The immune system
About the Immune System
- 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 body systems and cause disease.
- The immune system is made up of a network of cells, tissues, and organs that work together to protect the body. The cells involved are white blood cells, or leukocytes, which come in two basic types that combine to seek out and destroy disease-causing organisms or substances.
The two basic types of leukocytes
- Phagocytes, cells that chew up invading organisms
- Lymphocytes, cells that allow the body to remember and recognize previous invaders and help the body destroy them
Here's how it works
When antigens (foreign substances that invade the body) are detected, several types of cells work together to recognize them and respond. These cells trigger the B lymphocytes to produce antibodies, specialized proteins that lock onto specific antigens.
Once produced, these antibodies continue to exist in a person's body, so that if the same antigen is presented to the immune system again, the antibodies are already there to do their job. So if someone gets sick with a certain disease, like chickenpox, that person typically doesn't get sick from it again.
Humans have three types of immunity
- Innate- Everyone is born with innate (or natural) immunity, a type of general protection. Innate immunity also includes the external barriers of the body, like the skin and mucous membranes (like those that line the nose, throat) which are the first line of defense in preventing diseases from entering the body. If this outer defensive wall is broken (as through a cut), the skin attempts to heal the break quickly and special immune cells on the skin attack invading germs.
- Adaptive-The second kind of protection is adaptive (or active) immunity, which develops throughout our lives. Adaptive immunity involves the lymphocytes and develops as people are exposed to diseases or immunized against diseases through vaccination.
- Passive- Passive immunity is "borrowed" from another source and it lasts for a short time.