I started to read about the human body when my dad checked a book about the human body from the library. He checked it out to let me read about the nervous system. But I didn't find the nervous system very interesting.Then I found a few pages about the immune system. The immune system seemed much more interesting, so I read about it. Then I checked out many books about the immune system from two different libraries and found out a lot about the immune system. Once I even did a science project on the immune system.
I learned that the immune system fights bacteria, fungi, parasites, and viruses. It uses humoral immunity mostly to fight bacteria. This type of immunity involves antibodies, which are proteins produced by white blood cells called B cells that disable bacteria or mark them for destruction.
Sometimes your body is invaded by viruses. Your body rarely uses humoral immunity against viruses. It usually uses cellular immunity against viruses. The cells used in cellular immunity kill the cells that are already invaded by viruses. When they kill the cells, they kill the viruses inside them too.
Here's how humoral immunity works: When a B cell recognizes the organism it is supposed to fight, it starts to multiply. Some of the B cells turn into plasma cells, the cells that release antibodies. Free antibodies stick themselves onto the invading organisms and either destroy the organisms or mark them for destruction. Marked organisms will be destroyed by macrophages and chemicals.
Some B cells turn into memory B cells. These cells remember the organisms for a long time.
Here's how cellular immunity works: A killer T cell recognizes the organism it is supposed to fight and starts to multiply. It turns into memory T cells, which remembers the organisms for a long time.
A helper T cell will lock itself onto a cell that has already been invaded by a virus. Then it will inject a dose of lymphokines into the cell. Lymphokines kill the infected cell and the viruses inside it.
