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*
Department of Experimental Medicine, Human Anatomy Section, University of Genoa, Genoa, Italy; and
Laboratory of Oncology, Giannina Gaslini Institute, Genoa, Italy
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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. In contrast, the
production of cytokines that support T cell expansion and function
(e.g., IL-2, IFN-
, and IL-13) is significantly decreased. A
long-term effect of CD85/LIR-1/ILT2 and of CD152 occurs during
Ag-specific T cell activation and expansion. T cells, primed in the
presence of anti-CD85/LIR-1/ILT2 and anti-CD152 blocking mAb
(but in the absence of cross-linking), proliferate at higher rates and
produce higher amounts of IL-2, IFN-, and IL-13, in comparison with
T cells stimulated with the Ag alone. We also show that the inhibitory
receptors exert a similar effect during Ag activation of specific
CD4+ effector T cells. Ag-specific polyclonal
CD4+ T cell lines exhibit increased proliferation and IL-2,
IFN-, and IL-13 production when the CD85/LIR-1/ILT2 receptor is
blocked by specific mAb. In contrast, cross-linking of this receptor
down-regulates Ag-specific CD4+ T cell proliferation and
increases IL-10 and TGF- production. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The CD85/leukocyte Ig-like receptor (LIR)3-1/Ig-like transcript (ILT) 2 molecule binds to the nonclassical class I HLA-G protein, to some alleles of HLA-A, -B, and -C loci, and to the human CMV UL18 gene product, a viral homolog of HLA-class I (8, 11, 13). It is a transmembrane molecule that bears four immunoreceptor tyrosine-based inhibition motifs in its cytoplasmic domain (14, 15). Tyrosine phosphorylation of immunoreceptor tyrosine-based inhibition motifs establishes docking sites for the Src homology domain 2-containing phosphatase SHP-1 that subsequently transduces inhibitory signals by dephosphorylating and inactivating downstream tyrosine kinases (16). We have shown that CD85/LIR-1/ILT2 is expressed on the surface of the majority of T cells and in cytoplasmic transport vesicles of all T lymphocytes (6). Although membrane expression may vary at times, there is no apparent relationship between cell activation and CD85/LIR-1/ILT2 expression. CD85/LIR-1/ILT2 down-regulates the Ag-specific cytolytic activity of CD8+ T cells, and its cross-linking results in inhibition of proliferative responses to recall Ags by CD4+ T cells (6).
CD152 (CTLA-4) is an inhibitory molecule homologous to CD28 that
delivers a costimulatory signal and is an inducible receptor. Its mRNA
is detectable within 1 h after T cell activation, and cell surface
expression of the protein, although weak, reaches a peak 1–3 days
later (17, 18, 19). Moreover, its engagement triggers
phosphatases that dephosphorylate molecules of the CD3/TCR activation
cascade (1, 3, 20). In addition, it has been shown that
engagement of CD152 inhibits specific target cell lysis mediated by
CD8+ T lymphocytes (5),
down-regulates proliferation of T cells as well as IL-2, IFN-,
IL-4 (21, 22, 23, 24), and IL-13 production (7),
and up-regulates the production of IL-10 (25, 26, 27) and
TGF- (28, 29). Conversely, blockade of CD152 by
specific mAb increases proliferation of CD4+ T
cell blasts and clones (5, 21, 22).
In this study we have analyzed the function of resting/memoryand effector CD4+ T lymphocytes with the aim of understanding the effects of CD85/LIR-1/ILT2 and of CD152 (CTLA-4) on T cell proliferation and cytokine production in response to Ags. We show that these inhibitory receptors exert a dual function on T cell proliferation and that they modulate cytokine production when blocked or cross-linked.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Abs for immunophenotypic analyses were anti-CD4, anti-CD8, anti-CD20 mAb (BD PharMingen, Hamburg, Germany), anti-CD3 (clone OKT3; American Type Culture Collection, Manassas, VA), anti-MHC class II mAb (clone D1.12; kindly provided by R. S. Accolla, Unit of Cellular and Molecular Genetics, Advanced Biotechnology Center, Genoa, Italy), anti-CD152 mAb (kindly provided by A. Lanzavecchia, Institute for Research in Biomedicine, Bellinzona, Switzerland), HP-F1 (kindly provided by M. Lopez-Botet, Servicio de Immunologia, Hospital Universitario de la Princesa, Madrid, Spain), and anti-p58.2 (A3 mAb; produced in our laboratory). Ags used as stimulators were tetanus toxoid (TT), Candida albicans bodies (Ca), and Cryptococcus heat-inactivated yeasts (Cr).
