The stimulus-dependent release of eosinophil cationic protein and eosinophil protein x increases in apoptotic eosinophils

Apoptotic cells are regarded as inert bodies that turn off intracellular processes and functional abilities. To study the changes in the ability of eosinophils to release their granule proteins while undergoing apoptosis. Eosinophils were cultured for up to 72 h. Living cells were separated from the apoptotic cells and their release of eosinophil cationic protein (ECP) and eosinophil protein X (EPX) was measured in response to serum-opsonized sephadex particles and phorbol 12-myristate 12-acetate (PMA). Changes in cell structure were examined by electron microscopy, and surface receptor expression of beta1- and beta2-integrins was investigated by flow cytometry. Stimulus-dependent release of the granule proteins ECP and EPX was found to increase in apoptotic eosinophils, whereas surface expression of beta1- and beta2-integrins was downregulated. Ultrastructural examination revealed that the granules of apoptotic eosinophils were translocated to the periphery of the cell, just beneath the plasma membrane. Apoptotic eosinophils are able to release their toxic granule proteins, which is probably because of the rearrangement of the cytoskeleton and spontaneous translocation of granules to the membrane. Our results suggest that apoptotic eosinophils are potentially harmful cells that have retained their ability to react to certain extracellular stimuli. The findings point to unexpected consequences of eosinophil apoptosis.