Determination of the effector T cell response

T_h1/T_h2 Model for helper T cells. An antigen is ingested and processed by an APC. It presents fragments from it to T cells. The upper, T_h0, is a T helper cell. The fragment is presented to it by MHC2.^[1] IFN-γ, interferon γ; TGF-β, transforming growth factor β; mø, macrophage; IL-2, interleukin 2; IL-4, interleukin 4

	Type 1/ Th1	Type 2/ Th2
Main partner cell type	Macrophage	B-cell
Cytokines produced	interferon-γ and tumor necrosis factor-beta. (Interleukin-2 was classically associated with Th1 cells, but this association may be misleading; IL-2 is produced by all helper T cells early in their activation.)	interleukin-4, interleukin-5, interleukin-6, interleukin-10, interleukin-13
Immune stimulation promoted	Cellular immune system. Maximizes the killing efficacy of the macrophages and the proliferation of cytotoxic CD8+ T cells. Also produces opsonizing antibodies	Humoral immune system. Stimulates B-cells into proliferation, to induce B-cell antibody class switching, and to increase neutralizing antibody production.
Other functions	The Type 1 cytokine IFN-γ increases the production of interleukin-12 by dendritic cells and macrophages, and via positive feedback, IL-12 stimulates the production of IFN-γ in helper T cells, thereby promoting the Th1 profile. IFN-gamma also inhibits the production of cytokines such as interleukin-4, an important cytokine associated with the Type 2 response, and thus it also acts to preserve its own response.	The Type 2 response promotes its own profile using two different cytokines. Interleukin-4 acts on helper T cells to promote the production of Th2 cytokines (including itself; it is auto-regulatory), while interleukin-10 (IL-10) inhibits a variety of cytokines including interleukin-2 and IFN-γ in helper T cells and IL-12 in dendritic cells and macrophages. The combined action of these two cytokines suggests that once the T cell has decided to produce these cytokines, that decision is preserved (and also encourages other T cells to do the same).