IL‐13 production by allergen‐stimulated T cells is increased in allergic disease and associated with IL‐5 but not IFN‐γ expression

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Abstract
Interleukin‐13 (IL‐13) shares many, but not all, of the properties of the prototypic T‐helper type 2 (Th2) cytokine IL‐4, but its role in allergen‐driven T‐cell responses remains poorly defined. We hypothesized that allergen stimulation of peripheral blood T cells from patients with atopic disease compared with non‐atopic controls results in elevated IL‐13 synthesis in the context of a ‘Th2‐type’ pattern. Freshly isolated peripheral blood mononuclear cells (PBMC) obtained from sensitized atopic patients with allergic disease, and non‐atopic control subjects, were cultured with the allergens Phleum pratense (Timothy grass pollen) or Dermatophagoides pteronyssinus (house dust mite) and the non‐allergenic recall antigen Mycobacterium tuberculosis purified protein derivative (PPD). Supernatant concentrations of IL‐13, along with IL‐5 and interferon‐γ (IFN‐γ) (Th2‐ and Th1‐type cytokines, respectively) were determined by enzyme‐linked immunosorbent assay (ELISA). Allergen‐induced IL‐13 and IL‐5 production by T cells from patients with allergic disease was markedly elevated (P=0·0075 and P=0·0004, respectively) compared with non‐atopic controls, whereas IFN‐γ production was not significantly different. In contrast to allergen, the prototypic Th1‐type antigen M. tuberculosis PPD induced an excess of IFN‐γ over IL‐13 and IL‐5 production, and absolute concentrations of cytokines were not affected by the presence or absence of atopic disease. Addition of exogenous recombinant IFN‐γ or IL‐12, cytokines known to inhibit Th2‐type responses, significantly inhibited allergen‐driven production of both IL‐13 and IL‐5, but not T‐cell proliferation, whereas exogenous IL‐4 did not significantly affect production of IL‐13 or IL‐5. We conclude that allergen‐specific T cells from atopic subjects secrete elevated quantities of IL‐13 compared with non‐atopic controls, in the context of a Th2‐type pattern of cytokine production.

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