Proliferation and cytokine production in short-term cultured T cell lines
Freshly isolated PBMCs were isolated from heparinized venous
blood of healthy donors. CD4+ T lymphocytes were
negatively selected from PBMCs by MACS (Miltenyi
Biotec, Milan, Italy) and incubated with irradiated autologous
feeder cells pulsed with Ags (TT, Ca, and Cr), in the presence or
absence of mAb to inhibitory receptors (anti-CD152 or HP-F1) either
soluble or cross-linked by goat anti-mouse (GAM) antiserum. An
isotype-matched mAb (A3, IgG1) was used as a control. Supernatants were
collected on day 2 (Fig. 1
A)
and cytokine production was measured by an ELISA. After 10 days of
culture, cells were harvested, washed three times with PBS, and
restimulated with irradiated autologous PBMCs pulsed with the Ags used
previously. No inhibitory mAb were used in this latter phase of the
experiments. Supernatants were collected on day 12 to measure cytokine
production. Proliferation indexes were evaluated as
[3H]thymidine uptake on days 2 and 12 (as shown
in Fig. 1A).
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Ag-specific CD4+ T cell lines were
generated from total PBMCs by repeated stimulation with autologous
irradiated PBMCs pulsed with the appropriate Ag (Fig. 1
B).
Human rIL-2 (final concentration, 20 U/ml) was added to the cell
cultures every 2–3 days. Specificity of the response indicated by cell
proliferation at each stimulatory cycle point was evaluated by
[3H]thymidine uptake. Cultures were analyzed
for cytokine production when the cell phenotype was >97%
CD4+, MHC class II+,
CD8-, CD20-, and
CD16- (data not shown). Clones were produced by
plating T cells at a limiting dilution of 10 and 1 cells/well, in the
presence of 3 x 104 autologous irradiated
Ag-pulsed PBMCs.
Stimulation of CD4+ T cell lines
Ag-specific CD4+ T cell lines were diluted at 2 x 106/ml and dispensed into 96-well plates in a volume of 200 µl/well. Each well was precoated with anti-CD3 mAb (1 µg/ml) in 1x Dulbecco’s PBS (pH 7) at 4°C overnight. Ag-specific CD4+ T cell lines were subsequently incubated in the presence or absence of one of the inhibitory mAb (anti-CD152 or HP-F1 mAb) either soluble (receptor blockade) or cross-linked by GAM antiserum. An isotype-matched mAb (A3, IgG1) was used as a control. T cell proliferation was evaluated on day 2 by [3H]thymidine uptake and by flow cytometric DNA content measurements. Supernatants were collected on day 2 and cytokine production was measured by an ELISA.
Cell cycle analysis
Cells were activated by recall Ags as described above. Forty-eight hours after activation, cells were harvested, fixed with 70% ethanol, and stained with 30 µg/ml propidium iodide (Sigma-Aldrich, St. Louis, MO) in the presence of 0.5 mg/ml RNase for 30 min at room temperature. Flow cytometric measurements were performed using a FACSCalibur (BD Biosciences, Mountain View, CA). Frequency distributions of DNA content were analyzed for the evaluation of apoptosis and percentage of cells in the various phases of the cell cycle.
ELISAs
IL-2, IFN-, IL-10, IL-13, and TGF- ELISAs were performed
as indicated by the manufacturer (Diaclone Research, Besançon,
France). Supernatants were tested in triplicate adding a volume of 100
µl to each well. Deviation between triplicates was <10% for any
reported value. The lower sensitivity threshold of the ELISA is 10
pg/ml for IL-2, 5 pg/ml for IFN- and IL-10, 1.5 pg/ml for IL-13, and
1.9 pg/ml for TGF-.
Statistical analyses
Differences in cell proliferation and cytokine production between control and mAb-treated cells were observed. To assess their statistical significance, the Student’s t test was used with a level of p < 0.05.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The role of CD85/LIR-1/ILT2 and CD152 receptors on Ag-specific T cell activation was assessed by measuring proliferative responses to recall Ags and the pattern of cytokines produced 48 h after Ag stimulation.
PBMCs from healthy donors proliferated in the presence of Ags (TT, Ca, and Cr).
