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* Oncology Center and
Division of Comparative Medicine, Johns Hopkins Medical Institutions, Baltimore, MD 21231;
Department of Medicine, Chang Gung University School of Medicine and Hospital, Taiwan;
Department of Immunology, The Scripps Research Institute, La Jolla, CA 92037; and
¶ Center for Immunotherapy of Cancer and Infectious Diseases, University of Connecticut School of Medicine, Farmington, CT 06030
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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It has been well established that naive T cells receiving immunogenic stimulation undergo multiple rounds of division during which time they develop the ability to express effector functions, e.g., cytokine production, etc. (reviewed in Ref. 1). Interestingly, numerous in vivo models have indicated that naive T cells receiving a tolerogenic stimulus can undergo an initial proliferative phase before reaching a tolerant state (2, 3, 4, 5). It has not been clear, however, whether T cells that are undergoing tolerance induction can demonstrate effector function as do their counterparts that have received immunogenic stimuli, or whether this initial proliferative phase is unassociated with effector function.
Using a transgenic model system that we have previously established to study CD4+ T cell peripheral tolerance induction to self-Ags (5, 6), we provide evidence that a population of adoptively transferred naive clonotypic TCR transgenic CD4+ T cells encountering their cognate self-Ag do demonstrate transient effector function before reaching a tolerant state. These tolerizing CD4+ T cells manifest effector function by three separate parameters: the ability to produce the effector cytokine IFN-
upon Ag restimulation; the provision of help to CD8+ T cells; and the induction of inflammatory autoimmune pathology in an organ expressing the cognate Ag. These results indicate that immunogenic and tolerogenic T cell differentiation are more similar than previously thought, because both involve not only multiple rounds of proliferation but also the development of effector function. Thus, the main difference between the two pathways is the ability of immunized T cells to maintain effector function.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The C3-HA expressing transgenic mice have been previously described (6) (5). In short, the hemagglutinin (HA)2 gene derived from the influenza virus A/PR/8/34 (Mount Sinai stain) has been placed under the control of the rat C3(1) promoter. Two founder lines were established in the B10.D2 genetic background. These two founder lines, C3-HAhigh and C3-HAlow, which contain 30–50 and 3 transgene copies, respectively, express the C3-HA hybrid mRNA in the same set of nonlymphoid tissues including the lung and prostate (6). Although the difference in total HA protein expression between C3-HAhigh and C3-HAlow was not directly measured, in the lung and prostate the difference is roughly 1000-fold as shown by bioassay of tissue extract induced hybridoma cytokine release (5).
The TCR-transgenic mouse line 6.5, which expresses a TCR recognizing an I-Ed-restricted HA epitope (110SFERFEIFPKE120; generously provided by H. Von Boehmer, Harvard University, Boston, MA), was backcrossed nine generations onto the B10.D2 genetic background. The other TCR-transgenic mouse line Clone-4, which expresses a TCR recognizing a Kd-restricted HA epitope (518IYSTVASSL526; generously provided by L. Sherman, The Scripps Research Institute, La Jolla, CA), was backcrossed also for more than nine generations onto the Thy-1.1/1.1 B10.D2 genetic background. Because no clonotypic Ab is available for Clone-4 TCR, we use Thy-1.1 as a surrogate marker. Following adoptive transfer into Thy-1.2/1.2 recipients, we can assume that all the Thy-1.1+ CD8+ T cells express the HA-specific clonotypic TCR, because nearly all of the mature CD8+ T cells in the Clone-4 mice directly recognize the Kd-restricted HA epitope (7).
Transgenic mice were used for experiments between the ages of 8–24 wk. All experiments involving the use of mice were performed in accordance with protocols approved by the Animal Care and Use Committee of the Johns Hopkins University School of Medicine.
Adoptive transfer
Clonotypic CD4+ or CD8+ T cells were prepared from pooled spleens and LNs of 6.5 or Clone-4 transgenic mice. Clonotypic percentage was determined by flow cytometry analysis. The activation marker CD44 was analyzed to ensure that these clonotypic cells were not activated in donor mice and were naive in phenotype. After three washings with HBSS, an appropriate number of cells were resuspended in 0.2 ml of HBSS for i.v. injection through the tail vein.
