Helper T cells - Revision history

Ihjung at 20:08, 22 February 2007

2007-02-22T20:08:28Z

Ihjung at 20:02, 22 February 2007

2007-02-22T20:02:50Z

Ihjung at 20:01, 22 February 2007

2007-02-22T20:01:45Z

Ihjung at 19:58, 22 February 2007

2007-02-22T19:58:24Z

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Helper T cells are T lymphocyte that belong to the CD4+ subset. 
 
1. Types of Helper T Cells 
- Th1 ; These participate in cell-mediated immunity. They are essential for controlling such intracellular pathogens as viruses and certain bacteria, e.g., Listeria and Mycobacterium tuberculosis (the bacillus that causes tb). 
- Th2 ; These provide help for B cells and, in so doing, are essential for antibody-mediated immunity. Antibodies are needed to control extracellular pathogens (which — unlike intracellular parasites — are exposed to antibodies in blood and other body fluids). 
 
2. Origin of Helper T Cells 
Like all T cells, Th cells arise in the thymus.  
- When they acquire CD4, they are called pre-Th cells. 
- When they are presented with both an antigen and appropriate cytokines, they begin to proliferate and become activated. 
- It is the nature of the stimulation that determines which path they enter: the path leading to Th1 cells or the path leading to Th2 cells. 
 
The antigen-presenting cells (APCs) are called dendritic cells (DCs). There are several subsets of them: some produced by monocytes and others derived from a progenitor cell that gives rise to both them and monocytes. 
Dendritic cells 
- ingest antigen by phagocytosis or pinocytosis; 
- degrade it in lysosomes, and 
- display fragments of the antigen at their surface for presentation to T cells.  
- secrete cytokines. 
(Dendritic cells can also present intact antigen directly to B cells. In this case, the engulfed antigen is not degraded in lysosomes but is returned to the cell surface for presentation to B cells bearing BCRs of the appropriate specificity.) 
There are at least two kinds of dendritic cell that present antigens to T cells:  
- DC1 and DC2

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 </font><font size="2">- secrete cytokines. <br />
 (Dendritic cells can also present intact antigen directly to B cells. In this case, the engulfed antigen is not degraded in lysosomes but is returned to the cell surface for presentation to B cells bearing BCRs of the appropriate specificity.) </font></p>
-<p><font size="2">There are at least two kinds of dendritic cell that present antigens to T cells:&nbsp;<br />
+<p align="left"><font size="2">There are at least two kinds of dendritic cell that present antigens to T cells:&nbsp;<br />
 </font><font size="2">- DC1 and DC2&nbsp;<br />
 <br />
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 - recruit other leukocytes to the site producing inflammation.<br />
 <br />
-[[image:Th1_Th2.gif]]</font></p>
+[[image:Th1_Th2.gif]]<br />

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 - stimulate macrophages to kill the bacteria they have engulfed; <br />
 - recruit other leukocytes to the site producing inflammation.<br />
-</font></p>
+<br />

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 (Dendritic cells can also present intact antigen directly to B cells. In this case, the engulfed antigen is not degraded in lysosomes but is returned to the cell surface for presentation to B cells bearing BCRs of the appropriate specificity.) </font></p>
 <p><font size="2">There are at least two kinds of dendritic cell that present antigens to T cells:&nbsp;<br />
-</font><font size="2">- DC1 and DC2 <br />
+</font><font size="2">- DC1 and DC2&nbsp;<br />
 <br />
 </font></p>