Addition of soluble mAb to the inhibitory receptors enhances several T
cell functions (Fig. 2). This cannot be
due to activation via FcR, as control mAb of the same isotype as that
of HP-F1 and anti-CD152 mAb (i.e., A3) have no effect. Furthermore,
when isotype-matched mAb against other surface receptors (i.e.,
anti-CD4, anti-CD8, anti-class I, and
anti-HLA-DR) are included in the assay, no proliferative or
functional enhancement is observed (Refs. 5, 6 , and
24 , and data not shown). Hence, this augmented T cell
function is due to the interaction between mAb and inhibitory
molecules. Therefore, it is conceivable that engagement of the
inhibitory receptors by the specific mAb leads to a blockade of
receptor-ligand interaction due to steric hindrance. Thus, although
direct experimental evidence is not available, in Results we
refer to this effect as a receptor blockade.
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A shows results from one representative experiment, as
planned in Fig. 1A). Increased proliferation varied
according to the Ags used (from 20 to 126% increase), and it was
particularly relevant in low responders (Fig. 2A; the donor
is a low responder to TT). The positive effect of the inhibitory
receptor blockade was even sharper when the production of cytokines
that sustain cell-mediated immune responses was analyzed. As shown in
Fig. 2B, IL-2 and IFN- were detectable in Ag-stimulated
cultures after 48 h. IL-2 production ranged from 25 to 45 pg/ml
and IFN- production ranged from 5 to 95 pg/ml, according to the Ag
used. Addition of either HP-F1 or anti-CD152 mAb yielded an
increase of cytokine production varying from 50 to 270% for IL-2, and
from 20 to 1400% for IFN- after 48 h (Fig. 2B). In
these experimental conditions, IL-13 was undetectable in the culture
medium.
Cytokines that down-regulate proliferation of Ag-specific T cells were
also evaluated. Blocking of CD85/LIR-1/ILT2 and CD152 inhibitory
receptors by specific mAb resulted in a reduction of IL-10
production, whereas TGF- was undetectable after 48 h of
culture (Fig. 2C). The effect on IL-10 production was
specific for CD85/LIR-1/ILT2 and CD152, as an irrelevant
isotype-matched mAb (i.e., A3) did not influence cell proliferation and
cytokine production.
We also investigated the outcome of a physiological engagement of
CD85/LIR-1/ILT2 and CD152 inhibitory receptors, mimicking such
ligand/receptor interaction by cross-linking the two specific mAb
(HP-F1 and anti-CD152) using a GAM antiserum. CD85/LIR-1/ILT2 or
CD152 cross-linking resulted in decreased
[3H]thymidine uptake by anti-CD3-stimulated
T cells (data not shown). Ag-mediated proliferation of specific T cells
is shown in Fig. 2A. Inhibition of proliferation ranged
between 40 and 75%, according to the Ag used. Moreover, cross-linking
of CD85/LIR-1/ILT2 or CD152 reduced IL-2 and IFN- production (Fig. 2B). Altogether, these data suggest that an inhibition of
the events associated with the progression of resting T cell activation
is related to the engagement of the two inhibitory receptors.
As determined by flow cytometric analyses of the cell cycle
distribution, inhibition of CD4+ T cell
activation by CD85/LIR-1/ILT2 or CD152 is due to a restricted transit
from the G0/G1 to the
S/G2M phase of the cell cycle, rather than to an
enhancement of cell death (Table I).
Accordingly, no significant increase of Ag-specific
CD4+ T cell apoptosis by cross-linking of HP-F1
or anti-CD152 mAb by GAM antiserum was detected 48 h after
Ag-specific restimulation, but an accumulation of cells in
G1 occurred (Table I).
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that down-regulate T cell
responses was taken into account. IL-10 has been detected in all of the
experimental conditions, and its production increased when the two
inhibitory receptors were cross-linked by GAM antiserum. Increase of
IL-10 production ranged from 31 to 108% when CD85/LIR-1/ILT2 was
cross-linked, and from 23 to 308% following CD152 cross-linking (Fig. 2C), depending on the Ag tested. At variance, although
recall Ags did not increase detectable TGF- in the supernatants in
comparison with unstimulated cell cultures, a striking increase of this
cytokine above controls was induced by HP-F1 or anti-CD152
cross-linked with GAM antiserum (Fig. 2C). Addition in the assays of irrelevant mAb (i.e., A3), with or without cross-linking by GAM antiserum, had no effect on proliferation or cytokine production, thus providing a specificity control for the above experiments.
