Interleukin 5 release into asthmatic airways 4 and 24 hours after endobronchial allergen challenge: its relationship with eosinophil recruitment.

Interleukin 5 (IL-5), a cytokine with a range of activities on eosinophils, has been implicated in the allergic asthmatic reaction. We have investigated the kinetics of release of this cytokine into asthmatic airways as well as its relationship to eosinophil recruitment following allergen challenge. Twelve asthmatic patients underwent endobronchial allergen challenge and bronchoalveolar lavage (BAL) fluid was obtained either 4 h (n=6) or 24 h (n=6) after challenge. Four hours after challenge, levels of IL-5 were significantly increased in BAL fluid (10-fold concentration obtained from the allergen-challenge site compared with the saline control (median 2.67 pg/ml, range 1.0-7.4 pg/ml vs 1.0 pg/ml <1.0-2.4 pg/ml, P<0.05). At 24 h levels of IL-5 increased further at the allergen site but not at the saline control lavage (31.1 pg/ml, range 3.6-59. 0 pg/ml vs 1.5 pg/ml, range <1.5-4.9 pg/ml, respectively P<0.02). At 4h there was almost a three fold increase in IL-5 level, whereas at 24 h IL-5 levels were 20-fold greater. Differential cell counts showed that eosinophil numbers obtained 4 and 24 h after allergen challenge were 7 and 32 times higher than numbers after saline challenge. The parallel increase of eosinophil numbers and IL-5 concentrations in BAL fluid suggests that this cytokine may contribute to the eosinophil recruitment observed into asthmatic airways after allergen challenge. Copyright 1999 Academic Press.