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From the Second Department of Pathology,*
Kumamoto
University School of Medicine, Kumamoto, Japan; and the Department of
Adult Oncology,
Dana-Farber Cancer Institute
and Harvard Medical School, Boston, Massachusetts
| Abstract |
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| Introduction |
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GM-CSF is a 23-kd glycoprotein known as a hematopoietic growth factor
required for the proliferation and survival of hematopoietic cells
committed to granulocytic and macrophage cell lineages and myeloid
leukemic cells,23-26
and for differentiation of these
cells into neutrophilic or eosinophilic granulocytes, macrophages, bone
marrow macrophages, or dendritic cells.26-30
GM-CSF
increases the responsiveness of tissue macrophages to
M-CSF.26
In addition to stimulating the production of
granulocytes, macrophages, and dendritic cells, GM-CSF has a pronounced
capacity to increase the function of these cells in a variety of immune
reactions.31
Its in vivo effects include rapid
leukocytosis,31
increased numbers of granulocytes and
macrophages in tissues,31
stimulation of phagocytosis and
superoxide production by neutrophils and macrophages,32
induction of class II major histocompatibility complex expression and
urokinase-type plasminogen activator production by
monocyte/macrophages,33
enhancement of granulocyte and
monocyte cell adhesion,34,35
augmentation of
antigen-presenting function of macrophages,36
enhancement
of production of cytokines by mononuclear cells,37
and
enhancement of chemotaxis of neutrophils, monocytes, or dendritic cells
and of transendothelial migration of monocytes.38-40
GM-CSF is also important for survival of hemopoietic cells because the
human GM-CSF mutant E21R selectively binds to the
chain of GM-CSF
receptor, behaves as a GM-CSF antagonist, and causes apoptosis of
normal and malignant hemopoietic cells.41
Studies of the
signal transduction pathway of GM-CSF showed that stimulation by GM-CSF
increases protein tyrosine phosphorylation through activation of
multiple tyrosine kinases such as Src-like tyrosine kinases, Fes, and
p97.42-44
GM-CSF transgenic mice
develop a lethal disease accompanied by excessive accumulation of
macrophages in the eyes, muscles, peritoneal and pleural cavities,
liver, and lungs.45,46
In these transgenic mice,
peritoneal macrophages demonstrated long survival via self-renewal
independently of blood monocytes.45,46
Two groups of
investigators independently generated GM-CSF-deficient
(GM-CSF-/-) mice and their studies reported the
development of pulmonary alveolar proteinosis.47,48
However, these studies have also indicated that GM-CSF is not essential
in vivo in GM-CSF-deficient mice for maintenance of myeloid
progenitor cells at normal levels and that monocytes/macrophages and
dendritic cells develop normally in these mice.47,48
GM-CSF is also synthesized under the influence of estrogenic hormonal
stimulation by uterine luminal and glandular epithelial cells in humans
and other animals,49-51
and it is important for
intercellular communication in the female reproductive system and
fertility of mice.52
In a study of collagen-induced
arthritis in GM-CSF-deficient mice, Campbell and
colleagues53
demonstrated that inflammatory cell responses
were significantly reduced in the mutant mice, suggesting that GM-CSF
is required for the development of this type of arthritis. However,
little is known about the role of GM-CSF in hepatic granuloma formation
in vivo.
In this study, we injected zymocel (ß-glucan) intravenously into the GM-CSF-deficient mice and wild-type mice to examine how these mutant animals respond to this macrophage stimulant in vivo. After injection, the GM-CSF-deficient mice and wild-type mice were killed at various intervals, and granuloma formation in the liver of the animals was examined.
