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Departments of
*
Oncology,
Experimental Pathology, Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton, NJ 08543; and, Department of Microbiology, Bristol-Myers Squibb Pharmaceutical Research Institute, Wallingford, CT 06492
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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,2 MIP-1ß, and
RANTES (6, 7, 8, 9). However, MIP-1 and RANTES can also bind to CCR1 and
CCR3 (murine) (10, 11, 12, 13, 14). To date, CCR5 is the only known receptor for
MIP-1ß (6, 7, 8, 9). In vivo, MIP-1 has been shown to be involved in the
pathogenesis of type II collagen-induced arthritis (15, 16), the T
cell-mediated autoimmune disease, experimental autoimmune
encephalomyelitis (17), and virus-induced inflammation (18). The in
vivo function of MIP-1ß and RANTES has not yet been well
documented. All three CCR5 ligands can function as inhibitors of HIV-1 infection (19). Recently, five groups simultaneously identified CCR5 as the major coreceptor for macrophage-tropic HIV-1 isolates (20, 21, 22, 23, 24). Another chemokine receptor, CXCR4, was identified as a coreceptor for T cell-tropic HIV-1 isolates (25). Two other CC-chemokine receptors, CCR2b and CCR3, have also been shown to function as coreceptors for some, but not all HIV-1 strains (21, 23). Recently, several orphan chemokine receptors were shown to be able to function as HIV cofactors (26, 27). Moreover, a human CMV-encoded CC-chemokine receptor (US28) can also serve as a cofactor for HIV (28). Taken together, these findings suggest that HIV-1 may use a broad range of coreceptors for infection.
Nevertheless, CCR5 has been shown to be the essential receptor in the
establishment of HIV-1 infection. A 32-bp deletion allele of the
ccr5 gene (
ccr5) was detected at a frequency
of 20% heterozygosity and 1% homozygosity in the Caucasian population
(29, 30). Homozygosity for the ccr5 allele is strongly
associated with the resistance to HIV-1 infection (29, 30, 31, 32).
Heterozygosity for ccr5 leads to prolonged AIDS-free
survival time, diminished viral load, and slower decrease in their
CD4+ T cell count, suggesting that ccr5allele exerts a protective effect on these infected individuals
(33, 34). However, once AIDS is diagnosed, those individuals tend to
have an accelerated decrease in CD4+ cell counts and
reduced survival time, suggesting a dual effect of the ccr5allele (35).
Whereas the intensive study of the relation between CCR5 and HIV-1 has shed light on the mechanisms of HIV-1 entry into cells, the normal in vivo role of this receptor is still unknown. In the present study, we report a partial defect in macrophage function and an enhanced T cell-dependent (TD) immune response in the CCR5-deficient mice. Our results suggest that, in addition to the lack of HIV-1 docking molecule, the overactive immune system may also contribute to the protection effect in the CCR5 null and CCR5 heterozygous humans.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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A genomic clone containing the ccr5 locus was
isolated from a mouse library (cloned in 
DASHII from Stratagene, La
Jolla, CA) prepared from D3 (129/sv) ES cell DNA. The targeting vector
was constructed in the pPNT vector for positive/negative selection with
G418 (the nEo gene) and gancyclovir (the
tk gene). A 7.5-kb ClaI-SalI fragment
of the ccr5 clone was subcloned into the 3' flanking region
of the neo cassette, and a 3.8-kb
PstI-PstI fragment was subcloned into the 5'
flanking region of the neo cassette. As a result, a 0.77-kb
ClaI-PstI fragment encoding all of the
seven-transmembrane domains of the ccr5 gene was replaced by
the neo gene. The targeting vector was electroporated into
both CJ7 and R1 ES cells, and 19 targeted ES clones were obtained from
120 double-resistant colonies picked. Homologous recombination was
confirmed by Southern blot analysis of tail DNA digested with
EcoRI; the wild-type allele generates a 4-kb fragment, while
the targeted allele gives an approximately 14-kb fragment. Two
independent clones were selected for blastocyst injection into ICR
mice. Resulting male chimeras were mated with ICR females to yield
germline transmission of the targeted allele, and heterozygous
offsprings were then interbred.
