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Adaptive Immune System - Overview (view source)
Revision as of 14:02, 16 August 2010
, 14:02, 16 August 2010Created page with "==Introduction== Adaptive immunity is a defence system built on specific cellular targeting. It takes time for the immune system to develop its weaponry (up to 96 hours after in..."
==Introduction==
Adaptive immunity is a defence system built on specific cellular targeting. It takes time for the immune system to develop its weaponry (up to 96 hours after infection), but ultimately the adaptive response is far more effective because of its precision.
Once infection is identified, antigen is transported to [[Lymphoreticular System - Anatomy & Physiology|lymphoid organs]] where it is recognised by naive [[B cell differentiation|B]] and [[T cell differentiation|T]] cells. Clonal expansion and differentiation of these cells occurs, and then the battle begins. The immune system can take several tacks, depending on the type of infection encountered. Ultimately, the goals of the adaptive response are two-fold: to produce neutralising [[Immunoglobulins|antibody]], and to flag up infected cells for destruction. This annihilation can be carried out by the cells of both [[Innate Immune System|innate]] and adaptive immunity.
==Actions of the Adaptive Immune System==
[[Image:TCR.jpg|thumb|right|150px|T-cell receptor binds antigen fragments presented by MHC on the cell surface - B. Catchpole, RVC 2008]]
[[Image:BCR.jpg|thumb|right|150px|B-cell receptor binds two antigens in the ECF - B. Catchpole, RVC 2008]]
Adaptive immunity is stimulated by the generic actions of [[Innate Immune System|innate immunity]]. Once a foreign organism is identified by the [[Innate Immune System|innate immune system]], circulating [[Lymphocytes#T Cells|T-cells]] begin interacting with foreign antigen. Based on their encounter, they can do one of three things: they can kill infected cells directly, they can boost the actions of [[Macrophages|macrophages]] to kill infected cells, or they can return to [[Lymphoreticular System - Anatomy & Physiology|lymph tissue]] to incite a [[Lymphocytes#B Cells|B cell]] response. Stimulated [[Lymphocytes#B Cells|B cells]] will proceed to produce [[Immunoglobulins|antibody]], which can then circulate to fight the infection.
===Antigen Recognition===
"Antigen" refers to the parts of a foreign organism recognisable by the adaptive immune system. Typically, these are structural proteins, such as the spike proteins of viruses. Antigens can be huge, and are more often identified by '''epitopes''', or smaller fragments of the folded proteins. As such, a single antigen can be recognised by multiple antigen receptors. [[Immunoglobulins|Antibody]] has evolved to recognise a dizzying array of antigen epitopes. Antigen can be picked up by [[Lymphocytes|lymphocytes]] in the lymph tissues ([[Lymphocytes#T Cells|T cells]] and [[Lymphocytes#B Cells|B cells]]) or the blood stream ([[Lymphocytes#T Cells|T cells]] only).
[[Lymphocytes#T Cells|T cell]] receptors ('''TCR''') recognise '''antigen fragments''' (that is digestion products) on the '''surface of cells''', whereas [[Lymphocytes#B Cells|B cell]] receptors ('''BCR''') bind '''whole antigen''' in the '''extracellular fluid'''. [[Lymphocytes#T Cells|T cells]] only "see" antigen when it is presented by [[MHC - WikiBlood|'''MHC''']] (Major Histocompatibility Complex) on the cell surface. Antigen digestion and presentation is one of the major functions of the [[T cell differentiation#Antigen Presentation by Dendritic Cells|'''dendritic cells''']] (circulating [[Monocytes|monocytes]]) and '''[[Macrophages|macrophages]]'''. These are referred to as '''Antigen-Presenting Cells''' (APCs).
Naive B-cells express [[Immunoglobulin D|IgD]] and [[Immunoglobulin M|IgM]] on their cell surfaces, which bind antigen as it is washed into lymph tissue with the afferent lymph fluid. Antigen is presented to [[Lymphocytes#B Cells|B cells]] by [[B cell differentiation#Antigen Presentation by Follicular Dendritic Cells|'''follicular dendritic cells''' (FDCs)]], which are also classed as APCs. [[B cell differentiation#Antigen Presentation by Follicular Dendritic Cells|FDCs]] can endocytose antigen directly from the afferent lymph or receive them from [[Lymphocytes#Helper CD4+|CD4+ T-cells]].
