The appendix – Darwin’s mistake
Human appendix, computer illustration.Credit: SCIEPRO / SCIENCE PHOTO LIBRARY / Getty Images
Our gut health is helped by this unfairly maligned small organ writes Norman Swan.
The word says it all – appendix, a take it or leave it add-on at the end of a book or, in the case of our intestines, at the end of a pouch called the caecum that marks the beginning of the large bowel.
When I was a medical student we were taught Charles Darwin’s theory for the appendix, that it was merely a useless vestige of evolution, a small worm-like sac that was once a giant organ to aid the digestion of greens.
Medically, all the appendix was known for was its tendency to become inflamed and to require removal.
But over the last few years the thinking has changed. The appendix turns out not to be an evolutionary curiosity but a handy little organ with the potential to resuscitate the bowel. Back in 2007, researchers at Duke University in North Carolina proposed that the appendix was actually a “safe house” for normal gut bacteria that could be put to use when the bowel had been devastated by, say, an infection such as cholera and needed to be repopulated by healthy bacteria.
The Duke group had found colonies of protective microbes known as biofilms were disproportionately produced by the appendix. Ironically, the immune cells found in the gooey mucous lining of the appendix and bowel actually help these biofilms to form.
If this theory were true then people without an appendix might be more vulnerable to dangerous gut infections. A study a few years later found evidence for this. People who’d had their appendix removed were significantly more likely to suffer recurrently from the serious and potentially life-threatening recurrent Clostridium difficile infection.
Now research from Gabrielle Belz at the Walter and Eliza Hall Institute for Medical Research in Melbourne and colleagues has reinforced the appendix’s position as a key part of the bowel’s immune system.
They were fascinated that the lining of the appendix contains a newly discovered class of immune cells known as innate lymphoid cells. Other lymphoid cells must be specifically tuned to attack the latest strains of bacteria or viruses, but these cells come ready wired to respond to the wide range of biological insults that flow down the intestines from our daily diet.
Experimenting in mice, the researchers found that these innate lymphoid cells were critical to maintaining the tissue around the caecum. If the cells were removed, the caecum shrank, suggesting they played a vital role for the integrity of the tissue. They also found that mice without these innate lymphoid cells were more vulnerable to a pathological
gut infection. This supports the study I mentioned earlier where patients without their appendix were more likely to suffer from recurrent C. difficile infections.
There are many avenues for this research now. Gut immunity is vital for our overall health and wellbeing for a few reasons.
It may transpire that Darwin’s throwaway vestige of evolution is an organ that evolution has exquisitely tuned for our survival
First and foremost is the fact the lining of the bowel is exposed to the outside world. Think about it. The inside of the ‘tube’ is continuous with our mouth and anus – open to the external world. Food only enters our body when it’s absorbed from the contents of the tube.
So the gut’s immune system stands between us and the perils of our edible environment. It’s helped by the trillions
of friendly microbes that populate the bowel, preventing nasties from getting a toehold, an ecosystem also controlled
in part by the immune cells.
Another reason why gut immunity is so important is that gut lymphocytes circulate throughout the body having conversations with other immune cells. They pass on life-saving information about what could be assaulting us from the outside world.
It may transpire that Darwin’s throw-away vestige of evolution is actually an organ that evolution has exquisitely tuned for our survival.
Luckily, surgeons have worked out that they don’t always need to remove an inflamed appendix and that antibiotics can be the most appropriate therapy for appendicitis.
So let’s campaign to save the appendix.