About the Immune System

What is the Immune System?
The immune system, which is made up of special cells, proteins, tissues, and organs, defends people against germs and microorganisms every day. In most cases, the immune system does a great job of keeping people healthy and preventing infections. But sometimes problems with the immune system can lead to illness and infection.

What the Immune System Does
The immune system is the body's defense against infectious organisms and other invaders. Through a series of steps called the immune response, the immune system attacks organisms and substances that invade our systems and cause disease.

Things that can go wrong with the Immune System
Disorders of the immune system can be broken down into four main categories:

• immunodeficiency disorders (primary or acquired)
• autoimmune disorders (in which the body's own immune system attacks its own tissue as foreign matter)
• allergic disorders (in which the immune system overreacts in response to an antigen)
• cancers of the immune system