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Text replace - 'Macrophages - WikiBlood' to 'Macrophages'
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 [[Lymphocytes#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 - WikiBlood|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 [[Lymphocytes#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 - WikiBlood|Macrophages]] cause the TH<sub>0</sub> cell to develop into TH<sub>1</sub> cells caused by IL-12 production following [[Macrophages - WikiBlood|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. [[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.
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 [[Lymphocytes#T cells|T cells]] continues until antigen disappears.
==Common Functions of Th<sub>1</sub> and TH<sub>2</sub> Cells==
==Common Functions of Th<sub>1</sub> and TH<sub>2</sub> Cells==
* Both TH1 and TH2 cells produce IL-3 and granulocyte-[[Macrophages - WikiBlood|macrophage]] colony stimulating factor (GM-CSF).
* Both TH1 and TH2 cells produce IL-3 and granulocyte-[[Macrophages|macrophage]] colony stimulating factor (GM-CSF).
** These act to activate and induce proliferation of [[Neutrophils|neutrophils]] and also [[Macrophages - WikiBlood|macrophages]].
** These act to activate and induce proliferation of [[Neutrophils|neutrophils]] and also [[Macrophages|macrophages]].
*** [[Neutrophils|Neutrophils]] are the major phagocytic cells in the blood and the principal cells in acute inflammatory lesions.
*** [[Neutrophils|Neutrophils]] are the major phagocytic cells in the blood and the principal cells in acute inflammatory lesions.
**** Function chiefly in the defence against extracellular bacteria.
**** Function chiefly in the defence against extracellular bacteria.