Peripheral blood leukocytes that have staining characteristics and subcellular morphologies consistent with eosinophils deficient in MBP-1 and EPX are present in MBP-1^−/−/EPX^−/− mice. Flow cytometric assessments of WBCs (supplemental Figure 3) from mice of each genotype (ie, wild-type, MBP-1^−/−/EPX^−/−, MBP-1^−/−, and EPX^−/−) were used to sort cells, isolating eosinophils that were subsequently cytospun onto slides and stained with a Romanowsky dye set (top panels). Scale bar = 5 µm. The electron microscopic morphology of the eosinophils that remain in MBP-1^−/−/EPX^−/− mice (lower panels) showed that these cells retain the membrane-bound vesicles (ie, granules) found in wild-type, MBP-1^−/−, or EPX^−/− mice. As expected, these granules appear devoid of their electron-dense cores (MBP-1) and much of the electron-translucent matrices (characteristic of EPX) of these granules. Scale bars in panels highlighted by a single eosinophil = 1 µm. Scale bars in the insert panels representative of the cytoplasm = 200 nm.