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on Neutrophils Mediated by CCR11



*
Department of Microbiology and Immunology and Walther Oncology Center, Indiana University School of Medicine, and the Walther Cancer Institute, Indianapolis, IN 46202,
Laboratory of Host Defenses, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892; and
Department of Biological Sciences and the Immunomodulation Research Center, University of Ulsan, Ulsan, Korea
| Abstract |
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(hMIP-1
) and
eotaxin, which also use the CCR1 and CCR3 as their receptors. In this
report, we demonstrate that while hMIP-1
induced a negligible level
of calcium flux and chemotaxis, Lkn-1 produced a high level of calcium
flux and chemotaxis in human neutrophils. Lkn-1 cross-desensitized
hMIP-1
-induced calcium flux, but hMIP-1
had little effect on the
Lkn-1-induced response in human neutrophils. The same pattern was
observed in peritoneal neutrophils from wild-type mice, whereas
neutrophils from CCR1-/- mice failed to respond to either
MIP-1
or Lkn-1. Scatchard analysis revealed a single class of
receptor for both hMIP-1
and Lkn-1 on human neutrophils with
dissociation constants (Kd) of 3.2 nM and
1.1 nM, respectively. We conclude that CCR1 is a receptor mediating
responses to both MIP-1
and Lkn-1 on neutrophils and produces
different biological responses depending on the ligand
bound. | Introduction |
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), CC(ß), C(
), and CX3C (1, 2, 3). CXC chemokines
act primarily on neutrophils, but show some activity on T lymphocytes
(4, 5, 6, 7). CC chemokines function on monocytes, basophils, eosinophils, T
lymphocytes, NK cells, and dendritic cells but usually do not affect
neutrophils (4, 5, 6, 7, 8, 9, 10). The only known C chemokine is active on T
lymphocytes and NK cells (11, 12). Soluble CX3C chemokine
stimulates chemotaxis of T cells and monocytes. The membrane-bound form
of CX3C, which is induced on activated primary endothelial
cells, promotes strong adhesion of those leukocytes (3).
Leukotactin-1 (Lkn-1),4 a
recently described CC chemokine, contains two extra cysteines. Lkn-1
binds to both CCR1 and CCR3 and induces chemotaxis and calcium flux in
human neutrophils, monocytes, and lymphocytes (13) as well as
eosinophils (S.M.Z. and B.S.K., unpublished observations). Purified
rLkn-1 exhibited a site-specific cleavage and was 24 amino acids
shorter than intact Lkn-1, which consists of 92 amino acids. Chemotaxis
of neutrophils distinguishes Lkn-1 from other CCR1 agonists such as
human macrophage inflammatory protein-1
(hMIP-1
). MIP-5/HCC2, a
synthetic chemokine, has the same amino acid sequence as cleaved Lkn-1.
MIP-5/HCC2, a truncated form of Lkn-1, was reported to be an agonist
for CCR1 and CCR3 and to stimulate the chemotaxis of monocytes,
lymphocytes, and eosinophils but not neutrophils (14). In the present
study, we examined the mechanism of neutrophil migration by Lkn-1.
| Materials and Methods |
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His-tagged rLkn-1 containing an additional six His at the C
terminus was purified from Escherichia coli using an
activated nickel column (Novagen, Madison, WI) followed by a
heparin agarose column (Pharmacia, Piscataway, NJ) as previously
described (13, 15). The purified rLkn-1 migrated as a single band of
12 kDa on SDS-PAGE. This form of rLkn-1 is called an intact
form of rLkn-1 (rLkn-1i) (Fig. 1
). rLkn-1
was also produced in the High Five insect cell line (Invitrogen, San
Diego, CA) grown in EX-cell 400 medium (JRH Biosciences, Lenexa,
KS). rLkn-1 was purified from culture media by heparin and
HiTrap-SP columns (Pharmacia) (13). Fractions that showed a single band
of
9 kDa on SDS-PAGE were pooled. The N-terminal sequencing of
purified rLkn-1 revealed that it was 24 amino acids shorter than intact
rLkn-1, which was named cleaved rLkn-1 (rLkn-1c). Purified rLkn-1i and
rLkn-1c were dialysed against PBS (Life Technologies, Grand Island,
NY) then analyzed by immunoblotting with rabbit polyclonal
anti-Lkn-1 (13). Endotoxins in the rLkn-1 preparation were removed
by Affi-prep polymyxin matrix (Bio-Rad, Hercules, CA) according
to the manufacturers instructions.