| Materials and Methods |
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Mice deficient in GM-CSF production were kindly supplied by Dr. Glenn Dranoff and co-workers47 and germline transmitters of a mutant GM-CSF allele were crossed with C57BL/6 mice to produce mice heterozygous for a disrupted GM-CSF gene (GM-CSF+/-). The heterozygous (GM-CSF+/-) mice were mated to yield the homozygous mutant (GM-CSF-/-) mice, wild-type (GM-CSF+/+) mice, and heterozygous (GM-CSF+/-) mice. Animals were kept in the Animal Research Center at the Kumamoto University School of Medicine, were fed with a standard rodent chow and water ad libitum, and were housed with same sex littermates in sawdust-lined cages. For genotyping, tissues were taken from the tails of mice at 3 or 4 weeks after birth and polymerase chain reaction (PCR) was performed. Sequences of primers used are as follows: for normal sense: 5'-ACACAGAAGTTTGGCTCTGG-3', for antisense: 5'-GGCAGTATGTCTGGTAGTAG-3', and for disrupted GM-CSF gene antisense: 5'-GTGGATGTGGAATGTGTG CG-3' to distinguish GM-CSF-/- mice from GM-CSF+/+ and GM-CSF+/- mice. Homozygous and wild-type mice of both sexes were used at 8 to 20 weeks of age. Zymocel (2 mg) (Alpha-beta Technology, Worcester, MA) was injected into the tail vein of GM-CSF-/- and GM-CSF+/+ mice. All mice were killed under ether anesthesia at 2, 3, 5, 8, 10, 14, and 21 days after injection and their livers were removed. Some liver tissues were frozen in liquid nitrogen and stored for mRNA analysis or were embedded in OCT compound (Miles, Elkhart, IN) for immunohistochemistry; others were fixed in 10% formaldehyde solution for light microscopic studies. To examine the effects of GM-CSF, GM-CSF-/- mice were injected daily with 5 ng of recombinant murine (rm) GM-CSF from 5 days before zymocel injection and throughout the experiment; because this dose is most effective for differentiation, proliferation, and survival of macrophages.30
Light Microscopy
Liver tissues fixed in 10% formaldehyde were embedded in paraffin, paraffin sections were cut 3-µm thick, and slides were stained with hematoxylin and eosin for light microscopy. In paraffin sections, as well as in frozen sections, periodic acid-Schiff (PAS) method for detection of glucan particles was used.
Antibodies
Monoclonal antibodies used for immunohistochemistry were as
follows: anti-mouse monoclonal antibodies against mouse macrophages
F4/80,54,55
against monocytic cells
ER-MP2056,57
or myeloid macrophage precursor ER-MP58 and
ER-MP12,56,57
against T lymphocytes
Thy-1.2,58
against dendritic cells
NLDC-145,59-61
and against murine major
histocompatibility complex II antigen ERTR-3,61
(purchased
from BMA Biomedicals, August, Switzerland); as well as those against
CD86 co-stimulatory molecule B7-2, against CD80 co-stimulatory molecule
B7-1,62
and against murine B lymphocytes B220 (from
Pharmingen, San Diego, CA).63
Table 1
shows the antigenic specificities and
immunoreactive cells of the monoclonal antibodies used in the present
study. To produce a polyclonal antibody against ß-glucan, adult
Wistar rats received two intravenous injections, 1 week apart of 2 mg
of ß-glucan. Animals were killed at 1 week after the last injection,
and serum was obtained and used as the polyclonal antibody against
ß-glucan.
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Frozen tissues were cut by a cryostat into 5-µm-thick sections. After inhibition of endogenous peroxidase activity by the method of Isobe et al,64 the indirect immunoperoxidase method using the above mentioned monoclonal antibodies and polyclonal antibody was performed as described previously.4-6 As a secondary antibody, we used anti-rat immunoglobulin-horseradish peroxidase-linked F(ab')2 fragment (Amersham, Poole, UK). After application of 3,3'-diaminobenzidine, hematoxylin was used for nuclear staining and sections were mounted with malinol. Negative controls underwent the same procedures performed, but the primary antibodies were omitted.
Evaluation of Hepatic Granulomas
On the basis of previous studies,4-6 hepatic granulomas were defined as being composed of more than 10 cells. The number of granulomas per 1 mm2 was counted. In each section, 100 granulomas were randomly selected and evaluated.
