Abstract
The phenomena of infectious tolerance and linked-suppression are well established, but the mechanisms involved are incompletely defined. Anergic T cells can inhibit responsive T cells in vitro and prolong skin allograft survival in vivo. In this study the mechanisms underlying these events were explored. Allospecific mouse T cell clones rendered unresponsive in vitro inhibited proliferation by responsive T cells specific for the same alloantigens. The inhibition required the presence of APC, in that the response to coimmobilized anti-CD3 and anti-CD28 Abs was not inhibited. Coculture of anergic T cells with bone marrow-derived dendritic cells (DC) led to profound inhibition of the ability of the DC to stimulate T cells with the same or a different specificity. After coculture with anergic T cells expression of MHC class II, CD80 and CD86 by DC were down-regulated. These effects did not appear to be due to a soluble factor in that inhibition was not seen in Transwell experiments, and was not reversed by addition of neutralizing anti-IL-4, anti-IL-10, and anti-TGF-β Abs. Taken together, these data suggest that anergic T cells function as suppressor cells by inhibiting Ag presentation by DC via a cell contact-dependent mechanism.
Evidence that peripheral T cell tolerance is actively maintained was first provided over two decades ago in rodent models of transplantation, in which tolerance could be transferred by T cells from a tolerant to a naive host (1). Similar phenomena have been observed in several experimental models of autoimmune disease (2). However, the mechanisms responsible for this active regulation remain a matter of debate. The possibility that has received most attention is that the regulation is effected by cytokines, produced by Th2, Th3, or Tr1 cells secreting IL-4, TGF-β, or IL-10, respectively. These cytokines are thought to regulate the differentiation and/or effector function of pro-inflammatory Th1 cells. For example, recent studies have identified IL-10 as a differentiation factor for a novel subset of immune suppressive regulatory T cells (3). Although there is clear evidence that such regulatory cytokines contribute to the maintenance of peripheral tolerance to autoantigens (4, 5, 6), it is much less clear that the same mechanisms provide an adequate explanation for the maintenance of transplantation tolerance.
Given that the role of cytokines in the maintenance of transplantation tolerance is less than clear, we have explored an alternative possibility, namely that anergic T cells exert regulatory functions by a cytokine-independent mechanism. Their inhibitory properties were first demonstrated in a human in vitro system (7, 8), and have been reproduced using mouse cells (9). In addition, we have reported that anergic donor-specific T cells can prolong the survival of skin allografts in vivo (10). Related phenomena have been reported by other groups in human (11) and murine systems (12, 13).
In this study we have examined the mechanisms whereby anergic T cells inhibit responsive T cells, and have focused our attention on the possibility that their inhibitory effects are mediated through the regulation of APC function.
Materials and Methods
Mice
NODasp transgenic mice expressing a mutant MHC class II molecule (H2-Abg7, Ser57 to Asp) have been previously described (14). They were bred at the Biological Services Unit of the Imperial College School of Medicine. Male C57BL/10 mice were purchased from Olac Harlan (Bicester, U.K.). TCR-transgenic DO.11.10 mice were kindly provided by Drs. D. Gray and H. Reiser at our department.
T cell clones
2E4 and 1F8 are alloreactive (NOD anti-NODasp) CD4+ T cell clones (15). CTL10 is an H-Y-specific, H2-Db-restricted CD8+ T cell clone (16). All T cell clones were maintained in RPMI 1640 medium supplemented with 10% FCS (Globepharm, Esher, U.K.), 2 mM l-glutamine, 100 U/ml penicillin, 100 μg/ml streptomycin, and 5 × 10−5 M 2-ME, in the presence of rhIL-2 (10 U/ml for CD4+ and 20 U/ml for the CD8+ cells) (Boehringer Mannheim, Mannheim, Germany).
Antibodies
The following mAbs were purified from hybridoma culture supernatants by protein G affinity chromatography (Pharmacia, Uppsala, Sweden): anti-CD3 (145-2C11, CRL-1975; American Type Culture Collection (ATCC), Manassas, VA), anti-CD28 (37.51), and neutralizing anti-IL-4 (11B11, HB188, ATCC) mAbs. A total of 0.6 μg/ml 11B11 mAb was able to neutralize ∼1000 U/ml of recombinant mouse IL-4 in a CTLL-2 bioassay (data not shown). Neutralizing mAbs specific for murine TGF-β1, -β2, -β3 (code 80-1835-03), for IL-10 (clone JES052A5), and blocking mAb against Fas ligand (FasL)4g7); FITC-conjugated anti-H2-Db (KH95); FITC-conjugated anti-CD4 (RM4-4); FITC-conjugated anti-CD80 (16-10A1); FITC-conjugated anti-CD86 (GL1); FITC-conjugated anti-Fas mAb (Jo2); and PE-conjugated anti-CD40L (MR1). FITC-conjugated goat anti-mouse IgG and FITC-conjugated rabbit anti-rat IgG were supplied by Sigma (St. Louis, MO) and Dako (Carpinteria, CA), respectively. FICT-conjugated Annexin V was supplied by PharMingen.
