IL-4 production by human basophils found in the lung following segmental allergen challenge

Background: Human blood basophils secrete high levels of IL-4 following activation with specific allergen, yet their role as cytokine-producing cells in allergic lesions has not been described. Objective: Our objective was to investigate whether and under what conditions basophils infiltrating allergic lesions in the lung secrete IL-4 in vitro. Methods: Bronchoalveolar lavage (BAL) cells were recovered 20 hours after segmental allergen challenge. Basophils were enriched with Percoll using a protocol commonly used for blood basophils. IL-4 and histamine were measured in culture supernatants following activation with a variety of stimuli. Two-color flow cytometry was performed to detect intracellular IL-4. Results: IL-4 protein was detected in all basophil culture supernatants following a 4- to 5-hour incubation in medium alone; the levels obtained did not significantly increase with the addition of anti-IgE. BAL basophils failed to release histamine in response to specific allergen but showed nearly 60% histamine release with N-formyl-methionyl-leucyl-phenylalanine, suggesting that they were desensitized to IgE-mediated stimuli as a result of their activation in vivo. Using these same conditions, IL4 was not detected in BAL cell fractions enriched for lymphocytes and eosinophils. Ionomycyn induced IL-4 secretion by BAL basophils, and this response was reduced with the addition of phorbol myristate acetate. In contrast, phorbol myristate acetate promoted the secretion of IL-4 by BAL cells enriched for lymphocytes; both findings are identical to those reported for basophils and lymphocytes purified from blood. Flow cytometry confirmed the secretion of IL-4 by BAL basophils. Conclusions: These data suggest that basophils migrating to the lung following allergen challenge represent a major source of IL-4.