Picture this: you are playing laser tag with your friends, and there are two teams. Your goal is to eliminate everyone on the opposite team while keeping your friends on your team safe. Everything is going well, and you’re eliminating your opponents left and right. But then something goes wrong: you tag out someone from your own team.

Although it seems simple, a game of laser tag is similar to what our immune system does when it fights foreign invaders. More specifically, autoimmunity can be likened to eliminating someone on your own team; it is when our immune cells target self-cells instead of foreigners.

Autoimmune disease is also known as autoimmunity. Before we discuss further what autoimmunity is and how it is caused, let’s take a second to recap on what we’ve learned about the immune system so far.

Immune System Recap

The immune system is our mechanism of defense against foreign invaders like bacteria, viruses, and other infections. An important aspect of the immune system is that it must determine what is harmless and what is harmful; things that are “self” are harmless, and the immune system will not respond or kill them. What our bodies do attack are foreign pathogens, which can cause our bodies harm.

What is autoimmunity?

Autoimmunity is when there is an immune response to self-cells that causes disease.

Normally, our immune cells have “tolerance”; specifically, they have “self-tolerance” which means that there is no immune response to particles and cells that are naturally occurring in our bodies – examples of things that we have tolerance to are the harmless bacteria that live in our gut and the foreign food particles we eat. We don’t want our immune systems responding to these things because they are not causing our bodies any harm.

Cells are taught tolerance in the bone marrow and thymus, two organs that play important roles in the immune system. You can think of bone marrow and the thymus as teachers at school who educate the immune cells to not attack self-cells and particles.

When we do have an immune response to cells that are harmless, this results in autoimmunity, which causes the destruction of tissues and inflammation as immune cells kill self-cells.

What Causes Autoimmunity?

Although we understand how autoimmunity works, the exact cause is still unknown. The key aspect of autoimmunity is that it occurs when immune cell tolerance is broken. Tolerance can be broken as a result of taking certain drugs or environmental factors; it could also result from an infection where a foreign pathogen is very good at tricking the immune system. In this situation, instead of immune cells killing the harmful, foreign cells, they kill self-cells instead. With autoimmunity, the immune system becomes confused and cannot provide the correct mechanisms of response and kill the right cells.