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From the Services de Pneumologie et de Réanimation
Respiratoire,*
dHistologie et Biologie
Tumorale,
and dAnatomie
Pathologique,¶
Assistance Publique des hopitaux de
Paris, Hôpital Tenon, Paris; the Laboratoire de Biologie
Cellulaire et dImmunopathologie Pulmonaire,
Université Paris VI, Unité de formation et de Recherche
Saint-Antoine; and the Unité Inserm 408,
Université Paris VII, Bichat, Paris, France
| Abstract |
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had no significant effect. In an
attempt to identify the cell origin of anti-apoptotic
cytokines, we tested in vitro the effect of BAC
cells (A549 cell line and primary culture derived from a patients BAC
tumor) on the apoptosis of peripheral blood neutrophils. Cell-free
supernatants from tumor cells did not inhibit neutrophil apoptosis. In
contrast, cell-free supernatants from tumor cells previously
exposed to conditioned media from peripheral blood mononuclear cells
and alveolar macrophages significantly inhibited spontaneous neutrophil
apoptosis. This inhibition was partially lifted when conditioned media
from mononuclear cells were previously treated with Abs against IL-1ß
and tumor necrosis factor-
. As in vivo,
neutralizing Abs against GM-CSF significantly inhibited the
anti-apoptotic activity of cell culture supernatants, and
combination with Abs against G-CSF had an additive effect. In
vivo, GM-CSF and G-CSF were strongly expressed by tumor
cells and moderately or not expressed by the normal epithelium,
as assessed by immunohistochemical studies. These findings demonstrate
that the tumor environment generates local conditions that prolong
alveolar neutrophil survival through the production of soluble
factors, thereby contributing to the persistence of the
neutrophil alveolitis observed in BAC.
| Introduction |
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We have previously shown that the presence of increased numbers of tumor-infiltrating neutrophils is linked to poorer outcome in patients with adenocarcinoma of the BAC subtype11 and that tumor cells drive local neutrophil recruitment and activation via C-X-C chemokine release. In the present study, we examined the role of the tumor microenvironment in promoting neutrophil survival and in the persistence of the deleterious neutrophil alveolitis observed in this subtype of adenocarcinoma. We focused our attention on the neutrophil anti-apoptotic activity of tumor-derived cytokines.
| Materials and Methods |
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Patients with BAC
Between January, 1989, and January, 1999, BAC was diagnosed in 50 patients who were treated and followed-up in our chest department. The patients were 32 men and 18 women, with a mean age (±SD) of 64.8 ± 11 years (range, 34 to 81 years), and comprised 34 smokers and 16 nonsmokers. The diagnosis was based on previously published criteria;13,14 bronchoalveolar lavage (BAL) was used as a diagnostic procedure in 41 cases.15 Briefly, 200 ml of sterile saline in four 50-ml aliquots was infused into the radiologically abnormal segment or lobe. Fluid recovered by gentle suction was pooled, filtered through sterile gauze, and used for total cell counting. Differential cell counts and tumor cell counts were performed on cytospin preparations stained with modified Wright-Giemsa (Diff-Quick; Dade Behring, Paris, La Défense, France). Bronchoalveolar lavage fluid (BALF) containing >5% neutrophils was examined for the presence of apoptotic neutrophils (see below). For apoptosis assays and cytokine measurements, the remaining BALF was spun and the supernatant was aseptically removed and stored at -80°C.
Control Group
We used BALF supernatants obtained during a diagnostic procedure from six patients. The control patients were four men and two women aged 61 ± 7 years. Three were smokers. None had a history of neoplastic disease and all had normal results of BALF analysis (see below). Bronchoalveolar lavage was performed in the middle lobe and supernatants were stored at -80°C after centrifugation.
