ssRNA-induced activation of eosinophils. (A) Isolated splenocytes from hypereosinophilic mice were activated with ssRNA for 10 minutes, and peroxidase activity was measured to determine EPO release. (B) FACS-purified eosinophils were stimulated with medium (Bi-Bii) or ssRNA (1 μg/mL) (Biii, Biv) for 10 minutes, then changes in ultrastructural morphology were examined by electron microscopy. Arrows demarcate secondary granules, with irregular or faded electron-dense cores documenting degranulation in a representative micrograph. Scale bar equals 1 μM (left panels) and 2 μM (right panels) see “Materials and methods, Electron microscopy” for detailed image acquisition information. (C) Isolated mixed splenocytes from hypereosinophilic mice were treated with ssRNA for 10 minutes, then stained for CD11b expression. A representative histogram gated on eosinophils is presented in the left panel. The MFI of CD11b expression is shown in the right panel. These data were collected on a FACSort. (D) Eosinophils were isolated from hypereosinophilic MyD88-sufficient or -deficient mice and treated with ssRNA (1 μg/mL) for 10 minutes, then stained for CD11b expression. These data were collected on a BD CANTO. Data represent the mean plus or minus SEM (n = 3-8 mice per experimental group). **P < .01; ***P < .001; ###P < .001.