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Journal of Virology, May 2001, p. 4402-4406, Vol. 75, No. 9
Laboratory of Experimental
Chemotherapy1 and Laboratory of
Molecular Immunology,2 Department of
Microbiology and Immunology, Rega Institute for Medical Research,
Katholieke Universiteit Leuven, Leuven, Belgium
Received 14 September 2000/Accepted 29 January 2001
The CC-chemokines RANTES, macrophage inflammatory protein 1 Macrophage inflammatory protein 1 LD78 The chemokine receptor CCR5 is expressed by M/M and represents the most
important coreceptor for M-tropic R5 HIV type 1 (HIV-1) strains to
enter the cells (1, 13, 14, 34, 36, 39-41). Macrophages
may play an important role in all phases of HIV infection. Infected
macrophages are present in all body tissues of HIV patients (12,
17-19) and represent the most important cellular reservoir for
the virus during antiviral therapy (4, 24, 30). In fact,
M/M secreting nerve growth factor survive after HIV infection (9) and produce high and stable levels of virus for a long period of time (S. Aquaro, T. Guenci, P. Bagnarelli, M. Clementi, A,
Modesti, R. Caliò, and C. F. Perno, 4th Intl. Workshop HIV, Cells of Macrophages Lineage, and Other Reservoirs, p. 29, 1999). In
the central nervous system, more then 90% of the HIV-1-infected cells
are M/M (8, 12, 15, 37), and CCR5
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.9.4402-4406.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
The LD78
Isoform of MIP-1
Is the Most Potent
CC-Chemokine in Inhibiting CCR5-Dependent Human Immunodeficiency Virus
Type 1 Replication in Human Macrophages
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ABSTRACT
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Abstract
Text
References
(MIP-1
), and MIP-1
are natural ligands for the CC-chemokine receptor CCR5. MIP-1
, also known as LD78
, has an isoform,
LD78
, which was identified as the product of a nonallelic gene. The two isoforms differ in only 3 amino acids. LD78
was recently reported to be a much more potent CCR5 agonist than LD78
and RANTES
in inducing intracellular Ca2+ signaling and chemotaxis.
CCR5 is expressed by human monocytes/macrophages (M/M) and represents
an important coreceptor for macrophage-tropic, CCR5-using (R5) human
immunodeficiency virus type 1 (HIV-1) strains to infect the cells. We
compared the antiviral activities of LD78
and the other
CC-chemokines in M/M. LD78
at 100 ng/ml almost completely blocked
HIV-1 replication, while at the same concentration LD78
had only
weak antiviral activity. Moreover, when HIV-1 infection in M/M was
monitored by a flow cytometric analysis using p24 antigen intracellular
staining, LD78
proved to be the most antivirally active of the
chemokines. RANTES, once described as the most potent chemokine in
inhibiting R5 HIV-1 infection, was found to be considerably less active
than LD78
. LD78
strongly downregulated CCR5 expression in M/M,
thereby explaining its potent antiviral activity.
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TEXT
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Abstract
Text
References
(MIP-1
) exists in two nonallelic isoforms, LD78
and LD78
, with
high-level sequence homology. The secreted proteins differ in only 3 amino acids: the penultimate NH2-terminal residue and amino
acids 39 and 47 (10, 21, 23). The biological relevance,
also in terms of antiviral activity, of the NH2-terminal
residues of CXC- and CC-chemokines has been convincingly demonstrated
(26, 27, 29, 31-33, 42). Besides MIP-1
, the
CC-chemokines RANTES and MIP-1
are natural ligands for the
CC-chemokine receptor CCR5 and are inhibitors of macrophage-tropic (M-tropic) human immunodeficiency virus (HIV) strains (7).
was reported to be much more potent than LD78
and RANTES in
inducing intracellular Ca2+ signaling and chemotaxis
preferentially through the CC-chemokine receptor CCR5 (20, 22,
43). In these studies, the anti-HIV activity of LD78
in
peripheral blood mononuclear cells (PBMCs) was investigated
(20), however, its activity in human monocytes/macrophages (M/M) had not been determined.
32 heterozygosity prevents the development of the AIDS dementia complex
(38). At the same time, the downregulation of CCR5
expression by CC-chemokines in macrophages is correlated with a
reduction of virus entry and replication (11). These data
demonstrate the relevance of CCR5 and thus the important role of
CC-chemokines in reducing HIV entry and hence virus replication through
their interaction with CCR5. Here, we have studied the antiviral
efficacy of LD78
, in comparison with those of LD78
and the other
CCR5-interacting CC-chemokines, RANTES and MIP-1
, in purified
macrophages. To evaluate the antiviral activities of LD78
and
LD78
, M/M were incubated with the chemokines for 20 min at different
concentrations and then infected by the R5 HIV-1BaL strain.