Induction of T cell anergy in vitro, rechallenge cultures, and mixture experiments
Purified DO.11.10 CD4+ T cells or T cell clones were rendered anergic by immobilized anti-CD3 mAb as previously described (17). Briefly, 2E4 and 1F8 cells isolated from their last restimulation cultures at day 10–14, or purified CD4+ T cells (5 × 105/well), were cultured in 24-well plates precoated with 3–10 μg/ml of purified anti-CD3 mAb. T cells cultured with medium alone served as controls. Two days later, the T cells were isolated, washed, and recultured in fresh medium for at least 2 days. After the rest period, anti-CD3-treated and untreated T cells were tested for proliferative responses to Ag restimulation. Responsive T cells (1 × 104/well) alone, or mixed with irradiated (3000 rad) anergized T cells at a ratio of 1:1 or 1:3, were stimulated with irradiated NODasp DC in 96-well plates for 3 days. The proliferative responses were assessed by [3H]thymidine incorporation during the last 18 h of 96-h assays.
Generation of dendritic cells (DC) from bone marrow cultures
The protocol of Inaba et al. (18) was used to generate DC from bone marrow culture. Briefly, bone marrow cells (5 × 105/ml) were cultured with 10% FCS RPMI 1640 containing 5% supernatant (v/v) from a GM-CSF-secreting transfected cell line. On day 3 of culture, nonadherent cells were removed by gentle pipetting, and the adherent fraction was cultured with a fresh GM-CSF-containing culture medium for a further 4 days. Alternatively, to generate fully mature DC, the bone marrow-derived cells were cultured in the presence of 2 μg/ml of LPS (Sigma) for the last 2 days of culture.
T cell-activating capacity of DC after coculture with anergic T cells
DC (2 × 106) obtained 7 days after bone marrow culture as the nonadherent fraction, were cultured either alone or with responsive or anergic T cells (4 × 106) at a 2:1 ratio in 2-ml cultures in 24-well plates for 48 h. Both responsive and anergic T cells were irradiated (3000 rad). In some experiments the coculture was performed in the presence of neutralizing Abs against IL-4, IL-10 and TGF-β. For separation of T cells from DC, the DC/T cell cultures were treated with a cell dissociation solution (Sigma) for 15 min, washed twice, and then incubated with anti-CD4 mAbs (GK1.5 and YTS191) for 30–45 min at 4°C while rolling. After two washes the cells were incubated with sheep anti-rat IgG Dynalbeads (Dynal, Oslo, Norway) for 30–45 min followed by magnetic separation. The efficiency of T cell depletion was confirmed by flow cytometric analysis; <5% of cells were CD4 or CD3 positive. No differences in recovery or viability of isolated DC were observed among cells precultured with medium, responsive or anergic T cells (see Fig. 5⇓G). Isolated DC were assayed for their Ag-presenting capacity by a standard T cell proliferation assay. A titrated number of irradiated (3000 rad) DC (from 5 × 104 to 3 × 103/well) was cultured with responder T cells (4 × 104/well) in 96-well plates for 3 days.
Transwell experiments
In Transwell assays the cells were separated by a membrane (6.5 mm diameter, 0.4 μm pore size) in 24-well plates (Costar, Cambridge, MA). The lower compartment of the wells contained DC (2 × 106). The upper compartments contained medium alone, anergic, or responsive T cells (2 × 106) with added DC (1 × 106) in 2-ml culture medium. After 48 h, DC were harvested from the lower compartments and tested for their Ag-presenting capacity in T cell proliferation assays.
Flow cytometry
For the characterization of isolated DC populations, cells were stained in PBS, 1% BSA, and 0.1% NaN3 with the mAbs described above. Double stained populations were acquired and the CD11c-gated populations analyzed on a FACSCalibur (Becton Dickinson, Mountain View, CA).
