The relationship of sputum eosinophilia and sputum cell generation of IL-5

Background: Eosinophil recruitment to the airway after antigen challenge is regulated by many factors, including airway cell generation of cytokines. Objectives: The purpose of this study was to determine the relationship bet ween sputum cell generation of IL-5 and the appearance of eosinophils in th e sputum after antigen challenge. Methods: Sputum samples from 11 allergic subjects were collected before and again 4 and 24 hours after antigen challenge. In 6 of these subjects, indu ced sputum samples were also obtained 48 hours and 7 days after challenge. Sputum leukocyte differential and cell counts and eosinophil-derived neurot oxin levels were determined. Sputum cells were then cultured with PHA (10 m ug/mL) to stimulate IL-5 and IFN-gamma, which were measured in culture supe rnatants. Results: An increase in sputum eosinophils and eosinophil-derived neurotoxi n levels was detected at 4 hours after antigen challenge, with peak values at 24 hours. In contrast, significant increases in ex vivo generation of IL -5 by sputum cells was not seen until 24 hours after challenge. At 24 hours , PHA-induced IL-5 correlated with airspace eosinophil values (r(s) = 0.78, P < .01). In addition, the ratio of IFN-<gamma>/IL-5 decreased at 24 hours (P < .05) and had an inverse correlation with sputum eosinophils (r(s) = - 0.68, P < .05). Conclusion: Although eosinophils are increased in the airway lumen as early as 4 hours, the ex vivo generation of IL-5 by sputum cells is first noted in samples obtained 24 hours after antigen challenge, This suggests that th e early (4 hours) recruitment of eosinophils to the airway lumen may be reg ulated by factors other than IL-5 or that mucosal cells (rather than airspa ce cells) contribute to the IL-5 generation at this time point, Furthermore , IL-5 generation by airspace cells may be more responsible for either eosi nophil recruitment or retention at later time points.