TABLE 1.

Human T-helper (Th) cell subtypes

Type	Co-stimulatory cytokine	Transcription factors	Effector cytokines	Target
Th1	IL-12	T-bet, STAT1	IFN-γ, TNF, IL-2	Intracellular bacteria, viruses and mycobacteria
Th2	IL-4	STAT6, GATA3	IL-4, IL-5, IL-13	Extracellular parasites
Th17	IL-23	STAT3, RORγt	IL-17A, IL-17F, IL-21, IL-22	Extracellular bacteria and fungi

IL: interleukin; STAT: signal transducer and activator of transcription; IFN: interferon; TNF; tumour necrosis factor; RORγt: retinoic acid receptor-related orphan receptor γt.