Post by the Scribe on Apr 27, 2022 5:52:38 GMT
Adaptive Immune System
en.wikipedia.org/wiki/Adaptive_immune_system
The adaptive immune system, also known as the acquired immune system, is a subsystem of the immune system that is composed of specialized, systemic cells and processes that eliminate pathogens or prevent their growth. The acquired immune system is one of the two main immunity strategies found in vertebrates (the other being the innate immune system).
Google Ngram of "acquired immunity " vs. "adaptive immunity". The peak for "adaptive" in the 1960s reflects its introduction to immunology by Robert A. Good and use by colleagues; the explosive increase in the 1990s was correlated with the use of the phrase "innate immunity".
Like the innate system, the adaptive immune system includes both humoral immunity components and cell-mediated immunity components and destroys invading pathogens. Unlike the innate immune system, 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 immunological memory after an initial response to a specific pathogen, and leads to an enhanced response to future encounters with that pathogen. Antibodies 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 chickenpox. This process of adaptive immunity is the basis of vaccination.
The cells that carry out the adaptive immune response are white blood cells known as lymphocytes. B cells and T cells, 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 antibodies, which are proteins also known as immunoglobulins. 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.[1] Antigens 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 hayfever, asthma, or any other allergy.
In adaptive immunity, pathogen-specific receptors are "acquired" during the lifetime of the organism (whereas in innate immunity pathogen-specific receptors are already encoded in the genome). This acquired response is called "adaptive" because it prepares the body's immune system for future challenges (though it can actually also be maladaptive when it results in allergies or autoimmunity).
The system is highly adaptable because of two factors. First, somatic hypermutation is a process of accelerated random genetic mutations in the antibody-coding genes, which allows antibodies with novel specificity to be created. Second, V(D)J recombination randomly selects one variable (V), one diversity (D), and one joining (J) region for genetic recombination 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 lymphocyte. Since the gene rearrangement leads to an irreversible change in the DNA of each cell, all progeny (offspring) of that cell inherit genes that encode the same receptor specificity, including the memory B cells and memory T cells that are the keys to long-lived specific immunity.
Functions
Overview of the processes involved in the primary immune response
Acquired immunity is triggered in vertebrates when a pathogen evades the innate immune system and (1) generates a threshold level of antigen and (2) generates "stranger" or "danger" signals activating dendritic cells.[2]
The major functions of the acquired immune system include:
Recognition of specific "non-self" antigens in the presence of "self", during the process of antigen presentation.
Generation of responses that are tailored to maximally eliminate specific pathogens or pathogen-infected cells.
Development of immunological memory, in which pathogens are "remembered" through memory B cells and memory T cells.
In humans, it takes 4-7 days for the adaptive immune system to mount a significant response.[3]
Lymphocytes
Main article: Lymphocyte
T and B lymphocytes are the cells of the adaptive immune system. The human body has about 2 trillion lymphocytes, which are 20–40% of white blood cells; their total mass is about the same as the brain or liver. The peripheral bloodstream contains only 2% of all circulating lymphocytes; the other 98% move within tissues and the lymphatic system, which includes the lymph nodes and spleen.[1] In humans, approximately 1–2% of the lymphocyte pool recirculates each hour to increase the opportunity for the cells to encounter the specific pathogen and antigen that they react to.[4]
B cells and T cells are derived from the same multipotent hematopoietic stem cells, and look identical to one another until after they are activated. B cells play a large role in the humoral immune response, whereas T cells are intimately involved in cell-mediated immune responses. In all vertebrates except Agnatha, B cells and T cells are produced by stem cells in the bone marrow.[5] T cell progenitors then migrate from the bone marrow to the thymus, where they develop further.
