What is an autoimmune disease?

What is an autoimmune disease?

Researchers know a lot about what goes wrong in the body when it has an autoimmune disease. However, it is not yet known exactly why the body's immune system begins to behave incorrectly and attack the body's own cells.

What is autoimmunity?

An autoimmune disease means the body's own immune system is attacking the body. What should be the body's defense against external threats is instead targeting its own organs. In several diseases, such as rheumatoid arthritis, the body's immune system believes that some of the body's own cells are an external threat, like bacteria entering the body. The result is an inflammation that causes pain and swelling around the affected area. So your body really just wants you to be well and is trying to protect you. Research does not yet know why the immune system reacts incorrectly in this way.

What is really happening when a joint gets swollen?

In autoimmune rheumatic diseases, the cells in the joints are considered foreign by the immune system. What happens is exactly what happens in a "normal" reaction when the immune system protects us: the defense is activated, resulting in inflammation. You can read more about inflammation and the immune system here.


The picture above shows an example of a knee of a person who has RA. The left side of the image shows a healthy knee and the right side shows a knee that has an ongoing inflammation with many active immune cells. This causes the synovial tissue surrounding the knee joint to become swollen. It contributes to the accumulation of fluid called edema. The knee becomes swollen, reddened, hot and painful.

What contributes to autoimmunity?

Researchers do not know exactly why the immune system begins to behave incorrectly in an autoimmune disease. However, they know a lot about what happens when the body's immune system is incorrectly programmed in this way. The immune system has special control points, which ensure that incorrectly programmed immune cells are not allowed to be released into the blood. These so-called T and B cells should instead be cleared out if they have learned to attack the wrong kind of cells. This is where the researchers believe that the problem with an autoimmune disease lies. Either something has gone wrong with the checkpoint system or some cells are escaping from the control system.


1. Abul K. Abbas, (2014) Cellular and Molecular Immunology. Distinguished Professor and Chair, Department of Pathology, University of California San Francisco, San Francisco, California.