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in Response to IL-181
*
Biomedical Research Center, Osaka University Medical School, Osaka, Japan;
Department of Bacteriology and
Department of Immunology, Hyogo College of Medicine, Hyogo, Japan;
§
Genetics Institute Inc., Cambridge, MA 02140; and
¶
Fujisaki Institute, Hayashibara Biochemical Laboratories, Okayama, Japan
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussion References |
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production
by T cells. Using a T cell clone, we reported that IL-18 responsiveness
is generated only after exposure to IL-12. Here, we investigated the
induction of IL-18 responsiveness in resting CD8+,
CD4+, and CD4-CD8- T cells.
Resting T cells respond to neither IL-12 nor IL-18. After stimulation
with anti-CD3 plus anti-CD28 mAbs, CD8+,
CD4+, and CD4-CD8- T cells
expressed IL-12R, but not IL-18R, and produced IFN- in response to
IL-12. Cultures of T cells with anti-CD3/anti-CD28 in the
presence of rIL-12 induced IL-18R expression and IL-18-stimulated
IFN- production, which reached higher levels than that induced by
IL-12 stimulation. However, there was a substantial difference in the
expression of IL-18R and IL-18-stimulated IFN- production among T
cell subsets. CD4+ cells expressed marginal levels of
IL-18R and produced small amounts of IFN-, whereas CD8+
cells expressed higher levels of IL-18R and produced more IFN- than
CD4+ cells. Moreover, CD4-CD8-
cells expressed levels of IL-18R comparable to those for
CD8+ cells but produced IFN- one order higher than did
CD8+ cells. These results indicate that the induction of
IL-18R and IL-18 responsiveness by IL-12 represents a mechanism
underlying enhanced IFN- production by resting T cells, but the
operation of this mechanism differs depending on the T cell subset
stimulated. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussion References |
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, which is produced
mainly by
the Th1 type of lymphocytes (1), exhibits a number of immunoregulatory
effects, including the capacity to stimulate the activation of CTL (2, 3) and macrophages (4, 5, 6, 7). Through these effects, it is becoming
increasingly evident that this cytokine has an important role in the
manifestation of T cell-mediated inflammatory responses.
Like IL-2 production, IFN- production by Th1 cells is induced
following stimulation of their TCR and costimulatory receptor, CD28 (8, 9). Simultaneous ligation of TCR and CD28 molecules with anti-CD3
and anti-CD28 mAbs in the absence of APCs leads to significant
levels of IFN- production (10, 11). However, a number of studies
(12, 13, 14) have revealed that an APC-derived cytokine strikingly
stimulates T cells for IFN- production; IL-12 has been shown to
induce the production of IFN- by T cells and NK cells (12, 13, 14). More
recently, another cytokine, designated IFN--inducing factor (now
termed IL-18), was described to exhibit a more potent IFN--inducing
capacity than IL-12 (15). Regarding the functional relationship between
these two cytokines, our previous study (16) demonstrated that IL-12
and IL-18 exhibit a synergistic effect on IFN- production by a
particular T cell clone (IL-12-responsive T cell clone). It was also
shown that IL-12 allows T cells to respond to IL-18 by inducing the
expression of IL-18R (16). While this represented a mechanism
underlying synergy between IL-12 and IL-18 in enhanced IFN-
production by a single unique T cell clone, it remained to be solved
whether it holds true for various subsets of fresh resting T cells,
i.e., CD4+, CD8+, and
CD4-CD8- T cells.
The present study investigated how responsiveness to IL-12 and IL-18 is
induced in resting T cells. The results demonstrate that purified
resting T cells fail to respond to either IL-12 or IL-18 while all
subsets (CD4+, CD8+, and
CD4-CD8-) of
anti-CD3/anti-CD28-activated T cells expressed IL-12R and
produced IFN- in response to IL-12. The expression of IL-18R and
IL-18 responsiveness were induced when resting T cells stimulated with
anti-CD3 and CD28 were exposed to IL-12 but not to IL-2.
