Final answer:
TH17 cells do not produce CD4, which is a surface molecule present on helper T cells, including TH17 cells. The other options listed in the question (ICOS, IL-17, IL-21, and STAT3) are all produced by TH17 cells.
Step-by-step explanation:
TH17 cells are a subtype of helper T cells that are specifically responsible for the body's defense against chronic mucocutaneous infections. TH17 cells produce IL-17, which is a cytokine that plays a crucial role in inflammation and immune responses. They also produce ICOS (inducible T-cell co-stimulator), IL-21, and STAT3, all of which are involved in the function and development of TH17 cells. However, CD4 is not produced by TH17 cells. CD4 is a surface molecule that is present on helper T cells, including TH17 cells, but it is not produced by the cells themselves.