Measurement of 24-Hour Spontaneous Polymorphonuclear Neutrophil (PMN) Apoptosis
PMNs were isolated from peripheral blood of healthy human donors by means of density gradient centrifugation (Polymorphonuclear cell separation media; Eurobio, Les Ulis, France). PMNs were then separated from erythrocytes by hypotonic shock and washed three times in sterile saline. This method yielded >97% pure PMNs as assessed by May Grünwald Giemsa staining. Normal peripheral venous-blood PMNs at a density of 1 x 106/ml were incubated for 24 hours in Dulbeccos modified Eagles medium (Gibco, Cergy-Pontoise, France) with 5 mmol/L HEPES, 2 mmol/L L-glutamine, 105 units/L penicillin, 100 mg/L streptomycin (referred to as complete medium), and supplemented with 2% fetal bovine serum (FBS). At 24 hours the PMN preparation thus obtained was evaluated for apoptosis by using three different techniques.
Morphological Criteria for Apoptosis
One hundred µl of PMN preparation was cytospun. Cytospin slides stained with May Grünwald Giemsa were evaluated by two independent investigators by consensus. At least 200 PMNs were graded for apoptosis by using predetermined morphological criteria. PMNs were considered apoptotic if they showed dense condensation of chromatin in the form of either a single nucleus or nuclear fragments not connected by strands.16 The results are expressed as the percentage of apoptotic PMNs.
Annexin V-Fluos Expression by Flow Cytometry
One µl of PMN preparation was washed once with ice-cold phosphate-buffered saline (PBS) and centrifuged at 200 x g for 5 minutes. The cell pellet was resuspended at a density of 1 x 106 cells/100 µl in labeling buffer (10 mmol/L HEPES/NaOH, 140 mmol/L NaCl, 5 mmol/L CaCl2, pH 7.4) containing 20 µl/ml of Annexin V-Fluos (Boehringer Mannheim, Meylan, France) and 20 µl/ml of propidium iodide (50 µg/ml) (Sigma-Aldrich, Saint Quentin Fallavier, France). Cells were incubated for 10 minutes at room temperature in the dark and analyzed within 1 hour by flow cytometry (Elite flow cytometer; Beckman Coulter, Villepinte, France) with gating set on forward scatter and side scatter to identify PMNs and to exclude cell debris.17 The results are expressed as the percentage of PMNs that met criteria for apoptosis, ie, a strong annexin V-fluorescein isothiocyanate signal and a low propidium iodide signal (early apoptotic PMNs), or a strong annexin V-fluorescein isothiocyanate signal and a strong propidium iodide signal (late apoptotic PMNs).
DNA Fragmentation Analysis
Five µl of PMN preparation was washed once with PBS, gently resuspended in 0.5 ml of lysis buffer (50 mmol/L Tris, 10 mmol/L ethylenediaminetetraacetic acid, 1% sodium dodecyl sulfate, and 250 µg/ml proteinase K), and incubated for 24 hours at 37°C with 5% CO2. The lysate was extracted twice with phenol/chloroform/isoamyl alcohol (25:24:1 v/v/v) and precipitated with two volumes of cold ethanol and 0.5 volume of 10 mol/L ammonium acetate at 4°C overnight. The DNA pellet was washed once with 75% ethanol, resuspended in 30 µl of TBE buffer (89 mmol/L Tris, 89 mmol/L boric acid, 2 mmol/L ethylenediaminetetraacetic acid, pH 8.0) containing 250 µg/ml of RNase (Sigma) and incubated at 65°C for 5 minutes. Then, 0.1 volume of loading buffer (0.25% bromophenol blue, 0.25% xylene cyanol FF, 30% glycerol in water) was added to each sample, and electrophoresis was performed in 1.2% agarose gel at 50 V for 3 hours. After staining with ethidium bromide, DNA was visualized with UV light and photographed.