Importantly, the levels of both IL-18R and IFN- production as a
marker of IL-18 responsiveness were found to differ greatly among the T
cell subset; CD4+ T cells expressed marginal levels of
IL-18R and produced little IFN- in response to IL-18 whereas
CD8+ T cells exhibited higher levels of IL-18R expression
and IFN- production. While the IL-18R levels expressed on
CD4-CD8- T cells were comparable to those on
CD8+ T cells, these cells produced one order larger amounts
of IFN- than did CD8+ T cells. These results indicate
that IL-18 responsiveness is induced in various subsets of T cell
receptor-triggered T cells, but the magnitude of responsiveness is
determined by the levels of IL-18R induced by IL-12 as well as the
intrinsic properties (IL-18R-mediated signaling) of each T cell
subset.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussion References |
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C57BL/6 mice were purchased from Shizuoka Laboratory Animal Center, Hamamatsu, Japan and used at 7 to 9 wk of age.
Reagents
Murine rIL-12 purified from the supernatants
(SN)3 of Chinese hamster
ovary cells transfected with p35 and p40 (IL-12 subunits) cDNA plasmids
was from Genetics Institute (Cambridge, MA). Murine rIL-18 was obtained
by expression of the murine IL-18 cDNA in Escherichia coli
and purification by chromatography as described (17). Murine rIL-2 was
kindly provided by Shionogi (Osaka, Japan). Anti-CD3 (145-2C11) (18),
anti-CD28 (Pv-1) (19), anti-IL-2R 
-chain (7D4) (20),
anti-I-Ad/b (34-5-3S) (21), anti-CD4 (American Type
Culture Collection (Rockville, MD) clone GK1.5), anti-CD8 (ATCC
clone 2.43), and anti-murine IL-12 (C17.8) (22) mAbs were purified
from culture SNs or ascitic fluids of the respective hybridomas.
Anti-murine IL-18 polyclonal Ab was purified from immunized rabbit
sera. Phycoerythrin (PE)-conjugated anti-CD4, PE-conjugated
anti-NK1.1, FITC-conjugated anti-CD3
, and FITC-conjugated
anti-CD8 mAbs were obtained from PharMingen (San Diego, CA).
Biotinylated mouse anti-rat lgG and biotinylated goat
anti-rabbit lgG were purchased from Jackson ImmunoResearch (West
Grove, PA). PE-conjugated streptavidin and RED670-conjugated
streptavidin were from Becton Dickinson (Mountain View, CA) and Life
Technologies (Gaithersburg, MD), respectively. Normal rat lgG and
rabbit lgG (controls) were purchased from BioMeda (Foster City, CA) and
Jackson ImmunoResearch, respectively.
Preparation of T cell subsets
Negative selection. Lymph node or spleen cells were depleted of B cells and Ia+ APC by immunomagnetic negative selection as follows: Cells were allowed to react with anti-I-Ad/b mAb and then incubated with advanced magnetic particles bound to goat anti-mouse lg (Advanced Magnetic, Cambridge, MA). A T cell population depleted of anti-I-Ad/b-labeled and/or surface Ig+ cells was obtained by removing cell-bound magnetic particles with a rare earth magnet (Advanced Magnetic). CD4+ and/or CD8+ T cells were further depleted by incubating this population with anti-CD8 and/or anti-CD4 mAb followed by magnetic particles conjugated to goat anti-rat IgG (Advanced Magnetic). Purity of the resulting populations was checked by flow cytometry. The purity of CD4+, CD8+, and CD4-CD8- subsets was consistently >97%, >97%, and >95%, respectively.
Positive selection. Cells were labeled with superparamagnetic microbeads conjugated to goat anti-rat IgG mAb (Miltenyi Biotec, Sunnyvale, CA). Labeled cells were separated from unlabeled cells by magnetic cell sorting using the MiniMACS (Miltenyi Biotec) according to the procedure described in detail (23). The magnetic cells were retained in a MiniMACS column inserted into a MiniMACS magnet while the nonmagnetic cells passed through. Labeled cells were eluted after the column was removed from the magnet.
