Autoimmune diseases occur when the immune system attacks healthy cells in the body.
Your immune system's most important job is to protect your body from outside invaders (germs). It has to tell the difference between the stuff inside you (like your organs) and stuff outside of you (like germs and other things). But, what happens if the immune system makes a mistake? When this happens, the immune system attacks a healthy part of the body because it thinks it is a germ and is harmful, even though it isn't. This is called autoimmunity; "auto" means "self", so "autoimmunity" is when your immune system fights against self.
When an autoimmune reaction hurts the body it is called an autoimmune disease.
Autoimmune diseases are rare. Scientists still don’t know why the immune system does this and why only some people get autoimmune diseases. But, we are pretty sure that our genes (the DNA we get from our parents) and our environment matter.
You may know someone who has to take insulin shots because they have Diabetes. You may have seen them prick their finger and test their blood sugar. The sugar in your blood goes up after you eat. Insulin helps to bring it back down.
Diabetes is a type of autoimmune disease. People with Diabetes have immune cells that make a mistake and destroy special cells in your pancreas. The pancreas is an organ below your stomach. Special cells in the pancreas make insulin. People with diabetes don't have special cells, so they don't make insulin.
This means that their blood sugar stays high after they eat unless they take a shot to make sure they have enough insulin. Having too much sugar in your blood makes you very sick!
Autoimmune diseases occur when the immune system attacks healthy cells in the body.
Our immune systems are designed to be able to tell the difference between self and nonself, but what happens if the immune system makes a mistake? When this happens, the immune system attacks a healthy part of the body because it thinks it is a pathogen (germ) and is harmful, even though it isn't. This is called autoimmunity; "auto" means "self", so "autoimmunity" is an immune response against self. When an autoimmune reaction does harm the body it is called an autoimmune disease.
Autoimmune diseases are rare. Scientists still don’t completely understand why the immune system does this and why only certain individuals are affected while others are not, but there is a significant amount of evidence that shows that both genetics and our environment play an important role.
The Causes of Autoimmunity
Genetics seems to be important for determining if someone is likely to develop an autoimmune disease. For example, children who have parents or grandparents with Type I Diabetes are more likely to develop the disease than those who don't. Why does this happen? Sometimes, mutations in genes that are important for your immune system can cause it to make mistakes. These mutations are passed on to the next generation, and the cycle continues.
What kind of mutations can cause autoimmunity? That's a great question. When T cells are developing, your body eliminates T cells that bind to self antigens too tightly. If that process gets screwed up because of a mutation, then your body will allow T cells that are self-reactive (i.e., that bind to self antigens and get activated) to mature and enter the bloodstream!
Learn more about T cell development here >>
Or, what happens if you have immune cells that get turned on, but have a mutation that prevents them from turning off? Normally, your body stops fighting when the disease is gone. Since there are no more germs, there are no germ antigens around to activate the immune system. However, sometimes immune cells can't receive the signal to shut down. These cells are hyperactive and even though they started out fighting a germ, they can harm your own tissues!
Once an autoimmune reaction starts, it's almost impossible for your body to stop it. Why? Because the antigen that the cells are fighting is always around - it's a part of that person! For example, in Type I Diabetes, the immune system thinks that the beta cells of the pancreas are nonself and it destroys them. Well, our bodies are always regenerating our tissues, so the body keeps trying to make more pancreas cells. With pancreas cells around, the autoreactive immune cells think the germ is still there so they keep on fighting! When a disease like this keeps occurring, it's called chronic.
Learn more about Type I Diabetes here >>
Things in our environment can also cause autoimmunity. T cells and B cells match the shape of their receptors to the shape of the germ antigens. What if a germ antigen had a shape that was very, very similar to one of our self antigens? Then, the T or B cell might mistake our healthy tissue for the germ and destroy it! This can also happen if a drug, toxin or other chemical has a shape similar to a self antigen.
Learn more about antigen recognition here >>
What are Some Examples of Autoimmune Diseases?
There are over 80 different types of immune disorders, but some of the most common are Lupus Erythematosus, thyroid disorder, Mutliple Sclerosis, arthritis, celiac disease, and Type I Diabetes, to name a few. Some of these diseases affect only a specific organ or tissue in the body, so they are localized; others can affect the whole body, and are termed systemic. Localized diseases attack a specific area of the body, like tissues and joints, the nervous system, the blood, and the pancreas, for example. Metabolism, muscular movement, brain function—these are just some of the body’s major functions that can be disrupted by autoimmune disorders. The body is a highly interconnected system, so once one organ or individual system is attacked, the autoimmune disease can damage and disrupt many other functions of the body.
Autoimmune diseases have a tendency to be more prevalent in women than in men. About 75% of autoimmune diseases affect women. Some scientists believe that women have more complex immune systems than men, and so are more susceptible to complications, many of which can be set off by pregnancy.
