University of Virginia Health System

Segmented Neutrophil
(Polymorphonuclear Neutrophil, PMN)

Peripheral blood smear, Wright-Giemsa stain, 1000x

Description:

When the first segmentation of the nucleus occurs, the cell is referred to as a segmented neutrophil. Further segmentation usually occurs with the number of segments varying between 2 and 5. The lobes are connected by chromatin filaments of varying lengths. The filaments may not be visible when the lobes are partially superimposed but distinct lobes are usually identifiable.

Function:

Neutrophils serve a very important role in the innate immune response to infections by microorganisms. They also participate in the adaptive immune response by phagocytizing antibody-coated antigens through their Fc receptors and complement-coded antigens through their complement receptors. They also phagocytize and degrade scenecent or damaged cells or cell fragments.

Neutrophil Trafficking:

Neutrophils normally are not released from the bone marrow into the peripheral blood until they reach the segmented stage, but some bands are normally released. Earlier cells (e.g. myelocytes, promyelocytes) are not released unless there is a demand for more rapid production of neutrophils (e.g. infection), or there are abnormalities of the bone marrow architecture (e.g. myelofibrosis, tumor infiltration). The half-life of circulating neutrophils is approximately 6 hours. They are mobile and egress from the circulation into tissues and organs where they survive for about 2 days. In the circulation, the neutrophils are distributed between two pools, the circulating and the marginated. The marginated pool represents neutrophils in close proximity to the venular epithelial cells and is approximately 50% of the neutrophils contained within the vascular space. This percentage, however, is quite variable.

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