Vaccines
The immune system develops antibodies to attack a pathogen using one of two
methods: active immunity and passive immunity.
Active immunity occurs when the immune system generates antibodies on the
first exposure to the pathogen. This immune response is relatively slow, result-
ing in the patient showing the signs and symptoms of the disease.
However, the immune system remembers the pathogen and is quick to dispatch
antibodies should the pathogen attack a subsequent time. This happens faster than
the initial response and can generally eliminate the pathogen before the patient
experiences the signs and symptoms of the disease. The patient may have a life-
long immunity to the pathogen thanks to the body’s active natural immunity.
Active natural immunity can also occur through immunization when the patient
receives a vaccination against the pathogen. The vaccination contains a small
amount of the pathogen to stimulate the production of antibodies, but insufficient
in strength to develop the signs and symptoms of the disease.
There are five ways in which the pathogen in vaccines is produced.
1.Whole or components of an inactivated (dead) microorganism
2.Live, but weakened microorganisms
3.Toxoids, which are inactivated toxins produced by some microorganisms
4.Conjugates, which are vaccines that link a protein (toxoid) from an unre-
lated organism to the outer coat of the disease-causing microorganism. The
result is a substance that is recognized by the immature immune system of
young infants. Haemophilus influenzaetype b is an example.
5.Recombinant subunit vaccine is where DNA of a pathogen is inserted into
a cell or organism. The cell or organism then produces massive quantities
of the pathogen that are used in place of the whole pathogen. Examples are
hepatitis B and LYMErix for Lyme disease.A booster dose of a vaccine is sometimes required to maintain sufficient
immunity. The immune system has a memory and when the vaccinated individ-
ual is later exposed to the actual pathogen, the body can mount a rapid immune
response and prevent the disease. This is called artificially acquired immunity.
Passive immunity occurs when the patient receives antibodies from another
source rather than generating his or her own antibodies. Newborns have natural
passive immunity to protect them from pathogens. The newborn receives natu-
ral passive immunity from antibodies that cross the placenta. Antibodies may
CHAPTER 17 Immunologic Agents^321