| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
* Laboratory of Transplantation Immunology and
Nephrology Service of Notre Dame Hospital, Centre Hospitalier de l’Université de Montréal, Université de Montréal, Montreal, Quebec, Canada;
Department of Surgery, Second Affiliated Hospital of the Zhejiang Medical College, Zhejiang University, Hangzhou, Zhejiang, People’s Republic of China; and
Human Genome Sciences Inc., Rockville, MD 20850
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
in vitro in a Transwell assay. Such an effect could also be observed in T cells pretreated with soluble or solid-phase HveA-Fc or anti-LIGHT mAb, suggesting that LIGHT reverse signaling was likely responsible for chemotaxis inhibition. TR6 pretreatment also led to T cell chemotaxis suppression in vivo in the mice, confirming in vivo relevance of the in vitro observation. Mechanistically, a small GTPase Cdc42 failed to be activated after TR6 pretreatment of human T cells, and further downstream, p38 mitogen-activated protein kinase activation, actin polymerization, and pseudopodium formation were all down-regulated in the treated T cells. This study revealed a previously unknown function of TR6 in immune regulation, and such an effect could conceivably be explored for therapeutic use in controlling undesirable immune responses. |
Introduction |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
receptor (LTR) (1, 4, 6) in addition to TR6. It is expressed on the surface of activated T cells (6) and immature dendritic cells (7). Our recent study has shown that LIGHT is expressed in resting T cells as well according to confocal microscopy (8). LIGHT costimulates T cell responses via HveA (7, 9, 10). We have demonstrated that LIGHT, although being a ligand, also reversely transduces costimulatory signals into T cells (8, 11). Moreover, LIGHT induces apoptosis in cells expressing both HveA and LTR (12) or LTR alone (13). Soluble TR6 blocks the two-way costimulation between HveA and LIGHT among T cells (1), while TR6 on solid phase costimulates T cells via LIGHT reverse signaling (8, 11). TR6 can modulate dendritic cell maturation (14), whether this effect occurs via LIGHT reverse signaling remains a matter of debate. TR6 also blocks LIGHT-induced apoptosis of LTR-bearing cells (4). Since LTR is not expressed on lymphocytes, such an effect does not have significant relevance in the immune system. The third TR6 ligand, TL1A, is predominantly expressed on endothelial cells (5). TL1A is also a ligand of DR3 and can enhance T cell alloresponses via DR3 in vivo (5). TR6 strongly inhibits TL1A-augmented T cell proliferation and lymphokine secretion and also inhibits TL1A-triggered tumor cell apoptosis (5).
TR6 mRNA and protein are detectable in some malignant tumors (15). The inhibition of apoptosis and repression of T cell costimulation obviously represent plausible mechanisms for TR6-secreting tumors to gain survival advantage by avoiding apoptosis and evading immune surveillance. In this study, we discovered yet another function of TR6 in the immune system. We demonstrated that TR6 inhibited T cell chemotaxis both in vitro and in vivo, and such an effect was probably mediated by reverse signaling through LIGHT. A cascade of signaling and effector events such as Cdc42 activation, p38 mitogen-activated protein kinase (MAPK) activation, actin polymerization, and pseudopodium formation in CXCL12/stromal cell-derived factor 1 (SDF-1)-stimulated T cells was inhibited by TR6 pretreatment. The physiological significance of these findings is discussed.
|
Materials and Methods |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
The recombinant proteins, i.e., TR6 fused with Fc (TR6-Fc), HveA fused with Fc (HveA-Fc), and TR11/GITR fused with Fc (TR11-Fc), were described in our previous publication (1). Because TR11-Fc had no effect on T cell migration, compared with PBS or normal human IgG, it was used as a control protein for TR6-Fc. The Fc sequence in the recombinant protein was mutated, so that it did not bind to Fc
R on the cell surface. The endotoxin levels in all of the recombinant proteins were below 10 endotoxin units/mg (1). Human mAb against LIGHT was described in our earlier publication (8).