Modulation of 24-Hour Spontaneous PMN Apoptosis by Tumor Cells
Effect of Tumor Cell-Conditioned Media
To determine whether tumor cells can modulate PMN apoptosis, 1 x 106 PMNs were incubated for 24 hours in 1 ml of tumor cell-conditioned medium (CM) and evaluated for apoptosis. Tumor cell-CM was obtained with: 1) the A549 cell line (American Type Culture Collection, Rockville, MD) originally established from a person with BAC18 and cultured in complete medium (see above) supplemented with 10% FBS; and 2) a primary culture (first to third passage) of tumor cells obtained from a pleural effusion specimen recovered from a patient with BAC, as previously described by Oie and colleagues.19 Briefly, pleural fluid was centrifuged and pleural cells (tumor cells, 65%; inflammatory cells, 35%) were resuspended in Dulbeccos modified Eagles medium and separated by density gradient centrifugation (Lymphocytes separation medium, MSL1077; Eurobio, Les Ulis, France). The interface layer containing tumor cells was harvested, washed twice in Dulbeccos modified Eagles medium, and seeded into 25-cm2 flasks in complete medium with 10% FBS. The purity of the tumor cells thus obtained was verified by May Grünwald Giemsa staining. Then, cultured cells were routinely passaged every 7 to 15 days. Tumor cells, ie, A549 or primary BAC cells, were resuspended at a density of 1 x 105/ml in complete medium with 2% FBS and cultured in 24-well plates (500 µl/well) for 72 hours at 37°C. The medium was then harvested and confluent monolayers of tumor cells were exposed to complete medium with 2% FBS or to CM from inflammatory cells, ie, peripheral blood mononuclear cells (PBMCs), PMNs, and alveolar macrophages (AMs), prepared as described below. Cell-free supernatants were collected after 24 hours of incubation and stored at -80°C.
To obtain inflammatory cell-CM, PBMCs and PMNs were recovered from peripheral blood of healthy donors by density gradient centrifugation (Polymorphonuclear cell separation medium, Eurobio). Briefly, PMNs were separated as above. The PBMC layer was washed three times in sterile saline solution. PBMCs comprised 65 ± 10% lymphocytes and 35 ± 13% monocytes as evaluated by flow cytometry. AMs were isolated from BALF of controls (see above). AMs accounted for >90% of BALF cells (May Grünwald Giemsa staining). Cells were separated from the remaining BALF by centrifugation. PBMCs, PMNs, and AMs were resuspended at a density of 5 x 105/ml in complete medium with 2% FBS, then plated in 24-well plates (500 µl/well) and cultured at 37°C in humidified 5% CO2/95% air. After 24 hours, inflammatory cell-CM was collected and stored at -80°C.
Effect of BALF from BAC Patients
One million PMNs were incubated for 24 hours in 1 ml of BALF supernatant from patients and controls at a final concentration of 50 to 90% in complete medium with 2% FBS, and were then examined for apoptosis.
Neutralization Studies
Conditioned media and BALF supernatants were preincubated for 45
minutes with several goat polyclonal neutralizing antibodies (Abs)
directed against human 1) granulocyte-macrophage colony-stimulating
factor (GM-CSF) (1:250 dilution; R&D Systems, Abington, UK), 2)
granulocyte colony-stimulating factor (G-CSF) (1:125; R&D Systems), 3)
interleukin (IL)-8 (1:20; R&D Systems), 4) IL-6 (1:200; R&D Systems),
5) tumor necrosis factor-
(TNF-
) (1:250; Genzyme Diagnostics,
Cergy Saint-Christophe, France), 6) IL-1ß (1:100; R&D Systems) and
with irrelevant control goat polyclonal Abs (R&D systems). PMNs were
then incubated for 24 hours at 37°C in Ab-treated CM or BALF
supernatants and analyzed by means of flow cytometry. The results are
expressed as the percentage inhibition of anti-apoptotic activity
defined as follows:
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Enzyme-Linked Immunosorbent Assay (ELISA) Measurements
GM-CSF, G-CSF, IL-8, IL-6, IL-1ß, and TNF-
concentrations
were measured in CM and BALF supernatants by using commercially
available ELISA assays (R&D Systems). The ELISA kits were used as
indicated by the manufacturer and consistently detected GM-CSF,
G-CSF, IL-8, IL-6, TNF-
, and IL-1ß concentrations >3, 20, 10,
0.7, 4.4, and 1 pg/ml, respectively, in linear manner.
