Phagocytosis


Phagocytosis

Description, Causes and Risk Factors:

The process of ingestion and digestion by cells of solid substances, e.g., other cells, bacteria, bits of necrosed tissue, foreign particles.

Phagocytosis is a process which is used by cells to engulf and subsequently ingest particles of nutrients or bacteria. This process is a very important part of cell function, allowing cells to grab vital nutrients and allowing the body to protect itself from harmful bacteria. A cell which specializes in phagocytosis is known as a phagocyte. This process is one among a family of processes collectively referred to under the blanket term “endocytosis,” which refers to any sort of ingestion of material by a cell. The opposite, of course, is exocytosis, the expulsion of unwanted material from a cell.

Phagocytosis begins with the neutrophil or macrophage flowing around the pathogen and engulfing it so that it winds up enclosed in a phagosome (phagocytic vesicle). But this is only the first step, because the more challenging task of destroying the microorganisms remains. Indeed, some pathogens have special, effective mechanisms for frustrating this destruction step.

The next step is the fusion of lysosomes with the phagosome. The lysosomes break the phagosome down into its component materials, passing useful compounds on to other structures in the cell and expelling the rest as waste material. In the case of some infectious or harmful material, the phagosome may enter a peroxisome, a special cell structure which helps to rid the body of toxins. The result is called a phagolysosome. Lysosome are derived from the Golgi apparatus, much like secretion vesicles, but their contents are focused on destroying microorganisms.

Deficiencies in phagocytosis can involve acquired or congenital defects in any of these steps, or can be due to the available number of phagocytes. They often manifest as an increased susceptibility to bacterial infections of the skin, respiratory system, and GI tract. These infections respond poorly to antibiotics. Acquired phagocytic deficiencies include disorders that lead to profound and chronic depressions of WBC. Feline leukemia virus infection, feline panleukopenia virus infection, feline immunodeficiency virus infection, tropical canine pancytopenia, idiopathic granulocytopenias, drug-induced granulocytopenias (anticancer drugs, estrogens, anticonvulsants, sulfonamides, etc), and myeloproliferative disorders are a few conditions in which secondary infections can develop as life-threatening complications.

A cyclic decrease of all cellular elements, most notably neutrophils, occurs in the peripheral blood and lowers the resistance to infection of gray Collies and Collie crosses.

Congenital abnormalities that lead to impaired phagocytosis are well documented in humans. Deficiencies of opsonins, complement factors, chemotactic abilities, myeloperoxidase, and lysosomal enzyme activation have been recognized in humans but not in other animals.

Symptoms:

Common manifestations of primary phagocytic disorders include recurrent soft-tissue infections, severe dental infections leading to premature tooth loss, recurrent pneumonias, and perirectal infections. In more severe cases, infections can be systemic and sometimes fatal.

Diagnosis:

Diagnosis may include:

Motility: Capillary tube method.

Chemotaxis: Radical migration.

Intracellular killing (Respiratory burst):

  • Nitroblue tetrazolium dye reduction test.

  • Chemiluminescence.

Enzyme testing: Myeloperoxidase.

Peripheral blood smear:

  • Giant cytoplasmic.

  • Granular inclusions in leukocyte.

Treatment:

Key principles of management of such patients involve early recognition and aggressive treatment of infections and appropriate surgical d

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