Stimulation of T cells with anti-CD3 plus anti-CD28 mAb
Anti-CD3 and anti-CD28 mAbs (10 µg/ml each) were
coimmobilized to individual wells of 96-well flat-bottom microculture
plates (Corning 25860, Corning Glass Works, Corning, NY) in a final
volume of 0.1 ml or 24-well culture plates (Corning 25820) in a volume
of 1 ml. After 3 h, solutions were discarded and plates were
washed with PBS twice. Purified T cells were cultured in 0.2 ml
(96-well microplates) or 2 ml (24-well plates) of RPMI 1640 medium
supplemented with 10% FBS and 2-ME at 2.0 x 105
cells/well (96-well microplates) or 1.5 x 106
cells/well (24-well plates) in the presence of rIL-12 (1000 pg/ml) or
rIL-2 (100 U/ml) in a humidified atmosphere at 5% CO2 at
37°C. T cell proliferation was determined in 96-well microplates
after an 8-h pulse with 20 KBq/well of [3H]TdR. Results
were calculated from uptake of [3H]TdR and expressed as
the mean cpm ± SE of triplicate cultures. Cells and culture SNs
in 24-well culture plates were harvested and assessed for the
expression of IL-12R and IL-18R and for IFN- concentrations,
respectively.
Measurement of IFN- concentrations
IFN- concentrations were measured by ELISA. Mouse IFN-
ELISA kits were purchased from Genzyme (Cambridge, MA), and our own
ELISA system was prepared using two types of anti-mouse IFN- mAb
(XMG1.2 (Endogen, Cambridge, MA) and biotinylated R4–6A2 (R4–6A2 was
purified from R4–6A2 hybridoma and biotinylated in our laboratory)) as
well as mouse rIFN- provided by Shionogi. One U/ml in our ELISA
system corresponded to approximately 100 pg/ml in Genzyme ELISA
kits.
Immunofluorescence and flow cytometry
Cells were stained directly with FITC- or PE-conjugated
reagents. The detection of IL-2R -chain was accomplished by
incubating up to 1 x 106 cells with
biotinylated-anti-IL-2R -chain (7D4) mAb for 20 min, and then
incubating with PE-conjugated streptavidin. The detection of IL-12R was
performed as previously described (24). Briefly, cells were incubated
with 7.5 ng of rIL-12 in 10 µl medium for 60 min at 4°C. Cells were
washed and then incubated with 1 µg of rat anti-mouse IL-12 mAb
(C17.8) for 30 min at 4°C. After washing, cells were allowed to react
with 0.1 µg of biotinylated mouse anti-rat lgG followed by
incubation with RED670-conjugated streptavidin. The staining protocol
used in detection of IL-12R was applied to the detection of IL-18R.
Cells were incubated with 0.4 µg of rIL-18 in 40 µl medium for 60
min at 4°C. Cells were washed and then incubated with 0.1 µg of
rabbit anti-mouse IL-18 polyclonal Ab for 30 min at 4°C. After
washing, cells were allowed to react with 0.1 µg of biotinylated goat
anti-rabbit lgG followed by incubation with PE-conjugated
streptavidin. Stained cells were analyzed with a FACSCalibur (Becton
Dickinson).
