CD70 mice fail to produce eosinophils during experimental asthma and lack airway hyperresponsiveness. (A) Representative plots of Siglec-F staining on bone marrow and spleens of WT BALB/c and CD70TG BALB/c mice showing eosinophils as SSC^hiSiglec-F⁺ cells (percentages of eosinophils of all cells are shown) and (B) absolute numbers of eosinophils in the bone marrow and spleens of these mice. (C) WT BALB/c and CD70TG BALC/c mice were sensitized and challenged with OVA or treated with PBS as control. Contour plots display Siglec-F expression on eosinophils in the lung gated on CD4⁻ cells (percentages are shown) from PBS- and OVA-treated WT and CD70TG mice. (D) Absolute numbers of eosinophils in the lung were calculated. (E) Representative hematoxylin and eosin and periodic acid–Schiff staining on tissue slides of lungs from OVA-treated WT and CD70TG mice. Images were taken using an Olympus BX51 microscope (4×/0.3 NA objective) equipped with a mounted Olympus DP70 digital camera and ACDSee 5.0 software for image acquisition. (F) Eosinophil numbers in PBS- and OVA-treated mice from both groups were determined in bone marrow, spleen, and blood. Fold increase in eosinophil numbers compared with PBS-treated mice is shown. (G) Airway hyperresponsiveness to increasing concentrations of metacholine was measured in PBS- and OVA-treated WT and CD70TG mice. Data are from 5 mice per group for OVA-treated animals and 3 mice per group for PBS-treated animals. An identical experiment with comparable results was performed in WT and CD70TG mice on C57BL/6 background. Data are mean ± SD. *P < .05; **P < .01; ***P < .001. (D) *Difference between OVA-treated WT and CD70TG mice.