After activation by antigen-presenting cells, naive, antigen-specific CD4+ T cells differentiate into effector T cells. Two decades ago, Coffman and Mosman first discovered the heterogeneity of effector T cells, which were named as Th 1 or Th2 cells.1 Th 1 and Th2 cells are differentially induced and are involved in immunity against intracellular and extracellular pathogens, respectively, as well as immunopathologies such as autoimmunity and allergy.
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