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Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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, at least in part through CD58-CD2 interactions. Recently, the
B7-like molecule, B7-H1 (PD-L1), was described and shown to regulate T
cell activation; however, there are conflicting reports on whether it
stimulates or inhibits T cell cytokine synthesis. B7-H1 is not
expressed constitutively by ECs; however, it is rapidly induced by
IFN-, and synergistically by IFN- and TNF. In inflamed skin,
B7-H1 is expressed by a subset of microvessels, and by keratinocytes,
but is barely detectable in normal skin. Blocking the interaction of
EC-expressed B7-H1 with its T cell ligand, programmed death-1 (PD-1),
using a PD-1-Fc fusion protein, or by blocking B7-H1 expression with
morpholino antisense oligonucleotides, augments expression of IL-2 and
IFN-, implicating B7-H1 as a negative regulator of cytokine
synthesis. However, signaling through PD-1 does not affect induction of
the activation markers CD25 or CD69 on T cells, suggesting that its
effects are specific to cytokine synthesis. The suppressive effects of
B7-H1 on cytokine expression are proportional to the strength of the
primary stimulus, allowing for B7-H1 to determine the level of T cell
activation in response to ECs. Our results demonstrate that B7-H1
negatively regulates cytokine synthesis in T cells activated by
ECs. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The two signal hypothesis of T cell activation is well-established and several costimulatory molecules have been identified (7, 8, 9). B7.1 and B7.2 are crucial for activation of naive T cells but appear to be less important for activation of memory T cells (10). Costimulation enhances TCR signaling and decreases the threshold number of TCRs that must be engaged for T cell activation to be triggered (11). In this sense, the expression of costimulatory molecules can set a threshold level of Ag at which T cells will become activated (3, 12, 13). This may be particularly important in the periphery for maintenance of tolerance toward self Ags.
We and others have shown that human ECs lie along a spectrum of Ag presentation/costimulatory ability, with professional APC at one end, able to activate naive and memory T cells, and stromal cells such as fibroblasts and smooth muscle cells (SMCs) at the other, unable to activate either naive or memory T cells (3, 14, 15, 16). Human ECs lie between these two extremes and are able to activate resting memory T cells, but not naive T cells, and do so by promoting aggregation of lipid rafts on T cells at the interface with ECs (17). Human ECs do not express B7.1 or B7.2, but instead provide costimulatory signals through the binding of CD58 (LFA-3) on the ECs to CD2 on the T cells (18, 19). Human ECs have been reported to provide B7-dependent costimulation in trans (20). Mice lack the CD58 gene and instead use CD48 as a ligand for CD2; however, the affinities and cellular distribution of this family differ considerably between human and mouse, making mice a less than ideal model for this area of human immunology (21). Blocking Abs to CD2 or CD58 are not sufficient to completely block human EC costimulation, indicating the existence of alternative EC costimulatory molecules (22).
Recently, a new B7-like molecule, B7-H1, was described (23, 24) and reviewed (25, 26). B7-H1 was found in an
expressed sequence tag database search for homologous sequences
to human B7.1 and B7.2 (23) and is a type I transmembrane
protein with 20% amino acid identity to B7.1 and 15% amino acid
identity to B7.2. Costimulation of T cells with B7-H1-Fc fusion protein
has been shown to induce T cell proliferation and secretion of IL-10
and IFN-, but minimal IL-2 (23). Recently, contrary
data have been presented suggesting that B7-H1 (programmed death-1
ligand (PD-L)1) negatively regulates cytokine synthesis (24, 27). Programmed death-1 (PD-1) was identified as a receptor for
PD-L1 and contains an immune receptor tyrosine-based inhibitory motif
(ITIM). Coligation of PD-1 and the TCR leads to rapid phosphorylation
of SHP-2, a phosphatase suggested to attenuate TCR signaling
(28). Moreover, animals deficient in PD-1 succumb to
autoimmune disorders, including dilated cardiomyopathy
(29). In humans, B7-H1 has been shown to be expressed on a
subset of PHA-activated T cells, on IFN-- and LPS-activated
monocytes (23), and on IFN--treated keratinocytes
(24). A second ligand for PD-1, PD-L2, was recently
described and has a broadly similar distribution (30).
