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CUTTING EDGE |
,2
*
Inflammation Research Unit, School of Pathology, University of New South Wales, and
Centre for Virus Research, Westmead Institutes of Health Research, Westmead Hospital, University of Sydney, Sydney, Australia
| Abstract |
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| Introduction |
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, and MIP-1ß) and
CXC chemokine receptor 4 (stromal-derived factor-1) have been
demonstrated to inhibit HIV entry into CD4 T cells and PBMCs, as well
as monocytic and CD4 T cell lines (3, 4, 5, 6). Given these inhibitory
effects, increased production of these proteins has been suggested to
be a protective host immune response against HIV infection and disease
progression (3). However, there are conflicting reports regarding the
influence of ß-chemokines on HIV-1 replication in MDM and tissue
macrophages, with enhancement, inhibition, or no effect reported
(7, 8, 9, 10). The effects of ß-chemokines on HIV replication in monocytes
have not previously been reported. We have previously demonstrated that ß-chemokine expression is strongly enhanced in lymph nodes of patients with HIV disease (11). Thus, cells recruited to HIV lymph nodes are likely to interact with ß-chemokines before exposure to the virus given that the primary physiologic role of ß-chemokines is to direct the traffic of mononuclear cells to sites of inflammation (12). However, studies to date have examined the influence of ß-chemokines only when added simultaneously with and/or after HIV infection. Accordingly, we analyzed the effects of timing of exposure to ß-chemokines on HIV replication in monocytes and MDM using an in vitro system modeled on this in vivo scenario. ß-Chemokine exposure produced dichotomous effects on HIV replication in this system.
| Materials and Methods |
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Monocytes were isolated from PBMCs of uninfected healthy HIV-seronegative donors by countercurrent elutriation and anti-CD3 complement-dependent lysis as previously described (13). Monocytes were cultured at a density of 1 x 106 cells/ml either for 48 h at 37°C before HIV infection or for 7 days before infection to permit differentiation into MDM. All media, viral stock, and reagents were endotoxin free as assessed by the Limulus amebocyte lysate assay (Sigma Chemical Co., St. Louis, MO). Flow cytometry analysis revealed these cultures to have <1% CD3 contamination. Purity was further confirmed by the inability of T-tropic HIV strains such as HIV-1 PNL43 to grow in these cultures.
HIV infection of monocytes and MDM and p24 Ag assay
The laboratory monocytotropic strain HIV-1BaL, obtained from the National Institutes of Health AIDS Research and Reference Reagent Program, was used in this study. Cells were inoculated with cell-free HIV isolates at 1 x 105 cpm/ml of room temperature activity (105 TCID50 (tissue culture-infective dose)/ml on PBMCs and at a multiplicity of infection of 0.02/cell) and allowed to adsorb for 4 h before complete aspiration of medium, washing, and addition of fresh medium. Media was replaced every 3 days and supernatants were collected, stored at -20°C, and batched for HIV p24 Ag quantitation by ELISA (Organon Teknika, Durham, NC). Results above 12 pg/ml were considered positive. Results were expressed either as raw data or as a fold change of the untreated control culture according to the following formulae: fold change = (p24 Agtreated/p24 Agcontrol) - 1, when p24 Ag was increased in treated cultures; or fold change = -[(p24 Agcontrol/p24 Agtreated) - 1], when p24 Ag was decreased in treated cultures.
Chemokine and pertussis toxin treatment
Recombinant human RANTES, MIP-1
, or MIP-1ß (R&D Systems,
Minneapolis, MN) was added to cells either before, simultaneously with,
or after HIV infection in increasing concentrations from 0.1 to 500
ng/ml. In the preinfection treatment experiments, cell cultures were
exposed to chemokines for 48 h. In monocyte cultures,
chemokines were added to cells on the day of isolation, and the cells
were subsequently infected on day 2. In MDM cultures, chemokines were
added on day 5 after plastic adherence, and cells were infected on day
7. Before HIV infection, cell cultures were then washed three times,
replenished with fresh media not containing added chemokines, and then
infected with HIV. In the simultaneous infection treatment experiments,
cell cultures were treated with chemokines during the 4-h period of HIV
infection only. In the postinfection treatment experiments, chemokines
were initially added to the cultures immediately after the inoculum was
washed off and then every 3 days thereafter with each media change.