Cell culture, Northern blot analysis, and cytokine analysis
A quantity amounting to 1 x 106
peritoneal macrophages was cultured in medium alone (RPMI 1640 plus
10% filtered low endotoxin FBS) or in the presence of LPS (1 µg/ml)
(Escherichia coli 0111:B4; Sigma Chemical, St. Louis,
MO) and IFN-
(100 U/ml) (Sigma Chemical) for 24 h. Splenic T
cells were isolated with murine T cell enrichment columns (R&D Systems,
Minneapolis, MN). Cell purity was confirmed by FACS analysis, and more
than 80% of the cells were Thy-1.2+. Purified T cells
(1 x 106) were cultured in the presence of PMA (20
ng/ml) and PHA (1 µg/ml), or in dishes coated with anti-CD3 and
anti-CD28 Abs (1 µg/ml) for the indicated periods of time. Total
RNA was isolated using RNAzol (Cinna/BioTecx Laboratories, Friendswood,
TX), according to the manufacturer’s instructions. The
PstI-ApaI fragment of the ccr5 gene
and the XbaI-BamHI fragment of the
ccr2 gene that correspond to the 3' untranslated regions of
these genes were used as probes. The ccr1, ccr3,
and ccr4 probes were generated by reverse-transcriptase PCR
and contained the entire open reading frame of these genes. All of the
probes were labeled using RadPrime DNA labeling system (Life
Technologies, Rockville, MD) to similar specific activities. Cytokine
production of the culture supernatant was measured by ELISA (Life
Technologies).
Binding assays
A quantity amounting to 5 x 105 cells was
washed with PBS and incubated for 15 min at 37°C in 200 µl assay
buffer (HBSS, 25 mM HEPES, pH 7.4, 1 mM MgCl2, 1 mM
CaCl2, 0.1% NaN3, and 0.2% BSA) containing
0.05 to 2.5 nM 125I-MIP-1 in the presence or absence of
100-fold excess of unlabeled MIP-1. After incubation, cells were
washed three times with 500 µl assay buffer, and cell-bound
radioactivity was counted in a scintillation counter. Mouse rMIP-1
was purchased from R&D Systems. 125I-MIP-1 was labeled
by Bolton-Hunter to a sp. act. of 2200 mCi/mmol (DuPont NEN Custom
Iodination Laboratory, Boston, MA).
Thioglycolate-induced peritonitis
Six- to eight-week-old mice were injected i.v. with 3 ml sterile Brewer’s thioglycolate broth (3%) and sacrificed 72 h later. Total leukocytes elicited into the peritoneal cavity were harvested by peritoneal lavarges and counted with a hemacytometer. Differential cell counts were determined by Diff-Quick staining of cytospin slide preparations and counting cells of 10 high power views. The number of different cell populations was calculated by multiplying percentage by total cell counts.
Listeria monocytogenes infection
Six- to eight-week-old mice were injected i.v. with 2500 CFU of Listeria and sacrificed on day 5 after infection. Numbers of viable Listeria in lung, liver, and spleen of infected animals were determined by plating serial dilution of organ homogenates in PBS on sheep blood agar. Statistical analysis of the samples was performed using the Mann-Whitney two-sample test (unpaired nonparametric analysis), and the two-tailed p value was calculated.
Delayed-type hypersensitivity (DTH) reaction and histopathologic analysis
The mouse abdominal skin was shaved, and 400 µl FITC solution (0.5% in 1:1 acetone/dibutyl phathalate) or solvent, only for the nonsensitized group, was applied epicutaneously. After 6 days, the baseline thickness of the animal’s right ear was measured using a precision thickness gauge (0.01–12.5 mm; Swiss Precision Instruments, Los Angeles, CA). Each side of the right ear was then treated epicutaneously with 10 µl FITC solution, and the ear thickness was measured 24 h later. For histopathologic analysis, mice were sacrificed and one-half of the ears were fixed by immersion in 10% neutral buffered Formalin. Tissues were processed by standard methods, embedded in paraffin blocks, sectioned at 4 to 6 µm, stained with hematoxylin and eosin, and examined by light microscopy. Severity was graded without knowledge of treatment group, as follows: 0, none; 1, minimal; 2, mild; 3, moderate; 4, marked. Statistical analysis was performed using the unpaired Student’s t test to calculate the two-tailed p values. For immunohistochemical analysis, frozen tissue sections of the other half of the ears were stained with anti-CD4 Ab (Life Technologies; 1/100 dilution), or anti-Mac1 Ab (Boehringer Mannheim, Indianapolis, IN; 1/100 dilution).
