previously unknown microbes that could not be studied in traditional laboratories for various reasons. This new field of study of the human microbiome aims to characterize these microbes and understand their role in supporting health and triggering disease.
“The most important result in this study is the finding that a nonbacterial bug in our flora could potentially protect from severe intestinal infections,” says Dr. Merad. “This illustrates the need to study non-bacterial species of the microbiome, including protists, which remain very prominent in the developing world.” Further study, she adds, will likely identify novel “crosstalks” or interactions between the microbiome and immune cells that impact health and disease.