LD78
showed a potent dose-dependent inhibition and antiviral
activity against HIV-1BaL. As shown in Fig.
1, at an LD78
concentration of 100 ng/ml, viral p24 antigen (Ag) production dropped from 40,300 pg/ml to
2,070 pg/ml (94% inhibition). In contrast, LD78
only weakly
inhibited viral replication at a concentration of 100 ng/ml (roughly
20% inhibition) (Fig. 1). Thus, the antiviral activity of LD78
in
M/M was far superior to that of LD78
.

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FIG. 1.
Dose-dependent antiviral activity of LD78
in
HIV-1-infected M/M. Macrophages were obtained from the blood of healthy
HIV-seronegative donors by previously published procedures
(25). Briefly, PBMCs were separated by Ficoll-Hypaque
gradient centrifugation and seeded in plastic 48-well plates (Costar,
Cambridge, Mass.) at a density of 1.8 × 106 cells/ml
in RPMI 1640 (Gibco, Gaithersburg, Md.) supplemented with 50 U of
penicillin/ml, 50 µg of streptomycin/ml, 2 mM
L-glutamine, and 20% heat-inactivated, mycoplasma- and
endotoxin-free fetal calf serum (HyClone, Logan, Utah) (complete
medium). On the 5th day of culture, nonadherent cells were removed by
repeated gentle washing with warm complete medium. Adherent cells
obtained with this technique consisted of >95% differentiated M/M.
After purification, M/M were cultured in a humidified chamber with 5%
CO2 at 37°C in the presence of the same medium. Further
details are described elsewhere (25). Macrophages were
exposed to various concentrations of CC-chemokine LD78
(
) or
LD78
(
) for 20 min; then they were challenged with
HIV-1BaL at 300 50% cell culture infective doses per ml.
After 2 h of incubation, M/M were extensively washed with warm
complete medium to remove the excess virus and then cultured in the
presence of chemokines under the conditions used previously. M/M were
washed and fed every 5 days with fresh medium and replenished with
chemokines. Supernatants were collected at day 12 after virus
challenge, and virus production was determined by Ag capture assay with
a commercially available p24 Ag kit (NEN Life Science Products Inc.,
Boston, Mass.). Human recombinant MIP-1
isoform LD78
was
purchased from PeproTech Inc. (Rocky Hill, N.J.). The 7.793-kDa LD78
was synthesized by 9-fluorenylmethoxycarbonyl (fMOC) solid-phase
peptide synthesis (20). Data represent the means of values
from two independent experiments, each run in triplicate. Error bars
show the standard deviations.
The antiviral activities of LD78
and LD78
were also evaluated by
intracellular p24 Ag staining to determine the percentage of
HIV-1-infected M/M. As can be seen in Fig.
2, 42% of the cells from HIV-infected
M/M cultures stained positive for p24 Ag, whereas the level decreased
to about 11% in the LD78
-treated cells (at 100 ng/ml). In contrast,
no difference in numbers of p24 Ag-positive cells was observed between
the untreated HIV-infected and LD78
-treated HIV-infected cells (Fig.
2).
|
To compare the anti-HIV efficacy of LD78
with those of the other
CCR5-binding chemokines, RANTES and MIP-1
, additional experiments were performed in M/M. The MIP-1
isoform LD78
exhibited the highest antiviral activity against HIV-1BaL. RANTES reached
92% inhibition of HIV replication at a concentration of 500 ng/ml, while LD78
suppressed HIV replication by 93% at 100 ng/ml (i.e., at
a fivefold-lower concentration than RANTES); moreover, MIP-1
, considered the most specific CCR5 ligand, inhibited virus replication by about 30% at 500 ng/ml (data not shown). Therefore, as shown in
Table 1, the 50% effective concentration
(EC50) of LD78
against HIV-1BaL in M/M was
21 ng/ml, which is 16-fold lower than that of LD78
(EC50, 351 ng/ml). Also, a more than 10-fold difference in
the EC90s of LD78
and LD78
was observed (Table 1).
RANTES, with an EC50 and an EC90 of 149 and 478 ng/ml, respectively (Table 1), was six- to sevenfold less active than
LD78
. With an EC50 of almost 1,000 ng/ml (Table 1),
MIP-1
was found to be the least potent chemokine in inhibiting viral
replication.
|
To confirm that LD78
has potent antiviral activity against M-tropic
HIV strains, and not only against the cell culture-adapted virus strain
HIV-1BaL, we performed additional experiments with primary
R5 HIV-1 clinical isolate (HIV-1 isolate 15). This virus isolate was
obtained after only one passage in PBMCs and replicated in
U87.CD4.CCR5-transfected cells but not in U87.CD4.CXCR4 cells, confirming its CCR5 usage (data not shown). Here, again, the chemokine LD78
was the most active in inhibiting viral replication, with an
EC50 of 28 ng/ml (Table 1). The other chemokines were
somewhat more active against this clinical viral isolate than against
HIV-1BaL (Table 1).
