When the body's immune system turns bad
For treating diseases caused by noxious invaders like bacteria or viruses, the target is clear: Kill the foreign enemy. But what if the agent that's making you sick is also the very thing that normally keeps you healthy? This is the catch-22 posed by autoimmune disorders.
In this class of diseases, a person's immune system attacks his or her own body, causing a range of maladies. Type 1 diabetes is one of the most common autoimmune diseases, and there are about 80 others. Little is known about their causes, but researchers are urgently trying to understand them, because of one disturbing trend: Autoimmune disorders seem to be on the rise.
The human immune system is extremely complex, involving many different types of cells and multiple mechanisms for detecting and destroying disease-causing agents. The body's security system protects against bacteria, viruses, parasites, and even cancer cells.
The key to the immune system's success is its ability to distinguish between self and nonself. Early in its development, a person's immune system learns to recognize particular molecules that show up on the surface of every cell in the body. These chemicals are the person's biological signature, evidence that a particular cell or tissue belongs to the body. Any substance that doesn't carry this identification card is marked by the immune system for annihilation.
The immune system is sophisticated. In addition to being able to tell self from nonself, it can also learn to recognize particular pathogens, or disease-causing agents, based on features on their surfaces. These surface molecules, called antigens, are the identifiable face of the enemy. They trigger the body to produce proteins called antibodies, which have a complementary shape to an antigen. Antibody and antigen fit together much like a lock and key. Antibodies recruit a host of cells that fan out around the body and kill invaders that dare show their antigen.
A Critical Error
Sometimes, though, this powerful protection against disease can turn on itself. The result is an autoimmune disease. For reasons that aren't clear, sometimes a person's immune system begins to mistakenly identify a part of the body as an enemy that needs to be eradicated. In type 1 diabetes, the immune system's target is the insulin-producing beta cells in the pancreas. In rheumatoid arthritis, it's the joints. In Graves' disease, it's the thyroid gland. In celiac disease, it's the small intestine. And the list goes on.
To diagnose an autoimmune disease, doctors can do a blood test that looks for telltale antibodies. In addition to healthy antibodies for viruses or bacteria, people with autoimmune diseases will also have antibodies with shapes that fit with parts of healthy tissues. People with type 1 diabetes, for example, often have antibodies that pair with insulin. That directs them to march straight to the beta cells, with a troop of murderous immune system cells in tow.
Genetics plays a role in the development of autoimmune diseases. Researchers have identified several genes that make people more likely to develop specific autoimmune diseases, such as type 1 diabetes or celiac. But having a particular disease gene doesn't guarantee that someone will develop a disorder. Scientists believe that autoimmune diseases may be triggered by an environmental factor.
Much of the research aimed at vanquishing autoimmune disorders is focused on trying to identify their environmental triggers. One clue: Because autoimmune disorders are on the rise, it seems likely that the instigating agent (or agents) must also be increasingly present in the environment. There are various theories about what the triggers could be, including particular foods, pollutants, viruses, or drugs.
Since their causes aren't known, autoimmune diseases can't yet be prevented, though researchers are trying to fix the broken immune system in type 1 diabetes and other diseases. For now at least, the aim is to ease symptoms. Treatment of autoimmune diseases varies from disorder to disorder. For example, in celiac disease, gluten triggers an autoimmune response against the small intestine, so avoiding this wheat protein is a key part of treatment. For type 1 diabetes, the treatment involves replacing the insulin that is lost when beta cells are destroyed by the immune system. Insulin is given under the skin by syringe, pen, or pump to keep blood glucose levels down.
Autoimmune diseases often occur together. According to a May article in Diabetes Care, children with type 1 diabetes have a 1-in-3 chance of harboring at least one other autoimmune disorder. So people with type 1 need to be on the lookout for signs of other autoimmune disorders. They need to be particularly wary of autoimmune hypothyroidism, which causes decreased function of the thyroid gland. People with type 1 should be screened for hypothyroidism every year or two.
While the clustering of autoimmune disorders is cause for concern, it also gives hope: If researchers can figure out how one disease works, then that knowledge could be applied to combat them all. There is no cure yet for any autoimmune disease. But if one is discovered, that may lead to a general understanding of how to control a renegade immune system. And that could be the key to toppling all autoimmune diseases, including type 1 diabetes.