Flow cytometric detection and microscopic observation of activated eosinophils in peripheral blood

Eosinophils possess highly electron-dense granules with crystal-like structures and are characterized as high side scatter (SSC) areas by flow cytometry analysis. Eosinophils with low SSC features have been noted in extremely rare cases; however, the underlying cause remains unclear. Eosinophils in the low SSC area were analyzed using microscopy. A transmission electron microscope revealed the loss of crystal-like structures in granules with low electron density and piecemeal degranulation, which was undetectable by May-Grünwald-Giemsa staining. Based on the results of flow cytometry, May-Grünwald-Giemsa staining and transmission electron microscopy, SSC values could help potentially detect crystal-like structures and piecemeal degranulation eosinophils.