Autoradiography with [3H]Thymidine
[3H]Thymidine (specific activity, 0.3 to 0.5 MBq/mmol) was purchased from Amersham and stored at 4°C. At 2, 3, 5, 8, 10, 14, and 21 days after zymocel injection, mice were injected intraperitoneally with [3H]thymidine and were killed at 60 minutes after pulse labeling. After immunohistochemical staining with F4/80 and color development by 3,3'-diaminobenzidine, slides were dipped in a Sakura NR-M2 liquid emulsion (Konica, Tokyo, Japan) diluted 1:1 with distilled water, were kept for 7 days in a dark place, and were developed. Cell nuclei with 10 or more grains above the background level were defined to be labeled.2-6
RT Reaction with Nested PCR
To detect the GM-CSF mRNA, we used the RT reaction, performed as
reported previously,65,66
with a random primer,
nested PCR was done using the following primers. The sequences of outer
and inner primers of GM-CSF were as follows: outer primer: sense:
5'-TGAGGAGGATGTGGC-TGCA-3', antisense: 5'-CAGGCACAAAAGCAGCAGTC-3',
size of the amplified product, 488 bp; inner primer: sense:
5'-TGTGGTCTACAGCCTCTCAGCAC-3', antisense:
5'-CAAAGGGGATATCAGTCAGAAAGGT-3', size of the amplified product,
368 bp (Table 2)
.
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DNA nick-end labeling was used to detect apoptotic cells within or outside of hepatic granulomas; labeling was performed with the ApopTag detection kit (Intergen, Purchase, NY).67 Formalin-fixed paraffin sections were deparaffinized with xylene, and proteins were stripped off by incubation with 20 mg/ml proteinase K (Sigma Chemical, St. Louis, MO) for 15 minutes at room temperature. The tissues were washed in distilled water, and sections were immersed in 3% H2O2 solution for 5 minutes to inhibit endogenous peroxidase activity. The sections were exposed to an equilibration buffer and reacted with terminal deoxynucleotidyl transferase at 37°C for 1 hour, after which the reaction was stopped with stop/wash buffer. Samples were treated with anti-digoxigenin peroxidase conjugate and were incubated for 30 minutes at room temperature. After the sections were washed in phosphate-buffered saline, they were exposed to a peroxidase substrate containing 3,3'-diaminobenzidine. Hematoxylin was used as a counter stain for light microscopy. Positive control samples were prepared from the thymus of BALB/c mice given intraperitoneal injections of dexamethasone.
In Situ Hybridization
The in situ hybridization procedure was a modification of the procedure described elsewhere.68 Fresh frozen sections, 8-µm thick, were prepared from the livers of both types of mice at 5 days after zymocel injection and were mounted on silane-coated glass slides. In situ hybridization was performed using a mouse GM-CSF oligonucleotide probe cocktail (Funakoshi, Tokyo, Japan). The sections were fixed in 4% paraformaldehyde for 20 minutes, treated with proteinase K, and acetylated with 0.25% acetic anhydride in 0.1 mol/L triethanolamine-HCl buffer (pH 8.0) at room temperature for 10 minutes. After the sections were dehydrated and dried in air, they were treated with hybridization solution containing the probe cocktail and were incubated at 37°C for 24 hours in a humidified chamber. The sections were then washed briefly in 2x concentrated standard saline citrate (SSC) (1x SSC contains 0.15 mol/L NaCl and 0.015 mol/L sodium citrate) and in 50% formamide with 2x SSC at 40°C for 30 minutes. After reaction with a digoxigenin-labeled blocking reagent for 1 hour, the sections were exposed to anti-digoxigenin antibody overnight in 4°C. Hybridized digoxigenin-labeled probes were detected by the use of a nucleic acid detection kit (Boehringer-Mannheim, Mannheim, Germany) containing nitroblue tetrazolium chloride, 5-bromo-4-chloro-3-indolyl phosphate, and toluidine salt, and the sections were kept in a dark place for 24 hours. After the development of color, the sections were rinsed in 10 mmol/L Tris-HCl (pH 8.0) and 1 mmol/L ethylenediaminetetraacetic acid and were stained with methyl green for nuclear visualization. The specificity of the oligonucleotide probe used for this procedure was verified by comparison with slides treated with hybridization solution without the addition of the probe cocktail and with the slides of GM-CSF-deficient mice.
Electron Microscopy
Livers were taken from GM-CSF-deficient mice and wild-type mice after zymocel injection and were fixed in 2.5% glutaraldehyde and 1% osmium oxide. After fixation, tissues were dehydrated in a graded series of ethanol concentration, were processed in propylene oxide, and were embedded in Epok 812 (Okenshoji, Tokyo, Japan). Sections were cut 1-µm thick by use of an ultratome (MT-7000 Ultramicrotome, Research and Manufacturing Co. Inc., Tucson, AZ), were stained with toluidine blue, and were observed by a light microscope to detect the presence of apoptotic cells in the granulomas. Ultrathin sections were then cut, stained by lead acetate and uranyl acetate, and studied by use of an H-300 electron microscope (Hitachi, Tokyo, Japan).
