What is the immune system?
The immune system is a collection of cells and organs that work together to defend body from germs or substances (antigens), which may cause illnesses. This germs also called microrganisms include bacteria, viruses, parasites, and fungi (both the germ are foreign substances are called "antigens").
Let me give some summary that you need to know on immune system 
-The immune system is a collection of cells and substances that act as the body defence against foreign substances (antigens).
-An antigen is a substance which, when introduced into the body. stimulates the production of an antibody Antibodies are materials that form in a person’s blood when HIV or other antigens enter the body. Although antibodies usually defend against disease agents, after a time, especially without intervention, due to the replication of HIV, the immune system is no longer able to protect against disease agents.
-By the time people with HIV develop AIDS, the virus has usually destroyed the immune system and they develop disease, which most healthy people can resist or control.
- Such diseases are called opportunistic infections.
please let take a proper care of our immune system to live a healthy Life. GOOD MORNING.