http://sciencewithsusanna.com has diagrams, notes, and practice questions.
PASSIVE IMMUNITY is when antibodies are provided for the host - the best examples are
1. IgG antibodies from the mother cross the placenta and protect the fetus. These antibodies remain circulating for the early months of infancy.
2. Breast milk contains all classes of antibodies, especially IgA antibodies that protect the mucous membranes from diarrheal diseases. White blood cells from the mother actively protect the infant's GI tract, as well as releasing chemicals that stimulate the development of the baby's immune system. Interferon is found in breast milk, and helps protect intestinal cells from GI viruses.
3. Immunoglobulin injections may be given after possible exposure to a particularly virulent disease; rabies is a common example of when this can be done.
ACTIVE IMMUNITY is when the host's white blood cells respond to the pathogen, make antibodies to it, and develop memory cells that protect against future exposures to the pathogen.
1. Natural exposure to the disease will develop active immunity. Advantages of this natural exposure is that whatever route the pathogen used to get inside the body is most likely the area where our body is best at recognizing and defending against it.
2. Vaccines include pieces of a pathogen, or pieces of its toxin, in order to stimulate the immune cells. Streptococcus pneumonia vaccines include pieces of the cell wall; Clostridium tetani vaccines include pieces of the deactivated tetanus toxoid. Measles virus is a live attenuated (weakened) form of the virus.
Adjuvants are added to vaccines in situations where the vaccine may not cause a robust enough immune response.