Cell Enumeration in Tissues
In immunostained sections, numbers of cells positive for F4/80, ER-MP20, ER-MP58, Thy-1.2, ERTR-3, and B7-2 within and outside of the granulomas were counted per 1-mm2 section. In the paraffin sections, numbers of [3H]thymidine-labeled F4/80+ cells were counted after autoradiography was performed. In DNA nick-end-labeled paraffin sections, numbers of apoptotic cells were counted within and outside of the granulomas, and their numbers per 1-mm2 sections were calculated.
Statistics
Statistical significance of the data was evaluated by analysis of variance with post hoc testing. P values < 0.05 were considered significant.
| Results |
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After intravenous injection of zymocel, numbers of white blood
cells and monocytes increased in peripheral blood of
GM-CSF-/- and GM-CSF+/+
mice, peaked at 5 days, and then declined (Figure 1,A and B)
. The numbers of monocytes were
slightly lower in GM-CSF-/- mice than in
GM-CSF+/+ mice (Figure 1B)
. However, no
significant differences in blood monocyte counts were found between
both types of mice. These data indicate that the production of white
blood cells including monocytes in bone marrow and their mobilization
into peripheral circulation in response to zymocel stimulation are not
impaired in GM-CSF-/- mice.
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Before zymocel injection, the distribution and localization of
F4/80+ Kupffer cells in the livers of
GM-CSF-/- mice were similar to those of
GM-CSF+/+ mice. At 1 day after injection,
ER-MP20+ monocytes infiltrated the hepatic
sinusoids of GM-CSF+/+ and
GM-CSF-/- mice after polymorphonuclear
leukocyte infiltration. In GM-CSF+/+ mice,
F4/80+ cell aggregates collected in the hepatic
sinusoids at 2 days after injection, and granulomas started to form
(Figure 2)
. The numbers and mean
diameters of hepatic granulomas increased, peaked at 10 days, and then
declined (Figure 3,A and B)
. At 2 days
after zymocel injection, the development of hepatic granulomas in
GM-CSF-/- mice was impaired significantly
compared with that in GM-CSF+/+ mice (Figure 2A)
and granuloma numbers and mean diameters were smaller (Figure 3, A and B)
. At this stage, the percentages of F4/80+
cells and ER-MP20+ monocytes per granuloma were
significantly reduced in GM-CSF-/- mice (Figure 4)
. The numbers of
ER-MP58+ (Figure 5B)
or ER-MP12+
(data not shown) myeloid precursors in hepatic granulomas were small,
and no significant differences in the numbers were found in both types
of mice. After daily subcutaneous injection of GM-CSF into
GM-CSF-/- mice, the granuloma numbers and mean
diameters recovered to a certain extent, but not completely, to
approach those of GM-CSF+/+ mice (Figure 3, A and B)
. Also, the numbers of ER-MP20+ monocytes and
F4/80+ macrophages within the granulomas
increased in GM-CSF-/- mice after GM-CSF
injection. These data suggest that the development of hepatic
granulomas in GM-CSF-/- mice is reduced as a
result of the impaired influx of monocytes into the granulomas during
the early stage of hepatic granuloma formation.
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Local Proliferation and Death of Macrophages during Hepatic Granuloma Formation
Figure 6
shows infiltration of
[3H]thymidine-labeled
F4/80+ macrophages within hepatic granulomas of
GM-CSF+/+ mice and
GM-CSF-/- mice with or without daily GM-CSF
administration. The proliferative potential of macrophages within
granulomas of GM-CSF-/- mice was significantly
lower at 2 days after zymocel injection (Figure 7A)
compared with that of
GM-CSF+/+ mice (Figure 7B)
. GM-CSF-treatment of
GM-CSF-/- mice increased the proliferative
potential of granuloma macrophages to the level of
GM-CSF+/+ mice from 5 days after zymocel
injection. These data indicate that GM-CSF deficiency causes a
significant reduction in proliferative capacity of macrophages in the
early stage of zymocel-induced hepatic granuloma formation, suggesting
that impaired development of hepatic granulomas in the early stage is
partly because of a reduced proliferative potential of granuloma
macrophages in GM-CSF-/- mice.