Results
Anergic T cells inhibit the proliferation of responsive T cells stimulated by DC
Three mouse T cell clones were used for these experiments; two independently derived alloreactive clones (1F8 and 2E4) were specific for the amino acid-substituted NOD H2-A molecule, NODasp, and CTL10 was specific for a peptide of the male Ag, H-Y, restricted by H2-Db. The clones were rendered anergic by culture for 48 h in wells coated with anti-CD3 mAb in the complete absence of APC. The T cells were allowed to rest for a further 48 h before restimulation to allow TCR re-expression. The proliferative unresponsiveness of the two CD4+ T cell clones after the induction of anergy is shown in Fig. 1⇓, a and b. Production of several cytokines was similarly depressed after culture with anti-CD3 (10). We have reported previously in both human and mouse systems that anergic T cells inhibit proliferation by other T cells that interact with the same APC. Fig. 1⇓, c and d, show the titratable inhibition caused by anergic T cells from these two T cell clones when responsive T cells were stimulated with NODasp DC.
Anergic CD4+ T cells inhibit the proliferation of responsive T cells stimulated by DC. The T cell clones 2E4 (a) and 1F8 (b) were cultured with immobilized anti-CD3 mAb for 48 h and rested for 2 days. Anti-CD3-treated and untreated T cells (1 × 104/well) were restimulated with irradiated NODasp DC for 96 h. Responsive 2E4 (c) or 1F8 (d) T cells (1 × 104/well) alone, or mixed at different ratios (1:1 or 1:3) with irradiated anergic T cells were stimulated with irradiated NODasp DC for 96 h. These experiments were repeated four times with the same results.
Anergic T cells inhibit the Ag-presenting capacity of DC
To determine whether the inhibition caused by the anergic T cells required the presence of APC, T cells were stimulated in the absence of APC, using coimmobilized anti-CD3 and anti-CD28 Abs. As presented in Fig. 2⇓a, irradiated anergic 2E4 T cells caused no inhibition of proliferation by responsive 2E4 T cells under these conditions. Addition of irradiate, nonanergized 2E4 T cells led to significant enhancement of proliferation, presumably due to the secretion of IL-2 by the irradiated cells that cannot themselves divide and thereby consume growth factors.
Anergic T cells affect the Ag-presenting capacity of DC. a, In an APC-free system, the responsive T cell clone (2E4, 1 × 104/well) either alone, or mixed with irradiated anergic, or responsive T cells (ratio 1:3), were stimulated with coimmobilized anti-CD3 and anti-CD28 mAbs for 3 days. This experiment was repeated three times with the same results. b and c, NODasp DC (1 × 106/ml) were cultured with medium alone or with irradiated responsive or anergic 2E4 T cells (2 × 106/ml) for 48 h. After separation, NODasp DC were used in a 96 h proliferation assay to stimulate the responsive 2E4 T cells (b) or the CTL10 CD8+ T cells (c). The same results were obtained in three independent experiments. d, Anergic CD4+ T lymphocytes inhibit the Ag-presenting capacity of DC. Highly purified DO.11.10 CD4+ T lymphocytes were anergized in vitro by immobilized anti-CD3 mAb (10 μg/ml). BALB/c DC (1 × 106/ml) were cocultured with medium alone or with anergic CD4+ T lymphocytes (2 × 106/ml) for 48 h. After separation, DC (2 × 104/well) were used in a 96 h proliferation assay to stimulate freshly isolated D0.11.10 CD4+ T cells (4 × 104/well) in the presence of different concentrations of chicken OVA323–339 peptide. These experiments were repeated twice with similar results. e, Anergic T cells do not inhibit the Ag-presenting capacity of DC treated with LPS. Bone marrow GM-CSF-derived DC were treated with LPS for 48 h (2 μg/ml). After 48 h of incubation with either medium alone, or responsive, or anergic 2E4 T cells, DC were separated and used in proliferation assays to stimulate the responder 2E4 T cells. This experiment was repeated four times with the same results.
Having established that APC were required for the inhibition effected by anergic T cells, the possibility was examined that anergic T cells inhibited the Ag-presenting function of DC. The DC were cultured with anergic or responsive T cells with cognate specificity for the DC, or in medium with added T cells. GM-CSF was added to the culture medium in all the cases. After 48 h the T cells were removed using anti-CD4 Ab and magnetic beads, and the DC subjected to functional and phenotypic analysis. A representative experiment is shown in Fig. 2⇑b. Culture with anergic 2E4 T cells severely compromised the ability of the DC to restimulate responsive members of the same clone. In contrast, preculture with responsive members of the same clone enhanced the immunogenicity of the DC, possibly reflecting the ability of CD4+ T cells to “license” DC.