Preparation and culture of human T cells and mouse spleen cells
Adult PBMC were prepared by Lymphoprep gradient (Nycomed, Oslo, Norway), and T cells were prepared from PBMC by negative selection (deletion of cells positive for CD11b, CD16, CD19, CD36, and CD56) with magnetic beads (Miltenyi Biotec, Auburn, CA) according to the manufacturer’s instructions. Blood samples from different donors were used to prepare T cells for repeated experiments. Mouse total spleen cells were prepared by lysing RBC with 0.84% NH4Cl among the cells flushed out from the spleen. The cells were cultured in serum-free medium.
In vitro T cell migration assay
In vitro migration assays were performed in Transwell chambers (6.5 mm in diameter, 5-µm pore size; Costar, Cambridge, MA). The lower chamber contained 600 µl of serum-free medium in the presence of CXCL12/SDF-1 (80 ng/ml) or CCL21 (400 ng/ml; both from R&D Systems, Minneapolis, MN). The upper chamber held 100 µl of serum-free medium containing 0.3 x 106 T cells pretreated (16-h preincubation) with TR6-Fc, a control fusion protein, TR11-Fc (both at 20 µg/ml), or a p38 MAPK inhibitor, SB203580, or its nonfunctional structural analog, SB202474 (both at 5 µM). In some experiments, cross-linked human anti-LIGHT mAb was also used: the cells were preincubated with anti-LIGHT mAb (clone 1.2.2, 20 µg/ml) along with goat anti-human IgG (10 µg/ml). The Transwell ensemble was then incubated at 37°C for 2 h, and T cells migrating into the lower chamber were counted by flow cytometry. All the samples were in duplicate.
Flow cytometry
For F-actin staining, 1 x 106 T cells from PBMC were incubated with CXCL12/SDF-1 for 1 min at 37°C and then fixed with 3.7% Formalin for 30 min at room temperature. The cells were stained with Alexa Fluor-488-conjugated phalloidin (Molecular Probes, Eugene, OR). For CXCR4 staining, T cells were first stained with biotinylated anti-human CXCR4 (clone 44716.111; R&D Systems), followed by streptavidin-conjugated Alexa Fluor-488 (Molecular Probes). For CD69 staining, T cells were stained with PE-conjugated anti-CD69 mAb (clone FN50; BD PharMingen, Mississauga, Ontario, Canada). Mouse peritoneal exudate cells (PEC), including CFSE (Molecular Probes)-labeled cells, were stained with PE-conjugated anti-CD3 mAb (clone 2C11). The cells were analyzed with a Coulter Epics-XL flow cytometer (Coulter, St.-Laurent, Quebec, Canada).
In vivo T cell migration assay
BALB/c spleen cells were incubated overnight with serum-free medium containing TR6-Fc or TR11-Fc (both at 20 µg/ml). The cells were then labeled with CFSE (5 µM) for 10 min at room temperature. After washing, 6 x 107 labeled cells in 0.2 ml of HBSS were injected i.v. into the tail vein of a BALB/c mouse and 1 µg of CXCL12/SDF-1 in 2 ml of PBS was injected i.p. 2 h later. The mice were sacrificed after another 20 h. Their peritoneal cavities were rinsed with 8 ml of PBS, and PEC in PBS were analyzed by flow cytometry for total cell number, total CD3+ cell number, and CD3+CSFE+ cell number. For each experiment, three mice were used in each group and three independent assays were performed.
Confocal microscopy
Human T cells were cultured overnight in the presence of TR6-Fc or a control protein-Fc (TR11-Fc, both at 20 µg/ml). These cells were then stimulated with CXCL12/SDF-1 (80 ng/ml) for 1 min at 37°C and fixed with 3.7% Formalin for 30 min at room temperature. They were stained with Alexa Fluor-488-conjugated phalloidin (Molecular Probes) for 30 min on ice and mounted on slides with Prolong Anti-fade Mounting Medium (Molecular Probes) for examination by confocal microscopy. Digital images were processed with Photoshop (Adobe, Seattle, WA).