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Digestive Capacity of Granuloma Macrophages for Zymocel
To examine the digestive capacity of macrophages for zymocel
during hepatic granuloma formation in GM-CSF-/-
and GM-CSF+/+ mice, the numbers of glucan
particles within granuloma macrophages were counted by a
double-staining method (PAS reaction and immunostaining with a
polyclonal antibody against ß-glucan): zymocel (ß-glucan) particles
were clearly stained reddish purple by the PAS reaction and brown by
immunostaining with the anti-ß-glucan polyclonal antibody. The
numbers of glucan particles were counted, although because glucan
particles were digested and degraded within the macrophages with
subsequent loss of particular shape, they cannot be counted within
macrophages, particularly in the late stage of hepatic granuloma
formation. Figure 9
shows changes in the
numbers of granuloma macrophages ingesting glucan during hepatic
granuloma formation in GM-CSF-/- and
GM-CSF+/+ mice. The numbers of cells increased to
a peak at 8 days (Figure 7, C and D)
and declined thereafter in both
types of mice. These data suggest that the uptake and degradation of
zymocel particles by granuloma macrophages were not different in
GM-CSF-/- and GM-CSF+/+
mice.
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Small numbers of lymphocytes were usually found in the livers of
GM-CSF+/+ and GM-CSF-/-
mice. After zymocel injection, lymphocytes infiltrated the livers of
both types of mice. Most lymphocytes were
Thy-1.2+ T cells, only a few
B220+ B cells were present in and around the
granulomas. The numbers of T cells per 1 mm2
increased within hepatic granulomas in parallel with increases in the
numbers and diameters of hepatic granulomas (Figure 5A)
. In addition,
natural killer cells were observed in the hepatic granulomas (data not
shown). However, the numbers of T cells per 1 mm2
within and outside of the granulomas were lower in
GM-CSF-/- mice than in
GM-CSF+/+ mice at 8 days after zymocel injection;
this reduction in the GM-CSF-/- mice was not
significant statistically.
Activation of Macrophages during Hepatic Granuloma Formation
Figure 10A
shows changes in the
number of ERTR-3+ cells in hepatic granulomas of
GM-CSF-/- and GM-CSF+/+
mice after zymocel injection. Numbers of these cells increased in
parallel with increases in the number and size of granulomas, peaked at
8 days in both types of mice, and declined thereafter.
GM-CSF-/- mice had a smaller number of
ERTR-3+ cells at 2 days after injection, but
this difference was not statistically significant. Figure 10B
shows the
numbers of co-stimulatory molecule B7-2+ cells in
hepatic granulomas of both types of mice after zymocel injection.
B7-2+ cells were present throughout granuloma
formation and their numbers peaked at 8 days after injection in both
types of mice, but with no statistical difference in the two types of
mice. A few B7-1+ cells were present in
hepatic granulomas of both types of mice from 2 to 10 days after
injection (data not shown). NLDC-145+ dendritic
cells were present in granulomas of both types of mice from 2 days to
10 days after injection (data not shown). These data suggest that
activation of macrophages during zymocel-induced hepatic granuloma
formation is not impaired in GM-CSF-/- mice.
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To detect GM-CSF mRNA expression, the distribution of GM-CSF
mRNA-expressing cells in liver tissue sections was examined by in
situ hybridization using a GM-CSF oligonucleotide probe cocktail.
Purplish blue-stained positive signals were detected in livers of
GM-CSF+/+ mice, in the endothelial cells of lymph
vessels (Figure 11A)
, some granuloma
cells and hepatocytes (Figure 11B)
, and endothelium of blood vessels
(Figure 11C)
. However, GM-CSF-/- mice showed no
expression of this cytokine in any cells in livers throughout the
experimental period (Figure 11D)
. By RT-nested PCR, the expression of
GM-CSF mRNA was proved in the livers of GM-CSF+/+
mice before and after zymocel injection and not in those of
GM-CSF-/- mice throughout the experimental
period (Figure 11E)
.
