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Cutting Edge |

* Center for Immunology and Inflammatory Diseases, Division of Rheumatology, Allergy and Immunology and
Pulmonary and Critical Care Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114
| Abstract |
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i-coupled chemoattractant
receptors. We show here that in contrast to untreated Th2 cells,
pertussis toxin-treated Th2 cells were unable to traffic into the lung,
airways, or lymph nodes following Ag challenge and therefore were
unable to induce allergic inflammation in vivo. Pertussis toxin-treated
Th2 cells were functional cells, however, and when directly instilled
into the airways of mice, bypassing their need to traffic to the lung,
were able to induce airway eosinophilic inflammation. These
studies conclusively demonstrate that trafficking of Th2 cells into the
lung is an active process dependent on chemoattractant
receptors. | Introduction |
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Th2 cells have been shown to preferentially express the chemokine receptors CCR3, CCR4, CCR8, and the PGD2 receptor CRTH2, while Th1 cells preferentially express CCR5, CXCR3, CXCR6, and CX3CR1 (2). This has led into the speculation that selective chemokine receptor expression on Th2 cells may enable these cells to preferentially migrate to the sites of inflammation in response to locally produced chemokines. However, targeted deletion of CCR3, CCR4, and CCR8 have not ablated Th2 cell trafficking in vivo, leaving the question open as to whether chemoattractant receptors expressed on Th2 cells control their trafficking in vivo (3, 4, 5)
We have recently shown that Stat6 expression in the lung plays a critical role in Th2 cell recruitment and Th2-type chemokine expression in allergic pulmonary inflammation (6). We have speculated that Th2 cell trafficking to the lung is dependent on the expression of Stat6-inducible chemokines by resident cells in the lung, implying that chemoattractant receptor activation on Th2 cells is responsible for their trafficking to the allergic lung. However, since other Stat6-inducible genes may also play a role in this process, we have not conclusively proven that Th2 cell trafficking into the lung is dependent on Stat6-inducible chemokine activation of chemoattractant receptors expressed on Th2 cells.
To determine whether chemoattractant receptor activation is required
for Th2 cell trafficking into the lung, we pretreated Ag-specific Th2
cells with pertussis toxin
(PTX),3 a known
inhibitor of G
i-coupled chemoattractant receptor-induced chemotaxis
(7). We found that PTX-Th2 cells were unable to traffic
into the lung in response to Ag challenge. PTX-Th2 cells were fully
capable of secreting IL-4 and IL-5 however and were able to induce
airway eosinophilic inflammation following Ag challenge
when instilled directly into the airways. These studies demonstrate
that chemoattractant receptors mediate the trafficking of Th2 cells
into the lung during allergic inflammation.
| Materials and Methods |
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CD4 T cells were isolated from spleen and pooled lymph nodes
(LNs) of D011.10 mice and activated in the presence of mitomycin
C-treated BALB/c splenocytes (APCs), OVA peptide 323339 (OVAp), IL-4,
anti-IFN-
(R46A2), and anti-CD28 as previously described
(6). On day 5, Th2 cells were resuspended at 4 x
105 cells/ml and treated with PTX (100 ng/ml) for
24 h. An aliquot of cells was retained for FACS analysis, cytokine
secretion, and proliferation assays. For cytokine secretion, 1 x
106 Th2 or PTX-Th2 cells and 2 x
106 freshly isolated APCs were cultured with OVAp
(1 µg/ml) in 24-well plates. Supernatants were collected at 2448 h
after stimulation for ELISA. For the proliferation assays, indicated
numbers of T cells were incubated with 2 x
105 APCs and 1 µg/ml OVAp in 96-well plates.
Wells were pulsed with 1 µCi [3H]TdR for
18 h on day 2 and was harvested on day 3, and
[3H]TdR incorporation counted using a liquid
scintillation counter.
Transfer of Th2 cells and OVA challenges
Th2 cells or PTX-Th2 cells were harvested on day 6, washed twice in PBS, and 5 x 106 cells were injected i.v., using the tail vein, into BALB/c recipients. Mice were aerosol challenged for 20 min daily for 4 days with a 5% OVA solution using a nebulizer (Pulmo Aide; DeVil Biss, Somerset, PA). For the intratracheal instillations, mice were anesthetized, the trachea exposed, and 1 x 106 Th2 or PTX-Th2 cells in 80 µl of PBS were instilled directly into the trachea. The wound was closed using a 9-mm wound clip (Roboz Surgical Instruments, Rockville, MD) and removed before performing bronchoalveolar lavage (BAL). Mice were rested for a day and OVA aerosol-challenged for 20 min daily for 3 days.
