B7 costimulation is required for IL-5 and IL-13 secretion by bronchial biopsy tissue of atopic asthmatic subjects in response to allergen stimulation

Asthma is a complex disorder characterized by airway hyperreactivity and in flammation. To analyze cellular interactions required for the secretion of cytokines by the bronchial mucosa, we have evaluated the ex vivo response o f tissue explants to allergen. Endobronchial mucosal biopsy tissue from mil d atopic asthmatic subjects and normal control subjects were maintained in culture for 24 h. To detect reactivity to allergen, the explants were stimu lated with dust mite extract Dermatophagoides pteronyssinus (Der p). Our an alysis revealed that without any overt stimulation, mRNA transcripts for in terleukin (IL)-5 and IL-13 were expressed by asthmatic but not normal bronc hial tissue. In contrast, the expression of interferon-gamma was observed i n a higher proportion of cultured bronchial biopsies from the normal contro l subjects than in those from asthmatic subjects. Addition of Der p allerge n did not change the cytokine profile of the explants from control voluntee rs but augmented the expression of IL-5 mRNA and induced secretion of the p rotein by the asthmatic bronchial tissue. In most cases, allergen also incr eased the production of IL-13 by bronchial tissue from asthmatic subjects. The allergen-induced secretion of IL-5 and IL-13 was inhibited by the fusio n protein CTLA-4Ig, reflecting a requirement for CD80 (B7-1) and/or CD86 (B 7-2) costimulation for the for the expression of the Th2 cytokines. This re quirement for B7/CD28 costimulation is consistent with the hypothesis that IL-5 and IL-13 are produced by allergen-specific T cells resident in the as thmatic bronchial mucosa.