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| Discussion |
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In GM-CSF-/- mice, the early stage of hepatic
granuloma formation was impaired, in agreement with results from
previous studies of mice depleted of blood monocytes by
89Sr,4,5
osteopetrosis (op/op)
mice,3
and mice depleted of Kupffer cells by
administration of liposome-entrapped dichloromethylene
diphosphonate.2
In 89Sr-induced
monocytopenic mice and M-CSF-deficient op/op mice, the deficiency of
blood monocytes is the major cause of markedly impaired hepatic
granuloma formation. In op/op mice, the differentiation of monocytes
into macrophages is severely impaired because of the M-CSF deficiency.
The depletion of Kupffer cells in mice treated with liposome-entrapped
dichloromethylene diphosphonate results in impaired production of
monocyte chemoattractant protein (MCP-1), tumor necrosis factor
(TNF)-
, and interferon (IFN)-
, which induce monocyte migration
into hepatic granulomas and differentiation of monocytes into
macrophages, as well as macrophage activation within the
granulomas.2
However, data presented in previous
studies,47,48
have indicated that the development of
hematopoietic cells in the bone marrow and peripheral blood of
GM-CSF-/- mice was not impaired and that the
development and distribution of Kupffer cells were normal, as shown in
the current study. In the GM-CSF-/- mice
studied here, the production of white blood cells and monocytes in bone
marrow and their mobilization into peripheral blood in response to
zymocel injection were not impaired. In the early stage of granuloma
development in the liver of GM-CSF-/- mice, the
influx of ER-MP20+ monocytes into the liver was
not impaired. However, monocyte migration into granulomas and monocyte
aggregation were markedly impaired in GM-CSF-/-
mice, accompanied by a significant reduction in the proliferative
capacity of granuloma macrophages, as shown by their
[3H]thymidine-labeling rates. Because GM-CSF is
known to induce in vitro proliferation of
macrophages23,24
and chemotaxis of
monocytes,38,40
the reduced proliferative potential of
macrophages and the impaired influx of monocytes into hepatic
granulomas of GM-CSF-/- mice may be ascribed to
total deficiency of GM-CSF in loco.
GM-CSF is essential for the differentiation and survival, as well as the proliferation, of macrophages.23,24,41 In GM-CSF-/- mice, the influx of monocytes into hepatic granulomas and monocyte differentiation into macrophages in response to zymocel stimulation are impaired and these impairments are thought to be caused by GM-CSF deficiency. The rapid reduction in numbers of hepatic granulomas with their eventual disappearance in GM-CSF-/- mice from 10 days after zymocel injection is also essentially because of the lack of GM-CSF production in the liver: granuloma macrophages could not survive in GM-CSF-/- mice, and apoptotic cells were more numerous in the granulomas of GM-CSF-/- mice at 10 days after zymocel injection than in GM-CSF+/+ mice, as demonstrated by electron microscopy. These findings suggest that GM-CSF is important for the survival of macrophages and for the maintenance of the late stage of hepatic granulomas.
Zymocel is composed of ß-glucan, an intense stimulant of
macrophages,16
neutrophils,17
and natural
killer cells,18
and is taken up by macrophages via the
receptor for ß-glucan,19
which was recently demonstrated
to be a lectin domain of complement receptor type 3 (CR3 or
CD11b/CD18),20
exposing an I domain neoepitope for binding
to ß-glucan.69
In contrast, GM-CSF stimulates
macrophages to induce increases in protein tyrosine phosphorylation
through activation of multiple tyrosine kinases such as Src-like
tyrosine kinases, Fes, and
p97.42-44
In this way, signal
transduction and production of GM-CSF by macrophages and
lectin-dependent CR3-mediated signal transduction of ß-glucan through
CD11b/CD18 are considered to be unrelated. Our preliminary study has
demonstrated expressions of proinflammatory cytokines such as MCP-1,
TNF-
, and IFN-
mRNAs in the livers of
GM-CSF-/- mice after zymocel injection (data
not shown), a finding which seems to be induced by macrophages in
response to glucan stimulation. In contrast, our preliminary study has
also demonstrated expression of M-CSF, IL-1, IL-3, or IL-5 mRNAs in the
liver of GM-CSF+/+ mice before and after zymocel
injection (data not shown), a finding that reflects constitutive
production of these cytokines, although
GM-CSF-/- mice fail to produce GM-CSF in
tissues including the liver. In mice infected with L.