BAL and lymphocyte isolation from organs
BAL was performed 1824 h after the last aerosol challenge as described elsewhere (6). Lungs were minced and resuspended in PBS with 10% FBS, 850 U/ml hyaluronidase, and 150 U/ml collagenase A for 1 h at 25°C. Lymphocytes were obtained from the lung, LNs, and spleens following passage through a cell strainer and RBC lysis.
Cytokine assays
Levels of IL-4 and IL-5 were measured by ELISA (Endogen, Woburn, MA).
Flow cytometry and histology
Cell suspensions from organs were analyzed by two-color flow cytometry using anti-CD4 PE, anti-LFA-1 PE, anti-very late activation Ag 4 (VLA-4) PE (BD PharMingen, San Diego, CA), and anti-KJ126 FITC (Caltag Laboratories, Burlingame, CA), an Ab specific for the transgenic TCR in the D011.10 mice. The total number of KJ+ cells was calculated by multiplying the (percent KJ+ cells in the lymphocyte gate)/(total number of lymphocytes obtained from each of the organs). Lungs were harvested and inflation fixed to total lung capacity in 10% Formalin. Formalin-preserved lung tissue was stained with H&E or diastase periodic acid-Schiff stain.
Chemotaxis assays
Th2 or PTX-Th2 (treated with PTX for 2 h) cells were added (2.5 x 104 in 25 µl of RPMI 1640/1%BSA) into upper wells of a 5-µm filter 96-well ChemoTx plate (NeuroProbe, Gaithersburg, MD). Indicated concentrations of murine chemokines (PeproTech, Rocky Hill, NJ) were added in the bottom chamber in 31 µl of RPMI 1640/1% BSA. The plate was incubated for 1.5 h at 37°C in 5% CO2 and cells that migrated into the lower chamber were enumerated using a hemocytometer.
Statistical analysis
Students t test (unpaired, two tailed) was used to calculate significance levels for all measurements. A p < 0.05 was considered to be statistically significant.
| Results |
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To ensure that PTX treatment did not alter other functions of Th2
cells, we compared cytokine secretion, in vitro proliferation and cell
surface expression of key receptors on untreated Th2 and PTX-Th2 cells.
We found that 3 days of PTX treatment did not alter the viability,
secretion of IL-4 and IL-5, and did not affect Ag-induced proliferation
(Fig. 1
, A and B).
Since integrins are known to be involved in cell migration, we also
examined cell surface expression of LFA-1 and VLA-4 on Th2 and PTX-Th2
cells and found no differences between the two groups (Fig. 1
C). OVA-specific TCR (KJ) as well as CD4 staining were also
unchanged following PTX treatment. However, PTX treatment inhibited
chemotaxis of Th2 cells to stromal cell-derived factor 1
SDF-1
/CXCL12 as well as macrophage-derived chemokine MDC/CCL (Fig. 1
D). These results indicate that PTX treatment did not alter
IL-4 and IL-5 secretion, Ag-induced proliferation, and cell surface
expression of LFA-1, VLA-4, CD4, and the OVA-specific TCR but did
inhibit chemokine-induced chemotaxis of Th2 cells in vitro.
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To determine whether trafficking of Th2 cells into the lung is
chemoattractant dependent, we transferred 5 x
106 Th2 or PTX-Th2 cells by tail vein injection
followed by four OVA aerosol challenges (Th2-OVA vs
PTX-Th2-OVA). Twenty-four hours after the last challenge, mice
were sacrificed and BAL was performed. The total number of cells
recovered from the BAL of PTX-Th2-OVA mice were almost 10-fold reduced
compared with Th2-OVA mice (0.32 x 106 vs
2.26 x 106 cells) (Fig. 2
A). This is similar to mice
that did not receive adoptively transferred T cells but were subject to
full airway Ag challenge (data not shown). As expected, 6065% of the
cells in the BAL of Th2-OVA mice were eosinophils. In sharp
contrast, <5% of the cells were eosinophils in
PTX-Th2-OVA mice. The total number of macrophages and lymphocytes were
also significantly reduced in the BAL of PTX-Th2-OVA mice compared to
those of Th2-OVA mice. Histopathologic examination of lung tissue also
revealed a dramatic decrease in overall inflammation and goblet cell
mucus production in PTX-Th2-OVA mice compared with Th2-OVA mice (Fig. 2
B). Therefore, PTX treatment of Th2 lymphocytes prevented
the development of eosinophilic inflammation and goblet
cell mucus production in the airways and lungs of mice following
adoptive transfer and Ag challenge.
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To determine whether the lack of eosinophilic
inflammation in the BAL of PTX-Th2-OVA mice was due to the inability of
the PTX-Th2 cells to traffic to the sites of Ag challenge, we
analyzed the BAL, lung, paratracheal LNs (PLNs), spleen, blood, and
inguinal LNs (ILNs) for transferred lymphocytes using flow cytometry.