Extraction of lung-infiltrating lymphocytes
The lung was first minced by a surgical scalpel. Minced tissue was then digested with tissue digestion buffer (RPMI medium with 0.0025% hyaluronidase, 0.002% DNase, and 0.1% collagenase IV). Digestion was performed with gentle shaking at 37°C for 4–6 h. After passing through nylon mesh, the cell suspension was separated with Ficoll (Pharmacia, Peapack, NJ), and the buffy coat was collected.
Abs and flow cytometry
mAbs used for staining were: biotinylated anti-clonotypic TCR 6.5 (provided by H. Von Boehmer); avidin-PE (Caltag, Burlingame, CA); Cy-Chrome-conjugated anti-CD4 (RM4-5), Cy-Chrome-conjugated anti-CD8 (53-6.7), PE-conjugated anti-Thy-1.1 (OX-7), FITC-conjugated anti-CD44 (1 M7), biotin-conjugated B-220 (RA3-6B2), biotin-conjugated CD11c (HL-3), and biotin-conjugated NK1.1 (PK136) (all purchased from BD PharMingen, San Diego, CA). FACS (BD Biosciences, San Jose, CA) was used for flow cytometry event collection, and events were analyzed using CellQuest software (BD Biosciences).
CD8+ T cell depletion
Dynabeads M-280 streptavidin (100–150 x 106; Dynal, Oslo, Norway) were used for depleting CD8+ T cells from 100 x 106 splenocytes or LN cells. There were at least 4 beads per CD8+ T cell to be depleted. The magnetic beads were first washed once with Dynabeads Washing Buffer (1x PBS with 1% heat-inactivated FBS; Dynal). Splenocytes or LN cells were resuspended as 50 x 106/ml in Dynabeads Washing Buffer, and 10 µl of 0.5-mg/ml stock of biotinylated anti-CD8+ Ab (Ly-2, 53-6.7; BD PharMingen) were added for every 100 x 106 cells. Cells were incubated with Ab on a gently rocking rotator at 4°C for 30 min before two washings with Dynabeads Washing Buffer. Then Ab-treated cells were resuspended with beads at a concentration of 50 x 106 cells/ml. They were incubated again on a gently rocking rotator at 4°C for 30 min. Beads and bound cells were removed with a magnetic rack as all cells resuspended in a 15-ml conical tube with a final volume of 4–6 ml. Cell suspension free of magnetic beads was collected. This was repeated once to remove all beads in suspension completely. CD8+ T cell-depleted cells were then washed three times with HBSS and counted before resuspended into an appropriate volume for injection.
Proliferation assay
A total of 1.5 x 105 splenocytes or LN cells collected from transfer recipients were incubated in round-bottom 96-well tissue culture plates with various concentrations of indicated synthetic HA peptide, either HA class II (110SFERFEIFPKE120) for CD4+ 6.5 or HA class I (518IYSTVASSL526) for CD8+ Clone-4. From 24 to 72 h later, as indicated, cultures were pulsed with 1 µCi [3H]thymidine and incubated for an additional 16 h before harvest with a Packard Micromate cell harvester (Packard Bioscience, Meriden, CT). Determination of the amount of incorporated radioactive counts was performed with a Packard Matrix 96 direct beta counter (Packard Bioscience).
ELISA for cytokine release
IL-2 and IFN- were measured using ELISA kits purchased from Endogen (Woburn, MA), according to manufacturer’s instructions. Samples were the supernatant of 48 h in vitro cultures.
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Results |
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We have previously developed a model system for studying peripheral tolerance induction in CD4+ T cells, in which naive 6.5 TCR-transgenic CD4+ T cells specific for an I-Ed-restricted epitope from the influenza virus (PR8 strain) HA protein (8) are adoptively transferred into transgenic mice expressing HA as peripheral self-Ag (5, 6). The transgenic recipients express HA under the control of the rat C3(1) promoter, which directs HA expression to a number of parenchymal tissues, of which the lung expresses the highest levels. Two separate founder lines of C3-HA mice have been studied that express HA in the same subset of tissues but differ in the level of HA expression by at least three orders of magnitude (i.e., C3-HAhigh and C3-HAlow).
