Eosinophilic surface marker expression in the bone marrow. Panels show expression (by flow cytometric analysis) of Siglec-8, IL-5Rα, and/or EMR1 on bone marrow eosinophils before and after drug treatment. Siglec-8 and EMR1 expression was lower in 3 out of 4 responders at week 12 (on dexpramipexole), whereas IL-5Rα expression showed no consistent pattern. In nonresponders, none of the 3 parameters showed a consistent pattern at week 12 on dexpramipexole. EOS, eosinophils; MFI, mean fluorescence intensity; W, week.