Blockade or cross-linking of CD85/LIR-1/ILT2 or CD152 during Ag-specific T cell priming modulates T cell proliferation and cytokine production after secondary antigenic stimulation
The long-term effect of blocked or cross-linked inhibitory
receptors was also investigated. To this end, resting Ag-specific T
cells were activated by their respective recall Ags, in the presence of
soluble ("blocking") or cross-linked HP-F1 or anti-CD152 mAb.
Subsequently, as shown in Fig. 1A, secondary restimulations
were performed by Ags only, without further mAb addition. Forty-eight
hours later, proliferation and cytokine production were measured and
compared with those of T lymphocytes previously primed by recall Ags in
the absence of HP-F1 or anti-CD152 mAb (Fig. 1A).
Proliferation of T cells primed in a condition of inhibitory receptor
blockade was higher than that of T cells previously mAb untreated or
treated with an irrelevant mAb (Fig. 3A). Accordingly, the
antecedent blocking of inhibitory receptors increased the production of
IL-2, IFN-, and IL-13, as compared with control cultures primed in
the absence of the mAb (Fig. 3B). It is of note that a
secondary stimulation induced higher production of these cytokines,
particularly IL-13, than the first priming (compare mAb untreated
controls in Fig. 2B with the same controls in Fig. 3B).
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was not detectable during the 48 h that followed the
secondary Ag stimulation (Fig. 3C), as it occurred after the
first priming (Fig. 2C). In contrast, IL-10 was detected at
significant amounts, but its level was lower when T cells were primed
previously in the presence of soluble HP-F1 or anti-CD152 mAb,
which blocked the ligand/inhibitory receptor interaction (Fig. 3C).
Cross-linking of CD85/LIR-1/ILT2 or CD152 by GAM antiserum during T
cell priming inhibited Ag-specific T cell proliferation after secondary
restimulation (Fig. 3A). Likewise, IL-2, IFN- and IL-13
production was reduced (Fig. 3B).
Conversely, IL-10 production was higher than that detected when T cells
were primed in the absence of mAb, and the amount of TGF-,
otherwise undetectable, was sharply increased (Fig. 3C).
CD85/LIR-1/ILT2 inhibitory receptors regulate proliferation and cytokine production in Ag-specific CD4+ T cell lines
As blockade of CD85/LIR-1/ILT2 triggered cytokine polarization in
Ag-stimulated resting/memory T cells, we next evaluated whether the
HP-F1 mAb, soluble or cross-linked by GAM antiserum, could modulate
IL-2, IFN-, IL-13, IL-10, and TGF- production by effector/memory
human CD4+ polyclonal T cell lines generated by
repeated Ag stimulation (Fig. 1B).
To this end, Ag-specific CD4+ T cell
lines were restimulated by autologous irradiated PBMCs pulsed with the
respective Ags. Simultaneous addition in the culture of HP-F1 mAb,
cross-linked by GAM antiserum, inhibited proliferation as shown by a
reduced [3H]thymidine uptake (Fig. 4A). In contrast, addition of
soluble HP-F1, which blocks the receptors, increased specific
Ag-induced proliferation by 60–120% (Fig. 4A). Controls
with GAM antiserum alone, or with an isotype-matched irrelevant Ab
(A3), had no effect on Ag-induced proliferation (Fig. 4A),
both when added as soluble mAb and when cross-linked by GAM
antiserum.
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,
and IL-13. Blockade of the inhibitory receptors by the HP-F1 mAb
resulted in a further increased production of cytokines. The range of
increase was 25–200% for IL-2 and 28–45% for IFN- (Fig. 4B). The increase in IL-13 production was not
significant (Fig. 4B).
In all T cell lines tested, cross-linking of HP-F1 mAb by GAM antiserum
led to an almost complete inhibition of IL-2 production (Fig. 4B). In addition, we observed an inhibition of IFN-
production ranging from 50 to 80% and of IL-13 production ranging from
25 to 46.5% (Fig. 4B). Addition of an irrelevant mAb used
as control (i.e., A3, both soluble or cross-linked) had no effect on
cytokine production (Fig. 4B).
The presence of soluble HP-F1 mAb during Ag-mediated restimulation of
the T cell lines decreased the amount of IL-10 production (Fig. 4C). TGF- was not detectable during the first 48 h
of Ag restimulation, when cells were challenged both with the Ag alone
and in the presence of mAb blocking ligand/inhibitory receptor
interactions (Fig. 4C). In contrast, when HP-F1 mAb was
cross-linked by GAM antiserum, the amount of IL-10 was significantly
increased, by 120–300%, depending on the Ag (Fig. 4C), and
TGF-, otherwise undetectable, was produced at high amounts (Fig. 4C).