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussion References |
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A purified T cell population was prepared from normal C57BL/6
lymph node cells. Cells were cultured in anti-CD3- and
anti-CD28-coimmobilized 24-well culture plates. After 48 h,
activated T cells were harvested, washed, re-suspended in fresh medium,
and stimulated with various cytokines (Table I
). Stimulation with IL-2 and IL-12
induced high and moderate levels of proliferation, respectively,
whereas IL-18 elicited only a marginal proliferation. IFN-
production was inducible at weak albeit significant levels only by
stimulation with IL-12. In contrast to these
anti-CD3/anti-CD28-activated cells, freshly prepared T cells
failed to proliferate or produce IFN- in response to either type of
cytokines (data not shown). Anti-CD3/anti-CD28-activated T cells
were tested for the expression of IL-2R, IL-12R, and IL-18R (Fig. 1). These activated T cells were found to
express IL-2R and IL-12R, but not IL-18R. Figure 2 shows that IL-12R is induced not only
on both CD4+ and CD8+ T cell subsets
prepared from lymph node cells or spleen cells, but also on the
CD4-CD8- T cell subset from spleen cells
although the IL-12R levels are higher in CD4+ cells than in
CD8+ and CD4-CD8- cells. These
results indicate that the activation of T cells with anti-CD3 and
anti-CD28 induces IL-2 and IL-12 responsiveness along with IL-2R
and IL-12R expression, but does not induce IL-18 responsiveness/IL-18R
expression.
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Our preceding study demonstrated that IL-12 has the capacity to
induce IL-18R expression and IL-18 responsiveness in a particular Th
clone (IL-12-responsive) as well as unfractionated naive T cells
activated with anti-CD3 plus anti-CD28 (16). Here, we
determined whether IL-12 can induce IL-18R on all of the three T cell
subsets (CD4+, CD8+, and
CD4-CD8-) that have expressed IL-12R after
stimulation with anti-CD3 plus anti-CD28. Purified T cells were
stimulated with anti-CD3/anti-CD28 for 48 h. Cells
harvested were then stimulated with rIL-12 or rIL-2 as control. Figure 3A shows that exposure to
rIL-2 fails to induce IL-18R whereas stimulation with rIL-12 results in
the induction of IL-18R (upper panels), which
confirms our previous results (16). When analysis gates were set on the
CD4+ and CD8+ T cell populations in cell
preparations obtained following IL-12 stimulation, it was observed that
CD4+ T cells and CD8+ T cells expressed low and
high levels of IL-18R, respectively. However, we found that the
population obtained following IL-12 stimulation contains a large
proportion (
75%) of CD8+ T cells and a small proportion
(<18%) of CD4+ T cells. To more accurately examine the
IL-18R expression on CD4+ T cells, CD4+ T cell-
or CD8+ T cell-depleted T cell populations were prepared
and stimulated with anti-CD3/anti-CD28 followed by exposure to
rIL-12 (Fig. 3B). Using a CD4+ T
cell-depleted fraction as a starting population, 94% enriched
CD8+ T cells were generated following IL-12 stimulation. An
analysis gate was further set on the CD8+ cells. These
CD8+ T cells expressed high levels of IL-18R (Fig. 3B, middle panel), which is consistent
with the results of Figure 3A. Seventy-two percent of
CD4+ T cells were generated from a CD8+ T
cell-depleted starting population. This population was found to contain
26% of CD4-CD8- T cells. The expression
of IL-18R on cells gated for CD4+ and CD4- is
shown in Figure 3B (upper for
CD4+ and bottom for
CD4-CD8-). CD4+ T cells again
exhibited only weak levels of IL-18R expression. In contrast,
CD4-CD8- T cells expressed high levels of
IL-18R that are comparable with those observed on CD8+ T
cells.
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. The results show
that CD4+ T cells failed to express IL-18R whereas
CD8+ and CD4-CD8- populations
expressed comparable levels of IL-18R. The IL-18R levels on these two
populations were weaker than those induced by sequential stimulation
with anti-CD3/anti-CD28 and rIL-12 shown in Figure 3
. However,
the expression of IL-18R was apparently positive compared with the
groups that included rIL-2 instead of rIL-12.
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Unfractionated resting T cells stimulated with
anti-CD3/anti-CD28 in the presence of rIL-12 or rIL-2 (control)
were restimulated with different concentrations of rIL-18 or rIL-12.