Immunoblotting
Human T cells were cultured overnight in serum-free medium in 12-well plates at 5 x 106 cells/well in the presence of TR6-Fc or TR11-Fc (both at 20 µg/ml). After washing, the cells were stimulated with SDF-1 (80 ng/ml) in serum-free medium at 37°C for 10 min. The remainder of the immunoblotting procedure was detailed in our previous publication (16). Briefly, the cells were washed and lysed in lysis buffer for 10 min; the cleared lysates were resolved by 10% SDS-PAGE. The proteins were then transferred to Immobilon-P (Millipore, Bedford, MA) membranes, which were sequentially hybridized with rabbit anti-phospho-p38 MAPK and anti-p38 MAPK Ab (New England Biolabs, Mississauga, Ontario, Canada). Immunoreactive protein bands were visualized by HRP-conjugated goat anti-rabbit IgG followed by ECL.
Rac-1 and Cdc42 activity assays
Twenty million T cells were preincubated overnight with TR6-Fc or TR11-Fc (both at 20 µg/ml). After washing, the cells were stimulated with CXCL12/SDF-1 (80 ng/ml) for 5 min at 37°C. The cells were lysed and Rac-1 and Cdc42 activity in the lysates was measured by PAK-1 pull-down assays (Upstate Biotechnology, Lake Placid, NY) according to the manufacturer’s instructions. Briefly, GTP-loaded active Rac-1 and Cdc42 were precipitated with PAK-1 PBD-conjugated agarose beads and resolved in 12% SDS-PAGE. They were then detected with mouse mAb anti-Rac-1 and Cdc42, respectively, in immunoblotting.
|
Results |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
In the course of our study into TR6’s effect on T cells, we noticed that TR6-treated T cells presented an altered morphology upon mitogen stimulation. This prompted us to examine whether T cell mobility was affected by TR6. T cells from PBMC were pretreated with TR6-Fc or a control fusion protein TR11-Fc overnight in serum-free medium and then loaded in the upper Transwell chamber. A chemokine, CXCL12/SDF-1, which is known to induce T cell chemotaxis, was added to the bottom chamber at different concentrations. T cells were allowed to migrate for 2 h at 37°C. As illustrated in Fig. 1A, CXCL12/SDF-1 dose-dependently induced T cell migration into the lower chamber. At 80 ng/ml CXCL12/SDF-1, T cells precultured in plain medium or in the presence of TR11-Fc showed similar migration rates, but those precultured in the presence of TR6-Fc manifested a significantly reduced rate. Decreased migration of TR6-precultured T cells was also observed with CXCL12/SDF-1 at 20 and 5 ng/ml (p < 0.01 for all three concentrations, one-way ANOVA followed by Tukey’s multiple comparisons test).
|
receptor CXCR4 expression on TR6-Fc-treated T cells? Approximately 40% of fresh T cells expressed low intensity CXCR4 (Fig. 1C). After overnight culture in plain medium, CXCR4+ cells increased to 
90% with a concomitant rise in CXCR4 intensity. T cells treated with either TR6-Fc or TR11-Fc showed similar up-regulation of CXCR4 as T cells cultured in plain medium Fc (p > 0.05, one-way ANOVA followed by Tukey’s test for 2 x 2 comparison of all groups), indicating that TR6-Fc treatment did not affect CXCR4 expression. This result also confirms that T cell viability was not impaired by TR6-Fc pretreatment. The effect of TR6 on T cell migration was likely mediated by LIGHT
TR6 can bind to FasL and LIGHT, both of which are expressed on T cells. Our recent study revealed that TR6 is capable of triggering reverse signaling through LIGHT and such an effect results in T cell costimulation (8, 11). We investigated here whether the inhibition of T cell migration by TR6 involved LIGHT. For this purpose, human anti-LIGHT mAb was cross-linked by goat anti-human IgG in solution (human anti-LIGHT mAb at 20 µg/ml and goat anti-human IgG at 10 µg/ml were added to the culture at the same time) and was used in place of TR6-Fc during preincubation. As shown in Fig. 2A, cross-linked anti-LIGHT mAb pretreatment also suppressed T cell migration in response to CXCL12/SDF-1 in the Transwell assay compared with cross-linked normal human IgG as a control (p < 0.01, one-way ANOVA followed by Tukey’s multiple comparisons test). This suggests that such an effect involves LIGHT.
|
(p < 0.001, one-way ANOVA followed by Tukey’s multiple comparisons test), similar to TR6-Fc. This suggests that LIGHT is implicated in the process.
