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CUTTING EDGE |


*
Department of Immunology, Max-Planck-Institute for Infection Biology, Berlin, Germany;
Microscopy Unit, Max-Planck-Institute for Infection Biology, Berlin, Germany;
Department of Cell Biology and Immunology, Faculty of Medicine, Vrije Universiteit, Amsterdam, The Netherlands;
§
Department of Internal Medicine, University of Saarland, Homburg, Germany; and
¶
Department of Bacteriology, Nara Medical University, Nara, Japan
| Abstract |
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| Introduction |
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14 and J
281 gene segments
preferentially associated with TCRVß8.2 (1). The
development of V
14+NKT cells depends on CD1d
expressed on CD4+8+
cortical thymocytes (1, 2, 3, 4).
V
14+NKT cells encompass
CD4+ and
CD4-8- cell populations
and are prominent in the liver compared with other organs (5, 6). Evidence has accumulated that the thymus is essential for
the development of V
14+NKT cells (1, 6, 7, 8, 9, 10, 11, 12). LFA-1 (CD11a/CD18) is a cell adhesion molecule that mediates adhesion to various cells expressing their ligands, ICAM-1 (CD54) and ICAM-2 (CD102) (13). LFA-1/ICAM interactions play a crucial role in leukocyte recirculation and migration (13). LFA-1 is expressed on most leukocytes including NK cells and NKT cells (1, 13, 14, 15). In the liver, LFA-1 is also expressed on sinusoidal lining cells such as Kupffer cells (16, 17).
We have previously shown that LFA-1 plays a crucial role in the homing of thymic CD4+NKT cells to the liver (17). However, it remained elusive which cell type expressing LFA-1 participates in the homing of thymic CD4+NKT cells to the liver. The data presented here point to NK cells in the liver as a major cell population that directs thymic CD4+NKT cells to the liver.
| Materials and Methods |
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C57BL/6 scid/scid (SCID) mice were purchased from The Jackson Laboratory (Bar Harbor, ME). LFA-1-/- mice were generated as described previously (18). LFA-1-/- mice backcrossed onto C57BL/6 mice (more than three generations), SCID mice, and C57BL/6 mice were maintained under specific pathogen-free conditions, and female mice were used at 810 wk of age.
Antibodies
Anti-Fc
R mAb (2.4G2), anti-NK1.1 mAb (PK136),
anti-CD4 mAb (YTS191.1), anti-CD3
mAb (145-2C11), and
anti-F4/80 mAb (CI A31) were purified from hybridoma culture
supernatants. Anti-NK1.1 mAb was biotinylated, and anti-CD4 mAb and
anti-CD3 mAb were conjugated with FITC by standard methods.
PE-anti-CD4 mAb (H129.19) and streptavidin
(SA)4-Red 670 were
purchased from Life Technologies (Gaithersburg, MD).
FITC-anti-ICAM-2 mAb (3C4), biotin-anti-NK1.1 mAb (PK136),
FITC-anti-TCR
ß mAb (H57-597), and FITC-anti-rabbit IgG
were obtained from PharMingen (Hamburg, Germany). Anti-asialo GM1 Ab
and rabbit IgG were purchased from Wako Chemicals (Neuss, Germany) and
Sigma-Aldrich (Schnelldorf, Germany), respectively. Cy2-anti-rat
IgG was obtained from Jackson ImmunoResearch (West Grove, PA).
Cell preparation and flow cytometry
Liver mononuclear cells (LMNC) and intestinal intraepithelial
lymphocytes were prepared as described previously (6).
Lymphoid cells from other organs were prepared by conventional methods.
After blocking with anti-Fc
R mAb, cells were stained with
conjugated mAbs, and biotin-mAbs were visualized with SA-Red 670. After
staining, cells were washed and subsequently fixed with 1%
paraformaldehyde. Stained cells were acquired by FACScan (Becton
Dickinson, Mountain View, CA), and small lymphoid cells were analyzed
with CellQuest software (Becton Dickinson).