IFN- production in these cultures was determined by ELISA (Fig. 5). T cells activated with
anti-CD3/anti-CD28 in the absence of IL-12 (in the presence of
IL-2) failed to produce IFN- in response to IL-18 although they
produced moderate amounts of IFN- following IL-12 stimulation. In
contrast, anti-CD3/anti-CD28-activated T cells in the presence
of IL-12 produced large amounts of IFN- in response to rIL-18. The
levels of IFN- production by these T cells were higher than those
observed for T cells restimulated with rIL-12 instead of rIL-18. T
cells stimulated with anti-CD3/anti-CD28 in the presence of
IL-12 produced significant amounts of IFN- even when they were not
stimulated subsequently with either cytokine. This is considered to be
due to the action of IL-12 used in the first step of T cell activation
culture because T cells from cultures containing rIL-2 instead of
rIL-12 did not produce IFN- in the following cytokine-free cultures.
Thus, the results indicate that anti-CD3/anti-CD28-activated T
cells acquire IL-18 responsiveness along with the induction of IL-18R
expression following their exposure to IL-12.
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in response to rIL-18
We determined whether the IL-18R levels induced on the various T
cell subsets correlate with their IL-18 responsiveness. First, a
comparison was made between CD4+ and CD8+
T cell subsets from lymph node cells. A CD4+ or
CD8+ T cell population was prepared by depleting
CD8+ or CD4+ T cells, respectively, together
with B cells and APC. These two populations were stimulated with
anti-CD3/anti-CD28 in the presence of IL-12 for 48 h.
Cells harvested from each culture were approximately 90%
CD4+ or CD8+, but these two populations
contained significant percentages of the alternative phenotype of cells
and CD4-CD8- cells. Therefore,
CD4+ and CD8+ T cell populations with >98%
purity were isolated using a cell sorter (Fig. 6A). These sorted
CD4+ and CD8+ populations were stimulated with
different concentrations of rIL-18 or 1000 pg/ml rIL-12 (Fig. 6B). The results show that CD8+ and
CD4+ populations exhibit, respectively, high and low levels
of IFN- production in response to IL-18. It should also be noted
that there is a marked difference in IL-12-stimulated IFN-
production between CD8+ and CD4+ T cell
populations.
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). This population
consisted of approximately 50% CD3-NK1.1+
cells and 40% CD3+ (NK1.1+ or
NK1.1-) cells (Fig. 7). Following stimulation with
anti-CD3/anti-CD28 in the presence of IL-12 or IL-2, most cells
in either group remained CD4-CD8-, but the
proportion of CD3+NK1.1- cells increased in
both groups, especially in the anti-CD3/anti-CD28 plus IL-12
group (Fig. 7). These two groups of cells were stimulated with rIL-18.
As shown in Figure 8,
anti-CD3/anti-CD28-plus-IL-2-activated
CD4-CD8- cells produced moderate amounts of
IFN- in response to IL-18. In contrast, stimulation of
anti-CD3/anti-CD28-plus-IL-12-activated
CD4-CD8- cells with IL-18 resulted in
strikingly high levels of IFN- production. The levels were, in fact,
one order higher than those induced in CD8+ T cells as
shown in Figure 6. Activated CD4-CD8- cells
were also found to be high responders to IL-12 compared with activated
CD8+ T cells shown in Figure 6. Thus, these results
indicate that compared with the CD4+ T cell subset, the
CD8+ T cell subset has a larger capacity to produce IFN-
in response to IL-18, but CD4-CD8- cells can
exhibit much more potent IL-18 responsiveness.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussion References |
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production by T cells, but
there is a critical difference in the T cell activation stages that
prepare targets for these cytokines. Stimulation of resting T cells
with anti-CD3 and anti-CD28 results in responsiveness to IL-12
but not to IL-18, and IL-18 responsiveness is induced only after
TCR/CD28-activated T cells are exposed to IL-12. Resting
CD8+ and CD4+ T cells exposed to IL-12
during incubation with anti-CD3/anti-CD28 exhibited respective
high and low levels of IL-18R expression and IL-18-stimulated IFN-
production. Moreover, CD4-CD8- cells
(probably
CD3+CD4-CD8-NK1.1-
cells) exhibited levels of IL-18R expression comparable to those
observed on CD8+ T cells after IL-12 exposure, but
exhibited much more potent (one order stronger) IFN- production in
response to IL-18 than did CD8+ T cells. Thus, the present
results show that 1) resting T cells that have no IL-18 responsiveness
can respond to IL-18 only when their TCR/CD28 are stimulated in the
presence of IL-12; 2) there are substantial differences in the levels
of IL-18R expression and IL-18-stimulated IFN- production among T
cell subsets; and 3) the magnitude of IL-18-stimulated IFN-
production by these subsets is determined by the levels of IL-18R
induced as well as the cell type-associated property/strength of the
IL-18R-mediated signaling.