Ig production analysis
The TD Ag, keyhole limpet hemocyanin coupled to (4-hydroxy-3-nitro-phenyl) acetic acid (NP-KLH), was precipitated in alum. Mice were injected i.p. with either 100 µg of alum-precipitated NP-KLH or 10 µg of the T cell-independent (TI) Ag, NP-LPS, in a 200 µl vol and bled at 0, 7, 14, and 21 days postimmunization. Basal levels of serum Ig were determined by isotype-specific ELISA. The levels of NP-specific Ig were determined by the use of ELISA plates coated with NP17-BSA for capture, and goat anti-mouse isotype-specific Abs conjugated to horseradish peroxidase (Southern Biotechnology, Birmingham, AL), as previously described (36). The level of each Ag-specific isotype was determined by comparison with a standard curve. Statistical analysis was performed using the unpaired Student’s t test to calculate the two-tailed p values.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The ccr5 gene was deleted by replacing all of the
seven-transmembrane domains with the nEo gene
(Fig. 1
A). Germline
transmission was obtained with two independently isolated homologous
recombinant ES clones. Heterozygous matings generated offspring
homozygous for the disrupted ccr5 allele
(ccr5-/-) in Mendelian proportions.
Deletion of the ccr5 gene was confirmed by Southern blot
analysis (Fig. 1B). Since the highest levels of
ccr5 mRNA can be detected in peritoneal macrophages of
wild-type animals (Fig. 1C), its absence was
confirmed by Northern blot analysis of peritoneal macrophage RNA
hybridized with a ccr5-specific probe (Fig. 1D). The expression of other CC-chemokine receptor
genes, ccr1, ccr2, ccr3, and
ccr4, was not affected in the ccr5 knockout mice
(Fig. 1D).
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,
MIP-1ß, and RANTES can induce chemotaxis of certain cell populations
in vitro (37, 38), macrophage recruitment by thioglycolate elicitation
in CCR5-deficient mice was comparable with wild-type animals (data not
shown). Macrophage infiltration into glucan-induced granulomas in lung
or liver also revealed no significant difference between CCR5-deficient
mice and wild-type controls (data not shown), indicating that CCR5 does
not play an essential role in macrophage recruitment in mice. Decreased cytokine production in CCR5-deficient macrophages
In addition to CCR5, CCR1 and CCR3 also bind and respond to
MIP-1 or RANTES in vitro (10, 11, 12, 13, 14). Northern blot analysis revealed
that ccr1 and ccr3 were expressed at relatively
lower levels compared with that of ccr5, in both resident
and in vitro activated macrophages (Fig. 2A). To investigate the
MIP-1-binding capacity of macrophages in the absence of CCR5,
125I-MIP-1 binding was measured.
125I-MIP-1 bound to HEK293 cells expressing CCR5 with a
Kd of 0.1 nM. Equilibrium binding could be
reached within 15 min at 37°C and was saturable at 1 to 2 nM (Zhou et
al., unpublished observations). Under identical conditions, equilibrium
binding of increasing concentrations of 125I-MIP-1 to
resident wild-type macrophages approached, but did not reach,
saturation binding at 2.5 nM. Equilibrium binding of increasing
concentrations of 125I-MIP-1 to resident CCR5-deficient
macrophages showed a similar binding pattern to that of wild-type
controls; however, the overall binding was reduced compared with that
of wild type (Fig. 2B). Consistently, there was
decreased MIP-1 binding to in vitro activated CCR5-deficient
macrophages compared with that of wild-type controls (Fig. 2B). These results indicate that CCR5 contributes to
the MIP-1-binding activity in wild-type macrophages. Cytokine
production of the corresponding cell culture supernatants was measured
by ELISA. The production of granulocyte-macrophage CSF, IL-1ß, and
IL-6 by CCR5-deficient macrophages decreased to 50% compared with that
of wild-type controls (Fig. 2C, p < 0.003,
Student’s t test), while TNF- (Fig. 2C,
p = 0.99, Student’s t test) and IL-10 (data
not shown) production remained at similar level. These results
suggested a partial defective macrophage function in
CCR5-deficient mice.
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To assess the in vivo impact of the partial defective macrophage
function in CCR5-deficient mice, groups of mutant and wild-type animals
were analyzed for their responses in two infection and inflammation
models. First, the susceptibility to L. monocytogenes
infection was investigated. The intracellular bacterium
Listeria can survive in nonactivated macrophages, and
effective clearance of infection requires activation of macrophages
(39). Mice of 6 to 8 wk old were infected i.v. with 2500 CFU of
Listeria and sacrificed 5 days after infection.
