Figure 1:

Neutrophil development and granule formation. Myeloblasts are the first committed precursor cells of the neutrophil lineage. These differentiate into promyelocytes followed by myelocytes. These cells then proceed through maturation steps of metamyelocytes, band cells, and mature segmented neutrophils. As neutrophils mature, they develop granules which play a key role in neutrophil microbicidal activity. Primary (azurophilic) granules develop as neutrophils are differentiating from myeloblasts to promyelocytes. Secondary (specific) granules form in myelocytes and metamyelocytes. Tertiary (gelatinase) granules first appear in band cells. Secretory vesicles are small, easily exocytosed organelles, which are present only in mature, segmented neutrophils.