When spleen and LN preparations containing 2.5 x 106 naive 6.5 clonotypic CD4+ T cells were transferred into C3-HAlow mice, these 6.5 cells become anergic 7 days after transfer (6). C3-HAlow recipients tolerated transfer well and remained healthy. To our surprise, however, if C3-HAhigh mice were given the same number of naive 6.5 cells, they invariably died between 5 and 7 days after transfer. Pathological examination revealed that these animals displayed severe inflammatory changes in the lungs, with hepatization indicative of severe pneumonitis (Fig. 1A). Microscopically, there were dense inflammatory cell infiltrates around the pulmonary vessels. This vesicular cuffing was accompanied by endothelial changes suggestive of pulmonary vasculitis (Fig. 1B, top). A number of controls indicated that this pneumonitis was Ag specific. Neither transfer of nontransgenic (NT) B10.D2 spleen and LN preparations into C3-HAhigh recipients nor 6.5 transgenic spleen and LN preparations into NT B10.D2 mice caused pneumonitis. Furthermore, to determine whether pneumonitis required HA to be expressed in the lungs, 6.5 transgenic T cells were primed in NT recipients by inoculation with 1 x 107 PFU of recombinant vaccinia virus expressing HA (vacc-HA). Although these NT recipients did not express HA in their lungs, there was an increase in the cellularity of the lung parenchyma (Fig. 1B, bottom), consistent with recent reports that primed T cells migrate to the lung in an apparently Ag-nonspecific manner (9, 10). However, there was minimal inflammation around the pulmonary vessels, and the recipients remained healthy, indicating that the pulmonary vasculitis in our C3-HAhigh recipient mice required HA expression in the lung.
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Clonotypic CD4+ T cells become tolerized despite mediating autoimmune pathology
Because the adoptively transferred clonotypic CD4+ T cells mediated pathology in C3-HAhigh mice and even induced lethality, it was of interest to determine whether they had been induced to become effector/memory cells or anergized. To address this issue, clonotypic CD4+ T cells were recovered from the spleen 4 days after transfer (a time point before the onset of mortality) and analyzed for their ability to proliferate and secrete IL-2 in response to in vitro peptide stimulation. Because of the strong proliferation and expansion on encounter of the cognate Ag, 5% of the splenocytes of the C3-HAhigh recipient mice were 6.5 clonotypic CD4+ T cells by day 4 posttransfer. There were far fewer 6.5 CD4+ T cells in NT control reciients with transfer of the same number of naive 6.5 CD4+ T cells (0.2%). In contrast to splenocytes recovered from NT control recipients that exhibited strong peptide-specific proliferative and IL-2 responses, those recovered from C3-HAhigh recipients neither proliferated nor secreted IL-2 (Fig. 4). This anergic phenotype was observed regardless of whether lethal (2.5 x 106) or sublethal (1 x 105) doses of naive clonotypic cells had been transferred (Fig. 4). These results suggested that the C3-HAhigh recipient mouse is an in vivo environment that induces tolerance of naive 6.5 clonotypic CD4+ T cells. Although naive clonotypic CD4+ T cells develop the capacity to mediate pulmonary vasculitis, with sufficient numbers even to cause lethality, they become tolerized in C3-HAhigh recipients.
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Clonotypic CD4+ T cells encountering cognate self-Ag express transient effector function before becoming tolerized
The paradoxical finding that adoptively transferred naive 6.5 CD4+ T cells caused autoimmune pneumonitis in C3-HAhigh animals while becoming anergic suggested that CD4+ T cells undergoing tolerance induction pass through an early phase with effector function. To examine this possibility more closely, we assessed the ability of the clonotypic CD4+ T cells to express two classic effector functions, i.e., cytokine production and provision of help to CD8+ T cells, during the initial phases of tolerance induction.