Listeria titers of liver from CCR5-deficient mice were
10-fold higher than that of wild-type controls, while
Listeria titers of lung and spleen were at similar levels
(*p < 0.03,
**p = 0.5, ***p
= 0.1, Student’s t test) (Fig. 3), indicating a mildly reduced
efficiency in Listeria clearance in the liver of
CCR5-deficient mice.
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and RANTES have been shown to
mediate macrophage influx and early mortality in endotoxemia (40, 41).
Pretreatment with either anti-MIP-1 or anti-RANTES reduced
the mortality of lethal doses of LPS (40, 41). CCR5-deficient mice and
wild-type controls were administered i.p. with five doses of LPS, and
survival was monitored up to 4 days. As shown in Table I, treatment with the highest dose, 2
mg/animal, resulted in a 20% survival of CCR5-deficient mice vs 0%
survival of wild-type mice; the second highest dose, 0.8 mg/animal,
resulted in a 50% survival of mutant mice vs 17% of wild-type mice;
and treatment with the lower doses, 0.4, 0.2, or 0.1 mg/animal,
resulted in 78, 100, or 100% survival of mutant mice vs 50, 80, or
100% survival of wild-type mice. Spearman Karben Estemate calculated
LD50 values were 34.05 (mg LPS/kg animal body weight) for
mutant mice vs 18.15 (mg LPS/kg animal body weight) for wild-type mice
(*p < 0.03, unpaired nonparametric Mann-Whitney test).
These results indicated a significant protection in LPS-induced
endotoxemia in CCR5-deficient mice.
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CCR5 is expressed at relatively low levels on the surface of
resting T cells. Upon in vitro activation by anti-CD3 Ab and IL-2,
CCR5 protein levels increase dramatically, suggesting a role for CCR5
in T cell function (42). To investigate the possible redundancy among
receptors, we first checked the expression of all known MIP-1/RANTES
receptor genes in T cells by Northern blot analysis. ccr5
was the only receptor gene expressed in T cells, and the only gene
whose expression can be induced in vitro with either PMA plus PHA or
anti-CD3 plus anti-CD28 Abs. There was no detectable expression
of ccr1 or ccr3 (Fig. 4A). We then measured
the MIP-1-binding activity in T cells. Equilibrium binding of
increasing concentrations of 125I-MIP-1 to resting
wild-type T cells was saturable and reached maximal binding at 0.5 to 1
nM. In contrast, there was no detectable equilibrium binding of
125I-MIP-1 to resting CCR5-deficient T cells (Fig. 4B). Consistently, there was a dramatically decreased
MIP-1 binding to in vitro activated CCR5-deficient T cells compared
with that of wild-type controls at low concentrations of
125I-MIP-1 (Fig. 4B). However, with
increasing concentrations of 125I-MIP-1, a low affinity
MIP-1 binding was detected in both wild-type and CCR5-deficient T
cells (Fig. 4B), probably due to the induced
expression of CCR3 on a subset of activated T cells (Th2 cells) (43)
and/or to the induction of an unknown low affinity CCR5-binding
receptor. Cytokine production was also measured in the corresponding
culture supernatants. Surprisingly, there was a marked increase in the
production of IFN- (fivefold), granulocyte-macrophage CSF
(2.5-fold), and IL-4 (twofold) by CCR5-deficient T cells compared with
wild-type controls (*, **p < 0.0003,
***p < 0.02, Student’s t test), while no
significant difference in the production of IL-2 or TNF-
(§p = 0.13,
§§p = 0.22, Student’s t test)
(Fig. 4C). There was no difference in the production
of chemokine ligands of CCR5 (MIP-1, MIP-1ß, or RANTES, data not
shown).
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The elevated cytokine production by CCR5-deficient T cells
suggested an enhanced TD immune response in CCR5-deficient mice. To
test this hypothesis, we first compared the DTH reaction in
CCR5-deficient and control mice. It has been shown that patients with a
subnormal DTH reaction had a significantly more rapid progression to
AIDS than did patients with a normal DTH reaction (44). The abdominal
skin of both CCR5-deficient and wild-type animals was exposed to FITC.