We have previously shown that, using a recently established
IL-12-responsive T cell clone, the action of IL-18 depends on the
presence of IL-12 or preexposure to IL-12 (16). IL-12 was found to be a
particular cytokine capable of generating IL-18 responsiveness through
inducing IL-18R expression (16). These observations were made mainly on
a single T cell clone (24) and partly observed using unfractionated
resting T cells (16). The present study first confirmed that IL-12
contributes to IFN- production by T cells through direct action on T
cells and that IL-12 also functions to up-regulate IFN- production
by inducing IL-18R expression on T cells and endowing them with IL-18
responsiveness. Next, our results reveal that there is a fundamental
difference in the capacity to produce IFN- in response to IL-18
between CD8+ and CD4+ T cell subsets.
CD8+ T cells stimulated with anti-CD3/anti-CD28 in
the presence of IL-12 expressed high levels of IL-18R and produced
moderate amounts of IFN- in response to IL-18. In contrast,
similarly treated CD4+ T cells expressed only marginal
levels of IL-18R and produced much lower amounts of IFN- compared
with CD8+ T cells. It has been shown that T cells and NK
cells produce IFN- in response to IL-12 and that both
CD4+ and CD8+ T cells are primed for IFN-
production (13, 25, 26). In contrast to resting T cells, there is no
accessory cell requirement for activated T cells and NK cells to
respond to IL-12 (13). In the present study, purified CD4+
and CD8+ T cells that were activated with anti-CD3 plus
anti-CD28 expressed high and low levels of IL-12R, respectively.
Therefore, differential levels of IL-18R expression on CD8+
and CD4+ T cells exposed to IL-12 would not be ascribed to
a quantitative difference in IL-12R expression but rather to a
qualitative difference in IL-12R-mediated intracellular signaling
leading to IL-18R expression.
CD4+ and CD8+ T cells activated with
anti-CD3/anti-CD28 were shown to produce smaller and larger
amounts of IFN-, respectively, in response to IL-12. However, this
does not necessarily represent the difference in the overall capacity
to produce IFN- between CD4+ and CD8+ T
cells. Physiologically, T cells are activated through stimulation of
TCR and CD28 with their respective ligands on APC (8, 9). IL-12 is
produced by APC when APC are stimulated with CD40 ligand (27, 28, 29).
However, CD40 ligand expression is restricted to the CD4+ T
cell subset (30, 31). Therefore, when a separated CD4+ or
CD8+ T cell subset is stimulated with APC capable of
producing IL-12 instead of stimulation with anti-CD3/anti-CD28
plus rIL-12, the CD4+ T cell subset may be the stronger
IFN- producer.
