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Immunity can be acquired either actively or passively. Immunity is acquired actively when a person is exposed to foreign substances and the immune system responds. Passive immunity is when antibodies are transferred from one host to another. Both actively acquired and passively acquired immunity can be obtained by natural or artificial means.
Adaptive (or acquired) immunity creates an immunological memory leading to an enhanced response to subsequent encounters with that same pathogen. This process of acquired immunity is the basis of vaccination. Dysfunction of the immune system can cause autoimmune diseases, inflammatory diseases and cancer.
In immunology, passive immunity is the transfer of active humoral immunity of ready-made antibodies.Passive immunity can occur naturally, when maternal antibodies are transferred to the fetus through the placenta, and it can also be induced artificially, when high levels of antibodies specific to a pathogen or toxin (obtained from humans, horses, or other animals) are transferred to non-immune ...
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Immune tolerance is formally differentiated into central or peripheral; [2] however, alternative terms such as "natural" or "acquired" tolerance have at times been used to refer to establishment of tolerance by physiological means or by artificial, experimental, or pharmacological means. [13]
The innate immune system or nonspecific immune system [1] is one of the two main immunity strategies in vertebrates (the other being the adaptive immune system). The innate immune system is an alternate defense strategy and is the dominant immune system response found in plants , fungi , prokaryotes , and invertebrates (see Beyond vertebrates ).
An individual's immunity can be acquired via a natural infection or through artificial means, such as vaccination. [51] When a critical proportion of the population becomes immune, called the herd immunity threshold (HIT) or herd immunity level (HIL), the disease may no longer persist in the population, ceasing to be endemic. [5] [26]
Natural immunity is gained by those organisms whose immune systems succeed in fighting off a previous infection, if the relevant pathogen is one for which immunization is even possible. Natural immunity can have degrees of effectiveness (partial rather than absolute) and may fade over time (within months, years, or decades, depending on the ...