In this study, we have addressed two questions: first, whether B7-H1 is
expressed by human ECs; and, second, whether B7-H1 expression by APC
promotes or inhibits T cell cytokine synthesis. We find that B7-H1 is
inducible on human ECs by IFN-, both in vitro and in vivo, and that
inhibiting B7-H1 interaction with its receptor on T cells, PD-1,
augments T cell cytokine synthesis.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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rIFN- (supplied by units) and TNF-
(supplied by weight)
were obtained from BioSource International (Camarillo, CA). mAb to
B7-H1 and plasmids pcDNA3-B7-H1 and PD-1-Ig were provided by L. Chen
(Mayo Clinic, Rochester, MN). The control Ab, HB64, was isolated from
the hybridoma clone obtained from the American Type Culture Collection
(Manassas, VA). Anti-VCAM-1 and anti-ICAM-1 Abs were from the
Developmental Studies Hybridoma Bank (University of Iowa, IA). Goat
anti-mouse Ig FITC was from Jackson ImmunoResearch Laboratories
(West Grove, PA). Directly conjugated Abs to CD3, CD69, and CD25 were
from BD Biosciences (Mountain View, CA). PHA was obtained from
Sigma-Aldrich (St. Louis, MO).
Cell isolation and culture
HUVECs were isolated from umbilical veins and cultured as described previously (19) on 1% gelatin-coated tissue culture plastic in medium 199 (M199) supplemented with 20% FBS, antibiotics (all from Life Technologies, Grand Island, NY), endothelial growth supplement (Collaborative Biomedical Products, Bedford, MA), and heparin (Sigma-Aldrich). Lung microvascular ECs (LUMVECs) were purchased from Clonetics (Walkersville, MD). SMCs were cultured from umbilical artery explants grown in M199 with 10% FBS and antibiotics. Skin fibroblasts were purchased from ATCC and were grown in the same medium as the SMC. Purified T cells were prepared from peripheral blood as previously described (3).
RNA analysis
Cells were grown until confluent on 100-mm dishes and treated
with IFN- and/or TNF- at the concentration indicated for 4–24 h.
Total RNA was isolated using TRIzol reagent (Life Technologies). For
Northern analysis, 20 or 30 µg RNA was electrophoresed on a 1.2%
agarose-formaldehyde gel and then transferred to a nylon membrane using
a Turboblotter (Schleicher & Schuell, Keene, NH). Blots were
preincubated in hybridization solution (50% formamide, 1% SDS, 5x
SSC, 5x Denhardt’s solution, 2.5% dextran sulfate, and 100 µg/ml
denatured salmon sperm DNA) for 1 h at 42°C and then hybridized
at 42°C overnight in hybridization solution with 1 x
106 cpm/ml of a
[-32P]dATP-radiolabeled DNA probe. Probes
were prepared by random priming either the full-length B7-H1 cDNA or a
PCR fragment of GAPDH (Decaprime II kit; Ambion, Woodward, TX). Blots
were exposed to autoradiography film for 7–75 h or were analyzed on a
PhosphorImager (Molecular Dynamics, Sunnyvale, CA).
FACS analysis
ECs (2 x 105) were treated for
24 h with saturating doses of IFN- (100–1000 U/ml) and/or
TNF- (10 ng/ml). Cells were washed with HBSS, trypsinized, and
washed with 1x PBS/1% BSA. Cells were then incubated with 5
µg/ml B7-H1 mAb or HB64 control mAb in 1x PBS/1% BSA/1% goat
serum for 30 min on ice, washed in 1x PBS/1% BSA, and incubated
with goat anti-mouse Ig FITC (1:200) for 30 min on ice. Finally,
cells were washed once with 1x PBS/1% BSA, once with 1x
PBS, resuspended in 500 µl of 1x PBS, and analyzed immediately
on a FACSCalibur (BD Biosciences).
