How the Immune System drives the Triumph of “Good Bacteria” over the “Bad Bacteria”?

immune system
May 10, 2019 0 Comments

Humans are home to more than a billion bacterial cells, way more than human cells. These cells reside on the skin, in the nose and ears, and, most importantly, in the gut. Evolution has witnessed the genesis and growth of a harmonious and symbiotic relationship between humans and the gut microflora. These tiny creatures derive shelter and nourishment from us and as a payback, they play a pivotal role in maintaining our fitness and wellbeing by performing a plethora of various important functions which may include digestion, immunity, skin health and even providing energy.

There is a lot of interaction between the body’s immune system and bacteria in the gut. These microbiomes perform the job of shielding us from the bad- potentially harmful and infection-causing bacteria. So much so that researchers at Johns Hopkins are currently in the ground stages of understanding that how different diseases show a remarkably different gut composition, how the body’s immune system- the oldest, inherited weapon in our immunity arsenal, interacts with these tiny tenants and most importantly how does this relationship alter in case of different diseases.

Just like any other, this symbiotic relationship also works both ways and thus it is not just these tiny hitchhikers but also the body’s immune system that plays a key role. A study published in the journal Immunity by scientists from the University of Chicago in 2105, suggests that a single binding protein(called ID2) present in one type of innate immune cells is in charge of maintaining a balanced microbial community. It is in the absence of this protein that harmful bacteria are extremely likely to cause trouble. Though the reasons remain undefined yet, researchers suggest the immune system may be capable of recognizing the presence of harmful bacteria which invade the gut.

“Our study reveals how our body’s immune system shapes the gut microbiota to naturally limit infections,” said senior author Yang-Xin Fu, a professor at the University of Chicago Department of Pathology, also elucidating the fact that there is a rapid rise in harmful bacteria that are resistant to antibiotics. Further, he quotes that “For future patients who are infected with harmful bacteria, it might be beneficial to promote the development of good gut microbiota to indirectly kill harmful bacteria, instead of using antibiotics.”

Fu and his team concluded that the mechanism by which immune cells distinguish between beneficial and harmful bacteria so as to maintain a healthy microbiota is yet unknown, although it is noted that pathogens might produce some molecules that immune cells can sense.

Observations highlight that once these pathogens invade, intestinal immune cells–called type 3 innate lymphoid cells (ILC3s) produce higher levels of antimicrobial peptides. This was tested by infusing a germ-free mouse with microbiota from a mouse having dysfunctional intestinal immune cells. The recipient when later exposed to harmful bacteria was highly susceptible to diseases, whereas germ-free mice that received microbiota from animals with functional ILC3s could fight off the bacteria.

Hence, this suggests that transplantation of microflora from an individual with functional intestinal immunity cells (ILC3s) into patients with recurrent gut infections could be performed to catalyze the growth of good gut microbiota and eventually lead to the eradication of bad bacteria.

Constant efforts are being made to isolate those specific species of microflora that could potentially be used to prevent bacterial infections. Though many questions are yet to be answered, the major undoubtedly is this: how do immune cells distinguish between beneficial and harmful bacteria to maintain a healthy microbiota? Many types of research and studies are in progress on these similar lines thus calling it a patient wait for the striking revelation.

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