Immunity is best defined as the body’s ability to eradicate microbes or pathogens and to subsequently prevent further cases of reinfection. These functions are carried out by the innate and adaptive immune systems. The innate immune system is the fast acting immune system, which is not very diverse and does not contain memory cells. The adaptive immune system is slower acting, but contains memory cells and is much more diverse than the innate immune system. Two ways to activate the immune system is through passive and active immunity. Both passive and active immunity produce antibodies against foreign pathogens.  

Passive immunity is when antibodies are introduced into your body, but these antibodies were not produced in your own body. The antibodies are of foreign nature. One well known example of passive immunity is maternal immunity being passed on to the fetus. Maternal antibodies IgG cross the placenta to the reach the fetus. Maternal antibodies IgA reach the fetus through breast milk. Another example of passive immunity is taking antibodies from horses and transferring them to patients. Passive immunity is critical for new born babies who have not developed their own immune systems well enough to fight infections on their own.

Active immunity is when antibodies are produced by your own body. Active immunity occurs when someone is exposed to a pathogen which results in the production of antibodies against the antigen. Active immunity can also be acquired by artificial exposure to an antigen through a vaccination. The following picture is a well depiction of the differences between active and passive immunity: 

Active vs Passive Immunity

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