EC transfection
ECs were grown to 70% confluence in 24-well plates and then transfected with 0.25 µg/24-well of the indicated plasmid using Lipofectamine and Plus reagent, according to the manufacturer’s protocol (Life Technologies). Cells were rested overnight, then purified T cells and PHA at various concentrations were added. These cocultures were incubated for 48 h, after which supernatants were harvested for quantification of cytokines by ELISA. All cytokine ELISA kits were from R&D Systems (Minneapolis, MN).
Antisense morpholino oligonucleotides
An antisense morpholino oligonucleotide, specific for human B7-H1, was designed and synthesized by GeneTools (Corvallis, OR). The invert of this was used as a control. To load ECs with the morpholinos, cells were washed and then incubated with 1.4 µM antisense or invert along with EPEI special delivery reagent diluted in OptiMEM, according to the manufacturer’s instructions. After a 3-h incubation, cells were washed and then rested in medium for 4 h. Control experiments using a FITC-labeled morpholino indicated that essentially all cells took up the oligonucleotide, yielding a single peak by FACS (data not shown). Purified T cells (5 x 105/24-well) and PHA were then added, and the plates incubated for 24 h. Supernatants were then harvested for quantification of cytokines by ELISA.
Immunohistochemistry
Human skin was obtained from discarded elective surgery material
under protocols approved by the Institutional Review Board (Irvine,
CA). Small blocks (2 x 2 x 3 mm) of tissue were
maintained for 24 h, either in medium or medium containing IFN-
(1000 U/ml) and TNF (10 ng/ml), and then harvested, snap-frozen, and
cryosectioned. Sections (10 µm) were incubated for 1 h with
either control mAb (HB64) or with mAb to B7-H1 or CD31, washed, and
then incubated with a universal secondary Ab (Vector Laboratories,
Burlingame, CA), followed by detection with an ABC Elite kit (Vector
Laboratories).
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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To determine whether B7-H1 is expressed by human ECs, we performed
Northern blot analysis. Total RNA was isolated from untreated ECs or
from ECs treated with either IFN- (1000 U/ml) or TNF- (10 ng/ml)
for 20 h. As shown in Fig. 1
A, B7-H1 RNA was detectable
in ECs treated with IFN-, but not in resting or TNF--treated ECs.
In some cultures, very low levels of transcript are apparent in resting
cells, perhaps reflecting donor variability. A prominent transcript of
4.1 kb was observed; however, we did not see the 7.2-kb transcript seen
in some human tissues (23). Interestingly, we also
observed a smaller transcript of 1.8 kb, present at much lower levels
and only apparent after longer exposures (see Fig. 3A). This
smaller transcript is also present in the multiple tissue northern blot
published by Freeman et al. (24).
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but not by TNF-, we wanted to determine
whether its expression was synergistically induced by these cytokines.
Northern analysis was performed on ECs treated with various
concentrations of IFN- and TNF-, either alone or in combination.
As shown in Fig. 1
B, IFN- and TNF-, when used in
combination, had a greater than additive effect on the level of B7-H1
mRNA induced. IFN- alone induced B7-H1 RNA in a dose-dependent
manner, whereas TNF- alone was ineffective at any concentration
(Fig. 1B). A combination of 100 U/ml IFN- and 1, 10, or
100 ng/ml TNF- induced a 2-fold increase over the additive effect of
IFN- and TNF- used alone.
We next examined the effect of IFN- and TNF- on the levels of
B7-H1 protein expressed by ECs. ECs were treated with IFN- and
TNF-, either alone or in combination, for 20 h and then
analyzed by FACS using a B7-H1-specific Ab. Consistent with our
Northern data, IFN- and TNF- in combination had a 3-fold greater
than additive effect on the expression of B7-H1 (Fig. 1C).
Resting or TNF-treated ECs express little to no B7-H1 on their surface,
and the induction by combined cytokine treatment is homogenous across
the EC population.
