Siglec-F expression is induced on activated mouse T cells in vitro and in vivo. (A) Spleen mononuclear leukocytes and (B) peripheral-blood cells were isolated and T cells activated in vitro by anti-CD3 and anti-CD28 for 3 days. Activated cells were stained by anti–Siglec-F (line) or control antibody (shaded) and analyzed by flow cytometry. Anti-CD4 or anti-CD8 was used to gate on subgroups of T cells. (C) Lung sections from chronically OVA-challenged WT mice were stained with anti-CD4 and anti–Siglec-F antibodies. Background staining with secondary antibody alone was minimal (data not shown). A 40×/0.65 DPlan dry objective lens was used to visualize images, and an Olympus BH2 camera was used to capture them.