Editing T helper cell (section)

=== Differentiation (signal 3) ===
Once the two-signal activation is complete the T helper cell (T<sub>h</sub>) then allows itself to [[Cell growth|proliferate]]. It achieves this by releasing a potent T cell growth factor called [[interleukin 2]] (IL-2) which acts upon itself in an [[autocrine]] fashion. Activated T cells also produce the alpha sub-unit of the [[IL-2 receptor]] ([[CD25]] or IL-2R), enabling a fully functional receptor that can bind with IL-2, which in turn activates the T cell's proliferation pathways.{{citation needed|date=August 2020}}

The [[autocrine]] or [[paracrine]] secretion of IL-2 can bind to that same T<sub>h</sub> cell or neighboring T<sub>h</sub>'s via the IL-2R thus driving proliferation and clonal expansion. The T<sub>h</sub> cells receiving both signals of activation and proliferation will then become T<sub>h</sub>0 (T helper 0) cells that secrete IL-2, [[interleukin 4|IL-4]] and [[interferon gamma]] (IFN-γ). The T<sub>h</sub>0 cells will then differentiate into T<sub>h</sub>1 or T<sub>h</sub>2 cells depending on [[cytokine]] environment. IFN-γ drives T<sub>h</sub>1 cell production while [[interleukin 10|IL-10]] and IL-4 inhibit T<sub>h</sub>1 cell production. Conversely, IL-4 drives T<sub>h</sub>2 cell production and IFN-γ inhibits T<sub>h</sub>2 cells. These cytokines are [[pleiotropic]] and carry out many other functions of the immune response.{{citation needed|date=August 2020}}