How bacteria trick your immune system
Tuberculosis bacteria survive in the body by hiding inside your own cells. Scientists have now figured out how they pull it off: with a protein that slips directly into the cell nucleus and shuts down the immune response.
Mycobacterium tuberculosis, the bacterium that causes tuberculosis, is one of the most successful human pathogens ever known. It still infects more than ten million people worldwide every year. Much of that success comes down to one remarkable ability: it can survive inside the very immune cells that are supposed to destroy it. Exactly how it manages that molecular sleight of hand has been a central question in infection biology.
Researchers publishing in eLife have now uncovered a new mechanism. They identified a protein called MgdE, encoded by the gene Rv1075c in the tuberculosis genome, which the bacterium dispatches to the nucleus of the host cell. That is where the host's DNA is stored and where the instructions for mounting an immune response are generated. MgdE belongs to a class that biologists call a "nucleomodulin": a bacterial protein specifically designed to break into another cell's nucleus and disrupt what is happening there.
Hijacking an epigenetic complex
Once inside the nucleus, MgdE latches onto the COMPASS complex, a group of proteins that controls which genes in a cell are switched on or off through chemical modifications to DNA. This process is known as epigenetic regulation. By hijacking the COMPASS complex, MgdE effectively reprograms the host cell: genes that would normally drive an inflammatory response get silenced. The result is that the bacterium is less likely to be detected and attacked.
The study shows that MgdE is highly conserved across mycobacteria, appearing in many related bacterial species, not just in the tuberculosis bacterium itself. That points to an evolutionarily successful survival strategy that has been around for a long time, and one that may be relevant to other infections as well.
What this means for aging and immunity
The connection to longevity is indirect but real. As you get older, your immune system gradually weakens, a process known as immunosenescence. That makes older people not only more susceptible to infections like tuberculosis, but also less equipped to clear bacteria that use molecular evasion strategies like the one MgdE enables. Understanding how bacteria sidestep host immunity therefore also sheds light on why an aging immune system becomes more vulnerable.
Beyond that, the discovery of MgdE opens up a concrete therapeutic target. If the protein is what drives mycobacterial survival, it is at least theoretically possible to develop drugs that block this interaction, not by killing the bacterium outright, but by stripping away its hiding place. Whether that is achievable in practice is the next question to answer.