In the first experiment (Fig. 5), splenocytes were recovered from C3-HAhigh recipients 2, 3, and 4 days after transfer and analyzed for their ability to proliferate, as well as to secrete IL-2 and IFN-, in response to in vitro restimulation with cognate HA class II peptide for 6.5 clonotypic T cells. Two days posttransfer, at the beginning of 6.5 clonal expansion, the splenocytes exhibited strong proliferative and IL-2 responses upon in vitro restimulation. They also secreted significant levels of the Th1 effector cytokine IFN-, although much less than that induced by vacc-HA (data not shown). These responses were transient. Even though the 6.5 clonotypic population continued to expand and their number increased through days 3 and 4 posttransfer, these responses to in vitro peptide restimulation were diminished at day 3 and virtually absent by day 4. Because these experiments were performed by restimulating the bulk population of C3-HAhigh transgenic splenocytes, it is difficult to exclude the effect of transgene-driven HA expression. Therefore, the clonotypic 6.5 CD4+ T cells were isolated by cell sorting from these C3-HAhigh recipient mice also on 2, 3, and 4 days after transfer and restimulated in vitro with HA class II peptide-pulsed syngeneic NT splenocytes. The proliferative response and IL-2 and IFN- secretion of these purified cells also decreased with time (data not shown).
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elicited upon in vitro peptide stimulation was also dramatically enhanced by the CD4+ T cell cotransfer (Fig. 7B).
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The above data did not prove that the effector functions observed in our system were mediated by 6.5 CD4+ T cells that are truly naive. To address this issue, we performed three separate sets of experiments. First, donor 6.5 T cells were sorted based on CD44 expression, the presumption being that clonotypic cells that had encountered cross-reactive Ags would be rendered CD44high. Thus 99.9% pure CD44low 6.5 clonotypic CD4+ T cells, from 0.8 x 106 to 2.5 x 106, were transferred into C3-HAhigh recipients. The results showed that CD44low cells were as capable as unsorted 6.5 cells (90–95% CD44low) in mediating mortality. On the contrary, transfer of an equal number of purely CD44high 6.5 cells did not result in recipient mortality. We further explored the hypothesis that naive cells mediate mortality by specifically transferring activated effector/memory 6.5 T cells. T cells were activated in vitro with HA class II peptide (1–10 µg/ml) before transfer to C3-HAhigh recipients. These in vitro activated 6.5 T cells were not able to mediate mortality. We also activated clonotypic 6.5 T cells in vivo by transferring the cells to NT B10.D2 recipients followed by activation with vacc-HA. Clonotypic cells were sorted and then transferred to C3-HAhigh recipients. Again, in vivo activated clonotypic donor cells were unable to mediate mortality. Together these data supported the hypothesis that the mortality in our system was mediated by naive T cells (Table I). Interestingly, although CD44high or activated 6.5 T cells did not mediate the mortality of C3HAhigh recipient mice, they expanded nicely in the recipients and still caused significant pulmonary pathology. There was perivascular round cell infiltration that was at least as prominent as those of the C3HAhigh mice that died from adoptive transfer of naive T cells. However, their alveolar space was relatively spared (Fig. 8).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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when restimulated in vitro with peptide pulsed APCs. Although this activity was strong when the T cells were recovered 2 days post adoptive transfer, it was virtually absent 4 days posttransfer. Additionally, the CD4+ T cells undergoing tolerance induction were able to provide help to CD8+ T cells that were also specific for self-HA. It has previously been shown that naive CD8+ T cells encountering self-Ag undergo an initial proliferative phase before the development of tolerance (12, 13, 14). In our system, naive HA-specific CD8+ T cells also underwent an expansion phase subsequent to adoptive transfer into HA-expressing transgenic mice. Cotransfer of naive HA-specific CD4+ T cells resulted in even greater clonal expansion of the HA-specific CD8+ T cells, as well as the ability of these CD8+ T cells to secrete IFN- upon in vitro restimulation. This provides additional evidence that the CD4+ T cells expressed effector function before becoming tolerized. Perhaps the most significant example of effector function expressed by CD4+ T cells undergoing tolerance induction is their ability to mediate inflammatory autoimmune lung pathology in animals expressing high levels of HA and, with sufficient numbers, even to kill the recipient mice. An inevitable limitation of all studies like this is that it is almost impossible to conclude that the CD4+ T cells that ultimately become anergic are the same T cells that acquire effector functions initially. Similar uncertainty still exists about the lineage of memory cells in the process of induction of effector/memory T cells and memory responses (15, 16, 17). In both cases, the effector cells that appear during the early phase of T cell activation may all be deleted, and the anergized or the memory T cells that emerge later come from a distinctly separate lineage. Instead of addressing this argument, we emphasize the fact that not every single CD4+ T cell primed in vivo in a tolerogenic environment is anergized upon its first encounter with APCs. Most of the whole CD4+ T cell population acquires a full-blown effector phase during the process of in vivo tolerance induction in our system.
