Macrophage is another term for a member of the more familiar
phagocytes, leukocytes or white blood cells that engulf and destroy
invading infectious agents such as bacteria. The word comes from the
Greek, macros, long, and phagein, to eat, from their ability to
surround large (relatively speaking) antigens.
MACROPHAGE - Definition by Hyper Dictionary
"Definition: A type of large leukocyte that travels in the blood but
can leave the bloodstream and enter tissue; like other leukocytes, it
protects the body by digesting debris and foreign cells."
As such, macrophages can be detected most simply by the basic Complete
Blood Count (CBC), a microscopic test that physically counts the
number of white blood cells in a standard volume of blood. An
increased or elevated white blood cell count indicates infection, as
the body produces more leukocytes to attack the infection.
LAB RESULTS, Part 1: Complete Blood Count (CBC)
"Monocytes or Macrophages (Monos) make up 2% to 8% of WBCs. They fight
infections by "eating" germs and telling the immune system what germs
they have found. Monocytes circulate in the blood. When monocytes
settle in various tissues they are called macrophages. A high count
usually indicates a bacterial infection."
A more complex test that can indicate the presence of macrophages is
an immunohistochemical reactivity test, which looks for marker
chemicals that are produced as macrophages (and other cells) are
activated. As the name implies, the immune or allergic histamine
response results in the release of chemicals that in elevated amounts
will indicate infection or allergic reaction. One useful test looks
for induced nitric oxide synthase (iNOS). Macrophages produce nitric
oxide in a chemical reaction that is mediated by the enzyme iNOS.
Because nitric oxide vanishes from the blood too quickly to be
measured directly (half life of about 5 seconds), a test for iNOS is
conducted as an indirect measure of induced nitric oxide production.
Section 19.3 Probes for Nitric Oxide Research
"Nitric oxide (NO), the molecule that makes the firefly glow,[ref]
plays a critical role as a molecular mediator of a variety of
physiological processes, including blood-pressure regulation and
neurotransmission.[ref] In endothelial cells, as well as neurons and
astrocytes, NO is synthesized from L-arginine in a reaction catalyzed
by nitric oxide synthase [ref] (NOS) (Figure 19.13). NO that diffuses
into smooth muscle cells binds to the heme group of guanylate cyclase.
Because free NO is a transient species with a half-life of about five
seconds, many investigations of this gaseous molecule have relied
largely on studies of NOS."
"NO can also complex with superoxide to form the strong oxidant,
peroxynitrite anion [ref] (ONOO, Table 19.1), which may be a major
cytotoxic agent produced during inflammation, sepsis and
ischemia/reperfusion.[ref] Activated macrophage and neutrophils
produce nitric oxide and superoxide, and thus peroxynitrite anion, at
Nitric oxide and infectious diseases
"In contrast, inducible NOS (iNOS or NOS2) is absent in resting cells,
but the gene is rapidly expressed in response to stimuli such as
proinflammatory cytokines. Once present, iNOS synthesises 1001000
times more NO than the constitutive enzymes and does so for prolonged
The quantity of nitric oxide released by macrophages regulates
"Analysis of NO Production. To analyze the immunosuppressive
mechanism, we evaluated total serum nitritenitrate as an indicator of
cumulative NO production. Macrophage-released NO synthesized by NOS2,
the high output NOS isoenzyme, acts as a regulator of lymphocyte
growth and is immunosuppressive through the induction of apoptosis in
activated T cells (15)."
"NOS2 expression in Chlamydia-infected lung tissue was examined by
immunohistochemical staining. Lesions in infected lungs (Fig. 4, which
is published as supporting information on the PNAS web site,
www.pnas.org) were either double-stained (cryo-sections) or serial
sections single-stained (formalin-fixed sec-tions) with antibodies
against C. psittaci, NOS2, or the macrophage maturation marker
Coinduction of Nitric Oxide Synthase, Argininosuccinate Synthetase,
and Argininosuccinate Lyase in Lipopolysaccharide-treated Rats
Lipid Vesicle Size Determines the Th1 or Th2 Response to Entrapped
"The ability to phagocytose large particles is one of the features
that distinguishes macrophages from other APCs (37, 38), although some
capacity for ingestion of particulate Ags has been demonstrated for
dendritic cell progenitors in vitro (39, 40). In contrast, other APCs,
such as B lymphocytes, cannot phagocytose (37, 38) and must presumably
ingest Ag by pinocytic mechanisms, which effectively means they cannot
internalize particles greater than approximately 150 nm (35, 36)."
In cases of particulate induced infections, magnetic resonance imaging
(MRI) or transmission electron microscopy (TEM) or scanning electron
microscopy (SEM) sometimes can be used successfully. Naturally, the
type of particulate will determine which is appropriate.
Magnetic Resonance Imaging of Atherosclerotic Plaque With Ultrasmall
Superparamagnetic Particles of Iron Oxide in Hyperlipidemic Rabbits
Based on the observation that ultrasmall superparamagnetic particles
of iron oxides (USPIOs) are phagocytosed by cells of the mononuclear
phagocytic system, the purpose of this study was to evaluate their use
as a marker of atherosclerosis-associated inflammatory changes in the
vessel wall before luminal narrowing is present."
"ConclusionsUSPIOs are phagocytosed by macrophages in atherosclerotic
plaques of the aortic wall of hyperlipidemic rabbits in a quantity
sufficient to cause susceptibility effects detectable by MRI."
"Particle phagocytosis plays a key role in macrophage activation and
hence the size of the particle is significant. Histologic observations
of tissues around failed total joint replacements frequently note an
abundance of enlarged macrophages, often with visible particles within
(Contains microscopic slides of engulfed particles.)