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phagocyte disorders 569 phagocytosis
Schematic representation of phagocytosis.
and frequently digest particles such as bacteria, blood cells,
and carbon particles, among other particulate substances.
Neutrophils and macrophages are the main phagocytic cells
in mammals.
phagocyte disorders
Conditions characterized by recurrent bacterial infections
that may involve the skin, respiratory tract, and lymph
nodes. Evaluation of phagocytosis should include tests of
motility, chemotaxis, adhesion, intracellular killing (respiratory
burst), enzyme testing, and examination of a peripheral
blood smear. Phagocyte disorders include chronic
granulomatous disease, myeloperoxidase deficiency, Job’s
syndrome (hyperimmunoglobulin E syndrome), Chédiak–
Higashi syndrome, and leukocyte adhesion deficiency,
together with less common disorders.
phagocytic cell function deficiencies
Patients with this group of disorders frequently show
increased susceptibility to bacterial infections but are
generally able to successfully combat infections by viruses
and protozoa. Phagocytic dysfunction can be considered
as an extrinsic or intrinsic defect. Extrinsic factors include
diminished opsonins that result from deficiencies in
antibodies and complement, immunosuppressive drugs or
agents that reduce phagocytic cell numbers, corticosteroids
that alter phagocytic cell function, and autoantibodies
IgG receptor
Primary
granule
Fused granule
(azurophil) membrane
C3b receptor
Secondary
granule
Cationic
antimicrobial
proteins
against neutrophil antigens that diminish the number of
polymorphonuclear neutrophils (PMNs) in the blood circulation.
Complement deficiencies or inadequate complement
components may interfere with neutrophil chemotaxis to
account for other extrinsic defects. By contrast, intrinsic
defects affect the ability of phagocytic cells to kill bacteria.
This is related to deficiencies of certain metabolic enzymes
associated with the intracellular digestion of bacterial cells.
Among the disorders are chronic granulomatous disease,
myeloperoxidase deficiency, and defective glucose-6phosphate-dehydrogenase.
phagocytic cells
Polymorphonuclear neutrophils, eosinophils, and macrophages
(monomuclear phagocytes) that play a critical
role in defending a host against microbial infection.
Polymorphonuclear neutrophils and occasionally eosinophils
appear first in areas of acute inflammation followed
later by macrophages. Chemotactic factors including
N-formyl–methionyl–leucyl–phenylalanine (f-Met-Leu-Phe)
are released by actively multiplying bacteria. This is a
powerful attractant for PMNs whose membranes have
specific receptors for it. Different types of infectious agents
may stimulate different types of cellular responses. When
particles larger than 1 μm become attached and engulfed by
a cell, the process is known as phagocytosis. Various factors
present in the serum and known as opsonins coat microorganisms
and other particles and make them more delectable
to phagocyte cells. These include nonspecific substances
such as complement component C3b and specific antibodies
located in the IgG or IgG3 fractions. Capsules enable
microorganisms such as pneumococci and Hemophilus to
resist phagocytosis.
phagocytic dysfunction
An altered ability of macrophages, neutrophils, and other
phagocytic cells to ingest microorganisms or to digest them
following ingestion. This represents a type of immunodeficiency
involving phagocytic function.
phagocytic index (PI)
An in vivo measurement of the ability of the mononuclear
phagocyte system to remove foreign particles. It may be
represented by the rate at which injected carbon particles
are cleared from the blood. The PI is increased in graft-vs.host
disease.
phagocytosis
The uptake of particulate materials such as bacteria by endocytosis.
Particle ligands unite with numerous receptors on
the surfaces of phagocytes in a “zippering” effect and cause
Fused granule
(specific) membrane
Steps of phagocytic endocytosis.
Acidic phagolysosome
contains short-chain
fatty acids
P