In many TCR-transgenic systems, analysis of naive cells is often accomplished by crossing onto a recombination-activating gene (RAG)-/- background to eliminate endogenous TCR expression that produces populations of memory cells. In the case of the 6.5 transgenics on a B6 or B10 background, extremely few transgenic T cells develop on a RAG-/- background, and the few that do disappear rapidly when transferred into new recipients. We believed that this is because the 6.5 TCR is not efficiently selected positively in the B6/B10 background and requires a second TCR for positive selection. This does not render 6.5 mice a nonphysiological system because it appears that a significant proportion of normal T cells express two TCRs (18). There is also evidence that at least some of these dual TCR-expressing cells use one TCR for positive selection and the other for reactivity against a particular Ag (19, 20).
The phenomenon we have reported has both similarities to and differences from the phenomenon of activation-induced nonresponsiveness (AINR). AINR was defined as nonresponsiveness of CD8+ T cells following full stimulation through both the TCR and costimulatory receptors (21). In contrast, the classical anergic state originally described for CD4+ T cell clones follows TCR engagement in the absence of costimulation (22, 23, 24, 25). This developmental program of T cell activation is compatible with AINR of CD8+ T cells. However, the AINR CD8+ T cells originally described retain the ability to secrete IFN- upon TCR engagement (21, 26). Thus, AINR cells are similar to the classical anergic CD4+ T cell clones. On the contrary, the IFN- capacity of our CD4+ T cells is lost with development of nonresponsiveness.
This effector phase with in vivo tolerance induction is relatively efficient rather than merely abortive. Inflammatory tissue pathology was caused which is proportional to the number of clonotypic CD4+ T cells transferred, and in adequate numbers, these CD4+ T cells even mediate lethality of the transfer recipient mice. Although this is an artificial transgenic adoptive transfer system, we speculate a possible relevance to self-tolerance and autoimmunity because the pathology and mortality are the result of interaction between self-reactive T cells and self-Ag (27). In a normal repertoire with lower frequency of autoreactive T cells, which would be analogous to further titration down to results shown in Fig. 2, autoimmunity might also result from the process of tolerance induction rather than breaking self-tolerance. Given that it has been reported that lymphocytic choriomeningitis virus-specific CD8+ T cells might comprise up to 50–70% of activated splenic CD8+ T cells during acute infection (28), the clonotypic percentage resulted from adoptive transfer in our system, up to 15–20% of splenic CD4+ T cells, is probably not too much higher than what might happen in reality.
Because most of the described human or murine tumor Ags are nonmutated proteins also expressed in normal tissues, tumor immunity in many respects can be viewed as the flip side of autoimmunity, and the autoreactive T cell mediate beneficial antitumor effect. As we understand that there is an effector phase with tolerance induction by self-Ag, there should be antitumor activity before T cell tolerance by tumors. Similar results were observed in an analogous tumor system. As tumor specific CD4+ T cells were being anergized by a tumor Ag, they could nonetheless provide help for tumor specific CD8+ T cells in clearing lung metastasis (Z. Lu and H. I. Levitsky, unpublished data). In the context of tumor tolerance, this might actually explain the classical observation of concomitant tumor immunity. Even though the immune system may not eradicate large established tumors, new thymic emigrants of tumor-reactive T cells can be activated before they are tolerized and clear a smaller tumor implanted at the other site on that tumor-bearing animal. The implication for tumor immunotherapy is that, in addition to breaking tumor tolerance, how to sustain the antitumor activity before tolerance induction would be another feasible approach.