Immunohistochemical Studies of GM-CSF and G-CSF Expression in BAC and Normal Pulmonary Tissue
We examined tumoral and distant normal pulmonary tissues from three patients with BAC. Tissue fragments were immediately frozen in liquid nitrogen and stored at -80°C. Sections 4-µm thick were fixed in acetone and reacted with appropriate dilutions of monoclonal anti-human GM-CSF (Genzyme) and G-CSF Abs (R&D Systems). Isotype-matched Abs were used as controls (MOPC 21, IgG1; Sigma, Saint Louis, MO).
Positive cells were revealed by using the Vectastain ABC-alkaline phosphatase kit (Vector, Burlingame, CA) and Fast Red substrate. To test the specificity of immunostaining, Abs were omitted or replaced by an isotype-matched control. No positive cells were identified in these conditions. The intensity of immunostaining was graded from - (absent) to +++ (strongly positive). Complete agreement was obtained between the two independent observers.
Statistical Analysis
Spearmans
coefficient was used for correlation studies
between quantitative variables. Comparisons were made using the
Mann-Whitney nonparametric test for unpaired data and the Wilcoxon
nonparametric test for paired data. Statistical analysis was performed
using one-way analysis of variance for parametric data sets. Data are
presented as means ± SEM. P values of <0.05 were
considered to denote statistical significance.
| Results |
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Conditioned media from unstimulated A549 tumor cells did not
inhibit constitutive PMN apoptosis at 24 hours. Numerous PMNs showed
morphological characteristics of apoptotic cells, such as condensed
nuclei and apoptotic bodies, which were absent at T0 in cytospin
preparations (Figure 1, A and C)
. This
phenomenon was accompanied by the emergence of annexing V labeling
(Figure 1, B and D)
and DNA fragmentation (Figure 2)
. In contrast, cell-free supernatants
from A549 cells exposed to CM from PBMCs or AMs inhibited 24-hour
constitutive PMN apoptosis. In these conditions, PMNs were
morphologically normal (Figure 1, E and G)
. Flow cytometry showed the
loss of annexin V labeling (Figure 1, F and H)
, and DNA electrophoresis
showed a decrease in DNA fragmentation (Figure 2)
. Cell-free
supernatants from A549 cell cultures exposed to PMN-CM did not inhibit
24-hour constitutive PMN apoptosis (Figure 1, I and J
, and Figure 2
).
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to investigate their role in the ability of mononuclear
cells-CM, ie, PBMCs and AMs, to induce neutrophil anti-apoptotic
activity from A549-cells. As shown in Figure 4
Abs were previously added to PBMC-CM (Figure 4)
Abs were added to AM-CM (Figure 4)
Abs was associated with a
>90% reduction in G-CSF and GM-CSF production by A549 cells (data not
shown). The fact that A549 cells did not release detectable amounts of
IL-1ß or TNF-
, either constitutively or after exposure to
mononuclear cell-CM (Table 2)
production by A549
cells.
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To determine whether cytokines were responsible for the
anti-apoptotic activity of cell-free supernatants from A549 cells,
concentrations of cytokines known to be involved in neutrophil survival
were determined in cell culture supernatants by using specific ELISAs.
As shown in Table 2
, unstimulated A549 tumor cells constitutively
released moderate amounts of G-CSF, IL-8, and IL-6, but did not
detectably release GM-CSF, TNF-
, or IL-1ß. PBMC-CM and AM-CM
induced GM-CSF release and also enhanced G-CSF and IL-6 release.
Contrary to AM-CM, PBMC-CM enhanced IL-8 release by A549 cells.