monocytogenes, expression of IFN-
, TNF-
, IL-10, and GM-CSF
was detected in the early stage of hepatic granuloma
formation.15
On the basis of this information, it is
thought that the proinflammatory cytokines such as M-CSF, IL-1, IL-3,
IL-5, MCP-1, TNF-
, and IFN-
may induce differentiation,
maturation, activation, and proliferation of macrophages within hepatic
granulomas of GM-CSF-/- and
GM-CSF+/+ mice.
T cells also play important roles in macrophage activation during the
hepatic granuloma formation. Previous studies revealed marked delay in
hepatic granuloma formation in response to glucan stimulation, in
immunodeficient mice such as nude mice or scid mice, and T cells are
severely deficient in both types of mice.7
In contrast,
previous studies in glucan-induced hepatic granuloma formation in xid
mice, a model of impaired B cell proliferation and differentiation,
showed that T cell numbers in liver granulomas increased throughout the
experiment, granuloma formation peaked at 5 days and rapidly declined
thereafter and that uptake and degradation of glucan by granuloma
macrophages were accelerated, suggesting that increases in the number
of T cells within the granulomas induced a more marked activation of
macrophages.7
However, in
GM-CSF-/- mice studied here, the numbers of T
cells in hepatic granulomas were lower than those in
GM-CSF+/+ mice, although this reduction was not
significant statistically. Expression of IFN-
and TNF-
mRNAs in
the GM-CSF-/- mice was not impaired, and
expression of the CD80 and CD86 co-stimulatory molecules B7-1 and B7-2
in granuloma cells was not reduced in the
GM-CSF-/- mice. In the processes of glucan
uptake by macrophages via CR3, cyclooxygenase (prostaglandin
E2) and 5'-lipoxygenase (leukotriene C4) pathways
are used for the production of eicosanoids70
and are
independent of macrophage activation through GM-CSF signal transduction
pathways. These data suggest that activation of granuloma macrophages
is not impaired in the GM-CSF-/- mice and that
ß-glucan can stimulate and activate macrophages through pathways
different from those of GM-CSF signal transduction in mutant mice. The
present study also revealed that the uptake and degradation of glucan
particles by granuloma macrophages were not impaired in the mutant mice
compared with the GM-CSF+/+ mice.
In the present study, daily administration of GM-CSF into GM-CSF-/- mice induced a recovery of impaired hepatic granuloma formation nearly to the level of GM-CSF+/+ mice, accompanied by increased numbers of F4/80+ macrophages and ER-MP20+ monocytes within hepatic granulomas in the early stage and by decreased numbers of apoptotic cells at 10 days after injection. These data provide evidence to the facts that GM-CSF is essential for inducing chemotaxis of monocytes into granulomas, their differentiation into macrophages, and survival of macrophages within the granulomas. Previous studies showed that GM-CSF is constitutively produced by hepatocytes, Kupffer cells, fibroblasts, and sinusoidal endothelial cells,71-77 in agreement with the results of the present study that the in situ hybridization method showed positive signals in vascular endothelial cells, hepatocytes, and granuloma cells in the liver of GM-CSF+/+ mice. However, GM-CSF is not demonstrated at message level in the liver tissues of GM-CSF-deficient mice.
In conclusion, the data presented in this study provide evidence that GM-CSF participates in the proliferation, differentiation, and survival of macrophages within the hepatic granulomas, and induces monocyte chemotaxis and migration into the granulomas.
| Acknowledgements |
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| Footnotes |
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Supported in part by grants-in-aid for scientific research from the Ministry of Education, Science, and Culture, Japan (grant nos. 08457071 and 09877048).
Accepted for publication September 13, 2000.
| References |
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, interleukin-1ß and tumor necrosis factor by human mononuclear cells stimulated with granulocyte-macrophage colony-stimulating factor. Blood 1988, 72:1368-1374
stimulates human endothelial cells to produce granulocyte-macrophage colony-stimulating factor. Proc Natl Acad Sci USA 1986, 83:7467-7471This article has been cited by other articles:
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