B7-H1 is induced rapidly in ECs
The expression of B7.1 and B7.2 is temporally regulated, with B7.2
being induced much more rapidly. To determine the kinetics of induction
of B7-H1 on ECs, cells were left untreated or were treated with IFN-
and TNF-, either alone or in combination, and then harvested at
various times for Northern analysis. B7-H1 RNA was expressed by ECs as
early as 4 h in ECs treated with IFN-. Expression peaked
between 8 and 12 h and remained high at 24 h (Fig. 2A). Protein levels remained
high out to at least 72 h (Fig. 2B). The use of IFN-
and TNF- in combination did not affect the kinetics of expression of
B7-H1 (Fig. 2A).
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Having established the inducible expression of B7-H1 in large
vessel ECs (HUVECs), we next wished to examine its expression by
microvascular ECs as well as by stromal cells. HUVECs, LUMVECs,
SMCs, or fibroblasts were left untreated or were treated with IFN-
and TNF-, either alone or in combination for 20 h, and then
harvested for analysis by Northern blot. B7-H1 RNA was expressed by all
the cell types tested when treated with IFN-, or a combination of
IFN- and TNF- (Fig. 3).
B7-H1 regulates cytokine synthesis by ECs
We and others have previously reported that ECs provide
costimulation to resting T cells, resulting in cytokine synthesis. ECs
stimulate memory but not naive cells and promote the expression of IL-2
and IFN-, but not IL-4 (3, 4). Recently, conflicting
reports have appeared on the role of B7-H1 during T cell activation,
and in particular, whether it mediates positive (costimulatory) or
negative signals (23, 24). In part, this conflict may be
due to the use of B7-H1-Fc fusion proteins, either in soluble form or
bound to plates or beads. Under different conditions, binding of the
fusion proteins to PD-1 (the B7-H1 receptor on T cells) may be blocking
or stimulatory. To avoid these problems we have used PD-1-Fc fusion
protein, which we believe acts as a more reliable dominant negative.
This reagent binds B7-H1 on the APC and blocks receptor-ligand
interactions, thereby avoiding the potential for direct signaling
through PD-1.
In a preliminary series of experiments, we established that
PHA-activated T cells, cocultured with ECs, induce significant
expression of B7-H1 on ECs (Fig. 4A). Furthermore, supernatants
removed from 24-h cocultures of T cells and ECs are equally as
effective as cytokines in inducing B7-H1 on resting ECs (Fig. 4B). ECs were then transfected with either control plasmid
or expression plasmids encoding dominant negative PD-1, or full-length
B7.2, which we used as a positive control. Cells were cultured in
various concentrations of PHA, which we used as a primary stimulus, and
supernatants were harvested at 48 h for analysis of cytokine
secretion. Under these conditions, B7.2-expressing ECs strongly
enhanced T cell secretion of both IL-2 and IFN- (at a PHA
concentration of 10 µg/ml, control-transfected ECs induced 317 U/ml
IL-2 and 741 U/ml IFN-, while B7.2-transfected ECs induced 3580 U/ml
IL-2 and 3822 U/ml IFN-). Interestingly, we find that blocking
B7-H1-PD-1 interactions also enhances expression of these cytokines
(Fig. 4, C and D). This suggests that B7-H1
mediates a negative signal in this system; data that are consistent
with previous reports that PD-1, possibly through its ITIM motifs,
mediates a negative regulatory signal for T cell activation and
cytokine synthesis (31). Although secretion of both IL-2
and IFN- were augmented when B7-H1 signaling was blocked, we did not
see a consistent effect on IL-10 secretion (data not shown).
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and TNF-
and harvested after 24 h for analysis by FACS (Fig. 5A). We consistently saw a
70–85% decrease in mean fluorescence intensity in antisense vs invert
controls, indicating that the antisense molecules effectively blocked
B7-H1 translation. Neither antisense nor invert had any effect on
induced expression of ICAM-1 or VCAM-1 (Fig. 5B), indicating
that the antisense is specific for B7-H1 and does not globally suppress
translation.