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Generation of CCR1-/- mice was previously described (16).
Cell preparation
Human PBMC and neutrophils were isolated from healthy donors as previously reported (13, 15). The purity of neutrophils was >95% as determined by microscopic examination after Diff-Quick (Baxter Scientific, McGaw Park, IL) staining. The few contaminating cells were mononuclear cells and eosinophils. To obtain enriched mouse neutrophils, the mouse peritoneal cavity was washed with PBS 3 h after peritoneal injection of thioglycollate. The purity of neutrophils was >90% as assessed by light microscopic examination of Diff-Quick-stained cytospin preparations (16).
In vitro migration analysis
Migration of cells was assessed in a 48-well microchamber
(Neuroprobe, Cabin John, MD) as previously described (13). Briefly, the
lower wells were filled with 27 µl buffer alone or with buffer
containing rLkn-1, IL-8, or hMIP-1
, and the upper wells were filled
with 50 µl of neutrophils in 1x HBSS (Life Technologies) at 1
x 106 cells/ml. The two compartments were separated by a
polyvinylpyrrolidone-free filter (Nucleopore; Neuroprobe) with 3-µm
pores. After incubation for 1 h at 37°C, the filters were
removed from the chamber, washed, fixed, and stained with Diff-Quick.
The cells of five randomly selected oil-immersion fields were counted.
The chemotactic index (CI) was calculated from the number of cells that
migrated to the test chemokines divided by the number of cells that
migrated to the control. Significant chemotaxis was defined as CI
> 2.
To confirm that all the chemotactic activity for neutrophils was due specifically to rLkn-1, we blocked the activity in vitro with affinity-purified anti-Lkn-1 polyclonal Abs. rLkn-1 (1000 ng/ml) or IL-8 (500 ng/ml) was preincubated with 10 µg/ml affinity-purified rabbit anti-Lkn-1 Abs or purified Ig fraction of rabbit preimmune serum as a control for 30 min at 37°C, then used in the chemotaxis assay described above.
rLkn-1-induced migration may be separated into chemotactic and chemokinetic components. The chemotactic component was determined by the addition of rLkn-1 (1000 ng/ml) to the lower wells only, and the chemokinetic component was determined by the addition of rLkn-1 (1000 ng/ml) to both the upper and lower wells.
Calcium flux assay
The calcium mobilization assay was performed as previously described (13, 15).
Receptor binding studies
Purified rLkn-1 and hMIP-1
(carrier-free, R & D
Systems, Minneapolis, MN) were labeled with 125I using
Iodo-beads iodination reagent (Pierce, Rockford, IL) according to the
manufacturers instructions. The specific activities of the labeled
rLkn-1 and hMIP-1
were
2 x 107 cpm/µg
protein. Human neutrophils, prepared as described above, were suspended
in DMEM supplemented with 10% FCS at a concentration of 2 x
107 cells/ml; 100 µl of the suspension was added to each
tube. The cells were incubated in the presence of various
concentrations of labeled rLkn-1 or hMIP-1
with 100-fold excess of
the corresponding unlabeled ligand or with medium (200 µl of total
reaction volume) at 4°C for 1 h with continuous rotation.
Incubation was terminated by centrifuging the cell suspension
over 1 ml of 10% sucrose (Sigma, St. Louis, MO) cushion. Cell pellets
were cut from the tubes, and cpm were counted.