To understand whether such inhibition was due to TR6-triggered reverse signaling through LIGHT or due to disruption of existing interaction between LIGHT and HveA, we used solid-phase anti-LIGHT mAb, TR6-Fc, or HveA-Fc to condition the T cells. As shown in Fig. 2C, when T cells were cultured in well coated with these reagents, their subsequent migration toward CXCL12/SDF-1 in the Transwell assay were significantly reduced (p < 0.01 for all three reagents, one-way ANOVA followed by Tukey’s multiple comparisons test)
The amount of reagents coated on the wells was minute, and there was unlikely sufficient molecules to leak from solid phase into the solution to block the LIGHT and HveA interaction. This was proved as follows. Media were put in wells coated with TR6-Fc, HveA-Fc, LIGHT mAb, or control normal human IgG for 24 h, and these conditioned media were then used to culture T cells overnight. However, as shown in Fig. 2D, T cells cultured in these conditioned media had no difference in their migration capability toward CXCL12/SDF-1 (p > 0.001, one-way ANOVA followed by Tukey’s multiple comparisons test). This confirms that the inhibitory effect seen with solid-phase TR6-Fc, HveA-Fc, and anti-LIGHT mAb is not due to leaching of these molecules from the solid phase and suggests that TR6 triggers reverse signaling through LIGHT on the T cell surface and results in compromised T cell migration.
The observed migration inhibition by TR6-Fc and HveA-Fc was not due to contaminating endotoxin in the protein preparation, because their inhibitory effect could be destroyed by 5-min boiling (Fig. 2B; p > 0.05 for boiled TR6-Fc vs medium and for boiled HveA-Fc vs medium, one-way ANOVA followed by Tukey’s multiple comparisons test). To assess whether TR6 affected the general mobility of T cells and the observed effect was only restricted to CXCL12/SDF-1 stimulation, we tested the T cell response to another chemokine, CCL21. After incubation with TR6-Fc but not with a control fusion protein (TR11-Fc), T cells showed a significantly reduced migration rate toward CCL21 in the Transwell assay (Fig. 2E; p < 0.01, one-way ANOVA followed by Tukey’s multiple comparisons test). Therefore, it seems that TR6 pretreatment inhibited the general mobility of T cells.
TR6 inhibits T cell chemotaxis in vivo
To confirm that the observed inhibitory effect of TR6 on T cell migration in vitro had physiological relevance, we established an in vivo T cell chemotaxis model. BALB/c spleen cells were first precultured overnight in the presence of TR6-Fc or TR11-Fc and then labeled with CFSE. The labeled cells were injected i.v. into syngeneic BALB/c mice. Two hours later, CXCL12/SDF-1 was injected i.p. After another 20 h, PEC were analyzed for their total number, total T cell number, total CFSE-labeled T cell number, and percentage of CFSE-labeled T cells among total T cells. As shown in Fig. 3, CXCL12/SDF-1 injection into the peritoneal cavities resulted in a drastic increase of total PEC and T cells in PEC (Fig. 3, A and B). There was no significant difference in these parameters in mice that received TR6-Fc-, TR11-Fc-, or plain medium-precultured cells (p > 0.05, one-way ANOVA followed by Tukey’s multiple comparisons test), reflecting the fact that the majority of the exodus cells were of host origin (as CFSE-labeled donor cells showed difference, to be elaborated below). When CFSE-labeled exodus T cells were analyzed, there was a significant decrease in their number in mice receiving cells pretreated with TR6-Fc compared with mice receiving cells pretreated with TR11-Fc or plain medium (Fig. 3C; p < 0.001, one-way ANOVA followed by Tukey’s multiple comparisons test). Such a reduction in T cell number was also reflected in the percentage abatement of CFSE-labeled T cells among total exodus T cells (Fig. 3D; p < 0.001, one-way ANOVA followed by Tukey’s multiple comparisons test), because the number of the latter remained similar in mice receiving spleen cells with the different treatments (Fig. 3B). These data showed the in vivo relevance of compromised T cell chemotaxis after exposure to TR6.