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(Fig. 5, C and D). We found increases of 
2- to 3-fold
for IFN-, with more modest increases of 25–50% for IL-2. Again, we
did not see a consistent difference in expression of IL-10 when B7-H1
signaling was reduced (data not shown). The more modest increases seen
with antisense treatment compared with the expression of dominant
negative PD-1 may relate to the possible presence of alternative
ligands for the PD-1 receptor on ECs. A second ligand (PD-L2) was
recently reported (30), and whereas antisense to B7-H1
(PD-L1) would not reduce PD-L2 expression, the PD-1 fusion protein
would bind and block both ligands.
Interestingly, over the course of several dose-response experiments, we
failed to see an enhanced effect of B7-H1-PD-1 interaction at lower
levels of TCR stimulation, as has been reported previously (24, 30). Rather, our data suggest that B7-H1-PD-1 interaction
suppresses cytokine synthesis proportional to the strength of the
primary stimulus (Figs. 4 and 5). These data are consistent with a role
for B7-H1 in setting thresholds for T cell activation (see
Discussion).
B7-H1 signaling does not affect expression of T cell activation markers
We wondered whether B7-H1 signals generally suppressed T cell
activation or whether the signal was more specific. To investigate
this, T cells were cultured with morpholino-treated ECs as described
above and then harvested for analysis of CD3, CD25, and CD69
expression. CD69 is rapidly induced on activated T cells, whereas
CD25—the high affinity IL-2R—appears more slowly. T cells were
analyzed at both early and late times after activation and no
significant differences in expression of CD25 or CD69 were seen when
the cells were activated by invert or antisense-treated ECs (Table I). These data suggest that B7-H1
signaling by ECs affects the level of T cell cytokine expression, but
does not affect other aspects of activation as assessed by induction of
the activation markers CD25 and CD69.
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To examine the expression of B7-H1 under inflammatory conditions,
we used a previously described ex vivo model whereby small biopsies of
normal skin are cultured overnight in medium or medium containing
cytokines (32). Under these conditions, inflammatory
markers such as E-selectin and VCAM-1 can be reliably induced on ECs. A
control mAb did not stain untreated or treated tissue (Fig. 6, A and B);
however, blood vessels were easily detected in untreated skin using a
CD31 mAb (Fig. 6C). B7-H1 was barely detectable in untreated
skin, with only keratinocytes and occasional vessels showing very weak
staining (Fig. 6D). In contrast, there was a significant
up-regulation of B7-H1 on inflamed vessels induced by IFN- and
TNF- (Fig. 6, E and inset). Furthermore, it
appears that B7-H1 may only be present on a subset of vessels as fewer
vessel profiles were apparent than were detected using the CD31 mAb
(compare Fig. 6, C–E).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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There is now a mounting body of evidence supporting the contention that human ECs have an important role in initiating and shaping immune responses in the periphery (4, 5, 6), although there are also data suggesting otherwise (33, 34). The costimulatory and regulatory molecules used by ECs have not been well-defined. Neither resting nor activated ECs express the costimulatory molecules B7.1 and B7.2; however, there is some evidence that EC costimulation may involve B7 acting in trans (20). A receptor for B7-H1 (PD-L1) was recently identified on activated T cells and shown to be identical with PD-1 (24). PD-1 is weakly homologous to CTLA-4 and contains an ITIM, suggesting that it may serve an inhibitory function during T cell activation. In support of this, PD-1 knockout mice develop a lupus-like arthritis and glomerulonephritis, as well as augmented B cell proliferation (35). In addition, they develop an autoimmune-dilated cardiomyopathy (29). These data suggest that B7-H1 may serve to maintain peripheral tolerance by acting as a counter influence to costimulation through other members of the CD28 family (31). However, it should be noted that B7-H1 has also been shown to provide positive signals for T cell proliferation and cytokine synthesis (23). The basis for these conflicting findings has yet to be determined.
We find that B7-H1 is rapidly induced on HUVECs by IFN-, a result in
line with recent data showing induction of B7-H1 on mouse ECs
(36). In light of the significant differences between
mouse and human immunology as it relates to the endothelium, it is not
clear yet what might be the significance of this finding. We have
identified a putative promoter region for human B7-H1 in the High
throughput genomic sequencing database, and consistent with its
inducibility by IFN-, it contains several IFN--responsive
elements, including an IFN stimulation response element and
several IFN regulatory factor motifs (our unpublished
observations).
