Understanding the Immune System and Autoimmunity
Understanding the Immune System
The immune system is the body’s natural defense against infection. Through a series of steps, your body fights off invading infectious organisms and destroys them before they cause harm. When your immune system is functioning properly, it protects against infections that cause disease.
Scientists have begun to understand the immune system in detail. Researchers are continually generating more information on its operation and what happens when it malfunctions.
The Immune Response Process
The immune process begins when an infectious agent enters the body. This might be a flu virus entering the nose or a bacterium entering the blood through a puncture wound. Your immune system is always alert to detect and attack the infectious agent before it causes harm. Whatever the agent, the immune system recognizes it as a foreign body. These external bodies are called antigens, and they must be eliminated.
First Line of Defense: Macrophages
The first line of defense is a group of cells called macrophages. These cells circulate through the bloodstream and tissues of the body, guarding against antigens.
- When an invader enters, a macrophage quickly detects and captures it within the cell.
- Enzymes within the macrophage destroy the antigen, processing it into small pieces called antigenic peptides. Sometimes this process alone is sufficient to eliminate the invader. However, in most cases, other immune system cells must join the fight.
- Before other cells begin their work, the antigenic peptides within the macrophage bind to molecules called Human Leukocyte Antigens (HLA).
- The HLA molecule bound to the peptide, now called the antigenic complex, is released from the macrophage.
Mobilizing T Cells and B Cells
Cells called T lymphocytes (T cells) can then recognize and interact with the antigenic peptide-HLA complex located on the surface of the macrophage.
- Once this complex is recognized, T cells send chemical signals called cytokines.
- These cytokines attract more T cells and also alert B cells to produce antibodies.
- These antibodies are released into the bloodstream to find and bind more antigen, preventing the invaders from multiplying and causing illness.
- In the final step of this process, a cell called a phagocyte is responsible for removing the antigen from the body.
What is Autoimmunity?
Normally, the immune system is responsible for combating viruses, bacteria, or other infectious organisms that threaten your health. But if a failure occurs, the same system designed to protect you can backfire.
When the immune system is not working properly, its cells cannot differentiate self from non-self. Instead of fighting against foreign antigens, immune system cells (or the antibodies they produce) may mistakenly attack the body’s own cells and tissues.
This process is known as autoimmunity. The components involved in this erroneous immune response—including autoreactive lymphocytes and antibodies—are called autoantibodies. This failure contributes to several autoimmune diseases, including various forms of arthritis.