Siglec-8 cross-linking induces eosinophil death. Purified peripheral blood eosinophils were cultured under the indicated conditions. Viability was assessed using erythrosin-B dye exclusion. (A) Note that induction of cell death requires the presence of both 2E2 and secondary (2°) Abs. Data are mean ± SEM from 6 experiments. *P ≤ .05; **P ≤ .0005; ***P ≤ .005 for comparison of medium control versus 2E2 + 2° Ab. †P ≤ .05; ††P < .0005 for comparison of 2E2 Ab alone versus 2E2 + 2° Ab. (B) Siglec-8–mediated eosinophil apoptosis was concentration-dependent. Maximal apoptosis was observed at concentrations equal to or greater than 2.5 μg/mL 2E2 mAb (mean ± SEM; n = 4).