Our finding of induced expression of B7-H1 on ECs, both in vitro and in
vivo, suggests that this molecule may serve an immunomodulatory
function at the vessel wall. Importantly, by avoiding the potential
pitfalls associated with the use of ligand-Ig fusion proteins, and
using antisense and receptor-Ig fusion proteins, we have shown
unequivocally that blocking of B7-H1 on ECs leads to augmented IL-2 and
IFN- synthesis in vitro, implicating this molecule as a physiologic
inhibitor of T cell activation at the vessel wall in vivo.
Freeman and colleagues (24, 30) have proposed that B7-H1
(PD-L1) may be involved in setting thresholds for activation in the
periphery. We have previously reported that ECs lie along a spectrum of
Ag presenting ability and are able to activate resting CD45RO memory T
cells but not CD45RA naive T cells. Moreover, we found distinct
thresholds for activation of CD69 expression and IFN- and IL-2
synthesis (3). A balance must be met in the periphery
between tolerance and the ability to rapidly induce recall responses.
This likely involves the setting and maintaining of finely tuned
thresholds. TNF-inducible expression of the costimulatory molecule
inducible costimulator (ICOS) ligand (GL50/B7RP-1/B7 h/LICOS) on
cultured ECs has recently been reported (37), and we have
confirmed this finding (our unpublished observations).
Expression of ICOS ligand along with CD58 promotes T cell activation by
ECs (37). In the absence of B7.1 and B7.2 expression on
human ECs, the combination of CD2 and ICOS ligation by CD58 and ICOS
ligand, respectively, may be sufficient to promote T cell activation in
the presence of moderate doses of Ag. There may also be a contribution
late in the response from B7 expressed on T cells (20). At
lower doses of Ag, the suppressive effects of B7-H1 may limit local
IL-2 synthesis to a level insufficient to support T cell activation and
expansion. Similarly, limiting the level of IFN- may reduce EC
expression of adhesion, MHC and costimulatory molecules, and may also
reduce local activation of macrophages. There may also be reduced
expression of T cell activation markers, although this was not observed
in our experiments. In vivo, where blood flow through tissue can limit
local accumulation of cytokines, the immediate level of synthesis will
acutely affect the level of cytokines experienced by extravasated
leukocytes, thus a complex interplay between the concentration of Ags,
the density of MHC molecules, and the expression of costimulatory and
inhibitory molecules will act to set the threshold for peripheral T
cell activation (3).
Expression by ECs of different combinations of molecules mediating EC-T
cell interactions, such as CD58, B7-H1, ICOS ligand, OX40 ligand
(38), and CD40 (39) may be important in
shaping immune responses under different conditions. We have shown that
the initial phase of T cell activation in response to Ag presentation
by ECs involves synthesis of IL-2 and IFN-, but not IL-4
(3). Over the first 24 h, very little IL-10 is
synthesized; however, by 48 h, substantial quantities of IL-10 are
secreted. IL-10 can down-regulate IL-12 synthesis and may skew a
response more toward a Th2 type. However, we did not see evidence of
this, suggesting either that the combination of costimulatory molecules
expressed by ECs favors a more Th1-like response, or that Th2 cytokines
may be expressed later, a possibility consistent with the reported
requirement for several rounds of division before primed T cells
express IL-4 (40). Somewhat surprisingly, we did not see a
consistent role for B7-H1 in modulating IL-10 synthesis (23, 24). In some experiments, blocking B7-H1-PD-1 interaction
resulted in substantial increases in IL-10 synthesis, whereas in other
cultures there was no effect, even though IL-2 and IFN- were
significantly augmented (data not shown). It is possible that this
relates to donor differences, as both the ECs and T cells are from
multiple donors.
