MadSci Network: Immunology
Query:

Re: What's the difference of TH1 cells and TH2 cells effect?

Date: Sat May 8 16:49:54 1999
Posted By: Mimi Mong, Staff Research Associate,University of California at Berkeley
Area of science: Immunology
ID: 926099827.Im
Message:

The differentiation of CD4 T cells into TH1 or TH2 determines whether 
humoral or cell-mediated immunity will predominate.  TH1 cells lead to 
cell-mediated immunity which involves destruction of infected cells by 
cytotoxic T cells or destruction of intracellular pathogen by activated 
macrophages.  TH2 cells provide humoral immunity which activates B cells 
to make neutralizing antibody.  

Thus in general, effective host defense against intracellular pathogens 
like viruses and mycobacteria requires selective production of TH1 cells, 
while extracellular pathogens like worms, bacteria, fungi can be best 
eliminated with a humoral immunity with TH2 cells as the predominant 
effector cells. TH1 cells can also contribute to humoral immunity by 
inducing production of strongly opsonizing antibodies. The difference 
between TH1 and TH2 effector function is critical to the outcome of 
infection seen in leprosy, a disease caused by infection Mycobacterium 
leprae growing in macrophage vesicles.  If TH1 cells are preferentially 
induced, few live bacteria are found, little antibody is made, the patient 
can usually survive the disease.  However, if TH2 cells are preferentially 
induced, antibodies are made but cannot reach the intracellular bacteria, 
and patients develop leprematous leprosy which is eventually fatal.

In many infections, however, both cell-mediated and humoral immunity play 
a role such as reponse to Pneumocystis carinii, which requires antibody 
for ingestion by phagocytes and macrophage activaton for effective 
destruction of the ingested pathogen.


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