===Cellular response: Proliferation and Differentiation===
[[Image:TH1-2.jpg|thumb|right|150px|TH1 and 2 selection is influenced by infection - B. Catchpole, RVC 2008]]
[[Image:B-cell immunity.jpg|thumb|right|150px|B-cell differentiation - B. Catchpole, RVC 2008]]
*''[[Lymphocytes#T Cells|T cell]] response''
Once [[Lymphocytes#T Cells|T cells]] recognise antigen presence in the tissues, they go into action. Their first response is always to recruit help, which is accomplished by returning to the nearest [[Lymph Nodes - Anatomy & Physiology|lymph node]] to carry out clonal expansion. Daughter [[Lymphocytes#T Cells|T cells]] are created with identical TCRs in order to recognise the identified antigen. These daughter cells are then returned to the circulation via the efferent lymph.
[[Lymphocytes#T Cells|T cells]] can differentiate three different ways, based on their Cluster of Differentiation (CD) number. All [[Lymphocytes#T Cells|T cells]] are CD3+, and naive circulating [[Lymphocytes#T Cells|T cells]] will differentiate upon interaction with antigen to become either [[Lymphocytes#Cytotoxic CD8+|'''CD8+ (cytotoxic)''']] or [[Lymphocytes#Helper CD4+|'''CD4+ (helper)''']] [[Lymphocytes#T Cells|T cells]]. [[[[Lymphocytes#Helper CD4+|CD4+ T-cells]] will initially become CD4-TH<sub>0</sub> cells, and must differentiate to [[T cell differentiation#TH1 Cells|TH<sub>1</sub>]] or [[T cell differentiation#TH2 Cells|TH<sub>2</sub>]] depending on the whim of the adaptive response. TH<sub>1</sub> and TH<sub>2</sub> cells carry out different types of responses: TH<sub>1</sub> is responsible for enhancing the [[Macrophages|macrophage]] response, whereas TH<sub>2</sub> cells enhance the [[Lymphocytes#B Cells|B cell]] antibody production. Typically, animals produce a balanced response of TH<sub>1</sub> and TH<sub>2</sub> cells, though this can lead to pathology, as can a skewed response, depending on the nature of the foreign organism. For more on [[Lymphocytes#T Cells|T cell]] differentiation, see [[T cell differentiation|here]].
*''[[Lymphocytes#B Cells|B cell]] response''
Naive [[Lymphocytes#B Cells|B cells]] recognise antigen in the lymph tissue when it is presented to them by [[B cell differentiation#Antigen Presentation by Follicular Dendritic Cells|Follicular Dendritic Cells (FDCs)]]. They also undergo clonal expansion, creating a '''germinal center''' in the follicle as they develop and mature into [[B cell differentiation#Plasma Cells|'''plasma cells''']]. Once mature, [[B cell differentiation#Plasma Cells|plasma cells]] in the [[Lymph Nodes - Anatomy & Physiology|lymph node]] migrate to the medullary cords and begin secreting [[Immunoglobulins|antibody]] into the efferent lymph. [[Immunoglobulins|Antibody]] eventually reaches the circulation in order to wage war on the intruder. For more on [[Lymphocytes#B Cells|B cell]] differentiation, see [[B cell differentiation|here]].
==Tools of the Adaptive Immune System==
===Antigen Presenting Cells===
''To B-cells'':
*[[B cell differentiation#Antigen Presentation by Follicular Dendritic Cells|Follicular Dendritic Cells]]
''To T-cells'', via [[MHC - WikiBlood|MHC]] presentation on:
*[[Macrophages|Macrophages]]
*[[T cell differentiation#Antigen Presentation by Dendritic Cells|Interdigitating Dendritic Cells]]
**Only IDCs can incite a primary response in naive T-cells
*[[Helper CD4+|CD4+ Tcells]]
*[[B cells|B-cells]]
===Antigen Binding Molecules===
*[[Immunoglobulins|Immunoglobulins]]
*[[T cells|T-cell Receptor (TCR)]]
*[[Natural Killer cells|Natural Killer (NK) Cells]]
[[Category:Adaptive Immune System]]
Adaptive immunity is a defence system built on specific cellular targeting. It takes time for the immune system to develop its weaponry (up to 96 hours after infection), but ultimately the adaptive response is far more effective because of its precision.