After the afferent phase, the ears were treated epicutaneously with the
hapten solution, and the ear thickness was measured 24 h later.
While nonsensitized mice of both genotypes
(ccr5-/- and wild type) had no
significant changes in ear thickness, sensitized mice had a strong
reaction, and the response was twofold higher in CCR5-deficient mice
than in wild-type controls (*p < 0.02, Student’s
t test) (Fig. 5A). Histopathologic
analysis of ear sections showed that nonsensitized mice of both
genotypes were nonremarkable or had minimal inflammation (Fig. 5, B–D). In contrast, the sensitized wild-type mice
showed mild to moderate dermal edema and inflammatory infiltrates with
multifocal microabscesses consisting predominantly of neutrophils (Fig. 5, B and E). Sensitized CCR5-deficient
mice had histologic changes similar to the sensitized wild-type mice,
but with increased severity (**p < 0.03, Student’s
t test) (Fig. 5B). The ears of these mice
were moderately thickened, with dense infiltrates of neutrophils,
lymphocytes, and macrophages, and contained intraepithelial pustules
and microabscesses (Fig. 5, B and F).
Immunohistochemical staining with anti-CD4 and anti-Mac1 Abs
showed more CD4--positive and Mac1-positive cells in the
sensitized CCR5-deficient mice than in wild-type controls (data not
shown). Since the DTH reaction is mediated by CD4+ T cells,
these results indicate an enhanced cell-mediated immune response in
CCR5-deficient mice.
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To further analyze this issue, we compared the humoral response to
a specific antigenic challenge in CCR5-deficient and wild-type animals.
Mice were injected with either the TD Ag NP-KLH or the TI Ag NP-LPS,
and the Ig levels at 0, 7, 14, and 21 days postimmunization were
measured. Although basal levels of total Ig and different isotypes
remain similar between CCR5-deficient mice and wild-type controls (data
not shown), the production of NP-specific IgG1, the predominant isotype
produced during a normal TD response to soluble protein Ags, was
increased approximately twofold at days 7, 14, and 21 postimmunization
in CCR5-deficient mice (p < 0.02, Student’s
t test) (Fig. 6A). In contrast, the
production of NP-specific IgG3, the main isotype produced during a
normal TI response to carbohydrate Ag, was similar in mutant and
control mice (p > 0.05, Student’s
t test) (Fig. 6B). These results confirm
the enhanced immune reaction in CCR5-deficient mice, specifically in TD
responses.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The lack of the developmental defect correlates with the observation
that CCR5 null humans have no obvious health problems (29, 30, 31, 32).
Similarly, no developmental defects are observed in mice deficient for
either MIP-1 or CCR1 (18, 45). In contrast, mice deficient in the
CXC chemokine SDF-1 (46) or the CXC chemokine receptor CXCR2 (47) do
present developmental alterations, suggesting that the absence of one
of the CC chemokines or their receptors is better tolerated, possibly
due to the higher degree of redundancy in this chemokine subfamily
(4).
Even though all three ligands of CCR5 induce chemotaxis of certain cell
populations in vitro (37, 38), no recruitment defect was observed in
either macrophage or T cells in CCR5-deficient mice. This suggests that
CCR5 function is compensated by other CC chemokine receptors or that
CCR5 is not involved in chemotaxis in vivo. Severe defect in neutrophil
infiltration has been reported in the absence of either CCR1 or CXCR2
(45, 47), whereas CCR2 is essential for macrophage recruitment (48). To
date, there is no strong evidence for a chemokine receptor being
responsible for T cell migration in vivo. In the DTH model, more
CD4+ and Mac1+ cells were infiltrated in the
CCR5-deficient mouse ears than in wild-type ears (data not shown).
These results suggested that, in the wild-type animal, the abundance of
CCR5 on the surface of macrophages or T cells might dilute the
functional concentration of ligands (MIP-1/RANTES) to their
receptors (CCR1, CCR3, or others) and indirectly reduce the cell
infiltration to the inflammation site.
Peritoneal macrophages from CCR5-deficient mice after LPS challenge
were much smaller in size and less foaming compared with those from
wild-type mice (data not shown), indicating they are less active than
wild-type macrophages. Reduced production of several other cytokines by
macrophages in the absence of CCR5 also suggested a partially defective
macrophage function. However, a minor reduced efficiency in clearance
of Listeria infection indicated that CCR5 did not play a
major role in this macrophage-mediated host defense model.
