BLOOD AND BRONCHOALVEOLAR EOSINOPHILS IN ALLERGIC SUBJECTS AFTER SEGMENTAL ANTIGEN CHALLENGE - SURFACE PHENOTYPE, DENSITY HETEROGENEITY, AND PROSTANOID PRODUCTION

Eosinophil infiltration into the airways has been implicated in the pa thophysiology 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 allerg en challenge. Eosinophils were purified by discontinuous density gradi ent centrifugation, and their distribution at various layers was quant itated. Eosinophils at the 1.080 to 1.085 gm/ml interfaces from blood and BAL (purity > 70%) were analyzed by immunofluorescence and flow cy tometry for several surface markers including adhesion-activation anti gens. Eosinophils in BAL from antigen-challenged sites were markedly i ncreased compared with control diluent-challenged BAL sites (0.3% +/- 1% vs 28.1% +/- 9.7%, n = 12, p < 0.002), and a greater percentage wer e hypodense (specific gravity < 1.080 gm/ml) than in peripheral blood (51.3 +/- 5.3 vs 19.0 +/- 4.4, n = 15, p < 0.01). In vitro, resting an d activated BAL eosinophils biosynthesized less thromboxane B-2 than b lood eosinophils. Although both BAL and blood eosinophils expressed si milar levels of Fc gamma RII (CD32), CD11a, and CD45, resting levels o f Mo-1 (CD11b) were upregulated on BAL eosinophils (mean fluorescence intensity 316% +/- 48% of blood eosinophils, n = 5, p < 0.05). Blood e osinophils stimulated in vitro with 1 mu mol/L platelet activating fac tor or N-formyl-methionyl-leucyl-phenylalanine achieved levels of CD11 b expression similar to those of BAL eosinophils. In contrast, CD11b e xpression on BAL eosinophils could not be further increased. These res ults confirm that antigen challenge of the lower airways promotes eosi nophil infiltration in the lung. Because these eosinophils are of lowe r density express maximal amounts of CD11b, and are less responsive th an peripheral blood eosinophils, we conclude that eosinophils undergo activation during this recruitment process, which may be followed by a state of decreased responsiveness.