(polymorphonuclear leukocytes, PMNs, polys)
The neutrophil, or the heterophil in birds, reptiles and some mammals, is the
predominant granulocyte. In many species it is the predominant leukocyte in health. In health,
only mature neutrophils are released from marrow to circulate in blood. Since mature
neutrophils in prototypical human blood have nuclei that are segmented into lobes of
condensed chromatin connected by filaments, mature neutrophils are called segmented
neutrophils, or segs. The mature neutrophils of many animal species do not have a distinct
lobe and filament arrangement, nevertheless, they also are called segmented neutrophils.
The primary criterion for classification of neutrophils as either segmented (mature) or non-
segmented (younger stages including band neutrophils, metamyelocytes, and myelocytes) is
the shape of the nucleus. A neutrophil should be counted in the segmented category if the
nucleus has regions that are distinctly constricted or has lateral protrusions resulting in
irregular nuclear margins. A cell whose nuclear margins are smooth and parallel
(or nearly parallel) should be counted as a band neutrophil. The presence of non-segmented
neutrophils in blood is called a left shift. Inflammation is the most common cause of a
left shift, but some other conditions, such as hemolytic anemia and primary diseases
of marrow, also can cause release of immature neutrophils from marrow.
Normal mature neutrophils of several species are shown at the right. Canine neutrophils have white cytoplasm that contains small pink granules. Feline neutrophils have cytoplasm that is white and lacks visible granules. Equine neutrophils have white or slightly pink cytoplasm with no visible granules. The nuclei of equine neutrophils typically are long, thin and "knobby" with clumps of condensed chromatin projecting from the sides. Ruminant neutrophils have white cytoplasm with small pink granules; these impart an overall pink tint compared to the other species. Rabbits, birds, amphibians and reptiles have heterophils. In contrast to the inconspicuous granules of neutrophils, granules in heterophils are large and stained deep orange to red. A typical avian heterophil is shown in "Blood Cells by Species". A common and important morphologic abnormality of neutrophils is so-called "toxic change". |
Last updated on Thursday, February 08, 1996