|
T cell chemotaxis depends on cytoskeleton reorganization, for which actin polymerization plays an essential role. We, therefore, examined actin polymerization upon SDF-1 stimulation in T cells with or without TR6 pretreatment. The F-actin staining of T cells precultured in plain medium without subsequent CXCL12/SDF-1 stimulation was considered as background (0% positive, Fig. 4A). When such cells were stimulated by CXCL12/SDF-1 for 1 min, 65.9% of them became F-actin positive. Preculturing the cells in the presence of TR11-Fc overnight had no apparent effect on actin polymerization upon subsequent CXCL12/SDF-1 stimulation, and 65% of the cells were positive for F-actin staining. However, overnight TR6-Fc pretreatment significantly reduced F-actin-positive cells to 29.4% (p < 0.01, one-way ANOVA followed by Tukey’s test for 2 x 2 comparison of all groups). This result shows that TR6 conditioning of T cells leads to compromised actin polymerization.
|
rapidly (within 1 min) induced pseudopodium formation in T cells (Fig. 4B, comparing the upper left panel with upper right panel; quantitative assessment of Fig. 4B is shown as a bar graph in Fig. 4C). T cells cultured overnight in medium or TR11-Fc had a similar degree of pseudopodium formation upon CXCL12/SDF-1 stimulation (Fig. 4B, upper right panel vs lower left panel), but TR6-Fc pretreatment of the cells significantly inhibited this process (Fig. 4B, lower left panel vs lower right panel; p < 0.001, one-way ANOVA followed by Tukey’s multiple comparisons test). Thus, it appears that T cells receiving TR6 preconditioning have modified signaling pathways that lead to compromised actin polymerization, pseudopodium formation, and, eventually, chemotaxis. TR6 pretreatment of T cells compromises p38 MAPK activation
p38 MAPK is an upstream signaling molecule essential for actin polymerization (17). Its activity in TR6-treated T cells was investigated. T cells were precultured overnight in the absence (Med) or presence of TR6-Fc or TR11-Fc. The cells were washed and stimulated with 80 ng/ml CXCL12/SDF-1 for 10 min. p38 MAPK tyrosine phosphorylation, which represents p38 MAPK activation and total p38 MAPK in these cells, were assessed by immunoblotting. As shown in Fig. 5A, CXCL12/SDF-1 stimulation resulted in similar up-regulation of p38 MAPK tyrosine phosphorylation in T cells precultured in plain medium or in the presence of TR11-Fc. However, preculturing in the presence of TR6-Fc prevented such up-regulation.
|
stimulation, T cells were treated with a p38 MAPK-specific inhibitor, SB20358 (5 µM), for 2 h and then evaluated for their chemotaxis by the Transwell assay. The p38 MAPK inhibitor but not its nonfunctional structural analog, SB202474, suppressed the T cell chemotaxis upon CXCL12/SDF-1 stimulation (Fig. 5B), as expected, indicating that the compromised p38 MAPK activation in TR6-treated T cells is relevant and responsible for T cell chemotaxis inhibition. Compromised Cdc42 activation in T cells pretreated with TR6-Fc
Small G proteins Rac-1 and Cdc42, which are signaling molecules upstream of p38 MAPK, are important in cytoskeleton reorganization, which in turn controls pseudopodium formation and cell mobility (18). The activity of Rac-1 and Cdc42 of TR6-treated T cells was examined using a PAK-1 pull-down assay. T cells were preincubated overnight in the presence of TR6-Fc or TR-11-Fc and then stimulated with CXCL12/SDF-1 for 5 min. The activated GTP-associated Rac-1 or Cdc42 was pulled down using solid-phase (agarose beads) PAK-1, which is a substrate of and binds to GTP-associated Rac-1 and Cdc42. As shown in Fig. 6, Rac-1 activation, which was reflected by the levels of GTP-associated Rac-1, was not modulated by SDF-1 stimulation; TR11-Fc or TR6-Fc pretreatment did not affect its activity. In contrast, Cdc42 was rapidly activated by CXCL12/SDF-1; TR6-Fc but not control TR11-Fc pretreatment prevented its activation. The selective inhibition of Cdc42 activation, which is important in filopodium formation (18), by TR6 thus represents a plausible mechanism for the repressive effect of TR6 on T cell chemotaxis.
