Directly The immune system is designed to defend the body against foreign or dangerous invaders. Such invaders include
Microorganisms (commonly called germs, such as bacteria, viruses, and fungi)
Parasites (such as worms)
Cancer cells
Transplanted organs and tissues
To defend the body against these invaders, the immune system must be able to distinguish between
What belongs in the body (self)
What does not (nonself or foreign) normal immune response consists of the following:
Recognizing a potentially harmful foreign antigen
Activating and mobilizing forces to defend against it
Attacking it
Controlling and ending the attack
If the immune system malfunctions and mistakes self for nonself, it may attack the body’s own tissues, causing an autoimmune disorder, such as rheumatoid arthritis, Hashimoto thyroiditis, or systemic lupus erythematosus (lupus).