Similar data were obtained when the CD152 inhibitory receptor was blocked or cross-linked (data not shown), suggesting a similar role for this molecule in the regulation of the immune response at the effector cell level.
The HP-F1 mAb interacts with CD85/LIR-1/ILT2 expressed by T cells
The CD85/LIR-1/ILT2 inhibitory receptor is expressed by both T cells and APCs. Therefore, we asked whether the effects observed for Ag-specific T cells, which require APCs for appropriate Ag stimulation, are due to mechanisms directly related to T cells or to a CD85/LIR-1/ILT2-mediated down-regulation of Ag processing and presentation by APCs, which would indirectly down-regulate T cell function.
To this end, we performed experiments in a T cell activation model that does not require APCs. Proliferation and cytokine production after stimulation via CD3 were evaluated, in the absence or in the presence of soluble or cross-linked HP-F1 mAb.
As shown in Fig. 5, an Ag-specific
CD4+ T cell clone (RP.TT) increased its
anti-CD3-induced proliferation in response to soluble HP-F1 mAb and
decreased it when the mAb was cross-linked. Moreover, addition of
soluble mAb increased IL-2 and IFN- production, while its
cross-linking decreased it (Fig. 5). Conversely, TGF- production was
significantly increased when anti-CD3 stimulation was performed in
the presence of cross-linked CD85/LIR-1/ILT2.
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Modulation of cytokine production by inhibitory receptor blockade or cross-linking is prevented by addition of IL-2
We have shown that cross-linking of inhibitory receptors during T
cell activation leads to decreased IL-2, IFN-, and IL-13 production,
paralleled by decreased proliferation, and to an increase of IL-10 and
TGF- production. To determine whether such effects were caused by
decreased IL-2 production, exogenous IL-2 (50 UI/ml) was added to
cultures of CD4+ T cell lines during the
experiments. Cell cultures were restimulated with anti-CD3 in the
absence or presence of HP-F1 mAb, soluble or cross-linked by GAM
antiserum. An isotype-matched mAb (A3) was used as a control.
Addition of IL-2 prevented the decrease of IFN- and IL-13 production
and the increase of IL-10 and TGF- production, which occurred when
CD85/LIR-1/ILT2 was cross-linked (Fig. 6).
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). Exogenous IL-2 removed the
inhibitory effect of CD85/LIR-1/ILT2 cross-linking and allowed
transition to the S/G2M phases of the cell cycle
(Table II).
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In conclusion, it appears that the low response to Ag of T cells due to CD85/LIR-1/ILT2 and/or CD152 can be reverted by addition of IL-2.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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In all experiments, the inhibitory role of these molecules has been
demonstrated. It is of note that the production of IL-2, IFN-, and
IL-13 was sharply reduced following cross-linking of the receptors; in
contrast, the production of IL-10 and TGF- was significantly
increased. The biological roles played by these cytokines are
known (25, 28, 29, 33). IL-2 is a non-Ag-specific
proliferation factor for T cells that prompts cell cycle progression of
resting cells, thus allowing clonal expansion of activated T
lymphocytes. IFN- sustains the response of T cells to mitogens and
Ags; in addition, it acts in synergy with IL-2 and promotes the
expression of IL-2R on the membrane of T lymphocytes. IL-13 acts in
concert with IL-2 for the regulation of IFN- synthesis. IL-10
inhibits Ag- or anti-CD3-induced proliferation of T cells and
down-regulates the production of IL-2 and IFN-. Finally, TGF-
inhibits the proliferation of T lymphocytes mainly by reducing
IL-2-mediated signals (34). It follows that the outcome of
CD85/LIR-1/ILT2 and CD152 engagement results in a control of
cell-mediated immunity.
Our observations suggest that the inhibitory receptors play a dual role
and, while the biochemical pathways of inhibition are well understood
(2, 3), the mechanisms that enhance the production of
IL-10 and TGF- remain to be elucidated (25, 28, 35, 36). In our experimental model, the induction of IL-10 and
TGF- production could suggest an additional role of the inhibitory
receptors in the regulation of the intensity of immune responses. It is
of note that resting/memory T cells primed with Ag in a condition of
inhibitory receptor cross-linking were down-regulated also during the
secondary antigenic stimulation in the absence of CD85/LIR-1/ILT2
engagement. These cells were still able to proliferate, although at a
lower rate than mAb untreated ones, and to produce cytokines such as
IL-10 and TGF- that may control other T cell clones specific for the
same Ag. Such a mechanism could revert effector T cells to a
resting/memory condition when the immune response is no longer
needed.