We demonstrated previously that the antiviral activity of a compound
that inhibits virus entry in fresh monocytes (such as the sulfated
polysaccharide dextran sulfate or the bicyclam AMD3100) is different
from that in macrophages (3). Therefore, we also assessed
the anti-HIV efficacy of LD78
in freshly isolated monocytes. At a
concentration of 100 ng/ml, LD78
inhibited HIV replication by 85%
(EC50, 35 ng/ml). In sharp contrast, at a concentration of
100 ng/ml, RANTES had no antiviral activity in fresh monocytes (data
not shown). It has been previously reported that RANTES has no or only
weak activity against HIV-1 in freshly isolated monocytes (28,
31). A likely explanation for this phenomenon is that only the
NH2-terminally truncated form of RANTES has anti-HIV activity and that monocytes express very low, or undetectable, levels
of CD26/dipeptidyl peptidase IV, which is responsible for NH2-terminal truncation of RANTES (29).
Because previous studies demonstrated that downregulation of HIV
coreceptors by their natural ligands contribute to the inhibition of
viral replication (2, 16), we examined the efficiency of
LD78
at downregulating CCR5. As shown in Fig.
3, expression of CCR5 from the surface of
monocytes is shown for LD78
, in comparison with LD78
and
MIP-1
. LD78
was much more effective (after 1 h of incubation
at 37°C) than LD78
or MIP-1
at downregulating CCR5; it showed a
marked downregulation at 40 ng/ml, whereas for LD78
and MIP-1
a
weak effect was observed only at a concentration of 200 ng/ml. This
enhanced potency of LD78
in receptor binding and downregulation may
explain its potent anti-HIV activity and is probably due to its greater
affinity for CCR5 (20).
|
This study shows that the MIP-1
isoform LD78
is the most potent
CC-chemokine described so far in terms of inhibiting R5 HIV-1 infection
of macrophages and monocytes. The inhibitory effect of LD78
on viral
replication may be ascribed to its high affinity for CCR5 and the
subsequent downregulation of this coreceptor. The potent anti-HIV-1
activity of LD78
compared with that of LD78
is conferred by
differences in only 3 amino acids (20), with the
NH2-terminal dipeptide of LD78
seemingly important for receptor affinity (33).
Our findings that RANTES and MIP-1
/LD78
have EC50s of
about 60 and 120 ng/ml, respectively, are in agreement with previously published data (35). The previously reported order for the
anti-HIV activities of the CC-chemokines in M/M, RANTES > MIP-1
> MIP-1
/LD78
(5), should be changed
to the following order: MIP-1
/LD78
> RANTES > MIP-1
/LD78
> MIP-1
. Further experiments are required to
determine if MIP-1
/LD78
is consistently more potent than MIP-1
in inhibiting HIV-1 replication in M/M. The superior anti-HIV-1 activity of LD78
has to be interpreted in the light of the isolation from cultured T cells of MIP-1
, MIP-1
, and RANTES as suppressors of HIV-1 infection (7). Increased production of the
CC-chemokines MIP-1
, MIP-1
, and RANTES in repeatedly
HIV-1-exposed subjects is correlated with protection against HIV-1
infection; MIP-1
appears sooner and attains higher concentrations
than MIP-1
and RANTES (6, 44). These clinical data on
natural resistance to HIV-1 infection, not linked to a deletion
mutation in the CCR5 gene, are in agreement with the higher antiviral
potency of the LD78
isoform of MIP-1
, as previously shown in
PBMCs (20, 22) and here confirmed for M/M.
| |
ACKNOWLEDGMENTS |
|---|
We thank Sandra Claes and Erik Fonteyn for excellent technical assistance.
This work was supported by grants from the Fonds voor Wetenschappelijk
Onderzoek (FWO)
Vlaanderen (Krediet no. G.0104.98) and the
Geconcerteerde Onderzoeksacties (Vlaamse Gemeenschap) (Krediet no.
00/12). S.A. was supported by a grant from Istituto Superiore di
Sanità, Rome, Italy.
| |
FOOTNOTES |
|---|
* Corresponding author. Mailing address: Department of Experimental Medicine, University of Rome "Tor Vergata," Rome, Italy. Phone: 39 06 7259 6553. Fax: 39 06 72596552. E-mail: aquaro{at}uniroma2.it.
| |
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