We then used neutralizing Abs to examine the relative contributions of
these cytokines to the anti-apoptotic activity of A549 cells.
Neutralizing Abs to G-CSF, IL-6, IL-8, IL-1ß, and TNF-
, used
alone, had no significant effect on the anti-apoptotic activity of
cell-free supernatants from A549 cells stimulated with PBMC-CM (data
not shown). As shown in Figure 5
, top,
anti-GM-CSF Ab inhibited this anti-apoptotic activity by 21% when used
alone and by 51% when combined with anti-G-CSF Abs. The inhibition
induced by anti-GM-CSF was not enhanced by simultaneous addition of
each of the other anti-cytokine Abs (data not shown). Neutralizing Abs
to G-CSF, IL-6, IL-1ß, and TNF-
had no individual effect on the
anti-apoptotic activity of cell-free supernatants from A549 cells
stimulated with AM-CM (data not shown). Anti-GM-CSF and anti-IL-8 Abs
inhibited anti-apoptotic activity by 35% and 21%, respectively, when
used separately, and by 58% when combined (Figure 5
, bottom). However,
the IL-8 effect was related to AM release rather than to tumor cell
release (Table 2)
.
|
The mean percentage of neutrophils in BALF was 33 ± 5% in
patients with BAC and only 1.2 ± 0.2% in controls
(P = 0.03). In the 29 BALF samples showing
neutrophil alveolitis exceeding 5%, the mean proportion of apoptotic
PMNs was 11 ± 2% (median, 7%; range, 0.5 to 43%). In this
group, the degree of PMN alveolitis correlated negatively with the
percentage of apoptotic PMNs, as shown in Figure 6A
(P = 0.024).
|
To determine whether BALF supernatants from BAC patients inhibited
neutrophil apoptosis, we incubated normal peripheral blood PMNs for 24
hours in BALF supernatants from patients (n =
14) and controls (n = 6) at a final
concentration of 50% in complete media. These BAL samples were
selected on the basis of availability, with no knowledge of neutrophil
alveolitis or cytokine concentrations. As shown in Figure 6B
, BALF from
the patients inhibited PMN apoptosis relative to BALF from controls
(apoptotic PMNs: 64 ± 4% versus 90 ± 2%,
P = 0.04). This anti-apoptotic effect was
concentration-dependent, as the proportion of apoptotic PMNs reached
49 ± 5% (n = 4), when BALF from the
patients was used at a final concentration of 90%.
To evaluate whether the anti-apoptotic effects of BAC BALF depended on
the cytokines previously shown to be involved in neutrophil survival
in vitro, cytokine concentrations were determined using
ELISA methods. As shown in Table 3
, only
G-CSF was detectable in BALF from controls, whereas all of the
cytokines were detected in BALF from the patients; in addition, G-CSF
concentrations were significantly higher in BALF from patients than
controls. Only GM-CSF concentrations correlated with BALF
anti-apoptotic activity (P = 0.01,
n = 14). However, a positive correlation was also noted
between the BALF G-CSF concentration and the total neutrophil count
(P = 0.01, n = 14) and the
neutrophil percent (P = 0.01, n
= 14), as well as between the BALF GM-CSF concentration and the
neutrophil percent (P = 0.05, n
= 14).
|
had
no significant effect. Combinations of anti-cytokine Abs did not
further enhance PMN apoptosis (data not shown). By contrast,
anti-GM-CSF and anti-G-CSF Abs inhibited 15 to 40% and 34 to 63% of
the BALF anti-apoptotic activity, respectively, with an additive effect
of the two Abs used in combination (Figure 7)
|
To confirm observations with the A549 cell line, we used tumor
cells directly derived from the lung tumor of a patient with BAC (BAC
cells). As shown in Figures 8 and 9
, results with BAC cells were similar to
those obtained with A549 cells (Figures 3 and 4)
. First, the proportion
of apoptotic PMNs fell significantly from 82 ± 3% with BAC-CM to
20 ± 6% (P < 0.01) and 18 ± 6%
(P < 0.01) with cell-free supernatants from BAC
cells exposed to PBMC-CM and AM-CM, respectively. Second, neutralizing
Abs against GM-CSF and G-CSF significantly inhibited the anti-apoptotic
activity of cell-free supernatants from BAC cells exposed to PBMC-CM or
AM-CM, with an additive effect of the two Abs used in combination,
whereas neutralizing Abs against IL-8 had a significant effect only on
the cell-free supernatant of BAC cells exposed to AM-CM (Figure 9)
.