Although we were able to detect KJ+ cells in the BAL and
lungs of mice following Th2 cell transfer and OVA challenge, the number
of KJ+ cells recovered from mice that received PTX-Th2
cells were 10-fold reduced in the lung and almost 100-fold in the BAL
(Fig. 3F
3). PTX-Th2 cells were also detected at significantly lower
levels in the PLNs (20-fold) and ILNs (5-fold) with equivalent numbers
of transferred cells in the spleen (Fig. 3
) and blood (data not shown).
These results demonstrate that PTX treatment prevented the migration of
Th2 cells to sites of Ag challenge, including the BAL, lungs, as well
as secondary LNs, while accumulation of cells in the spleen and blood
were not altered.
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To demonstrate that PTX-Th2 cells were capable of inducing
eosinophilic inflammation in vivo, we directly instilled
Th2 or PTX-Th2 cells into the trachea of mice, thereby bypassing the
need for these cells to traffic into the BAL following aerosol
challenge. We speculated that both Th2 and PTX-Th2 cells should be able
to secrete cytokines, such as IL-4, IL-5, and IL-13, when stimulated
with Ag in vivo and induce allergic inflammation in the BAL. Following
intratracheal instillation and OVA aerosol challenges, mice that
received PTX-Th2 cells and Th2 cells were both able to develop
eosinophilic inflammation (Fig. 4
). In fact, mice that received PTX-Th2
cells intratracheally appeared to have more inflammatory cells in the
BAL following Ag challenge. Importantly, eosinophils and
KJ+ lymphocytes were detected in the airways to
the same extent in both groups. No eosinophils were
detected in BAL of mice following intratracheal instillation of Th2 or
PTX-Th2 cells with no OVA aerosol challenge (data not shown),
indicating that Th2 and PTX-Th2 cells required aerosol Ag activation.
These data clearly demonstrate that PTX-Th2 cells were functional Th2
cells in vivo because when directly instilled into the trachea
they were capable of inducing eosinophilic inflammation in
the airways following Ag-induced activation.
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| Discussion |
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i-coupled chemoattractant
receptors. We have previously demonstrated that Th2 lymphocyte recruitment into the lung and airways in allergic pulmonary inflammation is dependent on Stat6 expression in resident cells of the lung. Interestingly, in these mice, the transferred Th2 cells were able to traffic into secondary LNs, suggesting that Th2 trafficking into LNs is not dependent on Stat6-inducible chemokines (6). Taken together, our studies suggest that trafficking of Th2 cells into lung, airways, and LNs is dependent on chemoattractant receptor activation but trafficking of these cells into the lung and LNs is differentially regulated. Trafficking into the lung and airways is dependent on Stat6-inducible chemokines, while trafficking into LNs is independent of Stat6 but dependent on a different subset of chemokines.
Our intratracheal transfer experiments clearly demonstrated that
PTX-Th2 cells were functional Th2 cells as they were able to recruit
eosinophils into the BAL in vivo. The moderate inflammatory
response in comparison to the i.v. transfer of Th2 cells (Figs. 2
and 4
) is likely due to our inability to detect intratracheally transferred
Th2 cells in any other organs following Ag challenge (data not shown).
Although we believe that recruitment of Th2 cells into the lung is a
key early step that is essential for chemokine secretion by resident
parenchymal cells and subsequent amplification of the inflammatory
response, our data also suggest that the trafficking of effector Th2
cells into and out of LNs plays an important role in amplifying
allergic inflammation in the airways. It is also interesting to note
that dendritic cells have been shown to migrate into draining LNs
following intratracheal transfer (11), implying
differences in the ability of Th2 cells and dendritic cells to cross
the airway epithelial barrier.
In conclusion, our data demonstrate that trafficking of Th2 cells into the lung, airways, and LNs in allergic pulmonary inflammation requires the involvement of functional chemoattractant receptors expressed on Th2 cells and as such represent attractive targets for asthma therapy.
| Footnotes |
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2 Address correspondence and reprint requests to Dr. Andrew D. Luster, Center for Immunology and Inflammatory Diseases, 8th Floor, Massachusetts General Hospital, Building 149, 13th Street, Charlestown, MA 02129. E-mail address: luster{at}helix.mgh.harvard.edu ![]()
3 Abbreviations used in this paper: PTX, pertussis toxin; AHR, airways hyperresponsiveness; OVAp, OVA peptide 323339; BAL, bronchoalveolar lavage; LN, lymph node; PLN, paratracheal LN; ILN, inguinal LN; VLA-4, very late activation Ag 4. ![]()
Received for publication March 8, 2002. Accepted for publication May 15, 2002.
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