Once infection is identified, antigen is transported to [[Lymphoreticular System - Anatomy & Physiology|lymphoid organs]] where it is recognised by naive [[B cell differentiation|B]] and [[T cell differentiation|T]] cells. Clonal expansion and differentiation of these cells occurs, and then the battle begins. The immune system can take several tacks, depending on the type of infection encountered. Ultimately, the goals of the adaptive response are two-fold: to produce neutralising [[Immunoglobulins|antibody]], and to flag up infected cells for destruction. This annihilation can be carried out by the cells of both [[Innate Immune System|innate]] and adaptive immunity.
==Actions of the Adaptive Immune System==
[[Image:TCR.jpg|thumb|right|150px|T-cell receptor binds antigen fragments presented by MHC on the cell surface - B. Catchpole, RVC 2008]]
[[Image:BCR.jpg|thumb|right|150px|B-cell receptor binds two antigens in the ECF - B. Catchpole, RVC 2008]]
Adaptive immunity is stimulated by the generic actions of [[Innate Immune System|innate immunity]]. Once a foreign organism is identified by the [[Innate Immune System|innate immune system]], circulating [[Lymphocytes#T Cells|T-cells]] begin interacting with foreign antigen. Based on their encounter, they can do one of three things: they can kill infected cells directly, they can boost the actions of [[Macrophages|macrophages]] to kill infected cells, or they can return to [[Lymphoreticular System - Anatomy & Physiology|lymph tissue]] to incite a [[Lymphocytes#B Cells|B cell]] response. Stimulated [[Lymphocytes#B Cells|B cells]] will proceed to produce [[Immunoglobulins|antibody]], which can then circulate to fight the infection.
===Antigen Recognition===
"Antigen" refers to the parts of a foreign organism recognisable by the adaptive immune system. Typically, these are structural proteins, such as the spike proteins of viruses. Antigens can be huge, and are more often identified by '''epitopes''', or smaller fragments of the folded proteins. As such, a single antigen can be recognised by multiple antigen receptors. [[Immunoglobulins|Antibody]] has evolved to recognise a dizzying array of antigen epitopes. Antigen can be picked up by [[Lymphocytes|lymphocytes]] in the lymph tissues ([[Lymphocytes#T Cells|T cells]] and [[Lymphocytes#B Cells|B cells]]) or the blood stream ([[Lymphocytes#T Cells|T cells]] only).
[[Lymphocytes#T Cells|T cell]] receptors ('''TCR''') recognise '''antigen fragments''' (that is digestion products) on the '''surface of cells''', whereas [[Lymphocytes#B Cells|B cell]] receptors ('''BCR''') bind '''whole antigen''' in the '''extracellular fluid'''. [[Lymphocytes#T Cells|T cells]] only "see" antigen when it is presented by [[MHC - WikiBlood|'''MHC''']] (Major Histocompatibility Complex) on the cell surface. Antigen digestion and presentation is one of the major functions of the [[T cell differentiation#Antigen Presentation by Dendritic Cells|'''dendritic cells''']] (circulating [[Monocytes|monocytes]]) and '''[[Macrophages|macrophages]]'''. These are referred to as '''Antigen-Presenting Cells''' (APCs).
Naive B-cells express [[Immunoglobulin D|IgD]] and [[Immunoglobulin M|IgM]] on their cell surfaces, which bind antigen as it is washed into lymph tissue with the afferent lymph fluid. Antigen is presented to [[Lymphocytes#B Cells|B cells]] by [[B cell differentiation#Antigen Presentation by Follicular Dendritic Cells|'''follicular dendritic cells''' (FDCs)]], which are also classed as APCs. [[B cell differentiation#Antigen Presentation by Follicular Dendritic Cells|FDCs]] can endocytose antigen directly from the afferent lymph or receive them from [[Lymphocytes#Helper CD4+|CD4+ T-cells]].