It has been previously reported that transfer of large numbers of OVA-specific CD8+ T cells results in diabetes and death in transgenic mice expressing OVA as a self-Ag in pancreas (13). Although this work implies effector functions with in vivo interaction of autoreactive CD8+ T cells and their cognate self-Ag, it is not clear whether the CD8+ T cells were anergized later. Even though we also observed an apparent effector phase before in vivo tolerance induction of HA-specific Clone-4 CD8+ T cells in our C3-HA transgenic system, there seems to be a couple of fundamental difference between CD4+ and CD8+ T cells. First, deletion plays a more important role in CD8+ tolerance. Deletion prevents the proliferating autoreactive CD8+ T cell population from expanding in a system with lower Ag concentrations in which the effector function is not detectable (29). Autoreactive CD8+ T cells do proliferate and expand and obtain effector functions in our C3-HAtransgenic system, which probably contains higher Ag concentrations. Deletion is also required here to remove the cells with effector functions to make the whole CD8+ population tolerant (C.-T. Huang, Y. Yang, and D. Pardoll, manuscript in preparation). Second, the effector function of CD8+ T cells undergoing tolerance induction can be significantly enhanced with CD4+ T helper cells (Fig 7B).
The pulmonary pathology and lethality induced by these CD4+ T cells are directly proportional to the numbers that were adoptively transferred. Interestingly, we previously found that i.p. transfer of clonotypic CD4+ T cells into C3-HAhigh mice did not induce lethality (using the same number of cells that induce lethality when transferred i.v. in the current study) (5). Because the mice receiving i.p. transfers develop lung inflammation as do those receiving i.v. transfers (data not shown), it is likely that the lack of lethality associated with i.p. transfer simply results from slow diffusion of T cells from the peritoneal cavity into the blood stream. Thus, i.p. transfer appears to have a similar effect to decreasing the number of transferred CD4+ T cells. In contrast, pulmonary pathology in 6.5 TCR- and HA-expressing double-transgenic mice further exemplifies the quantitative nature of our observation. Although adoptive transfer of naive 6.5 TCR transgenic T cells into C3-HAlow mice does not cause any pathology, there is significant pulmonary vasculitis in double-transgenic mice generated by crossing 6.5 TCR to C3-HAlow HA-expressing transgenic mice (data not shown). Continuous thymic output of 6.5 CD4+-transgenic T cells in these 6.5/C3-HAlow double-transgenic mice is probably the cause of lung pathology.
These results are consistent with the concept that localization, dose, and time of availability of Ag are critical elements that determine the outcome of immune response (30). An interesting possibility raised by this notion is that CD4+ T cell tolerance results from chronic antigenic stimulation as previously suggested (31, 32). Thus, the tolerogenic APCs that present self-Ags (6, 33, 34) and immunogenic APCs that present pathogen-derived Ags (35, 36, 37) might deliver similar signals to the cognate naive CD4+ T cells which induces effector function. However, due to the constitutive and steady level presentation of self-Ags, compared with the potentially transient and fluctuating presentation of Ags deriving from rapidly cleared pathogens, effector function generated toward self-Ags might be attenuated due to T cell overstimulation. It has been shown recently that persistent presence of Ag, as a result of repeated vaccination, will not result in tolerance (38). Although it is not surprising that repeated vaccination does not result in tolerance, it does indicate that the simple presence of Ag alone is inadequate for T cell tolerance induction. Nonetheless, our data do not rule out the possibility that tolerogenic and immunogenic APCs deliver qualitatively different signals that commit cognate naive T cells toward differentiating into either tolerized or effector/memory cells, respectively, upon initial APC-T cell interaction.
This effector phase accompanied by tolerance induction might be organ specific. The different context in different organs could change the outcome of Ag encounter. Although the CD4+ T cells in effector phase caused vasculitis in the lung, actually there was no immune cell infiltrate in the other organs of high level HA expression in our C3-HAhigh transgenic mice, i.e., the male reproductive organs.