|
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
There are two possible mechanisms to explain the T cell migration inhibition caused by TR6. In the first possible mechanism, constitutive interaction between LIGHT and HveA on T cells promotes T cell mobility; soluble TR6-Fc, anti-LIGHT mAb, or HveA-Fc interferes with such interaction and leads to inhibited T cell mobility. To examine the plausibility of this mechanism, we coated TR6-Fc, anti-LIGHT mAb, or HveA-Fc on solid phase. In this case, only a minute amount of those molecules were actually adsorbed to the plate surface, and there were unlikely sufficient molecules leaking into the solution to block the LIGHT and HveA interaction (indeed, media conditioned in TR6-Fc-, anti-LIGHT mAb-, or HveA-Fc-coated wells had no effect on T cell migration). Moreover, these molecules fixed on a flat surface would probably not be able to interfere with the three-dimensional interaction between LIGHT and HveA on the cell surface. We showed that those solid-phase molecules could still inhibit T cell chemotaxis, suggesting that this first mechanism does not seem plausible.
The second possible mechanism dictates that TR6 triggers a negative signal reversely transmitted through a TNF family member(s) on the cell surface, most likely through LIGHT, and such signaling results in reduced T cell mobility. There are a couple of lines of evidence supporting this mechanism. First, we have recently proved that TR6 can transduce costimulation signals reversely via LIGHT into T cells (8, 11); such reverse signaling is not entirely out of the norm and has been reported for several other TNF family members, e.g., CD40L (19), CD30L (20), TNF- (21), TNF-related activation-induced cytokine (22), FasL (23), and TRAIL (24). Second, when TR6-Fc, anti-LIGHT mAb, or HveA-Fc was put on solid phase, they could also inhibit T cell chemotaxis, as described above, likely by cross-linking their binding partners on the T cell surface. These data strongly suggest that the second mechanism is in operation. If so, how do we explain that TR6-Fc, HveA-Fc, and anti-LIGHT mAb in solution could inhibit T cell chemotaxis? It is possible that a low degree of cross-linking by the bivalent TR6-Fc or HveA-Fc, or their aggregates, is enough to trigger reverse signaling. For the anti-LIGHT mAb in solution, it was only effective after being cross-linked by antihuman IgG and without cross-linking, the mAb was not effective in solution (data not shown), suggesting the necessity of LIGHT cross-linking for the T cell migration inhibition.
TR6 could in theory reversely signal through LIGHT or FasL to achieve its effect in chemotaxis inhibition. Which one mediates such an effect of TR6? Our following observation is worth mentioning in this regard: 1) HveA-Fc, which binds to LIGHT but not FasL, had a similar effect as TR6-Fc (Fig. 2, B and C), suggesting that the effect could be achieved through LIGHT without FasL. 2) Anti-LIGHT mAb could inhibit T cell migration (Fig. 2, A and C), further suggesting that LIGHT mediated the effect. 3) LIGHT is expressed on resting T cells as we demonstrated before (8), and this provides a basis for TR6 to act on resting T cells. 4) The binding of TR6-Fc to T cells was predominately through LIGHT, because TR6-Fc could associate with >80% wild-type T cells and only with <20% LIGHT-/- T cells (data not shown). Taking together, these data suggest that LIGHT but not FasL is the main mediator for the observed effect of TR6 in chemotaxis inhibition. With that said, we cannot totally exclude the possibility that reverse signaling through FasL, or maybe some so far unidentified TR6-binding partner on the T cell surface, contributes to a lesser extent to the observed T cell chemotaxis inhibition by TR6. In this regard, it is worth mentioning that soluble TR6 have been shown to suppress soluble FasL-induced chemotaxis of microglial cells in a Transwell assay (25). In that system, the proposed mechanism is the blockage of forward signaling from FasL to Fas on the microglial cell surface by soluble TR6. However, it will be interesting to know whether such inhibition is the result of the general decrease of cell mobility by TR6 treatment.
