Vaccines

Vaccines expose the body to antigens, which are specific molecules from the pathogen, without causing disease. This causes the body to have a much quicker response when under attack from the pathogen in the future. There are several different types of vaccines such as live attenuated vaccines (introducing the body to a weaker or asymptomatic form of the pathogen), inactivated vaccines (introducing dead pathogen into the body), and subunit/conjugate vaccines (isolating a specific protein/carbohydrate from pathogen), but all of them are meant to train the body to respond to a pathogen without causing illness.
Vaccines imitate an infection and cause the body to make T-lymphocytes (a type of defensive white blood cell that attacks infected cells in the body) and antibodies. After the imitation infection goes away, the body is left with memory T-lymphocytes and B-lymphocytes (a type of white blood cell that produce antibodies that attack antigens left by macrophages), which will remember how to fight that pathogen in the future.

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