Nevertheless, this minor defect might still be enough to take account
for the partial protection of LPS-induced endotoxemia in CCR5-deficient
mice. Lethal dose LPS-induced septicemia includes shock, multiorgan
dysfunction, and death (49). Mice died of acute suppurative hepatitis,
lympholysis in multiple lymphoid organs, and acute adrenocortical
necrosis (data not shown). It has been shown, in addition to
neutrophils, lymphocytes and macrophages (either newly recruited blood
monocytes or resident tissue macrophages) also contribute to the
endotoxin-induced organ injury (50). Thus, partial impaired macrophages
in CCR5-deficient mice might be less virulent in damaging tissues; as a
result, mice might have better chance to recover. TNF- is one of the
important cytokines involved in LPS pathway. However, we did not
observe reduced TNF- production. TNF- receptor-deficient mice
were only resistant to low doses of LPS after sensitized by
galactosamine, but not to high doses of LPS (51, 52, 53), indicating that
the TNF- pathway is not involved in the high dose LPS-induced
endotoxemia, which was the experiment performed in our studies. At the
later stage of AIDS development, when patients’ lymphoid tissues are
quantitatively and qualitatively impaired, and CD4+ cells
are steadily declining, tissue macrophages play a critical role in
fighting opportunistic infections (54). AIDS patients heterozygous for
the ccr5 allele have an accelerated decrease in CD4+
cell counts and reduced survival time (35). We speculate that
macrophages in these patients might also be partially defective and
have reduced capacity in clearance of opportunistic infection.
The increased production of both type 1 (IFN-1) and type 2 (IL-4)
cytokines by CCR5-deficient T cells is different from that observed in
CCR1-deficient mice, in which an impaired type 1-type 2 cytokine
balance was observed (45). These results indicate a novel role for CCR5
in down-modulating T cell function. There are at least two explanations
for the overproduction of cytokines in the absence of CCR5. First,
signaling through CCR5 might function as part of a negative regulatory
cycle of T cell activation. To date, CCR5 is the only known receptor
for MIP-1ß (6, 7, 8, 9). MIP-1ß inhibits MIP-1-induced macrophage
activation (55). However, the activities of MIP-1 and MIP-1ß on T
cell activation have not been well studied. Second, the overproduction
of cytokines in the absence of CCR5 might be the result of enhanced
signaling through other receptors having overlapped ligand-binding
profile with CCR5. Even though the production of chemokines did not
increase in the absence of CCR5 (data not shown), the ligand-receptor
ratio might still increase in the absence of the abundant
CCR5.
CD4 facilitated the direct interactions between CCR5 and HIV-1 envelope protein gp120, suggesting that CD4--dependent CCR5-gp120 binding is important to HIV-1-membrane fusion and virus entry (56, 57). Therefore, it was hypothesized that the resistance to HIV-1 infection in CCR5 null individuals was due to the lack of HIV-1 docking molecules (29, 30). However, identification of increased number of HIV-1 coreceptors argues that this hypothesis is the sole explanation for the hyperresistance to HIV-1 infection in CCR5 null individuals (26, 27, 28). Our results of enhanced TD immune responses in the CCR5-deficient mouse model suggest that there might be an additional level of defense in the CCR5 null humans: the overreactive immune system in these individuals might trigger a stronger immune response at the early phase of viral infection and clear viral particles more efficiently. Therefore, our data favor the efforts to look for reagents that block both CCR5-ligand and CCR5-gp120 interactions as preventive therapeutics against HIV-1 infection.
The levels of CCR5 expression on T cells vary dramatically from individual to individual (42). Our results further suggest that investigation of the correlation between the expression levels of CCR5 and the intensity of immune responses might be very informative to understand the pathology of allergic or autoimmune diseases. The CCR5-deficient mice will provide a useful tool to study the potential role of ligand-CCR5 interactions in these and other inflammatory or infectious models.
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Acknowledgments |
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Footnotes |
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2 Abbreviations used in this paper: MIP, macrophage-inflammatory protein; DTH, delayed-type hypersensitivity; 125I-MIP-1, 125I-labeled macrophage-inflammatory protein-1; KLH, keyhole limpet hemocyanin; NP, (4-hydroxy-3-nitro-phenyl) acetic acid; TD, T cell-dependent; TI, T cell-independent.
Received for publication September 5, 1997. Accepted for publication December 11, 1997.
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