Changes

==Lymphocyte Surveillance==

==Lymphocyte Surveillance==

<p>About two thirds of lymphocytes (all immunocompetent) are circulating in the blood and lymph systems. Most of these are [[Lymphocytes - WikiBlood#T cell|T cell]] and long lived. In the lymphatic system they survey tissues. The other third do not circulate and are either short lived or immature, or can be specific cells destined for certain tissues i.e. cells that line connective tissue under the epithelium of respiratory, intestinal and urogential systems.</p>

<p>About two thirds of lymphocytes (all immunocompetent) are circulating in the blood and lymph systems. Most of these are [[Lymphocytes#T cell|T cell]] and long lived. In the lymphatic system they survey tissues. The other third do not circulate and are either short lived or immature, or can be specific cells destined for certain tissues i.e. cells that line connective tissue under the epithelium of respiratory, intestinal and urogential systems.</p>

<p>[[Lymph Nodes - Anatomy & Physiology#High endothelial venules|High Endothelial Venules (HEV)]] are used for lymphocytes to access the [[Lymph Nodes - Anatomy & Physiology|lymph nodes]] from the bloodstream. Once inside the [[Lymph Nodes - Anatomy & Physiology|lymph node]], the naive lymphocytes search for antigen. If there is no antigen present, the naive lymphocytes leave via the efferent lymphatic vessel and return back to the bloodstream. Each lymphocyte can search several [[Secondary Lymphoid Tissue - Anatomy & Physiology|secondary lymphoid organs]] each day. This process is called '''surveillance'''.</P>

<p>[[Lymph Nodes - Anatomy & Physiology#High endothelial venules|High Endothelial Venules (HEV)]] are used for lymphocytes to access the [[Lymph Nodes - Anatomy & Physiology|lymph nodes]] from the bloodstream. Once inside the [[Lymph Nodes - Anatomy & Physiology|lymph node]], the naive lymphocytes search for antigen. If there is no antigen present, the naive lymphocytes leave via the efferent lymphatic vessel and return back to the bloodstream. Each lymphocyte can search several [[Secondary Lymphoid Tissue - Anatomy & Physiology|secondary lymphoid organs]] each day. This process is called '''surveillance'''.</P>

<p>If a naive lymphocyte recognises an antigen then it differentiates into its adult (mature) form. [[T cell differentiation - WikiBlood#Dendritic Cells|Interdigitating dendritic cells]] present antigen to [[Lymphocytes - WikiBlood#T cells|T cells]] and [[B cell differentiation - WikiBlood#Follicular Dendritic Cells|follicular dendritic cells]] present antigen to [[Lymphocytes - WikiBlood#B cells|B cells]].</p>

<p>If a naive lymphocyte recognises an antigen then it differentiates into its adult (mature) form. [[T cell differentiation - WikiBlood#Dendritic Cells|Interdigitating dendritic cells]] present antigen to [[Lymphocytes#T cells|T cells]] and [[B cell differentiation - WikiBlood#Follicular Dendritic Cells|follicular dendritic cells]] present antigen to [[Lymphocytes#B cells|B cells]].</p>

<p>[[Lymphocytes - WikiBlood#B cells|B cells]] proliferate into [[B cell differentiation - WikiBlood#Plasma cells|plasma cells]] in germinal centres, producing antibody.</p>

<p>[[Lymphocytes#B cells|B cells]] proliferate into [[B cell differentiation - WikiBlood#Plasma cells|plasma cells]] in germinal centres, producing antibody.</p>

<p>[[Lymphocytes - WikiBlood#T cells|T cells]] leave the lymph node in '''attack mode''' to locate the infectious organism. The surface molecule L-selectin (which allows the naive lymphocyte to enter the lymph node via an [[Lymph Nodes - Anatomy & Physiology#High endothelial venules|HEV]]) is replaced by the adhesion molecule VLA-4. At the site of inflammation, the VLA-4 receptor recognises VCAM-1 on endothelial cells and the [[Lymphocytes - WikiBlood#T cell|T cell]] enters the site of disease. [[Lymphocytes - WikiBlood#Helper CD4+|CD4+ T cells]] search for infected macrophages and [[Lymphocytes - WikiBlood#Cytotoxic CD8+|CD8+ T cells]] look for virus infected cells creating an immune response. After the infection has been defeated, memory cells develop which express L-selectin (rather than VLA-4) and continue to search the body in surveillance mode in case the host is re-infected with the disease producing organism.

<p>[[Lymphocytes#T cells|T cells]] leave the lymph node in '''attack mode''' to locate the infectious organism. The surface molecule L-selectin (which allows the naive lymphocyte to enter the lymph node via an [[Lymph Nodes - Anatomy & Physiology#High endothelial venules|HEV]]) is replaced by the adhesion molecule VLA-4. At the site of inflammation, the VLA-4 receptor recognises VCAM-1 on endothelial cells and the [[Lymphocytes#T cell|T cell]] enters the site of disease. [[Lymphocytes#Helper CD4+|CD4+ T cells]] search for infected macrophages and [[Lymphocytes#Cytotoxic CD8+|CD8+ T cells]] look for virus infected cells creating an immune response. After the infection has been defeated, memory cells develop which express L-selectin (rather than VLA-4) and continue to search the body in surveillance mode in case the host is re-infected with the disease producing organism.

==Links==

==Links==

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<center><b><sup>Blood cells: [[Erythrocytes - WikiBlood|Erythrocytes]] |  

<center><b><sup>Blood cells: [[Erythrocytes - WikiBlood|Erythrocytes]] |  

[[Basophils - WikiBlood|Basophils]], [[Eosinophils - WikiBlood|Eosinophils]], [[Lymphocytes - WikiBlood|Lymphocytes]], [[Macrophages - WikiBlood|Macrophages]], [[Mast Cells - WikiBlood|Mast cells]], [[Monocytes - WikiBlood|Monocytes]] & [[Neutrophils|Neutrophils]] |  [[Thrombocytes|Thrombocytes]] & [[Thrombopoiesis - WikiBlood#Megakaryocyte|Megakaryocytes]]</sup></b></center>

[[Basophils - WikiBlood|Basophils]], [[Eosinophils - WikiBlood|Eosinophils]], [[Lymphocytes|Lymphocytes]], [[Macrophages - WikiBlood|Macrophages]], [[Mast Cells - WikiBlood|Mast cells]], [[Monocytes - WikiBlood|Monocytes]] & [[Neutrophils|Neutrophils]] |  [[Thrombocytes|Thrombocytes]] & [[Thrombopoiesis - WikiBlood#Megakaryocyte|Megakaryocytes]]</sup></b></center>