One explanation for these results was that exposure to anergic T cells led to selective internalization of the “cognate” MHC molecule:peptide complexes from the DC surface, so that the inability of the DC to restimulate the clone was due to the lack of cognate ligand. To test this possibility, the ability of the DC to stimulate the CD8+ T cell clone, CTL10, after culture with anergic 2E4 was tested. As displayed in Fig. 2⇑c, the ability of the DC to induce proliferation by CTL10 was also markedly reduced after culture with anergic 2E4, indicating that the Ag-presenting ability of the DC was comprehensively reduced.
To assess the physiological relevance of these findings, we used freshly purified CD4+ T cells from DO.11.10 TCR-transgenic mice instead of mouse T cell clones. Fig. 2⇑d shows that anergic CD4+ T cells were also able to inhibit the Ag-presenting capacity of DC.
To determine whether fully mature DC were susceptible to the inhibitory effects of anergic T cells, we used bone marrow-derived DC generated in the presence of GM-CSF and LPS. As shown in Fig. 2⇑e, preculture with anergic 2E4 T cells caused no inhibition of the Ag-presenting capacity of LPS-treated DC. Furthermore, preincubation with responsive 2E4 T cells did not further enhance the immunogenicity of the DC. These data support previous findings showing that fully mature DC are refractory to both inhibitory and activating stimuli (19).
The inhibition of DC function by anergic T cells requires cell:cell contact
One obvious candidate mechanism for these effects was the secretion of a cytokine, such as IL-10, by the anergic cells which inhibited DC differentiation and/or function. This was explored in two ways; first, a series of Transwell experiments was performed. The bone marrow-derived DC were cultured in the lower chamber, and anergic cells, with DC, were placed in the upper chamber. The DC in the lower chamber were tested as APC to stimulate 2E4 T cells after 48 h. The results presented in Fig. 3⇓a show that no inhibition was observed when the upper chambers contained anergic T cells and DC, suggesting that direct contact between the anergic T cells and the DC is required. Second, neutralizing Abs against IL-4, IL-10, and TGF-β were added to cultures containing DC and anergic T cells. As can be seen in Fig. 3⇓b, the addition of a cocktail of the three Abs completely failed to protect the DC from the inhibition caused by the anergic T cells.
Suppression by anergic T cells is not mediated by inhibitory cytokines. a, The effects of anergic T cells on DC were investigated using a Transwell system. Cell:cell contact was abolished by separating DC from cocultures of DC and responsive or anergic 2E4 cells by a 0.4-μm membrane. After 48 h the DC in the lower chambers were used to stimulate responsive 2E4 T cells. This experiment was repeated three times with similar results. b, NODasp DC (1 × 106/ml) were cocultured either with medium, or with irradiated responsive or anergic 1F8 T cells (2 × 106/ml) in the presence of neutralizing Abs against IL-4 (10 μg/ml), IL-10 (2 μg/ml), and TGF-β1, -β2, -β3 (10 μg/ml) for 48 h. After separation, NODasp DC were used in a 96-h proliferation assay to stimulate the responsive 1F8 T cells. The same results were obtained in three additional experiments. c, Suppression by anergic T cells was not mediated by Fas-FasL interactions. NODasp DC (1 × 106/ml) were cocultured with medium alone or with irradiated anergic 2E4 T cells (2 × 106/ml) in the presence of blocking Abs against FasL (10 μg/ml) for 48 h. After separation, NODasp DC were used in proliferation assays to stimulate the responsive 2E4 T cells. This experiment was repeated twice with similar results.
In an attempt to identify the cell surface molecules that might be involved in sending negative signals to DC, experiments with a blocking anti-FasL Ab were performed. As displayed in Fig. 3⇑c, the addition of the Ab did not prevent the inhibition of DC by anergic T cells.
