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MACROPHAGES
DEPARTMENT OF PHARMACEUTICS
MACROPHAGE
Macrophage Definition
A type of cell derived from white blood cells
ingests (takes in) foreign material.
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that
Macrophages are WBC produced by the differentiation
of monocytes in tissues
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• is a kind of swallowing cell, which means
it
functions by literally swallowing up other particles or
small cells.
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 Taken
from Greek Words (Greek: big eaters, from makros
"large" + phagein "eat"; abbr. MΦ).
 Human macrophages are about 21 micrometres
(0.00083 in) in diameter.
 They move by action of Amoeboid movement.
 Life time depends on the type of tissue, viability ranges
between 6 and 16 days.
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Formation of Macrophage
 Development in bone marrow and passes
through the following steps:
stem cell  committed stem cell 
monoblast  promonocyte 
monocyte (bone marrow) – monocyte
(peripheral blood)  macrophage
(tissues)
Monoblasts(least mature cell of mono
nuclear phagocyte system)
Differentiate in to
monocytes
Remain in bone marrow for
24 hours
Enter into
Peripheral blood
From
monocytes
migrate to
Extra vascular tissue( where they differentiate into macrophages)
 The blood monocytes are young cells (immature
macrophage) that already possess migratory,
chemotactic, pinocytic and phagocytic activities.
 Under migration into tissues, monocytes undergo
further differentiation (at least one day) to become
multifunctional tissue macrophages.
MONOCYTE
NEUTROPHILL
 Macrophages are enriched in
spleen,lymph,brain,thymus,lungs,liver,conne
ctive tissue,bonemarrow.
The precursors of macrophages are
Monocyte
Promonocyte
Monoblast
all of these cells comes from a common
progenitor called the colony forming unit.
Function of Macrophage
Exhibit 3 main functions in body:
1. Destroy bacteria by phagocytosis
2. Activate other immune function
3. Phagocytose apoptotic cells
Function of Macrophage
• Once it leaves blood vessel and migrated to
tissue, the next job is to EAT the pathogen.
This human macrophage, like neutrophil, is
a professional "phagocyte" or eating cell
(phago = "eating", cyte = "cell").
• Furthermore, the pathogen will be digested
by using enzyme from macrophage, in the
end resulting antigen and waste material.
 Steps of phagocytosis:
1.Ingestion through phagocytosis ,a phagosome is
formed.
2. the fusion of lysosomes with the phagosome creates
a phagolysosome .
3.Pathogen is broken down by enzyme
4.Wastematerial is expelled or assimilated.
1.Pathogens
2.Phagosome
3.Lysosome
4.Wastematerial
5.Cytoplasm
6.Cell membrane
2. Perform Specific Immune Function
 After digesting a pathogen,present antigen
(a
molecule, most often a protein found on the surface of
the pathogen, used by the immune system for
identification)of the pathogen to the corresponding
helper T-cell
 The presentation is done by integrating it into the cell
membrane, indicating to other white blood cells that
the macrophage is not a pathogen, despite having
antigens on its surface.
 Antigen presentation results in the production of
antibodies that attach to the antigens of pathogens,
making them easier for macrophages to adhere to with
their cell membrane and phagocytose.
Secrete hormones cytokines
 To attract system immune cells to
the site
and activate cells involved in
tissue repair
 To send signaling path to injury
site.
Phagocytose apoptotic cells:
 reduces the potential for an inflammatory response
by ensuring that the dying cells are cleared before
their intracellular contents are released.
 Why targeting is required?
 To activate macrophages
 Some of the intracellular micro organisms may enter
macrophages so in order to kill them, targeting drug to
macrophages is necessary.
 Drug administration in soluble form,fraction of drug
entering macrophages is limited so in order to improve
amount of drug retained targeting is required.
 PROBLEMS INVOLVED IN TARGRTING TO
MACROPHAGES:
 It involves in phagocytosis.
 Enemity towards foreign particles(drug).
Carriers for drug delivery to
macrophages
Liposomes:
 Liposomes are microscopic vesicles composed of
phospholipid bilayers surrounding aqueous compartments.
 Liposomes have been used extensively as drug carriers.
Potential applications in cancer chemotherapy, enzyme
therapy, immuno-modulation, antimicrobial therapy, metal
detoxification, diagnostics, and topical therapy.
Uptake of liposomes by macrophages
 The complex interaction of liposomes with phagocytic
cells is described in different steps:
 stable adsorption to the cell surface,
 cellular uptake of intact vesicles by an energy-dependent
mechanism.
 lysosomal degradation of the liposomes and their
content.