In vivo depletion of Kupffer cells or NK cells
Multilamellar liposome-encapsulated dichloromethylene bisphosphonate (Cl2MBP-L) was prepared as described previously (19). Cl2MBP was a gift from Boehringer Mannheim (Mannheim, Germany). To deplete Kupffer cells, mice were injected i.v. with 200 µl of Cl2MBP-L (containing 1 mg of Cl2MBP) suspended in PBS as described previously (19). As a control, mice were injected i.v. with 200 µl of liposome-encapsulated PBS (PBS-L). To deplete NK cells, mice were injected i.p. with 5 mg of anti-asialo GM1 Ab. Rabbit IgG was used as a control. Kupffer cell- or NK cell-depleted SCID mice, as well as control SCID mice, were fed water containing antibiotics throughout the experiment.
Detection of Kupffer cells
SCID mice were treated with Cl2MBP-L or PBS-L as described above, and 3 days later livers were collected. Liver cryosections were stained with anti-F4/80 mAb followed by Cy2-anti-rat IgG. In Cl2MBP-L-treated mice, Kupffer cells were depleted by 90100%.
Thymocyte reconstitution
SCID mice were reconstituted i.v. with 3 x 107 thymocytes. LMNC as well as lymphoid cells from other organs of recipients were prepared after reconstitution, and the proportion of CD4+NKT cells in recipients was analyzed by flow cytometry.
| Results |
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SCID mice were reconstituted with thymocytes from C57BL/6 mice,
and the appearance of donor CD4+NKT cells in the
liver of recipients was monitored by microfluorometry. A small
population of CD4+NK1+
cells was identified in the liver of SCID mice before reconstitution
(Fig. 1
A), although these
cells did not express TCR (data not shown). A distinct population of
CD4+NK1+ cells was
identified in the liver of recipients on day 3 after reconstitution,
and the proportion remained virtually unchanged until day 7 (Fig. 1
A). Recovery numbers of LMNC were comparable on days 3, 5,
and 7 after reconstitution. A vast majority of
CD4+NK1+ cells in the liver
of recipients expressed TCR
ß, but not TCR
(data not shown).
Thus, donor thymocyte-derived CD4+NKT cells
accumulated in the liver of recipients by day 3 after reconstitution.
We next examined the tissue distribution of donor thymocyte-derived
CD4+NKT cells in recipients on day 3 after
reconstitution. The accumulation of donor CD4+NKT
cells in recipients was prominent in the liver, scarce in the spleen,
and no accumulation was found in other organs analyzed (Fig. 1
B). These results indicate that thymic
CD4+NKT cells preferentially home to the
liver.
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SCID mice were reconstituted with thymocytes from
LFA-1-/- or C57BL/6 mice, and the presence of
donor CD4+NKT cells in the liver of recipients
was assessed on day 3 after reconstitution. Numbers of donor
CD4+NKT cells in the liver of recipients were
increased regardless of the origin of thymocytes used for
reconstitution, although the accumulation efficacy of
CD4+NKT cells from
LFA-1-/- donors was slightly higher compared
with that from C57BL/6 donors (Fig. 2
).
This was probably due to a dilution effect because
CD4+8+ thymocytes from
C57BL/6 mice accumulated more efficiently in the liver of recipients
than those from LFA-1-/- mice (data not shown).
These results indicate that homing of thymic
CD4+NKT cells to the liver occurs independently
of LFA-1 expression on these cells. It appears more likely that LFA-1
on liver cells directs CD4+NKT cells to this
organ.
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Because Kupffer cells express LFA-1 (16, 17), we
asked whether LFA-1 on Kupffer cells participates in the homing of
thymic CD4+NKT cells to the liver. To address
this issue, Cl2MBP-L was employed to deplete
Kupffer cells in vivo (19). SCID mice were injected with
Cl2MBP-L, and 3 days later the depletion of
Kupffer cells was assessed by immunohistochemical procedure using
anti-F4/80 mAb. Consistent with previous findings
(19), Kupffer cells became undetectable on day 3 after
Cl2MBP-L treatment (data not shown). No
measurable alterations were found in LMNC by
Cl2MBP-L treatment (data not shown). We then
assessed the consequences of Kupffer cell depletion on homing of thymic
CD4+NKT cells to the liver. SCID mice were
injected with Cl2MBP-L, reconstituted with
thymocytes from C57BL/6 mice, and the proportion of donor
CD4+NKT cells in the liver of recipients was
assessed on day 3 after reconstitution. The proportion of
CD4+NKT cells in the liver of recipients was
comparable among Cl2MBP-L-, PBS-L-, or
PBS-treated groups (Fig. 3
). These
results suggest that Kupffer cells are not essential for the homing of
thymic CD4+NKT cells to the liver.
