Is it possible for the immune system to work too well?

Those of you who have been keeping up with The Infectious Doctor may have noticed that a common theme in discussing infections, is the immune system. The immune system is a complex of cells and reactions that quickly springs to attention when there is a threat of infection to the body. The strength of one’s immune system often makes the difference between getting, and not getting an infection, and also how severe that infection is.

But…imagine if your immune system worked too well. Yes! It is in fact possible for the immune system to kick into action so aggressively in response to an invader, that in addition to fighting the germs that try to attack the body, the immune system ends up fighting against the normal cells of the body…by accident. This sets the stage for an autoimmune disease.

Before I delve into the processes causing autoimmune diseases, let me first rapidly summarize what happens during a normal immune response. When there is the threat of an infection from some type of germ, the body’s immune system produces antibodies (and other substances) to kill the germ. The antibodies bind to the germ particles thereby inactivating them. The complexes of germ bound together with antibody, are then carried to areas such as lymph nodes and the spleen, where they are destroyed.

Now, let’s explore the processes causing autoimmune diseases. The word autoimmune essentially means, the presence of antibodies (immune) which fight against naturally occurring cells in one’s own (auto) body. So, as was noted above, antibodies are produced in response to invading germs. However, during autoimmunity, the antibodies recognize some of the normal cells of the body as foreign. This happens by accident. The phenomenon is called “molecular mimicry” because the germ mimics the natural tissue so that the antibody is not able to distinguish between the two. Antibodies bound to natural tissues cause inflammation and eventual destruction of these tissues (as if they were germs). An example of this type of autoimmunity is the development of Guillain-Barre syndrome (paralysis from damage to the nerves) following gastroenteritis caused by the bacteria Campylobacter. The nerve tissues are mistaken for the bacteria. Another example, is rheumatic heart disease developing after a streptococcal throat infection. The tissues of the heart are mistaken for the streptococcal bacteria and the antibodies attach to these tissues causing inflammation of the heart, and sometimes heart failure.

Another way that autoimmune diseases occur after an infection, is when the antibody-germ complex mentioned above, gets deposited into normal tissues. The complexes cause inflammation and destruction of the affected tissues. Streptococcal throat infection as well as a streptococcal skin infection, can trigger this autoimmune response in the kidneys. Chronic hepatitis B and C are viral infections that have also been associated with autoimmune kidney disease. Vaculitis (inflammation of the blood vessels) is another autoimmune complication of chronic hepatitis B and C infections. Reactive arthritis (inflamed, swollen, tender joints) may occur after gastroenteritis from Salmonella and Shigella.

There are over 80 different autoimmune diseases affecting hundreds of millions of people around the world. Most of them are not felt to be associated with a preceding infectious disease. There has been some suspicion that the autoimmune disease lupus may be triggered by an infectious process, but this has not been proven. Some suspect that multiple sclerosis is triggered by autoimmune activity following an infection, but again, this has not been proven.

Fortunately, autoimmune diseases complicating infections are overall not common. It is not clear what determines why one person would get such a complication, and another not. Genetic factors are thought to play a role but do not explain all cases.

Treatment of autoimmune diseases associated with infections entails first and foremost, treating the infection. Anti-inflammatory medications are also used. Steroids are popular but there are other anti-inflammatory medications that can be used. Often, several different specialists must come together to optimally treat these complicated cases.