Eosinophil Siglec-F expression level is up-regulated upon OVA challenge. WT mice with OVA sensitization and challenge (OVA) were compared with OVA-sensitized and PBS-challenged control mice (NO OVA) for Siglec-F expression. Leukocytes from (A) peripheral blood, (B) bone marrow, or (C) spleen were stained with anti-CCR3 and anti–Siglec-F (or a control antibody). Cells were analyzed by flow cytometry and data plotted as the median fluorescence intensity (MFI) of anti–Siglec-F staining. (D) Peripheral-blood neutrophils serve as a control to show the specific change in eosinophil Siglec-F expression (note the different Y-axis, indicating that the expression levels on neutrophils are also much lower). Histogram profiles were unimodal, making the MFI a valid means of presenting the comparisons (n = 6; individual mice shown as ♦; averages shown as bars; data shown are representative of 3 experiments). **P < .01.