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NK cells are abundant in the liver and express high levels of
LFA-1 (14). Therefore, we wondered whether LFA-1 on NK
cells plays a role in the homing of thymic
CD4+NKT cells to the liver. Consistent with
previous findings (20, 21), a vast majority of liver NK
(CD3-NK1+) cells expressed
high levels of asialo GM1 on their surface, whereas asialo GM1 was not
expressed on conventional CD4+T cells (Fig. 4
). Asialo GM1 was marginally expressed
on CD4+NKT cells (Fig. 4
). Accordingly, most
liver NK (CD3-NK1+) cells
were depleted on day 3 after anti-asialo GM1 Ab treatment (Fig. 5
), whereas the frequency of
CD4+NKT cells remained virtually unaffected (Fig. 5
). Selective depletion of NK cells, but not NKT cells, by
anti-asialo GM1 Ab treatment is consistent with findings by others
(22). Administration of rabbit IgG did not affect any of
these cell populations, thus excluding nonspecific effects (Fig. 5
).
These results suggest that NK cells are not essential for the
persistence of CD4+NKT cells in the liver.
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| Discussion |
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The number of NKT cells in the liver was markedly reduced in LFA-1-/- mice compared with C57BL/6 mice (15, 25). This reduction was restricted to the liver only, and no measurable alterations were found in other organs. A small, but distinct population of NKT cells was detectable in the liver of LFA-1-/- mice, and the proportion in the liver was comparable to that in the spleen (15, 25). These findings not only imply that the homing of a vast majority of NKT cells to the liver is LFA-1 dependent, but also suggest that the homing of a small population of NKT cells to the liver, and of virtually all NKT cells to other peripheral lymphoid organs such as spleen, is LFA-1 independent. Recent studies have indicated control of NK cells by NKT cells (26, 27). Taken together with our findings, the picture of a bidirectional cross-talk between NK cells and NKT cells emerges.
The number of CD4+NKT cells was slightly reduced in the liver of ICAM-1-/- mice compared with C57BL/6 mice (15). In addition to ICAM-1, ICAM-2 is also a ligand for LFA-1 in the mouse (13). Because CD4+NKT cells also expressed ICAM-2 (M. Miyamoto and M. Emoto, unpublished observation), LFA-1/ICAM-2 interactions could also participate in homing. Further studies are aimed at clarifying the role of ICAM-2 in the homing of CD4+NKT cells to the liver.
In summary, our data reveal a possible contribution of NK cells to the homing of thymic CD4+NKT cells to the liver. Because NK cells express high levels of LFA-1, we consider LFA-1 expression on NK cells critical.
| Acknowledgments |
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| Footnotes |
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2 M.M. and M.E. contributed equally to this work. ![]()
3 Address correspondence and reprint requests to Dr. Stefan H. E. Kaufmann, Department of Immunology, Max-Planck-Institute for Infection Biology, Monbijoustrasse 2, 10117 Berlin, Germany. ![]()
4 Abbreviations used in this paper: SA, streptavidin; LMNC, liver mononuclear cells; Cl2MBP-L, multilamellar liposome-encapsulated dichloromethylene bisphosphonate; PBS-L, liposome-encapsulated PBS. ![]()
Received for publication March 7, 2000. Accepted for publication June 12, 2000.
| References |
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ßTCR+NK1.1+ cells. J. Immunol. 145:3209.[Abstract]
ß+ thymocytes. J. Immunol. 146:1113.[Abstract]
/ß+ thymocytes associated with intact thymic structure. Proc. Natl. Acad. Sci. USA 94:2472.
14+ natural killer-T cell development. Eur. J. Immunol. 29:3313.[Medline]
ß+ cell development: evidence that liver NK1.1+TCR
ß+ cells originate from multiple pathways. J. Immunol. 162:3753.This article has been cited by other articles:
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