Culture with anergic T cells leads to reduced expression of MHC class II, CD80, and CD86 molecules by DC
Following coculture with anergic or responsive T cells, the phenotype of the DC was examined by double staining the cells with anti-CD11c and a variety of Abs specific for key cell surface molecules. The results are displayed in Fig. 4⇓. After culture in medium alone, the DC were heterogeneous, containing cells of different stages of maturity. Indeed, the pattern of CD86 expression suggested that there were two somewhat distinct populations. Following culture with the responsive T cells, expression of MHC class II, CD86, and CD40 was up-regulated. For CD86 this was reflected in an increase in the CD86high population from 20 to 30%; for MHC class II and CD40 there was an increase in the mean fluorescence intensity of the whole population. The levels of expression of MHC class I and CD80 were slightly decreased and the expression of Fas was unchanged. In contrast, after 48 h culture with the anergic T cells expression of MHC class I, CD80, and CD86 was reduced to 40, 45, and 30% of the control levels, respectively. Expression of CD40 was increased, although to a lesser extent than following culture with the responsive T cells (437 vs 500 of mean of fluorescence).
FACS analysis of DC populations after T cell depletion. The cells were double stained with PE-conjugated anti-CD11c mAb and FITC-conjugated anti-class II, CD86, CD80, Fas, and class I mAbs. For the CD40 molecule we used an unconjugated mAb and a FITC-conjugated secondary Ab. Conjugated or purified isotype-matched Abs with irrelevant specificity were used as controls. The results are expressed as mean of fluorescence (m.f.) and percentage of positive cells of CD11c-gated populations. This experiment was repeated three times with similar results.
Anergic and responsive T cells expressed comparable levels of CD40 ligand (CD40L) and did not kill DC during the T:DC coculture.
To determine whether coculture of DC with T cells, either responsive or anergic, led to apoptosis, DC were stained with PE-conjugated anti-CD11c and FITC-conjugated-Annexin V. As shown in Fig. 5⇓, A–C, the staining profiles in DC preincubated with medium, responsive, or anergic T cells were identical. Little if any cell death was detectable, in contrast with cells incubated with anti-Fas mAb (Fig. 5D). Confirmation that the effects of anergic T cells on DC were not accompanied by cell death was provided by measuring cell recovery after coculture with T cells. As can be seen in Fig. 5⇓G, no significant differences in the numbers of recovered cells were seen under any of the conditions used in these experiments.
A–D, T cells did not kill DC during the T-DC coculture. NODasp DC (1 × 106/ml) were cocultured with medium alone (A), irradiated responsive (B) or anergic (C) 2E4 T cells (2 × 106/ml), or with medium in the presence of anti-Fas mAb (10 μg/ml) (D) for 48 h. After separation, NODasp DC were stained with PE-conjugated anti-CD11c and FITC-conjugated Annexin V. The results are expressed as mean of fluorescence (m.f.) of CD11c-gated populations. This experiment was repeated three times with similar results. E and F, Anergic and responsive T cells expressed a comparable level of CD40L. Responsive (E) and anergic 2E4 cells (F) were stained with PE-conjugated anti-CD40L (thin line) or isotype-matched control (dotted line). The m.f is indicated. G, Number of CD11c+ NODasp DCs recovered from T:DC cocultures. NODasp DC (1 × 106/ml) were cocultured with medium alone, irradiated responsive, or anergic 2E4 T cells (2 × 106/ml) for 48 h. After separation, NODasp DC were counted and stained with PE-conjugated anti-CD11c and FITC-conjugated anti-CD4. The results are expressed as mean ± SD of CD11c+ cells from four independent experiments.
A molecule that has recently been shown to influence DC maturation is CD40. Ligation of CD40 by CD40L-expressing CD4+ T cells appears to provide an important differentiation signal for DC (20, 21, 22). With this in mind, the levels of CD40L expressed by responsive and anergic T cells were compared. As shown in Fig. 5⇑, E and F, anergic and responsive 2E4 cells expressed comparable levels of CD40L.
Discussion
The data presented in this paper indicate that culture with anergic alloreactive T cells reduces substantially the immunogenicity of bone marrow-derived DC. The inhibition does not appear to be due to known inhibitory cytokines, was dependent upon cell:cell contact, and only affected immature DC.
Several groups have reported that anergic T cells, or T cells with a phenotype closely resembling that of an anergic T cell, can act as regulatory cells. We first described this using human cells in an in vitro system (7, 8). More recently we demonstrated that anergic mouse T cells can prolong skin allograft survival (10). Similar phenomena have been described using rat T cells in vitro; a requirement for the presence of APC for this inhibition to be observed was also noted in this study (23). The third set of related findings have emerged from the study of day three thymectomized mice that develop a variety of autoimmune pathologies spontaneously (12), and lack a small population of CD4+, CD25+ peripheral T cells. The significance of these cells became apparent when they were adoptively transferred from a normal, into a day three thymectomized mouse, in that they protected the recipients from the onset of autoimmune disease. When characterized functionally in vitro, these CD4+, CD25+ cells had the characteristics of anergic T cells, in that they could not undergo autocrine proliferation, made little if any cytokines, but could proliferate in response to exogenous IL-2. Furthermore, they were potent inhibitors of proliferation and IL-2 secretion by normal T cells.