An interesting aspect of the present study concerns the induction of
IL-18 responsiveness in CD4-CD8- cells. The
splenic CD4-CD8- population contained
approximately 40% of CD3+ cells. Stimulation of this
population with anti-CD3/anti-CD28 resulted in an increase in
the proportion of CD3+
(CD3+NK1.1-) cells especially when cultures
included IL-12. Conversely, the proportion of
CD3-NK1.1+ decreased from 50% to less than
10%. Stimulation of the CD4-CD8- population
with anti-CD3/anti-CD28 in the presence of IL-2 also increased
the proportion of CD3+NK1.1- cells along with
a decrease in the proportion of CD3-NK1.1+
cells. Of the resultant two populations, the group including IL-12
induced IL-18R but the other group failed to induce the receptor
although this group contained more CD3-NK1.1+cells than the former group. Moreover, we have recently observed
that while CD3-NK1.1+ cells can be activated
in response to the combination of cytokines including IL-18, IL-18R was
undetectable on this subset before and after activation (our
unpublished observations). Together, it is unlikely that
CD3-NK1.1+ cells (9%) in the population
prepared following stimulation with anti-CD3/anti-CD28 plus
IL-12 express IL-18R. Nevertheless, it will be required to determine
whether IL-18R is actually expressed by activated
CD3+NK1.1- cells that are the predominant cell
type (65%).
Besides IL-12, IL-2 also stimulates production of IFN- from T and NK
cells (32, 33). Our results demonstrated that IL-2 failed to induce
IL-18R in CD4+ and/or CD8+ T cells as well as
in CD4-CD8- cells. In contrast, it is obvious
that IL-12 is a representative cytokine capable of inducing IL-18R.
However, it remains to be investigated whether IL-12 is absolutely
required for inducing IL-18 or whether there are other cytokine
substitutes.
More important is that, while CD4-CD8- cells
activated with anti-CD3/anti-CD28 plus IL-12 expressed levels
of IL-18R comparable with those observed on CD8+ T cells,
the former cells produced much greater (one order) amounts of IFN-
in response to IL-18. These observations are similar to those made for
IFN- following IL-12 stimulation; namely, despite comparable levels
of IL-12R expression on anti-CD3/anti-CD28-activated
CD4+, CD8+, and
CD4-CD8- cells, the amounts of IFN-
produced by these three subsets greatly differed. Thus, similar to a
difference in the IL-12-stimulated IFN- production, the marked
capacity of CD4-CD8- cells to produce IFN-
in response to IL-18 may be understood mainly by considering the
structure of IL-18R and/or the prominent efficacy of IL-18R-mediated
intracellular signaling. IL-18R was recently cloned and shown to be a
single chain with the homology to IL-1R (34). The possibility still
exists that there are other subunits of the IL-18R that affect IL-18
responsiveness but not ligand binding.
Our results illustrate that IL-12 is capable of inducing IL-18R
expression and IL-18 responsiveness in TCR/CD28-stimulated T cells that
lead to high levels of IFN- production and that this effect is
expressed differently by various T cell subsets:
CD4-CD8- >>> CD8+ >
CD4+. The magnitude of IFN- production induced by T
cells through collaboration between IL-12 and IL-18 is determined not
only by the levels of IL-18R induced by IL-12 but also by the
intracellular signaling machinery leading to IFN- production, Thus,
it would be important to investigate how the operation of such
machinery is regulated by external and internal stimuli and whether the
IL-12-IL-18 collaboration has the biologic significance in some
pathophysiologic conditions.
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Acknowledgments |
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Hiromi Fujiwara, Biomedical Research Center, Osaka University Medical School, 2–2, Yamada-oka, Suita, Osaka 565-0871, Japan. E-mail address:
3 Abbreviations used in this paper: SN, supernatant; PE, phycoerythrin.
Received for publication September 2, 1997. Accepted for publication December 17, 1997.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussion References |
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. J. Immunol. 136:2445.[Abstract]
-inducing factor in enhanced production of IFN-. J. Immunol. 159:2125.-inducing factor (IGIF) is a costimulatory factor on the activation of Th1 but not Th2 cells and exerts its effect independently IL-12. J. Immunol. 158:1541.[Abstract]
by resting human T cells and large granular lymphocytes: requirement for accessory cell factors, including interleukin-1. Cell. Immunol. 113:130.[Medline]
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A. A. Akhiani, K. Schon, and N. Lycke Vaccine-Induced Immunity against Helicobacter pylori Infection Is Impaired in IL-18-Deficient Mice J. Immunol., September 1, 2004; 173(5): 3348 - 3356. [Abstract] [Full Text] [PDF]
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