The inhibitory effect of CD85/LIR-1/ILT2 and CD152 cross-linking on T lymphocyte proliferation could be due to an enhancement of apoptotic cell death or to an arrest in the G1 phase of cell cycle. Interestingly, during early stages of T cell activation induced by recall Ags or anti-CD3 mAb in the absence of exogenous IL-2, analyses of DNA histograms revealed no increased induction of apoptosis by CD85/LIR-1/ILT2 or CD152 engagement. Rather, the reduction of [3H]thymidine uptake is related to an accumulation of T cells in the G0/G1 phase of the cell cycle. It is of note that CD85/LIR-1/ILT2 or CD152 engagement even reduced the percentage of T cells undergoing apoptosis, possibly because of the lower proliferation as an effect of CD85/LIR-1/ILT2 and CD152 cross-linking.
Because expression of CD85/LIR-1/ILT2 is not restricted to T lymphocytes but is also found in APCs, it was important to rule out the possibility that anti-CD85/LIR-1/ILT2 mAb had a direct effect on T lymphocytes or an indirect effect on Ag presentation by APCs. With regard to this, it is important to assess that CD85/LIR-1/ILT2 is certainly inhibitory on T cell functions as shown in non-Ag-specific assays (6). In these models, such as that of the redirected killing assays, inhibition of OKT3-induced proliferation and of cytokine production does not require the presence of APCs. Nevertheless, the function of CD85/LIR-1/ILT2 on APCs is not completely understood, and there is no evidence as to the ability of CD85/LIR-1/ILT2 to down-regulate endogenous pathways of Ag presentation by APCs.
In this work we show that blockade of the inhibitory receptors during
the initial Ag priming of T lymphocytes up-regulates their response.
CD85/LIR-1/ILT2 and CD152 blockade during Ag restimulation resulted in
higher proliferative responses and increased IL-2, IFN-, and IL-13
production, as well as decreased IL-10 and TGF- release. These
results are in support of a critical involvement of inhibitory
receptors during Ag-specific activation of resting/memory T
lymphocytes. Although the molecular bases of such phenomena are
not defined yet, it seems that the possibility to use mAb blocking the
inhibitory receptors as an adjuvant in the planning of vaccines,
especially for individuals that are low responders to exogenous Ags,
bears some relevance.
Finally, several signal pathways have been shown to induce secretion of
various cytokines. Some of them, i.e., IL-4 and IFN-, have been
shown to be IL-2 dependent (25). In addition, inhibition
of priming mediated by CD152 cross-linking has been reversed by
addition of IL-2 (25). In our experimental models, a
prevention of the inhibitory effect obtained by cross-linking of HP-F1
or anti-CD152 mAb occurs after addition of exogenous IL-2 to
activated T cells. It is of note that IL-2 blocks the production of
IL-10 and TGF-, thus preventing their negative effects on T
lymphocyte functions. We confirm that IL-2 plays a critical role in the
activation pathway of memory/effector CD4+ T
cells, and we show that it contrasts with CD85/LIR-1/ILT2- and
CD152-mediated inhibition.
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Daniele Saverino, Department of Experimental Medicine, Human Anatomy Section, University of Genova, Via De Toni 14, 16132 Genova, Italy. E-mail address: Daniele.Saverino{at}unige.it
3 Abbreviations used in this paper: LIR, leukocyte Ig-like receptor; ILT, Ig-like transcript; GAM, goat anti-mouse; TT, tetanus toxoid; Ca, Candida albicans bodies; Cr, Cryptococcus heat-inactivated yeasts.
Received for publication August 16, 2001. Accepted for publication November 1, 2001.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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(TGF-) production by murine CD4+ T cells. J. Exp. Med. 188:1849. in leishmanial infection: a parasite escape mechanism. Science 257:545. production. J. Exp. Med. 179:299. and IL-4 cause helper T cell precursors to develop into distinct effector helper cells that differ in lymphokine secretion pattern and cell surface phenotype. J. Immunol. 147:2991.[Abstract]
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, samples where receptor blockade is exerted by soluble mAb;
, samples with receptors cross-linked by mAb plus GAM
antiserum.
