Why the immune system is key to understanding host-microbe interactions

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In 2015, scientists published more than 500 papers on the microbiome and immunity. This is not surprising to Dr. Joaquín (Quim) Madrenas, professor and Canada Research Chair in Human Immunology at McGill University (Canada) — he sees the immune system as a key factor in understanding the relationship between microbiota and host.

“A host responds to these microbes, without allowing them to go rampant in the body and cause disease, but without going overboard and eliminating them,” he says in a recent interview with GMFH editors. Thus, Madrenas sees the immune system as a dial that turns inflammatory responses up or down to help maintain homeostasis. “Inducing a bit of inflammation keeps the microbes at bay but does not completely get rid of the microbes. When this balance is tilted toward a predominance of the inflammatory response, you may see the generation of an inflammatory environment that favors chronic immune-mediated diseases such asCrohn’s disease, colitis, or arthritis.”

His own research focuses on how one microbe in the nasal microbiome,Staphylococcus aureus, can be both a commensal bug and a ‘superbug’ that causes severe disease and mortality. “How come these microbes can be so lethal, and so innocuous? And what we have discovered is that these microbes contain, in their cell walls, molecules that modulate this balance between inflammation and anti-inflammation. We see a selection for strains of these microbes that are very modulatory — in other words, that induce a little bit of inflammation but not too much.”

He notes that his work may have applications outside the nasal microbiome, too. “Some of the mechanisms that we have seen being used by S. aureus are applicable to some of the microbes in the gut.”

In September, 2015, Madrenas co-organized a conference dedicated to this hot research topic of microbes and immunity: an international symposium called ‘Human Immunity and the Microbiome in Health and Disease‘. He explains, “We brought investigators working in many different disciplines, but with a common interest in discovering how microbes in our bodies and in the environment can promote health and prevent disease.”

From his point of view, several key points emerged from the conference. First, he says, “The study of the human microbiome will require a multidisciplinary approach focused on the development of tools that will allow not only looking at large bodies of data through new bioinformatic approaches, but also following these data across time.”

In addition, he says, “We need to go beyond correlation and into understanding how it works. For example, how come the administration of antibiotics early in life is associated with an increase in allergies? Is it because there is a change in the development of particular immune cells in these individuals? Is it because there is a change in the metabolites that the gut microbes generate that can have an effect [on] the host cells, and if so, how do these metabolites have that effect?”

“Perhaps the most important thing is that we are building the framework of a new way of doing science, a framework based on multidisciplinary approaches to a particular problem and having impact on different outcomes. There are investigators that are more interested in health outcomes, there are investigators that are interested in disease outcomes, and there are investigators that are interested in the mining of these data to develop new treatments. And all these investigators came together at the meeting to start what I hope will be a periodic meeting to discuss the human microbiome, both in health and disease, from a multidisciplinary perspective.”

Kristina Campbell
Kristina Campbell
Science writer Kristina Campbell (M.Sc.), from British Columbia (Canada), specializes in communicating about the gut microbiota, digestive health, and nutrition. Author of the best selling Well-Fed Microbiome Cookbook, her freelance work has appeared in publications around the world. Kristina joined the Gut Microbiota for Health publishing team in 2014.  Find her on: GoogleTwitter