We have identified signaling alternation in T cells treated with TR6. Selective change was revealed in one of the small GTPases, Cdc42, known to be essential in filopodium formation (18). This was followed by inability of p38 MAPK activation, which is essential for actin polymerization. Largely remaining unknown is how signals are initiated from LIGHT in the first place. LIGHT has a short featureless cytoplasmic tail (6) and certainly has no signaling capability by itself. It is reasonable to hypothesize that signaling from LIGHT depends on the adaptor molecules it associates with and such a hypothesis is under investigation.
TR6 is secreted by several kinds of tumors (15). In addition to its effect of blocking Fas-mediated apoptosis of tumor cells (15) and interfering with the two-way T cell costimulation mediated by HveA and LIGHT, TR6 now has a newly found function: inhibition of T cell chemotaxis. Consistent with this finding, in the rat glioma with forced expression of exogenous TR6, tumor-infiltrating T cells are significantly reduced compared with tumors without TR6 expression (25); our additional study discovered that serum TR6 levels of gastric cancer patients were inversely correlated to degree of lymphocyte infiltration in their tumor mass (data not shown). Therefore, T cell chemotaxis inhibition seems to be an additional strategy TR6-secreting tumors employ to evade immune surveillance by keeping potential tumor-infiltrating T cells at bay.
Although tumors might deploy TR6 to promote their survival, TR6 could also be used for a good cause. We previously demonstrated, in a mouse heart transplantation model, that TR6 administration results in prolonged heart allograft survival (1). Such a beneficial effect was initially explained by inhibition of LIGHT to HveA forward costimulation (1) and later by inhibition of the two-way costimulation between HveA and LIGHT on T cells by TR6 (1, 8). Obviously, our current finding provides an additional mechanism to explain the prolonged graft survival. Under the influence of TR6, alloresponsive T cells have reduced chemotaxis toward the allograft or its draining lymphoid organs and this will repress T cell activation, which eventually translates into reduced graft rejection force. Such a property of TR6 could be exploited in the future to repress local or systemic immune responses.
|
Acknowledgments |
|---|
|
Footnotes |
|---|
2 Address correspondence and reprint requests to Dr. Jiangping Wu, Laboratory of Immunology, Research Centre, Notre Dame Hospital, Centre Hospitalier de l’Université de Montréal, Pavilion DeSève, Room Y-5616, 1560 Sherbrooke Street East, Montreal, Quebec H2L 4M1, Canada. E-mail address: jianping.wu{at}umontreal.ca
3 Abbreviations used in this paper: L, ligand; LT, lymphotoxin; MAPK, mitogen-activated protein kinase; SDF-1, stromal cell-derived factor 1; PEC, peritoneal exudate cell; Med, medium.
Received for publication March 11, 2003. Accepted for publication July 29, 2003.