===Cellular response: Proliferation and Differentiation===
[[Image:TH1-2.jpg|thumb|right|150px|TH1 and 2 selection is influenced by infection - B. Catchpole, RVC 2008]]
[[Image:B-cell immunity.jpg|thumb|right|150px|B-cell differentiation - B. Catchpole, RVC 2008]]
*''[[Lymphocytes#T Cells|T cell]] response''
Once [[Lymphocytes#T Cells|T cells]] recognise antigen presence in the tissues, they go into action. Their first response is always to recruit help, which is accomplished by returning to the nearest [[Lymph Nodes - Anatomy & Physiology|lymph node]] to carry out clonal expansion. Daughter [[Lymphocytes#T Cells|T cells]] are created with identical TCRs in order to recognise the identified antigen. These daughter cells are then returned to the circulation via the efferent lymph.
[[Lymphocytes#T Cells|T cells]] can differentiate three different ways, based on their Cluster of Differentiation (CD) number. All [[Lymphocytes#T Cells|T cells]] are CD3+, and naive circulating [[Lymphocytes#T Cells|T cells]] will differentiate upon interaction with antigen to become either [[Lymphocytes#Cytotoxic CD8+|'''CD8+ (cytotoxic)''']] or [[Lymphocytes#Helper CD4+|'''CD4+ (helper)''']] [[Lymphocytes#T Cells|T cells]]. [[[[Lymphocytes#Helper CD4+|CD4+ T-cells]] will initially become CD4-TH<sub>0</sub> cells, and must differentiate to [[T cell differentiation#TH1 Cells|TH<sub>1</sub>]] or [[T cell differentiation#TH2 Cells|TH<sub>2</sub>]] depending on the whim of the adaptive response. TH<sub>1</sub> and TH<sub>2</sub> cells carry out different types of responses: TH<sub>1</sub> is responsible for enhancing the [[Macrophages|macrophage]] response, whereas TH<sub>2</sub> cells enhance the [[Lymphocytes#B Cells|B cell]] antibody production. Typically, animals produce a balanced response of TH<sub>1</sub> and TH<sub>2</sub> cells, though this can lead to pathology, as can a skewed response, depending on the nature of the foreign organism. For more on [[Lymphocytes#T Cells|T cell]] differentiation, see [[T cell differentiation|here]].
*''[[Lymphocytes#B Cells|B cell]] response''
Naive [[Lymphocytes#B Cells|B cells]] recognise antigen in the lymph tissue when it is presented to them by [[B cell differentiation#Antigen Presentation by Follicular Dendritic Cells|Follicular Dendritic Cells (FDCs)]]. They also undergo clonal expansion, creating a '''germinal center''' in the follicle as they develop and mature into [[B cell differentiation#Plasma Cells|'''plasma cells''']]. Once mature, [[B cell differentiation#Plasma Cells|plasma cells]] in the [[Lymph Nodes - Anatomy & Physiology|lymph node]] migrate to the medullary cords and begin secreting [[Immunoglobulins|antibody]] into the efferent lymph. [[Immunoglobulins|Antibody]] eventually reaches the circulation in order to wage war on the intruder. For more on [[Lymphocytes#B Cells|B cell]] differentiation, see [[B cell differentiation|here]].
==Tools of the Adaptive Immune System==
===Antigen Presenting Cells===
''To B-cells'':
*[[B cell differentiation#Antigen Presentation by Follicular Dendritic Cells|Follicular Dendritic Cells]]
''To T-cells'', via [[MHC - WikiBlood|MHC]] presentation on:
*[[Macrophages|Macrophages]]
*[[T cell differentiation#Antigen Presentation by Dendritic Cells|Interdigitating Dendritic Cells]]
**Only IDCs can incite a primary response in naive T-cells
*[[Helper CD4+|CD4+ Tcells]]
*[[B cells|B-cells]]
===Antigen Binding Molecules===
*[[Immunoglobulins|Immunoglobulins]]
*[[T cells|T-cell Receptor (TCR)]]
*[[Natural Killer cells|Natural Killer (NK) Cells]]
[[Category:Adaptive Immune System]]