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To determine the cellular origin of GM-CSF and G-CSF in the tumor
environment in vivo, we performed an immunohistochemical
study of both tumoral and adjacent normal lung tissue (Figure 10)
. The results obtained with three
different specimens were similar. Tumor cells strongly expressed GM-CSF
(+++), whereas interstitial mononuclear cells (++), AMs (++), and
resident cells (++) expressed it less intensely. G-CSF was also
strongly expressed by tumor cells and less intensely by interstitial
mononuclear cells (++) and AMs (++) but not by resident cells. The
expression of the two cytokines was homogenous and cytoplasmic. In
normal lung tissue distant from the tumor, GM-CSF was also expressed by
normal epithelial cells (++) and interstitial mononuclear cells (+),
whereas G-CSF was only expressed by bronchiolar cells (+).
|
| Discussion |
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.21,23-26
All
these cytokines were present in patients BALF, whereas only G-CSF (at
a significantly lower concentration) was found in controls.
Importantly, G-CSF and GM-CSF concentrations in patients correlated
with the intensity of neutrophil alveolitis, and GM-CSF concentrations
also correlated with neutrophil anti-apoptotic activity. Both GM-CSF
and G-CSF seem to be involved in the anti-apoptotic effect, because Abs
against the two cytokines significantly and independently inhibited
BALF supernatant anti-apoptotic activity. Our use of peripheral blood
neutrophils instead of alveolar neutrophils could limit the in
vivo relevance of these findings. Indeed, endothelial
transmigration by neutrophils could modulate their sensitivity to
apoptosis, through adhesion molecule engagement.27
We thus
counted apoptotic alveolar neutrophils in BALF cytospin preparations
from patients with BAC. Interestingly, we found a negative
correlation between the degree of alveolar neutrophil apoptosis
and that of neutrophil alveolitis, suggesting that an alteration of
programmed neutrophil death might contribute to the persistence of
neutrophil alveolitis in vivo. In an attempt to mimic the tumor environment and identify the respective roles of tumor cells and inflammatory cells in the prolongation of neutrophil survival, we tested the effect of A549 cell-derived cytokines in vitro on the 24-hour spontaneous apoptosis of peripheral blood neutrophils after culturing A549 cells under basal conditions and with media conditioned by several types of inflammatory cells. Although A549 cells constitutively released several of the anti-apoptotic cytokines tested (G-CSF, IL-8, and IL-6), A549 cell CM obtained under basal conditions did not prevent neutrophil apoptosis. By contrast, CM of A549 cells exposed to inflammatory cells (PBMCs and AMs) inhibited 24-hour spontaneous neutrophil apoptosis by 68% and 78%, respectively. This phenomenon was also observed when primary culture of BAC cells directly derived from lung tumors was used instead of the long-term established A549 cell line. Media directly conditioned by PBMCs and AMs also had anti-apoptotic activity, but less than tumor cells.
