Background: This study assessed the heterogeneity of cytokine expression in asthma before and after local allergen challenge.

Methods: BAL T cells were obtained 10 min or 24 h after local endobronchial allergen challenge in atopic asthmatic subjects. T cells were cloned by direct limiting dilution. mRNA expression was assessed by RT‐PCR, and cytokine protein production by ELISA.

Results: Unstimulated baseline BAL T cells expressed mRNA for IFN‐γ, IL‐13, and TNF‐α. A minority of samples expressed IL‐4 and IL‐5, but no IL‐3 mRNA was detected. PHA stimulation increased expression of IL‐3, IL‐4, and IL‐5 mRNA in 4/6 samples. IL‐13 and GM‐CSF mRNA were found in BAL cells after allergen challenge, but expression of IFN‐γ was reduced. Both IL‐4 and IL‐3 were strongly upregulated after PHA stimulation, while the expression of TNF‐α and IFN‐γ was reduced, compared to equivalent baseline samples. Seventeen panels of BAL T‐cell clones were derived (average cloning efficiency 1/40 T cells). Seven panels survived to 8 weeks for analysis. Clones derived 4 h after saline challenge showed strong mRNA signals for IL‐13, IL‐4, and IFN‐γ, whereas clones derived 24 h after allergen challenge expressed IL‐13, GM‐CSF, IL‐3, IL‐4, and often IL‐5 (i.e., closer to the Th2 profile). There was considerable heterogeneity in the patterns of cytokine mRNA and protein production by different clones.

Conclusions: T cells from asthmatic airways produce IL‐13, IFN‐γ, and TNF‐α, but after allergen challenge, type 2 cytokines are upregulated. mRNA and protein analysis provide complementary information on airways T‐cell cytokine profiles.

Abbreviations: BAL: bronchoalveolar lavage; FEV₁: forced expiratory volume in 1 s; IFN: interferon; IL: interleukin; PBMC: peripheral blood mononuclear cells; PBS: phosphate‐buffered saline; PC: cumulative provocative concentration producing 20% fall in FEV₁; PE: phycoerythrin; Per‐CP: peridin chlorophyll‐protein conjugate; PHA: phytohaemagglutinin; TNF: tumour necrosis factor.