Category:Lymphocytes
T cells
B cells
Natural Killer cells
Lymphocyte Surveillance
About two thirds of lymphocytes (all immunocompetent) are circulating in the blood and lymph systems. Most of these are 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.
High Endothelial Venules (HEV) are used for lymphocytes to access the lymph nodes from the bloodstream. Once inside the 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 organs each day. This process is called surveillance.
If a naive lymphocyte recognises an antigen then it differentiates into its adult (mature) form. Interdigitating dendritic cells present antigen to T cells and follicular dendritic cells present antigen to B cells.
B cells proliferate into plasma cells in germinal centres, producing antibody.
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 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 T cell enters the site of disease. CD4+ T cells search for infected macrophages and 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.
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Pages in category "Lymphocytes"
The following 7 pages are in this category, out of 7 total.