Background: The related T(H)2 cytokines IL-4 and IL-13 are produced during allergic responses, signal through receptors that contain IL-4 receptor (IL-4R) alpha, and promote allergic inflammation by activating signal transducer and activator of transcription 6. IL-4 promotes T(H)2 response induction, and IL-13 is necessary and sufficient to induce airways hyperresponsiveness (AHR) and goblet cell hyperplasia in some mouse models of asthma. The nonredundant role of IL-13 could reflect unique IL-13 activation of a signaling pathway, inhibitory effects induced by IL-4 but not IL-13, or greater production-potency of IL-13 than IL-4.
Objectives: We sought to distinguish among these possibilities by determining whether IL-4 inhalation can induce acute allergic airways disease in the absence of IL-13.
Methods: Mice were inoculated intratracheally with IL-13 or a long-acting formulation of IL-4. Responses of IL-13-deficient and IL-13-sufficient mice were compared, as were responses in mice treated with a potent IL-13 antagonist, anti-IL-4Ralpha antibody, or control reagents.
Results: IL-4 inhalation stimulated bronchoalveolar lavage fluid eosinophilia, AHR, and goblet cell hyperplasia. These responses were similar in IL-13-deficient and IL-13-sufficient mice and were not inhibited by an IL-13 antagonist but were blocked by anti-IL-4Ralpha antibody.
Conclusion: IL-4 can induce IL-13-independent AHR and goblet cell hyperplasia. Thus the greater role for IL-13 than IL-4 in the induction of these acute allergy-related changes reflects increased production, potency, or both of IL-13 relative to IL-4 rather than a unique IL-13-signaling pathway or a suppressive effect of IL-4.
Clinical implications: Dual IL-4/IL-13 inhibition might be more effective than selective IL-13 inhibition at suppressing allergic inflammation in some circumstances.