Difference T helper 1 vs 2 immune response

[Monique]

I am getting a hold on immunological responses at the moment, but I am not familiar yet with the difference between T helper 1 and T helper 2 (Th1, Th2) immune response.

I know that: Th1 cells produce IL-2 and IFN-gamma, which activate CD8+ T cells, NK cells, and macrophages; whereas Th2 cells secrete IL-4 and IL-5, which activate B cells and switch antibody synthesis to IgE.

So basically a dichotomy in cytokine production, where Th1 seems to be involved in protection against viruses and delayed-type hypersensitivity; Th2 is involved in allergy and parasitic infections.

Um, so: Th1 = CD8+ T cells, NK cells, macrophages; Th2 = B cells and IgE.
Is there any logic why these two programs are seperated??
There is actually negative feedback between them, if one is activated it will downregulate the other.

 

[iansmith]

the only logic seem to be influence by the enviromental signal. IL12 is directly release by Th1 and IL12 has an postive impact on the division of Th0 towards Th1. Th2 release IL10 and IL4. IL10 has a negative impact on the division of Th0 towards Th1 and IL4 has positive impact on the division of Th0 towards Th2.

Other immune system cell produce these IL and it is probably because Th1 and Th2 are need in different situation. This is probably link to a genetic level of expression. A set of genes probably can only be activated at any given when the other set is repressed.

 

[Monique]

You have just explained how the processes are being separated in a regulatory fasion: positive and negative feedback loops.

But what I am interested in finding out is why such a thing of two groups evolved; why are macrophages, natural killer cells, CD8+ T cells in one group and B cells, IgE production in another.

Is there some common denominator that I am missing?

 

[iansmith]

There migth be not common denominator. Maybe both branch have evolve seperatly. Also it is more efficient to only turn on some of these genes and cells when they are require then to turn on the whole system. Insect have sognalling pathways that are specialize depending if it is a fungi, a gram-positive bacteria or a gram-negative bacteria. Each invader have different weakness and strengths and a specific strategy is required for each.

 

[Monique]

Yes, so if the two branches evolved seperately, and it is more efficient to turn on part of the system, and it is respons specific, there MUST be something which is a fundamental difference beteen Th1 and Th2 respons.

All I want is a description why Th1 would be so fit for a certain immune response and Th2 fitter in another..