Neutrophils

Figure16. EM of a human neutrophil

Neutrophils measure 10-12 μm in diameter. They constitute 60-70% of circulating leukocytes. Neutrophils are so called because of its ability of staining with acidic and basic dyes. The mature neutrophil has three to five lobes of nuclear material joined by thinner nuclear strands. The cytoplasm of the neutrophil contains two kinds of granules: specific granules and azurophilic granules.

Specific granules are small and most numerous. They contain bacteriostatic and bacteriocidal agents, such as lysozyme, as well as alkaline phosphatases.

Azurophilic granules are larger and less numerous. They contain peroxidase and acid phosphatases and lysosomal enzymes.

In the female, few neutrophils can be seen containing the inactive X chromosome (Bar body) appearing as a drumstick-shaped nuclear appendage.

Main functions are:

Neutrophils constitute a defense against invasion by microorganisms, especially bacteria. They are active phagocytes of small particles and have sometimes been called microphages to distinguish them from macrophages, which are larger cells.

Bacteria first adhere to the neutrophil surface and then are surrounded and engulfed by pseudopodia.

When a bacterium is phagocytized, the specific granules fuse with the membrane of phagosome and their bacteriocidal content is emptied into the phagosome.

Azurophilic granules fuse with the phagosome-specific granule complex somewhat later; the hydrolytic enzymes of the lysosomal azurophilic granules digest the microorganism.

Дата добавления: 2015-07-25