ABSTRACT
This chapter outlines the ultrastructural morphology of mature human eosinophils and their immature myelocyte precursors, as well as the major contents of their granules and lipid bodies—two important organelles that respond to activation and secretion stimuli. Activation morphology of eosinophils in vivo and in vitro involves changes in the number, size, and contents of granules and lipid bodies. The chapter presents Ultrastructural secretion and release morphology in three general categories: injury, regulated secretion and piecemeal degranulation. Eosinophils are classic secretory cells that store important cell synthetic products in membrane-bound cytoplasmic secretory granules. Potent cytotoxic granule proteins can be released to the microenvironment by extrusion of membrane-free granule contents. Mature and immature human eosinophils are morphologically identifiable by their subcellular contents; mature eosinophilic granulocytes, in addition to polylobed nuclei, contain a mixture of crystalloid core-containing secondary granules, core-free primary granules, small granules, vesiculotubular structures and lipid bodies.