 Liposome adsorption to the cell surface seems to be the
rate limiting step, since it can be assumed that stably
adsorbed vesicles are more susceptible to subsequent
uptake than vesicles that are only loosely interacting with
the cell surface.
 several conditions to be satisfied for liposomes deliver
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biologically active agents to mononuclear phagocytes,
i.e. macrophages.
liposomes must readily bind to and be phagocytosed by
free and fixed phagocytes.
They must prevent degradation of entrapped drug.
They must retain the encapsulated agent for delivery to
the intracellular compartment of RES cells.
They should have low systemic half-life 8 hrs.
 Liposomes are the most widely studied carrier in drug
targeting to macrophages. Almost all types of drugs
involved in macrophage-associated disorders have been
studied using liposomes as carrier. However,
 The extent of liposome binding and subsequent ingestion
by macrophages depends on a number of factors of the
intended liposomes.
 These include composition
size
type
surface properties of liposomes
 Influence of surface charge, liposome size,
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concentration, and composition on the uptake by macrophages:
The potency of a liposome encapsulated drug is affected by
liposomes-surface -charge
-size
Charge:
Negatively charged liposomes associate more affectively and
deliver their content more efficiently than neutral liposomes
Size:
small liposomes deliver drugs more effectively than larger
liposomes
optimal delivery is observed with negatively charged
liposomes of 0.05-0.1μm in diameter
Composition:
systemic evaluation of MLV with different phospholipid
composition.
 Composition:

systemic evaluation of MLV with different
phospholipid composition reveals that certain classes
of phospholipids are recognised preferentially by
macrophages.
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commonly used lipid for formulating liposomesphosphotidyl choline(pc) (neutral charge)
 Inclusion of negatively charged phospholipids such as
phosphotidyl serine
phosphotidyl glycol in MLV consisting of pc
greatly enhances their binding to macrophages and
phagocytosis by macrophages.
 In contrast neutral MLV’s composed of pc are not
efficiently bound by macrophages.
 The effect of liposome composition, size,concentration
and incubation time on the uptake of liposomes by
murine bonemarrow macrophages was observed that
liposome uptake increased linearly with the incubation
time and concentration.
 Inclusion of increasing amounts of cholesterol and
sphingomyelin reduces the targeting to macrophages.
 Recently developed developed polyethylene glycol-
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coated liposomes, known as Stealth liposomes, are not
readily taken by macrophages in the reticuloendothelial
system, however, stay in the circulation for a long period
of time.
Inclusion of ligands:
Fc receptors
Mannosyl
Galactosyl
Fibronectic lipoprotein
Complement
Many other receptors
 These macrophage surface receptors determine the
control of activities such as
 Activation
 Recognition
 Endocytosis
 Secretion etc;
 A usual approach for promoting the uptake of liposomal
content by macrophages is to incorporate ligands capable
of interacting with macrophage surface receptors.
 Mannose receptors on the macrophage surface have
been exploited by developing neoglycoprotein and mannose
residue.
 If liposomes surface has some mannose residues like
manoarachidic acid residue-such liposomes are called
mannosylated liposomes
these liposomes have more recognising capacity
to macrophages
 95% of control liposomes without MAE(monoarachidic
acid esters)remained in the circulation even at 30
minutes after administration
 On the contrary,liposomes with MAE were rapidly
eliminated from blood.
 Fc receptors:
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fragments of immunoglobulins-these fragments
used to liposomes-immunogenic liposomes-specificity
increases so surface adsorption is improved.
Fc receptor-mediated targeting:
Both invitro and in vivo uptake of liposomes have been
increased extraordinarily by targeting these carriers
through Fc surface receptors to macrophages
Derksen studied rabbit immunoglobulin and modified
mouse monoclonal antibody incorporated liposomes.
Coupling of rabbit immunoglobulin with liposomes
increases the uptake by rat liver macrophages more than
five times compared with control liposomes.
 In-vivo study demonstrated by that 80–85% of the coupled
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liposomes were accumulated in the liver within 1-h of the
injection this is because of the presence of the Fc moiety in
immunoglobulin-coupled liposomes.
Fc receptors mediated targeting of liposomes to human
monocyte macrophages :the uptake of antibody conjugated
liposomes was 4-6 times higher than that of plain
liposomes.this increase in uptake was thought to be due to
the Fc receptor mediated binding.
Grafted liposomes:protein grafted liposomes have more
oppourtunity for targeting to liposomes.
protein-may be fragments of collagen
,globulin,gelatin,immunoglobulin enhances efficiency.
Bovine serum albumin retard the efficiency.
Efficiency also influenced by concentration of cross linking
agent like glutaraldehyde or gelatin.
