Even Your ‘Friendly’ Bacteria Can Cause Inflammation, Research Finds – Here’s How
Scientists have known for years that the billions of tiny inhabitants in the digestive tract have a big say in overall health. But until recently, they didn’t know how viruses deliver the message.
According to a recent study published in the scientific journal Nature, researchers have discovered a molecular mechanism that allows intestinal bacteria to inject their proteins directly into human cells. This discovery could redefine the understanding of immune responses and chronic conditions such as Crohn’s disease.
Researchers have previously linked the microbiome to immune disorders, metabolic disorders and chronic inflammation. However, much of that evidence was based on correlation.
This study, led by researchers at the German research center Helmholtz Munich, aims to change that.
Veronika Young, first author of the study, summarizes the findings:
“Our goal was to better characterize some of the basic mechanisms of how gut bacteria affect human health. By systematically mapping protein-protein interactions between bacterial and human cells, we can now suggest the molecular mechanisms behind these associations.”
Bacterial injections can interfere with cell signaling
Your gut is full of commensal bacteria that are generally considered friendly or neutral.
But according to research, those normally harmless viruses can contain type III derivatives. These are tiny syringes that allow bacteria to inject proteins directly into human cells. Previously, experts believed that these systems were specific to harmful bacteria such as Salmonella.
To better understand what bacteria do inside human cells, researchers have created a large map that shows more than a thousand specific interactions between bacterial proteins and human proteins.
They found that these bacterial proteins tend to target pathways responsible for immune regulation and metabolism. Laboratory experiments have confirmed that viruses can alter important immune signals, particularly those that affect pathways involving cytokines.
Cytokines are signaling molecules that help coordinate the immune system to prevent it from overreacting. But too many cytokines can cause excessive inflammation.
Researchers found that people with Crohn’s disease carry more of these specific bacterial genes in their gut.
Link to inflammatory bowel disease
This suggests that bacteria that inject proteins directly into human cells could be a driver of chronic inflammation and possibly explain how gut bacteria can cause or exacerbate inflammatory diseases, a link scientists had seen but did not fully understand until now.
“This dramatically changes our view of normal bacteria,” said Pascal Falter-Braun, co-author of the study. “It shows that these non-pathogenic bacteria are not just passive citizens but can control human cells by injecting their proteins into our cells.”
It is unclear whether these bacterial injections are from pathogenic sources or commensal bacteria that have adapted to injection systems.
However, the researchers say the study could help shift the focus of future studies from correlation to causation, which could lead to better treatments for chronic inflammatory diseases that start in the gut.
