Onset of allergic diseases may be determined by the ratio of proinflammatory T-cell subsets (T
17 and iT
2) versus T
subsets. A, In patients with chronic allergic diseases, proinflammatory T-cell subsets, that is, Th17 cells and Th2 cells that are capable of producing high levels of TNF-α (iTh2 cells) are upregulated. B, In asymptomatic atopic individuals, Th2 cells that are capable of producing IL-10 (rTh2 cells) may be up-regulated, and Th17 cells may be inactivated.