Blood and bronchoalveolar eosinophils in allergic subjects after segmental antigen challenge: Surface phenotype, density heterogeneity, and prostanoid production

Abstract

Eosinophil infiltration into the airways has been implicated in the pathophysiology of asthma. To improve our understanding of the function of eosinophils in asthma, we have compared the phenotype and function of eosinophils obtained simultaneously from blood and bronchoalveolar lavage (BAL) of allergic subjects 19 hours after segmental lung allergen challenge. Eosinophils were purified by discontinuous density gradient centrifugation, and their distribution at various layers was quantitated. Eosinophils at the 1.080 to 1.085 gm/ml interfaces from blood and BAL (purity > 70%) were analyzed by immunofluorescence and flow cytometry for several surface markers including adhesion-activation antigens. Eosinophils in BAL from antigen-challenged sites were markedly increased compared with control diluent-challenged BAL sites (0.3% ± 1% vs 28.1% ± 9.7%, n = 12, p < 0.002), and a greater percentage were hypodense (specific gravity <1.080 gm/ml) than in peripheral blood (51.3 ± 5.3 vs 19.0 ± 4.4, n = 75, p < 0.01). In vitro, resting and activated BAL eosinophils biosynthesized less thromboxane B 2 than blood eosinophils. Although both BAL and blood eosinophils expressed similar levels of FcγRII (CD32), CD11a, and CD45, resting levels of Mo-1 (CD11b) were upregulated on BAL eosinophils (mean fluorescence intensity, 316% ± 48% of blood eosinophils, n = 5, p < 0.05). Blood eosinophils stimulated in vitro with 1 μmol/L platelet activating factor or N-formyl-methionyl-leucyl-phenylalanine achieved levels of CD11b expression similar to those of BAL eosinophils. In contrast, CD11b expression on BAL eosinophils could not be further increased. These results confirm that antigen challenge of the lower airways promotes eosinophil infiltration in the lung. Because these eosinophils are of lower density, express maximal amounts of CD11b, and are less responsive than peripheral blood eosinophils, we conclude that eosinophils undergo activation during this recruitment process, which may be followed by a state of decreased responsiveness.