Before chemokine treatment cells were exposed to 500 ng/ml of pertussis toxin (Calbiochem, San Diego, CA) for 12 h. Cells were treated with pertussis toxin once only except for cells that were treated with ß-chemokines following HIV infection, where pertussis toxin was applied every 3 days with fresh media.
| Results and Discussion |
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caused greater increases in HIV replication in MDM than did
either RANTES or MIP-1ß. By contrast, addition of ß-chemokines
either simultaneously with or after HIV infection inhibited subsequent
viral replication. Under these conditions, all three chemokines
inhibited HIV-1 replication to a comparable degree. Inhibition ranged
from 20 to 88% compared with untreated controls. These effects
persisted for up to 14 days in culture. While maximal inhibition was
achieved when chemokines were added both simultaneously with and after
HIV infection, they were negated by pretreatment with ß-chemokines
(data not shown).
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-chemokine, had no effect on
HIV replication (data not shown).
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Our data conflict with two previous reports. The first demonstrated enhancement of HIV replication in day 7 MDM that had been exposed to ß-chemokines simultaneously with and after HIV infection (7). Differences in viral inoculum, viral strain, and culture conditions may have contributed to these conflicting results. The viral inoculum used in this previous study was five times lower than that used in our study. The increased numbers of uninfected cells in the culture system immediately following HIV inoculation would thus be exposed to ß-chemokines before HIV infection. Our data would suggest, therefore, that HIV replication in these cells would be subsequently increased. Indeed, when we repeated the experiment using a viral inoculum of 0.004 multiplicity of infection/cell, five times lower than the inoculum used in our initial experiments, enhancement of HIV replication was observed even when ß-chemokines were added simultaneously with and after HIV infection. A second study reported insensitivity of day 14 MDM to the effects of ß-chemokines (21). We have shown here and in other work (M. Kelly, unpublished observations) that the sensitivity to ß-chemokines decreases as the monocyte matures following adherence to plastic. These observations broadly correlate with the alterations in permissiveness to HIV infection by differentiating monocytes (H. Naif, unpublished observations) and changes in CCR5 surface expression which increases in the early stages of monocyte differentiation (22). However, preliminary work suggests that CCR5 expression is not altered by 48 h of chemokine treatment or chemokine withdrawal at physiologic concentrations.
The mechanisms producing the dichotomous effects of ß-chemokines on
HIV replication in monocytes and MDM have not been established. As has
been previously reported (5), we found that the inhibitory effects of
ß-chemokines when applied either simultaneously with (Fig. 3
) or after (data not shown) HIV
infection were insensitive to pertussis-toxin and therefore do not
involve signaling through pertussis toxin-sensitive G proteins.
However, the stimulatory effects of ß-chemokines were dependent on
cell signaling events via pertussis toxin-sensitive G protein-linked
pathways. While the downstream signaling events in this system have not
been elucidated, ß-chemokines may stimulate a number of intracellular
mechanisms that may lead to increased HIV replication. ß-Chemokines
have been demonstrated to provide costimulatory signals for human T
lymphocytes (17, 18), and MIP-1
has been demonstrated to increase
proliferation and cytokine production of murine tissue macrophages
(19). While the effects of ß-chemokines on human monocytes and MDM
are unknown, activation of these cells by ß-chemokines may be
expected to increase subsequent HIV replication as has been shown for
other stimuli, such as TNF-
(20). Furthermore, ß-chemokines may
up-regulate nuclear transcription factors, such as nuclear
transcription factor
B, that may, in turn, augment HIV
transcription. TGF-ß, IFN-
, IL-4, and IL-13 also have dichotomous
effects on HIV replication in vitro (23, 24). Some of these effects are
concentration dependent and vary according to the timing of HIV
infection. However, the exact mechanisms of their effects have not been
established.
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Preliminary work in our laboratory suggests that CD4 T lymphocytes are also susceptible to the enhancing effects of ß-chemokines on HIV-1 replication observed in monocytes and MDM. Furthermore, primary clinical isolates have also demonstrated similar sensitivity as HIV-1BaL to the dichotomous effects of ß-chemokines (M. Kelly, unpublished observations).
The data presented here suggest that ß-chemokines have dichotomous and opposing effects on HIV replication. Because variation in experimental conditions such as the size of the inoculum, degree of maturation of the target cell, and other unidentified host factors alter the in vitro effects observed further studies are required to determine which of these effects are dominant in vivo. Therefore, until the exact role of ß-chemokines in HIV disease has been established, treatment approaches with these proteins or pharmacologic analogues should proceed only with caution.
| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. Hassan Naif, Molecular Pathogenesis Laboratory, Centre for Virus Research, Westmead Hospital, Westmead, New South Wales 2145, Australia. E-mail address: ![]()
3 Abbreviations used in this paper: CCR5, CC chemokine receptor 5; MDM, monocyte-derived macrophages; T-tropic, T cell line tropic; MIP-1, macrophage inflammatory protein-1. ![]()
Received for publication September 22, 1997. Accepted for publication January 27, 1998.
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