Adaptive immune system

The adaptive immune system (AIS), also known as the acquired immune system, or specific immune system is a subsystem of the <a href="/facts/Immune_system/HRCTf1pb">immune system</a> that is composed of specialized cells, organs, and processes that eliminate <a href="/facts/Pathogen/axMXtV1M">pathogens</a> specifically. The acquired immune system is one of the two main <a href="/facts/Immunity_(medical)/vLPpzSNL">immunity</a> strategies found in <a href="/facts/Vertebrate/tT54FSTT">vertebrates</a> (the other being the <a href="/facts/Innate_immune_system/lz4BpSQI">innate immune system</a>).
Like the innate system, the adaptive immune system includes both <a href="/facts/Humoral_immunity/qG9I4pGf">humoral immunity</a> components and <a href="/facts/Cell-mediated_immunity/vPX39rt1">cell-mediated immunity</a> components and destroys invading pathogens. Unlike the <a href="/facts/Innate_immune_system/lz4BpSQI">innate immune system</a>, which is pre-programmed to react to common broad categories of pathogen, the adaptive immune system is highly specific to each particular pathogen the body has encountered.
Adaptive immunity creates <a href="/facts/Immunological_memory/PVTllYEY">immunological memory</a> after an initial response to a specific pathogen, and leads to an enhanced response to future encounters with that pathogen. <a href="/facts/Antibody/MX8pdTdP">Antibodies</a> are a critical part of the adaptive immune system. Adaptive immunity can provide long-lasting protection, sometimes for the person's entire lifetime. For example, someone who recovers from measles is now protected against measles for their lifetime; in other cases it does not provide lifetime protection, as with <a href="/facts/Chickenpox/XkGzx2GE">chickenpox</a>. This process of adaptive immunity is the basis of <a href="/facts/Vaccination/3SfpzPsd">vaccination</a>.
The cells that carry out the adaptive immune response are white blood cells known as <a href="/facts/Lymphocyte/pS2pv2Ma">lymphocytes</a>. <a href="/facts/B_cell/6Y1tgwwp">B cells</a> and <a href="/facts/T_cell/5z6PQ9UN">T cells</a>, two different types of lymphocytes, carry out the main activities: antibody responses, and cell-mediated immune response. In antibody responses, B cells are activated to secrete <a href="/facts/Antibodies/MX8pdTdP">antibodies</a>, which are proteins also known as <a href="/facts/Immunoglobulins/MX8pdTdP">immunoglobulins</a>. Antibodies travel through the bloodstream and bind to the foreign antigen causing it to inactivate, which does not allow the antigen to bind to the host. <a href="/facts/Antigens/9JlAernG">Antigens</a> are any substances that elicit the adaptive immune response. Sometimes the adaptive system is unable to distinguish harmful from harmless foreign molecules; the effects of this may be <a href="/facts/Allergic_rhinitis/ukE6bkIs">hayfever</a>, <a href="/facts/Asthma/7GkJvxn3">asthma</a>, or any other <a href="/facts/Allergy/dYAVosh8">allergy</a>.
In adaptive immunity, pathogen-specific <a href="/facts/Immune_receptor/myRgAvX0">receptors</a> are "acquired" during the lifetime of the organism (whereas in innate immunity pathogen-specific receptors are already encoded in the <a href="/facts/Genome/tjhWET4V">genome</a>). This acquired response is called "adaptive" because it prepares the body's immune system for future challenges (though it can actually also be <a href="/facts/Maladaptation/n8awwPnV">maladaptive</a> when it results in allergies or <a href="/facts/Autoimmunity/5cASmcfI">autoimmunity</a>).
The system is highly <a href="/facts/Adaptation/5K2gNpDB">adaptable</a> because of two factors. First, <a href="/facts/Somatic_hypermutation/6xXQSNsY">somatic hypermutation</a> is a process of accelerated random genetic <a href="/facts/Mutation/Ee4NnWbY">mutations</a> in the antibody-coding genes, which allows antibodies with novel specificity to be created. Second, <a href="/facts/V(D)J_recombination/UpKylxB1">V(D)J recombination</a> randomly selects one variable (V), one diversity (D),
and one joining (J) region for <a href="/facts/Genetic_recombination/uocNH0m7">genetic recombination</a> and discards the rest, which produces a highly unique combination of antigen-receptor gene segments in each lymphocyte. This mechanism allows a small number of genetic segments to generate a vast number of different antigen receptors, which are then uniquely expressed on each individual <a href="/facts/Lymphocyte/pS2pv2Ma">lymphocyte</a>. Since the gene rearrangement leads to an irreversible change in the <a href="/facts/DNA/nB89Iauz">DNA</a> of each cell, all <a href="/facts/Offspring/v7LD4qBl">progeny</a> (offspring) of that cell inherit genes that encode the same receptor specificity, including the <a href="/facts/Memory_B_cell/3Qaz8Pxd">memory B cells</a> and <a href="/facts/Memory_T_cells/xsavrTuS">memory T cells</a> that are the keys to long-lived specific immunity.

Adaptive immune system open-in-new

Adaptive immune system