New insights reveal how T cells know not to go after our beneficial microbiota
The immune system continuously protects the body from attack by foreign intruders. T lymphocytes play a crucial role in defending against any pathogen's assault. T cell development takes place in the thymus where these cells undergo "thymic education" and learn how to differentiate between self and foreign invaders. And yet the human gastrointestinal (GI) tract is inhabited with trillions of beneficial commensal bacteria. They help to regulate host nutrient metabolism and immune cell homeostasis, and they also protect from pathogen infection. Surprisingly, T cells learn to ignore beneficial microbiota in the intestine while they immediately try to recognize and eliminate any foreign invader in our body.
It has been known that once T cells leave the thymus, they are again educated in the gastrointestinal tract, or gut, to differentiate between beneficial and harmful foreign bacteria. This dual education strategy is important to establish the tolerance to commensal bacteria in the intestine which in turn maintains a healthy immune function. In a normal scenario, tolerance to commensal bacteria remains intact throughout the lifetime of the individual. However, some genetic risk factors or environmental insults may lead to breaking the tolerance, and as a result the immune system attacks beneficial bacteria in the intestine.
Previous studies have shown evidence that inflammatory processes may contribute to disease progression such as inflammatory bowel disease (IBD), HIV, viral hepatitis, cardiovascular disease, obesity, diabetes, and cancer. A research team at Weill Cornell Medical College made a breakthrough by showing how the immune system prevents chronic inflammation in the intestine . The group has previously reported that innate lymphoid cells (ILCs) interact with T cells in the GI tract and critically regulate immune cell interactions with bacteria. These ILCs separate the immune system and intestinal beneficial bacteria by forming a physical barrier. In the recent study, researchers found that ILCs directly educate T cells in the intestine and instruct not to attack beneficial bacteria . The impairment of ILCs' function leads to intestinal inflammation. They also reported that ILCs interact with T cells through the MHCII machinery to educate T cells in the intestine, and the loss of MHCII on the surface of ILCs is linked to pro-inflammatory cells in patients with IBD.
This study strongly details how the immune system learns to differentiate between self and harmful bacteria. Future investigations into eliminating pro-inflammatory T cells' reaction may provide new therapeutic opportunities to treat IBD, including Crohn's disease and ulcerative colitis. HemaCare is a leading provider of high quality blood product for your research for over 35 years, supplying a wide variety of lymphocytes and immune cell products for your needs.
1. Group 3 innate lymphoid cells mediate intestinal selection of commensal bacteria-specific CD4+ T cells. Science DOI: 10.1126/science.aaa4812