In addition to B7-H1 and ICOS ligand, two other B7-like molecules have
recently been cloned. PD-L2 is a second ligand for PD-1
(30) and seems to have a similar function. B7-H3 is
expressed on dendritic cells and appears to be a costimulatory molecule
for IFN- synthesis (41). Interestingly, we found
evidence supporting an alternative form of B7-H1 expressed on ECs,
although we have not confirmed this directly. The antisense morpholinos
completely blocked B7-H1 expression on >70% of cells, but did not
affect expression on the remaining cells. We found no heterogeneity in
uptake of the morpholino, suggesting that the heterogeneity lies at the
level of mRNA or protein expression. We have identified a shorter
transcript on Northern blots and several ESTs exist that code for a
shorter protein, beginning at an alternative initiation codon.
Translation of this protein would not be inhibited by the morpholino we
used. Additional experiments are required to confirm expression, and to
determine the functional relevance of this putatively truncated
protein.
In summary, our data show that expression of B7-H1 is inducible on ECs,
both in vitro and in vivo. Furthermore, B7-H1 negatively regulates T
cell synthesis of IL-2 and IFN-, and possibly IL-10, but does not
affect expression of T cell activation markers in vitro. In conjunction
with in vivo studies (29, 35), our data suggest that
expression of B7-H1 in the periphery may regulate local levels of
immune inflammation.
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Acknowledgments |
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Christopher C. W. Hughes, Department of Molecular Biology and Biochemistry, University of California, 3205 Bio Science II, Irvine, CA 92697. E-mail address: cchughes{at}uci.edu
3 Abbreviations used in this paper: EC, endothelial cell; LUMVEC, lung microvascular EC; SMC, smooth muscle cell; PD-1, programmed death-1; ITIM, immune receptor tyrosine-based inhibitory motif; PD-L, programmed death-1 ligand; ICOS, inducible costimulator.
Received for publication April 30, 2002. Accepted for publication July 22, 2002.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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L. Chen, Z. Zhang, W. Chen, Z. Zhang, Y. Li, M. Shi, J. Zhang, L. Chen, S. Wang, and F.-S. Wang B7-H1 Up-Regulation on Myeloid Dendritic Cells Significantly Suppresses T Cell Immune Function in Patients with Chronic Hepatitis B J. Immunol., May 15, 2007; 178(10): 6634 - 6641. [Abstract] [Full Text] [PDF]
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M. R. Nazareth, L. Broderick, M. R. Simpson-Abelson, R. J. Kelleher Jr., S. J. Yokota, and R. B. Bankert Characterization of Human Lung Tumor-Associated Fibroblasts and Their Ability to Modulate the Activation of Tumor-Associated T Cells J. Immunol., May 1, 2007; 178(9): 5552 - 5562. [Abstract] [Full Text] [PDF]
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H. Maier, M. Isogawa, G. J. Freeman, and F. V. Chisari PD-1:PD-L1 Interactions Contribute to the Functional Suppression of Virus-Specific CD8+ T Lymphocytes in the Liver J. Immunol., March 1, 2007; 178(5): 2714 - 2720. [Abstract] [Full Text] [PDF]
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 M. Isobe, H. Kosuge, and J.-i. Suzuki T Cell Costimulation in the Development of Cardiac Allograft Vasculopathy: Potential Targets for Therapeutic Interventions Arterioscler. Thromb. Vasc. Biol., July 1, 2006; 26(7): 1447 - 1456. [Abstract] [Full Text] [PDF]
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H. K. Kim, H. Guan, G. Zu, H. Li, L. Wu, X. Feng, C. Elmets, Y. Fu, and H. Xu High-level expression of B7-H1 molecules by dendritic cells suppresses the function of activated T cells and desensitizes allergen-primed animals J. Leukoc. Biol., April 1, 2006; 79(4): 686 - 695. [Abstract] [Full Text] [PDF]
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L. M. Holets, J. S. Hunt, and M. G. Petroff Trophoblast CD274 (B7-H1) Is Differentially Expressed Across Gestation: Influence of Oxygen Concentration Biol Reprod, February 1, 2006; 74(2): 352 - 358. [Abstract] [Full Text] |
) as a negative control. Error bars represent SEM; where
absent, the error bar was smaller than the symbol. *, Significantly
different from control (p < 0.05 by Student’s
t test). One of three similar experiments.