Have you ever wondered why you have to use a variety of vaccines in your life?
Are you interested in knowing how they work?
There are many organisms living on the beautiful earth.
But in the process of life development, they are suffering from pathogens.
Humans have invented various vaccines in order to fight the spread of infectious diseases.
Smallpox was once the enemy of all mankind.
In the 18th century, 
about 150 million people in Europe died of smallpox.
Edward Jenner found that after suffered from mild vaccinia,
can immunize smallpox for life.
He is the first person to use a vaccine.
Now, we have finally eliminated the smallpox.
First, let us know how the immune system works？
The immune process is to identify and destroy the "non-self" enemies ,which we call them antigens.
Antigens include foreign invasions.
for example viruses,bacteria,fungi,
and parasites.
Also includes self-variation，
for example damaged cells and cancer cells.
Antigens can stimulate the body to produce antibodies，
antibodies are immune proteins that bind to the antigen to inactivate it.
Immune defense include Skin, mucous membranes and Macrophages.
They are non-specific immunity,
and have a wide range of pathogen defense capabilities.
The main immune organs include bone marrow, thymus, lymph nodes,
which generate immune cells.
immune cells make up specific immunity against the pathogen,
called immune response.
First stage of immune response is antigen recogniting phase.
Antigens were presented by macrophages or dendritic cells to T lymphocytes and B lymphocytes.
Second stage is lymphocyte activating phase.
After T-lymphocyte activation, cytotoxic T cells and cytokines are produced.
In the third stage of antigen-eliminating phase,
cell mediated immunity are formed，
eliminate infected cells.
Afte activation of B lymphocytes into plasma cells,
antibodies are produced to destroy the antigens, called humoral immunity.
Also immunological memory cells formed.
As the number of contacts with specific antigens increases,
memory cells will increase and time to resist antigen will be longer.
Vaccine is active immunity,
inactivated or attenuated antigens is used
to provide long-term protection by immune memory.
More immunology will be developed by you and me, treating malaria and HIV is coming soon!
see you later~
