The human neutrophilic myelocyte

Summary The developmental changes in the neutrophilic myelocyte from normal human bone marrow have been analyzed by means of phase contrast and electron microscopy. This developmental stage is characterized principally by the elaboration of secondary (specific) granules. In addition, there is a modest decrease in cell size, a decrease in the number and mean size of primary (azurophil) granules, a decrease in the number of polysomes, free ribosomes and mitochondria, a depletion of rough endoplasmic reticulum, an increase in cytoplasmic glycogen, an increase in chromatin aggregations and a loss of nucleoli, and the formation of a markedly indented nucleus. The myelocyte stage has been subdivided into three arbitrary phases based upon morphological and functional characteristics which relate to the onset, active production and cessation of secondary granulogenesis.Supported by Grant No. AM-HE-12084-13 from the National Institutes of Health, Bethesda, Maryland.Appreciation is expressed to Dr. Arthur Sagone who performed the bone marrow aspirations and to Anita Topson, Barbara Jordan and Marjorie Griffith for their technical assistance.