As in in vivo experiments, only tumor-derived GM-CSF and
G-CSF were clearly involved in the in vitro prolongation of
neutrophil survival. IL-8 had an additive effect on GM-CSF in the AM
model but was released by AMs and not by tumor cells. Moreover, the
similar pattern of results obtained with A549 cells and primary
cultured BAC cells directly derived from lung tumor, as well as with
patients BALF supernatants, strongly supports the in vivo
relevance of our in vitro findings. Unlike Daffern and
colleagues,28
we found that IL-6 did not contribute to the
anti-apoptotic activity of tumor epithelial cells. However, these
latter authors used nasal-derived primary epithelial cells previously
stimulated by high concentrations of recombinant
TNF-
.28
In the same way, IL-1ß and TNF-
did not
play a role in neutrophil survival in our study, but these cytokines
were not produced by the A549 cell line whatever the stimulus used. By
contrast, we showed that PBMCs and AMs derived IL-1ß and TNF-
contribute to the release of neutrophil anti-apoptotic factors (GM-CSF
and G-CSF) by tumor epithelial cells, as previously suggested by other
studies.28-30
Furthermore, TNF-
up-regulation of
GM-CSF receptor expression on PMNs might also indirectly contribute to
this phenomenon.31
Finally, the fact that anti-GM-CSF and
anti-G-CSF Abs did not completely abrogate the anti-apoptotic effect of
tumor cell CM suggests that cytokines or soluble factors not studied
here could partly explain our findings.21,28
To examine the respective roles of tumor cells and tumor-infiltrating
inflammatory cells in the production of anti-apoptotic factors in
vivo, we then evaluated G-CSF and GM-CSF protein expression in
specimens of tumorous and distant normal pulmonary tissue from patients
with BAC. We observed strong expression of both cytokines by tumor
cells. GM-CSF, but not G-CSF, was strongly expressed by the
tumor-associated stroma reaction thickening the tumor alveolar wall. In
distant normal lung tissue, GM-CSF was detected in epithelial cells as
well as in monocytes/macrophages, fibroblasts, and endothelial cells,
whereas G-CSF was only detected in bronchial cells. However,
immunostaining of these two cytokines was less intense in distant
normal lung than in tumoral areas. The accumulation of GM-CSF and G-CSF
in tumoral areas, demonstrated by immunochemical studies and BALF
cytokine measurements, suggest a possible up-regulation of GM-CSF and
G-CSF production by the tumor microenvironment. Our in vitro
results support the hypothesis that mononuclear cells such as AMs and
PBMCs, which have close contacts with tumor cells in
vivo,11,13
might contribute to this cells
previously reported paracrine feedback loop between tumoral and
inflammatory.32-35
It is also reasonable to suppose that
mononuclear cell-derived TNF-
and IL1-ß influence GM-CSF and G-CSF
production by tumoral epithelia in vivo.
Although the mechanisms by which neutrophils influence the prognosis of BAC is unclear, it has been postulated that the persistence of neutrophil alveolitis would result in persistent release of proinflammatory mediators such as cytokines, proteases, and reactive oxygen and nitrogen species that can damage DNA and activate oncogenes.36,37 We have also previously postulated that neutrophils might be involved in luminal tumor spread by promoting tumor cell shedding.11 In addition, GM-CSF itself could be involved in tumor progression through its proliferative effect on type II alveolar epithelial cells, possible precursors of BAC.38,39 Lastly, in vivo alterations of phlogistic phagocytic clearance of apoptotic neutrophils also results in a lack of release of anti-inflammatory mediators such as transforming growth factor-ß,40,41 which functions as a classic tumor suppressor.42
In conclusion, we demonstrate that the BAC tumor microenvironment generates local conditions that prolong alveolar neutrophil survival through the production of soluble factors, and thereby contributes to the persistence of the deleterious neutrophil alveolitis observed in this setting. We also provide additional evidence of possible cooperation between tumor and inflammatory cells in tumor progression, possibly warranting clinical trials of local anti-inflammatory adjuvant therapy.
| Footnotes |
|---|
Supported by grants from "Pneumologie developpement" and "La Ligue Nationale contre le cancerComite de Paris."
M. Wislez is a doctoral fellow of "LAcadémie de Médecine" and "Les Fonds dEtude et de Recherche du Corps Médical des Hôpitaux de Paris"
Accepted for publication July 9, 2001.
| References |
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