Defence Against Pathogens
Human Biology (Year 12)
What is immunity and what are the main types?
Immunity is the resistance to infection by invading micro-organisms, and the presence of memory cells allows the body to respond quickly enough to deal with any invasion by pathogenic micro-organisms before symptoms of disease occur.
The ability to respond rapidly may be natural or artificial, where natural immunity occurs without any human intervention whilst artificial immunity results from giving people an antibody or antigen, and either of the types can be passive or active.
What is passive immunity?
Passive immunity is when a person receives antibodies produced by someone else, meaning that the individual’s body plays no part in the production of antibodies.
This can occur naturally when antibodies from the mother pass across the placenta to a developing foetus or when the mother’s antibodies are passed to the baby in breast milk, or it can also be gained artificially when a person is injected with antibodies to combat a particular infection.
Artificial injections are often done when a person is exposed to pathogens that cause serious diseases, such as tetanus, diphtheria and rabies – antibodies are given so that immunity is established immediately. Passive immunity is short-lived, and only lasts until the antibodies are broken down and excreted.
What is active immunity?
Active immunity results when the body is exposed to a foreign antigen and manufactures antibodies in response to that antigen.
While the amount of antibody decreases, this type of immunity lasts longer in comparison to passive immunity due to the presence of memory cells. Should a subsequent infection involving the same antigen occur, the appropriate antibodies can be produced very quickly, eliminating the antigen before the infection can produce any symptoms of disease.
Active immunity to a disease can develop from having the disease and recovering (natural active immunity) or from an infection of the antigens associated with the disease (artificial active immunity).
Summary: four main types of immunity
Passive natural immunity: e.g., mother passing antibodies to baby via placenta or breast milk
Passive artificial immunity: e.g., treatment given in response to serious disease-causing pathogens to rapidly establish immunity
Active natural immunity: e.g., getting a disease and recovering
Active artificial immunity: e.g., getting vaccinated against a disease
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