|
References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
are ligands for herpesvirus entry mediator. Immunity 8:21.[Medline]
receptor and TR2/HVEM induces apoptosis and suppresses in vivo tumor formation via gene transfer. J. Clin. Invest. 102:1142.[Medline]
receptor is necessary and sufficient for LIGHT-mediated apoptosis of tumor cells. J. Biol. Chem. 275:14307. by activated Th1 cells occurs via reverse signaling through TNF-related activation-induced cytokine. J. Immunol. 166:270. production in T cells by signal transduced through TNF-related apoptosis-inducing ligand. J. Immunol. 167:1347.This article has been cited by other articles:
|
|
 |
|
  H.-F. Chen, J.-S. Chen, C.-T. Shun, Y.-F. Tsai, and H.-N. Ho Decoy receptor 3 expression during the menstrual cycle and pregnancy, and regulation by sex steroids in endometrial cells in vitro Hum. Reprod., June 1, 2009; 24(6): 1350 - 1358. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B Funke, F Autschbach, S Kim, F Lasitschka, U Strauch, G Rogler, G Gdynia, L Li, N Gretz, S Macher-Goeppinger, et al. Functional characterisation of decoy receptor 3 in Crohn's disease Gut, April 1, 2009; 58(4): 483 - 491. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P.-H. Chen and C.-R. Yang Decoy Receptor 3 Expression in AsPC-1 Human Pancreatic Adenocarcinoma Cells via the Phosphatidylinositol 3-Kinase-, Akt-, and NF-{kappa}B-Dependent Pathway J. Immunol., December 15, 2008; 181(12): 8441 - 8449. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. Li, Z. Guo, X. Jiang, H. Zhu, X. Li, and N. Mao Mesenchymal Stem Cells Alter Migratory Property of T and Dendritic Cells to Delay the Development of Murine Lethal Acute Graft-Versus-Host Disease Stem Cells, October 1, 2008; 26(10): 2531 - 2541. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. Han, R. Bojalil, L. M. Amezcua-Guerra, R. Springall, H. Valderrama-Carvajal, J. Wu, and H. Luo DcR3 as a diagnostic parameter and risk factor for systemic lupus erythematosus Int. Immunol., August 1, 2008; 20(8): 1067 - 1075. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Terra, H. Luo, X. Qiao, and J. Wu Tissue-specific expression of B-cell translocation gene 2 (BTG2) and its function in T-cell immune responses in a transgenic mouse model Int. Immunol., March 1, 2008; 20(3): 317 - 326. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S.-M. Ka, H.-K. Sytwu, D.-M. Chang, S.-L. Hsieh, P.-Y. Tsai, and A. Chen Decoy Receptor 3 Ameliorates an Autoimmune Crescentic Glomerulonephritis Model in Mice J. Am. Soc. Nephrol., September 1, 2007; 18(9): 2473 - 2485. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. J. Bendall, R. Baraz, J. Juarez, W. Shen, and K. F. Bradstock Defective p38 Mitogen-Activated Protein Kinase Signaling Impairs Chemotaxic but not Proliferative Responses to Stromal-Derived Factor-1{alpha} in Acute Lymphoblastic Leukemia Cancer Res., April 15, 2005; 65(8): 3290 - 3298. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Shi, J. Mao, G. Yu, J. Zhang, and J. Wu Tumor Vaccine Based on Cell Surface Expression of DcR3/TR6 J. Immunol., April 15, 2005; 174(8): 4727 - 4735. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. J. Levine Mechanisms of Soluble Cytokine Receptor Generation J. Immunol., November 1, 2004; 173(9): 5343 - 5348. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Y.-Y. Wu, Y.-C. Chang, T.-L. Hsu, S.-L. Hsieh, and M.-Z. Lai Sensitization of Cells to TRAIL-induced Apoptosis by Decoy Receptor 3 J. Biol. Chem., October 15, 2004; 279(42): 44211 - 44218. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H.-H. Sung, J.-H. Juang, Y.-C. Lin, C.-H. Kuo, J.-T. Hung, A. Chen, D.-M. Chang, S.-Y. Chang, S.-L. Hsieh, and H.-K. Sytwu Transgenic Expression of Decoy Receptor 3 Protects Islets from Spontaneous and Chemical-induced Autoimmune Destruction in Nonobese Diabetic Mice J. Exp. Med., April 19, 2004; 199(8): 1143 - 1151. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
CXCL12: mice receiving CFSE-labeled spleen cells precultured in medium, followed by CXCL12 injection (1 µg/mouse) i.p; TR11-Fc