This study demonstrates that CD4+ T cells undergoing peripheral tolerance induction express transient effector function before reaching a tolerant state, indicating that the tolerogenic and immunogenic CD4+ T cell differentiation pathways are more similar than previously thought. Thus, the main difference between the two pathways is not their ability to generate effectors, but rather their ability to sustain them.
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Footnotes |
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2 Abbreviations used in this paper: HA, hemagglutinin; NT, nontransgenic; vacc-HA, recombinant vaccinia virus expressing HA; RAG, recombination-activating gene; AINR, activation-induced nonresponsiveness.
Received for publication July 24, 2002. Accepted for publication February 3, 2003.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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chains: dual receptor T cells. Science 262:422.This article has been cited by other articles:
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  J. Waithman, T. Gebhardt, G. M. Davey, W. R. Heath, and F. R. Carbone Cutting Edge: Enhanced IL-2 Signaling Can Convert Self-Specific T Cell Response from Tolerance to Autoimmunity J. Immunol., May 1, 2008; 180(9): 5789 - 5793. [Abstract] [Full Text] [PDF]
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 G. N. Huang, D. L. Huso, S. Bouyain, J. Tu, K. A. McCorkell, M. J. May, Y. Zhu, M. Lutz, S. Collins, M. Dehoff, et al. NFAT Binding and Regulation of T Cell Activation by the Cytoplasmic Scaffolding Homer Proteins Science, January 25, 2008; 319(5862): 476 - 481. [Abstract] [Full Text] [PDF]
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 P. E. Zarek, C.-T. Huang, E. R. Lutz, J. Kowalski, M. R. Horton, J. Linden, C. G. Drake, and J. D. Powell A2A receptor signaling promotes peripheral tolerance by inducing T-cell anergy and the generation of adaptive regulatory T cells Blood, January 1, 2008; 111(1): 251 - 259. [Abstract] [Full Text] [PDF]
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N. J. Singh, M. Cox, and R. H. Schwartz TLR Ligands Differentially Modulate T Cell Responses to Acute and Chronic Antigen Presentation J. Immunol., December 15, 2007; 179(12): 7999 - 8008. [Abstract] [Full Text] [PDF]
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J. Waithman, R. S. Allan, H. Kosaka, H. Azukizawa, K. Shortman, M. B. Lutz, W. R. Heath, F. R. Carbone, and G. T. Belz Skin-Derived Dendritic Cells Can Mediate Deletional Tolerance of Class I-Restricted Self-Reactive T Cells J. Immunol., October 1, 2007; 179(7): 4535 - 4541. [Abstract] [Full Text] [PDF]
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R. J. Steptoe, J. M. Ritchie, N. S. Wilson, J. A. Villadangos, A. M. Lew, and L. C. Harrison Cognate CD4+ Help Elicited by Resting Dendritic Cells Does Not Impair the Induction of Peripheral Tolerance in CD8+ T Cells J. Immunol., February 15, 2007; 178(4): 2094 - 2103. [Abstract] [Full Text] [PDF]
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D. Mayerova, L. Wang, L. S. Bursch, and K. A. Hogquist Conditioning of langerhans cells induced by a primary CD8 T cell response to self-antigen in vivo. J. Immunol., April 15, 2006; 176(8): 4658 - 4665. [Abstract] [Full Text] [PDF]
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 H. L. Zwickey, J. J. Unternaehrer, and I. Mellman Presentation of self-antigens on MHC class II molecules during dendritic cell maturation Int. Immunol., January 1, 2006; 18(1): 199 - 209. [Abstract] [Full Text] [PDF]
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 K. A. Whartenby, P. A. Calabresi, E. McCadden, B. Nguyen, D. Kardian, T. Wang, C. Mosse, D. M. Pardoll, and D. Small Inhibition of FLT3 signaling targets DCs to ameliorate autoimmune disease PNAS, November 15, 2005; 102(46): 16741 - 16746. |