 NANOPARTICLES OR MICROSPHERES:
 Nanoparticles and microspheres are under extensive
study for delivering drugs to macrophages. They may be
polymeric—biodegradable or nonbiodegradable and
proteinaceous in nature.
 The size range covered by microparticles is between 1
and 1000 mm.
 Microspheres are monolithic or matrix-type
microparticles, whereas microcapsules are of reservoir
type.
 In contrast to microspheres, nanoparticles are in the size
ranging between 10 and 1000 nm.
 Uptake of microspheres/nanoparticles by
macrophages:
 As that of liposomes, size, surface property,composition,
concentration, and hydrophilicity or lipophilicity of
microspheres and nanoparticles play a significant role in
the uptake by macrophages.
 For phagocytosis to occur particles are first contacted by
pseudopods of macrophages and engulfed into the
cytoplasm by lamellipods .
 Hydrophobic and relatively large microspheres are more
susceptible to phagocytosis than their hydrophilic
counterparts.
 Likewise, nanoparticles with lipophilic coating are better
phagocytosed than their hydrophilic counterparts.
 The extent of phagocytosis can be improved by coating
the particle surface with opsonic materials and activating
macrophages with various activating factors.
 Incubation time and dose of the vehicles can also control
the process of phagocytosis. Because of the scarcity of
experimental data.
 Influence of microsphere size,
composition,concentration and surface property.
 The influence of surface charge and size of
microspheres on their phagocytosis by mouse
peritoneal macrophages were studied by using
polystyrene and phenylated polyacrolein microspheres
of different diameter as well as modified cellulose
microsphere with different surface charge.
 Size:maximum phagocytosis took place when their size
was in the range of 1-2 μm and the uptake was
maximum with in a one hour period of incubation.
 charge: for both negatively and positively charged
particles ,the extent phagocytosis was increased.with
increasing zetapotentials and was lowest when
zetapotential was zero(some charge is required)
 Surface hydrophobicity:
 Hydrophobic microspheres prepared from benzoyl cellulose were
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most susceptible to phagocytosis and the non-ionic hydrophilic
spheres with opsonic materials and amphiphiles can one was the
least.
Similarly nanoparticles made from
Polyalkylcyanoacrylate
polymethylmethacrylate, and
human serum albumin
microspheres have been used to study the influence of various
parameters on the uptake by human macrophages.
The more lipophilic polymethylmethacrylate were phagocytosed
better than polyalkylcyanoacrylate nanoparticles of similar size.
Polybutylcyanoacrylate nanoparticles coated with lipophilic
Pluronic F68—a biocompatible poloxamer—increased
phagocytosis by nearly 50%, shows more uptake;
while Pluronic F108 had no influence or no change.
 Coating
of microspheres with opsonic materials and
amphiphiles, and activation of macrophages:
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coating of microspheres with opsonic materials and
amphiphiles can modify significantly the extent of phagocytosis
by macrophages depending on the state of macrophage activation.
A study about the influence of several proteins on the
uptake of macrophages revealed that
Gamma-globulin
Human fibronectin,
Bovine tuftsin and
Gelatin - enhance the phagocytosis, while
bovine serum albumin reduces the phagocytosis of cellulose
microspheres.
 It was also demonstrated that precoating or surface
immobilization with gelatin was the most effective
method to enhance the phagocytosis among all other
opsonic proteins.
 Phagocytic uptake tests carried out at 37(degree
centigrade) showed that microspheres coated with any
surfactants cause a decrement in the phagocytosis in
both condition— either in the presence or absence of
serum.
 Microspheres from some biodegradable substances
such as copolymers of polylactic acid and polyglycolic acid,cross-linked potato starch, hydroxyethyl
starch and cross linked starch, dextran, lichenan and
mannan are found to besuccessfully phagocytosed by
macrophages.
drugs used to target macrophages
 Cephalosporins
 Pencillins
 Amino glycoside antibiotics
 Immunomodulators
interferons
interleukins
muramyl dipeptide
muramyl tripeptide
 Anticancer drugs
doxorubicin
daunorubicin under clinical trials
 Marketed formulations for macrophages
ambisome – with amphotericinB
Used in the treatment of leishmaniasis- parasite disorder.
References
 M.J. Auger, J.A. Ross, in: C.E. Lewis, J.O’D. McGee
(Eds.),the natural Immune System: The Macrophage,
Oxford University Press, New York, 1992, pp. 2–74.
 I.J. Fidler, Targeting of immunomodulators to
mononuclear phagocytes for therapy of cancer, Adv.
Drug Deliv. Rev.2(1988) 69–106.
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