Table 1 Brief description of major T helper type 1 and 2 (Th1 and Th2) cytokines.

Cytokine	Description
Th1 cytokines
IFNγ	Most reliably produced by Th1 cells
	Th2 antagonist through activation of T cell transcription factor, T‐bet and subsequent inhibition of Th2 cell differentiation
	Activates macrophages
	Stimulates production of IgG
	Inhibits IL4‐induced IgE synthesis in human PBMCs
TNFα	Stimulates phagocytosis, and production of IL1 and oxidants
TNFβ	Involved in cell proliferation, differentiation and apoptosis
	Cytotoxic to a range of tumour cells
IL12	Produced by various APCs
	Induces IFNγ
	Inhibits IL4
Th2 cytokines
IL4	Reliably Th2
	Polarises naive T cells towards the Th2 phenotype, through activation of the transcription factor GATA3
	With IL13 causes isotype switching of B cells to synthesise IgE after exposure to allergen
	Activates and stimulates bone marrow production of eosinophils
IL5	Activates and stimulates bone marrow production of eosinophils
IL9	Involved in eosinophil and mast cell development
IL13	With IL4 causes isotype switching of B cells to synthesise IgE after exposure to allergen in humans
	Contributes to airway hyper‐reactivity in animals

APC, antigen‐presenting cell; IL, interleukin; IFN, interferon; PBMC, peripheral blood mononuclear cell; TNF, tumour necrosis factor.