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Phagocytosis:
Phagocytosis is the active cellular uptake of particulate
matter (e.g. bacteria).
The phagocytic process involves specific membrane-recognition
events, surface attachment of the leukocyte to the particle, engulfment,
formation of a phagocytic vacuole, and fusion of that vacuole with lysosomes,
exposing the imprisoned object to the action of the lysosomal contents.
The ultimate purpose of bacterial phagocytosis is to
kill and degrade bacteria. During phagocytosis neutrophils show a burst
of metabolic activity, characterized by a two- to three-fold increase
in oxygen consumption. This so called "respiratory burst"
indicates the activation of the oxygen-dependent killing mechanisms.
The major features of the respiratory burst are:
Increased oxygen utilization by the cell
Increased glucose oxidation by the hexose monophosphate shunt (HMPS)
Generation of reactive oxygen species, including the superoxide anion,
hydrogen peroxide and the hydroxyl radical.
Generation of hydrochlorous acid
There are also oxygen-independent killing mechanisms.
These mechanisms rely on components present in the leukocyte granules:
Lysoszyme attacks bacterial cell walls.
Lactoferrin binds iron, sequestering it away from those microbes
that require iron to grow.
Cathepsin G is a proteinase that has anti-microbial properties
for both gram-positive and gram-negative bacteria, as well as some
fungi.
 
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