In vivo activity
To test the in vivo chemotactic effects of rLkn-1, rLkn-1i was injected into the peritoneum of C3H mice at 0.5 µg in 0.5 ml PBS per mouse. Human serum albumin (HSA; Sigma), or PBS, was applied to Affi-prep polymyxin matrix columns to remove endotoxin, and then injected i.p. as a control (six mice/group). Two hours after injection, peritoneal exudate was collected and the total number of cells counted by hemocytometer. Leukocytes in three randomly selected oil-immersion fields were counted differentially after Diff-Quick staining.
| Results |
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or eotaxin, is a potent neutrophil
chemoattractant
We examined chemotaxis stimulated by the two forms of
rLkn-1, i.e., the intact form (rLkn-1i) and the cleaved form (rLkn-1c),
and compared the chemotaxis with hMIP-1
, eotaxin, and IL-8. Both
forms of rLkn-1 were chemotactic for neutrophils at concentrations from
100 to 1000 ng/ml. Maximum migration was reached with 1000 ng/ml Lkn-1i
(CI, 7.87 ± 0.18) or Lkn-1c (CI, 6.8 ± 0.12) and 100 ng/ml
IL-8 (CI, 8.43 ± 0.39) (Fig. 2
A). hMIP-1
failed to
induce significant chemotaxis of neutrophils (maximal CI of 1.97
± 0.20 at 1000 ng/ml, Fig. 2
A). Eotaxin was not able to
induce chemotaxis in neutrophils (data not shown). Anti-Lkn-1 Abs
neutralized almost all neutrophil chemotactic activity but did
not affect the chemotaxis of IL-8. Control rabbit Ig failed to
block the activity of rLkn-1 (Fig. 2
B). Moreover, a
checkerboard analysis (17) revealed that the migration-stimulating
effect of rLkn-1 was chemotactic in nature but not chemokinetic for
neutrophils (Fig. 2
C).
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share a neutrophil signaling pathway to
calcium mobilization
While Lkn-1 and hMIP-1
share certain properties such as
binding to CCR1 and suppression of colony formation by bone marrow
stem/progenitor cells, only Lkn-1 is chemotactic for neutrophils. We
then examined their receptor usage using a calcium flux assay. The two
forms of Lkn-1 induced calcium flux in neutrophils and fully
desensitized each other, which is consistent with the chemotaxis data
(Fig. 2
). Importantly, Lkn-1i completely desensitized the response of
neutrophils to 50 nM hMIP-1
. However, hMIP-1
failed to
desensitize the response of neutrophils to the same amount of rLkn-1i
(Fig. 3
A). The rLkn-1-induced
calcium flux in neutrophils was dose-dependent with a threshold <
5 nM (Fig. 3
B). hMIP-1
strongly induced calcium
mobilization in PBMC, demonstrating that the chemokine was active (data
not shown). These data suggest that rLkn-1 shares a signaling pathway
with hMIP-1
, but that rLkn-1 was a more potent inducer of calcium
mobilization than was hMIP-1
in human neutrophils.
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CCR1 mediates Lkn-1 action in mouse neutrophils
Lkn-1 is an agonist for human CCR1 and CCR3 (13), but as stated
above, neutrophils do not express CCR3 (19). We used neutrophils from
CCR1+/+ and CCR1-/- mice to assess the role
of CCR1 in Lkn-1 signaling. In neutrophils from CCR1+/+
mice, rLkn-1i was a potent inducer of calcium mobilization.
Cross-desensitization experiments demonstrated that rLkn-1i completely
desensitized the response of neutrophils to hMIP-1
, while hMIP-1
at 200 nM failed to abolish the calcium flux response to Lkn-1i in
mouse neutrophils (Fig. 4
A).
Notably, rLkn-1i did not affect FMLP-induced calcium flux (Sigma) in
neutrophils. In neutrophils from CCR1-/- mice, the
FMLP-induced signal was observed, but responses to hMIP-1
and
rLkn-1i were absent (Fig. 4
B). These results demonstrate
that CCR1 is a receptor for Lkn-1 and MIP-1
on mouse neutrophils.
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We next compared the binding properties of hMIP-1
and rLkn-1 to
human neutrophils. Scatchard analysis revealed a single class of
receptors for hMIP-1
and for rLkn-1 on human neutrophils with
Kd of
3.2 nM and 1.1 nM, respectively. These
data indicate that the receptor(s) shows different affinity for
hMIP-1
and rLkn-1 and that human neutrophils expressed receptors for
both Lkn-1 and hMIP-1
at a density of
2 x 104
binding sites per cell (Fig. 5
).
