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Immunity to pathogens and the ability to control pathogen growth can be acquired by active or passive means. Active and passive means can also be categorized as natural or artificial. See Figure 1, Table 3, and the information that follows for a description of active and passive immunity.
Figure 1
(1) Active immunity is acquired through an immune response (development of antibodies) when the body is exposed to the pathogen. It can be of natural or artificial mechanisms.
- Natural active immunity occurs when a person is exposed to a live pathogen, and develops a primary immune response, which leads to immunological memory. This type of immunity is "natural" because it is not induced by deliberate exposure. An example of this would be developing chicken pox after exposure to the viral pathogen.
- Artificial active immunity is achieved through artificial means such as is the case with immunizations or vaccine injections. A person is injected with a weakened strain of the pathogen to prompt the body to produce antibodies and memory cells for immunity. It is “active” because the body produces antibodies, but “artificial” because it is a deliberate infection of the antigens.
(2) Passive immunity is acquired through the transfer of antibodies from an immune individual to a nonimmune one. The individual does not create the antibodies, but receives them, and is only immune while receiving the antibodies. The immune system does not develop memory cells. This type of immunity can be obtained through natural or artificial mechanisms.
- Natural passive immunity is the transfer of antibodies from the maternal circulation to the fetus via the placenta, protecting the fetus from infection and protecting the newborn for the first few months of its life. Antibodies are also passed to infants through milk during breastfeeding. No memory cells are produced.
- Artificial passive immunity usually involves injections of immunoglobulins (or antibodies) taken from animals previously exposed to a specific pathogen. This treatment is a fast-acting method of temporarily protecting an individual who was possibly exposed to a pathogen. Rabies exposure would require these kinds of injections. No memory cells are produced.
See Table 3 for a comparison chart between active and passive immunity.
Table 3: Passive and Active Immunity Comparisons
|
Natural |
Artificial |
Active |
(Infection) |
(Immunization) |
Passive |
(Maternal) |
(Antibody Transfer) |
Check for understanding:
-What is the main difference between passive and active immunity?
-What is the main difference between natural and artificial immunity?
