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==Introduction==
==Introduction==
Within the blood and lymphoid organs the majority of [[Lymphocytes#Helper CD4+|CD4+ T cells]] are antigen-naive T-cells. There is only a small proportion of memory T-cells.
Within the blood and lymphoid organs the majority of [[Helper CD4+|CD4+ T cells]] are antigen-naive T-cells. There is only a small proportion of memory T-cells.
Naive T-cells have yet to encounter antigen and can only be activated by antigen presented by dendritic cells. After initial antigenic activation, naïve T-cells develop into an intermediate stage cell called the TH<sub>0</sub> cell which can then be activated by any antigen-presenting cell, e.g. Dendritic cells, [[Macrophages|macrophages]] or [[Lymphocytes#B cells|B-cells]].
Naive T-cells have yet to encounter antigen and can only be activated by antigen presented by dendritic cells. After initial antigenic activation, naïve T-cells develop into an intermediate stage cell called the TH<sub>0</sub> cell which can then be activated by any antigen-presenting cell, e.g. Dendritic cells, [[Macrophages|macrophages]] or [[B cells|B-cells]].
The TH<sub>0</sub> cells have the capacity to differentiate into TH<sub>1</sub> and TH<sub>2</sub> cells. The type of cell that develops depends on the antigen presenting cell. [[Macrophages|Macrophages]] cause the TH<sub>0</sub> cell to develop into TH<sub>1</sub> cells caused by IL-12 production following [[Macrophages|macrophage]]-antigen interaction. [[Lymphocytes#B cells|B-cells]] cause the TH<sub>0</sub> cell to develop into TH<sub>2</sub> cells caused by IL-10 production following B-cell-antigen interaction. On antigenic stimulation the TH<sub>1</sub> or TH<sub>2</sub> cells become activated, undergo clonal expansion and secrete a range of different cytokines.
The TH<sub>0</sub> cells have the capacity to differentiate into TH<sub>1</sub> and TH<sub>2</sub> cells. The type of cell that develops depends on the antigen presenting cell. [[Macrophages|Macrophages]] cause the TH<sub>0</sub> cell to develop into TH<sub>1</sub> cells caused by IL-12 production following [[Macrophages|macrophage]]-antigen interaction. [[B cells|B-cells]] cause the TH<sub>0</sub> cell to develop into TH<sub>2</sub> cells caused by IL-10 production following B-cell-antigen interaction. On antigenic stimulation the TH<sub>1</sub> or TH<sub>2</sub> cells become activated, undergo clonal expansion and secrete a range of different cytokines.
For any one cell the cytokine-secreting activation state is short-lived, lasting between 4 - 40 hours. After this time these cells either die, or mature into the long-lived memory cells. The proliferation of [[Lymphocytes#T cells|T cells]] continues until antigen disappears.
For any one cell the cytokine-secreting activation state is short-lived, lasting between 4 - 40 hours. After this time these cells either die, or mature into the long-lived memory cells. The proliferation of [[T cells|T cells]] continues until antigen disappears.
==Dendritic Cells==
==Dendritic Cells==
**From plasmacytoid precursor cells
**From plasmacytoid precursor cells
*Stimulate a primary T cell response
*Stimulate a primary T cell response
*Migrate through tissues, track to [[Lymphocytes#T cells|T cells]] dependent areas of [[Lymph Nodes - Anatomy & Physiology|lymph node]] and cluster with [[Lymphocytes#T cells|T cells]]
*Migrate through tissues, track to [[T cells|T cells]] dependent areas of [[Lymph Nodes - Anatomy & Physiology|lymph node]] and cluster with [[T cells|T cells]]
*Dendritic cells have unique capabilities to take up antigen by pathways involving phagocytosis, macropinocytosis and clathrin-coated pits
*Dendritic cells have unique capabilities to take up antigen by pathways involving phagocytosis, macropinocytosis and clathrin-coated pits
*Cell-surface antigen phenotype distinguishing it from [[Monocytes]]/macrophages and [[Lymphocytes#B Cells|B cells]]
*Cell-surface antigen phenotype distinguishing it from [[Monocytes]]/macrophages and [[B Cells|B cells]]
*Cell-surface expression pattern according to their differentiation/maturation/activation
*Cell-surface expression pattern according to their differentiation/maturation/activation
*Main function is priming of [[Lymphocytes#T cells|T helper cells]]
*Main function is priming of [[T cells|T helper cells]]
*Produces [[Cytokines - WikiBlood#Chemokines|chemokines]]
*Produces [[Cytokines - WikiBlood#Chemokines|chemokines]]