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We further tested whether rLkn-1 can attract neutrophils in vivo
because it induced chemotaxis in human neutrophils and calcium
mobilization in neutrophils from wild-type mice. Intraperitoneal
injection of rLkn-1i produced a remarkable increase in the total number
of peritoneal cells within 2 h, increasing in the number of
neutrophils from (0.23 ± 0.01) x 106 cells per mouse
injected with PBS or (0.46 ± 0.07) x 106 cells per
mouse injected with HSA, to (1.13 ± 0.14) x 106
cells per rLkn-1-injected mouse (Fig. 6
)
(p < 0.006, compared with HSA). The increase
in the number of neutrophils seen with HSA injection may indicate a
nonspecific recruitment of neutrophils in response to the foreign
protein. rLkn-1 injection also increases the number of monocytes and
lymphocytes (data not shown). These in vivo results support our
findings with human neutrophils in vitro.
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| Discussion |
|---|
|
|
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. McColl et al. (22) and Gao et
al. (23) found that hMIP-1
, which has
43% identity to Lkn-1 at
the amino acid level (13), was able to induce calcium flux in
neutrophils. However, McColl et al. observed no detectable effect on
chemotaxis (22), which agrees with the results presented in this
report. Lkn-1 elicited both calcium mobilization and chemotaxis in
human neutrophils (Figs. 2
stimulation was not adequate to activate a calcium-dependent
response such as chemotaxis (24). Interestingly, mouse MIP-1
,
unlike hMIP-1
, induces both chemotaxis and calcium mobilization by
signaling through CCR1 in mouse cells (16). CCR1 may play a more
important role in mouse neutrophils than human neutrophils to
compensate for the apparent absence of CXCR1 on mouse neutrophils
(16). However, the finding that human neutrophils lack expression of
CCR1 (25) is inconsistent with data from our and other labs (13, 15, 16, 18).
Both chemotaxis and calcium mobilization data (Figs. 2
and 3
)
indicated that an unidentified receptor specific for Lkn-1 may exist on
neutrophils or that Lkn-1 may have higher binding affinity than
hMIP-1
to CCR1 on human neutrophils. To determine whether there is
an unidentified receptor specific for Lkn-1 on neutrophils, we used
CCR1-deficient mice to examine whether Lkn-1 induced calcium
mobilization in CCR1-/- neutrophils. As shown in Fig. 4
B, CCR1 is the only class of receptor used to mediate
responses of murine neutrophils to hMIP-1
and Lkn-1. We next
compared the binding affinities between hMIP-1
and rLkn-1 in human
neutrophils. Scatchard analysis demonstrates that Lkn-1 has a higher
binding affinity than hMIP-1
to its receptor on human neutrophils,
but that both chemokines bind to receptors with a single affinity (Fig. 5
).
The structural difference between hMIP-1
and Lkn-1 may be
responsible for the difference of their biological effects. Lkn-1
contains two extra cysteines, which may form a third disulfide bond.
How this structural change may effect receptor interactions is unclear.
We are unable to explain the discrepancy between our data (13 and
this report) and the report where MIP-5/HCC2 was shown to be inactive
on human neutrophils (14). The observed differences in neutrophil
chemotaxis may be a result of different assay conditions for chemotaxis
or alternate methods of neutrophil isolation. In summary, we have
demonstrated that Lkn-1 is a strong chemoattractant for neutrophils by
both in vivo and in vitro assays. Our data supports that even though
hMIP-1
and Lkn-1 signal through CCR1 in neutrophils, only Lkn-1 is
chemotactic for neutrophils. The factors responsible for differential
sorting of receptor signals to effector functions remains to be
determined.
| Acknowledgments |
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| Footnotes |
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2 S.M.Z. and B.S.Y. contributed equally to this work. ![]()
3 Address correspondence and reprint requests to Dr. Byoung S. Kwon, Department of Microbiology and Immunology, Indiana University School of Medicine, 635 Barnhill Drive, Indianapolis, IN 46202-5120. E-mail address: ![]()
4 Abbreviations used in this paper: Lkn-1, leukotactin-1; hMIP-1
, human macrophage inflammatory protein 1
; rLkn-1i, intact rLkn-1; rLkn-1c; cleaved rLkn-1; CI, chemotactic index. ![]()
Received for publication May 26, 1998. Accepted for publication January 29, 1999.
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