Changes

==Development of CD4+ T-Cell Subpopulations==

==Development of CD4+ T-Cell Subpopulations==

* Within the blood and lymphoid organs the majority of CD4+ T cells are antigen-naive T-cells.

Within the blood and lymphoid organs the majority of CD4+ T cells are antigen-naive T-cells. There is only a small proportion of memory T-cells.  

** There is only a small proportion of memory T-cells.  

 

* Naive T-cells have yet to encounter antigen.

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 TH₀ cell which can then be activated by any antigen-presenting cell, e.g. Dendritic cell, macrophage or B-cell.  

** can only be activated by antigen presented by dendritic cells.  

 

* After initial antigenic activation, naïve T-cells develop into an intermediate stage cell.

The TH₀ cells have the capacity to differentiate into TH₁ and TH₂ cells. The type of cell that develops depends on the antigen presenting cell. Macrophages cause the TH₀ cell to develop into TH₁ cells caused by IL-12 production following macrophage-antigen interaction. B-cells cause the TH₀ cell to develop into TH₂ cells caused by IL-10 production following B-cell-antigen interaction, on antigenic stimulation the TH₁ or TH₂ cells become activated, undergo clonal expansion and secrete a range of different cytokines.

** The TH₀ cell.

 

** Can then be activated by any antigen-presenting cell.

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 continues until antigen disappears.

*** Dendritic cell, macrophage or B-cell.  

* The TH₀ cells have the capacity to differentiate into TH₁ and TH₂ cells.

** The type of cell that develops depends on the antigen presenting cell.

*** Macrophages cause the TH₀ cell to develop into TH₁ cells.

**** Caused by IL-12 production following macrophage-antigen interaction.

*** B-cells cause the TH₀ cell to develop into TH₂ cells.

**** Caused by IL-10 production following B-cell-antigen interaction,  

* On antigenic stimulation the TH₁ or TH₂ 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.

**** 4 - 40 hours.

**** After this time these cells either:

***** Die, or  

***** Mature into the long-lived memory cells.  

* The proliferation of T cells continues until antigen disappears.

===TH₁ Cells===

===TH₁ Cells===