The appendix has long been treated as an organ that serves little purpose. Even in less serious cases, doctors have removed the appendix to prevent future infections and ruptures. A new study related to innate lymphoid cells (ILCs, which are responsible for protecting us when the body’s immune system is overwhelmed) found that people may have misunderstood this organ. For herbivores, the appendix is the organ that holds the bacteria needed to digest plants, but for omnivores like humans, the role of the appendix has long been unclear, and for a long time it was thought to be a useless organ with no role. However, some studies have shown that the appendix can actually control the balance of bacteria in the intestine. The team compared mice with an open appendix to mice with an open appendix and no appendix to study the effects of appendectomy. It was found that the number of IgA-positive cells (a type of plasma cell that produces IgA antibodies that inhibit the reproduction of bacteria in the body) was hardly increased in the large intestine of the appendectomized mice. They further found that the appendix is the organ that produces IgA-positive cells, and that IgA-positive cells produced here move to the large intestine as well as the small intestine. It was previously known that IgA-positive cells produce IgA antibodies that bind to specific intestinal bacteria and inhibit their multiplication, thus regulating the balance of intestinal bacteria. If the appendix is removed before the increase of IgA-positive cells in the intestine of mice, the composition of the intestinal flora will be very different from that of mice without the appendix. In other words, the appendix is an essential organ for controlling the balance of intestinal bacteria. There are more than a thousand species of bacteria living in the human intestine, with a total number of more than 100 trillion and a total weight of up to 1.5 kg. The intestine remains healthy only if the small intestines each maintain the right flora. However, if the number of certain intestinal bacteria, which should be small, suddenly increases, the balance of the flora can be disrupted, which can lead to food poisoning, obesity, inflammatory reactions, etc. In the lymphoid tissue inside the appendix, cells essential for the production of IgA-positive cells are gathered. Here, there are B cells that differentiate into IgA-positive cells and M cells that engulf bacteria from the intestine into the lymphoid tissue. The bacterial composition of the appendiceal canal is very similar to the bacterial composition of the interior of the large intestine. Therefore, the lymphoid tissue, having received information about the intestinal bacteria in the appendiceal duct, produces the IgA-positive cells needed primarily to maintain the balance of the colonic flora. Of course, readers who have already had their appendix removed for appendicitis need not be pessimistic. The effects of appendectomy on the body are not yet clear. Even if the appendix is removed, the IgA-positive cells that were previously produced are still present in the body, so there should be no significant effect on the body. If the appendicitis keeps getting worse, it should still be removed.