In an adult animal, the peripheral lymphoid organs contain a mixture of B and T cells in at least three stages of differentiation:
Naive B and naive T cells, which have left the bone marrow or thymus and entered the lymphatic system, but have yet to encounter their matching antigen
Effector cells that have been activated by their matching antigen, and are actively involved in eliminating a pathogen
Memory cells, the survivors of past infections
en.wikipedia.org/wiki/Adaptive_immune_system
The adaptive immune system, also known as the acquired immune system, is a subsystem of the immune system that is composed of specialized, systemic cells and processes that eliminate pathogens or prevent their growth. The acquired immune system is one of the two main immunity strategies found in vertebrates (the other being the innate immune system).
Google Ngram of "acquired immunity " vs. "adaptive immunity". The peak for "adaptive" in the 1960s reflects its introduction to immunology by Robert A. Good and use by colleagues; the explosive increase in the 1990s was correlated with the use of the phrase "innate immunity".
Like the innate system, the adaptive immune system includes both humoral immunity components and cell-mediated immunity components and destroys invading pathogens. Unlike the innate immune system, 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 immunological memory after an initial response to a specific pathogen, and leads to an enhanced response to future encounters with that pathogen. Antibodies 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 chickenpox. This process of adaptive immunity is the basis of vaccination.
The cells that carry out the adaptive immune response are white blood cells known as lymphocytes. B cells and T cells, 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 antibodies, which are proteins also known as immunoglobulins. 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.[1] Antigens 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 hayfever, asthma, or any other allergy.
In adaptive immunity, pathogen-specific receptors are "acquired" during the lifetime of the organism (whereas in innate immunity pathogen-specific receptors are already encoded in the genome). This acquired response is called "adaptive" because it prepares the body's immune system for future challenges (though it can actually also be maladaptive when it results in allergies or autoimmunity).
The system is highly adaptable because of two factors. First, somatic hypermutation is a process of accelerated random genetic mutations in the antibody-coding genes, which allows antibodies with novel specificity to be created. Second, V(D)J recombination randomly selects one variable (V), one diversity (D), and one joining (J) region for genetic recombination 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 lymphocyte. Since the gene rearrangement leads to an irreversible change in the DNA of each cell, all progeny (offspring) of that cell inherit genes that encode the same receptor specificity, including the memory B cells and memory T cells that are the keys to long-lived specific immunity.
Functions
Overview of the processes involved in the primary immune response
Acquired immunity is triggered in vertebrates when a pathogen evades the innate immune system and (1) generates a threshold level of antigen and (2) generates "stranger" or "danger" signals activating dendritic cells.[2]
The major functions of the acquired immune system include:
Recognition of specific "non-self" antigens in the presence of "self", during the process of antigen presentation.
Generation of responses that are tailored to maximally eliminate specific pathogens or pathogen-infected cells.
Development of immunological memory, in which pathogens are "remembered" through memory B cells and memory T cells.
In humans, it takes 4-7 days for the adaptive immune system to mount a significant response.[3]
Lymphocytes
Main article: Lymphocyte
T and B lymphocytes are the cells of the adaptive immune system. The human body has about 2 trillion lymphocytes, which are 20–40% of white blood cells; their total mass is about the same as the brain or liver. The peripheral bloodstream contains only 2% of all circulating lymphocytes; the other 98% move within tissues and the lymphatic system, which includes the lymph nodes and spleen.[1] In humans, approximately 1–2% of the lymphocyte pool recirculates each hour to increase the opportunity for the cells to encounter the specific pathogen and antigen that they react to.[4]
B cells and T cells are derived from the same multipotent hematopoietic stem cells, and look identical to one another until after they are activated. B cells play a large role in the humoral immune response, whereas T cells are intimately involved in cell-mediated immune responses. In all vertebrates except Agnatha, B cells and T cells are produced by stem cells in the bone marrow.[5] T cell progenitors then migrate from the bone marrow to the thymus, where they develop further.
In an adult animal, the peripheral lymphoid organs contain a mixture of B and T cells in at least three stages of differentiation:
Naive B and naive T cells, which have left the bone marrow or thymus and entered the lymphatic system, but have yet to encounter their matching antigen
Effector cells that have been activated by their matching antigen, and are actively involved in eliminating a pathogen
Memory cells, the survivors of past infections