DC are professional bone marrow-derived APC that play a dominant role in the initiation and regulation of immune responses. They exhibit phenotypic and functional diversity that is related to their stage of maturation (24) and/or to their myeloid or lymphoid origin (25). Culture of bone marrow cells with GM-CSF alone does not yield fully mature DC, but induces an intermediate state of maturation with respect to phenotype and Ag-presenting capacity (24, 26). It has also been reported that bone marrow-derived immature DC can induce hyporesponsiveness in allogeneic T cells (27) and significantly prolong cardiac allograft survival when injected into recipient mice (28). Previous studies have reported that the contact between activated T cells and DC, involving several members of the TNF family, induces maturation and activation of DC with subsequent enhancement of expression of MHC and costimulatory molecules (29). Culture of bone marrow-derived DC with anergic T cells had the opposite effect in that the immunogenicity of the DC was profoundly diminished, and expression of MHC class II, CD80, and CD86 molecules was reduced. However, it is not clear whether the impaired Ag-presenting capacity of the DC can be explained only by the decreased expression of MHC class II and costimulatory molecules, or whether additional mechanisms are involved. The responsive and anergic T cells expressed comparable levels of CD40L (Fig. 5⇑, E and F), suggesting that lack of CD40 ligation did not contribute to the observed effects of anergic T cells.
The functional and phenotypic analysis of the DC after culture with anergic T cells suggest that a negative signal was delivered to the DC that both caused maturation arrest, and down-regulated the most mature cells in the cultures. An alternative possibility was that the most mature cells were selectively killed as a result of culture with anergic T cells. This did not appear to be the case, in that the same numbers of cells were recovered from the different culture conditions (Fig. 5⇑G), and Annexin V staining did not indicate apoptosis of CD11c+ cells (Fig. 5⇑, A–D).
Several cytokines have been shown to affect the differentiation and function of DC. TGF-β and IL-10 can suppress DC functions and interfere with DC maturation (24). However the inhibition of DC function by anergic T cells required cell:cell contact and addition of neutralizing Abs specific for IL-4, IL-10, and TGF-β failed to protect the DC from the inhibitory effects of anergic T cells. These results are in accordance with our and other previous findings showing that the regulatory effects of anergic T cells are not mediated by soluble factors (7, 8, 23). Furthermore, the inhibition of DC functions by anergic T cells seems not to be due to Fas-FasL interaction as showed in Fig. 3⇑c; however, the molecular basis of this mechanism remains undefined.
The critical question is how this mechanism might contribute to physiological immunoregulation in vivo. The most extensively studied means of inducing T cell anergy in vitro has been costimulation-deficient Ag presentation. We, and others, have demonstrated that Ag presentation by primary cultures of allogeneic epithelial cells from the thyroid, or the kidney, induce allospecific hyporesponsiveness in resting (30) and recently activated (31) peripheral blood CD4+ T cells. This is likely to be a prominent event, in vivo, once tissue inflammation is well established, and parenchymal cell MHC class II expression has been induced. Such costimulation-deficient Ag presentation is likely to induce a cohort of anergic T cells with the potential to inhibit the Ag-presenting capacity of newly recruited DC, and thereby help to damp down the inflammatory response. In the context of transplantation, the suppressive effects of anergic T cells may be most relevant to inhibiting the indirect pathway of allorecognition by down-regulating recipient DC as they traffic through the graft before they present donor-derived peptides in the draining lymph node.
Footnotes
-
↵1 This work was supported by the Medical Research Council of the U.K. and by a Ph.D. fellowship (to S.V.) from the University of Palermo, Palermo, Italy.
-
↵2 S.V. and J.-G.C. are co-first authors.
-
↵3 Address correspondence and reprint requests to Dr. Robert Lechler, Department of Immunology, Imperial College School of Medicine, Hammersmith Hospital, Du Cane Road, London, U.K. W12 ONN. E-mail address: r.lechler{at}ic.ac.uk
-
↵4 Abbreviations used in this paper: FasL, Fas ligand; DC, dendritic cells; CD40L. CD40 ligand.
- Received November 29, 1999.
- Accepted April 24, 2000.
- Copyright © 2000 by The American Association of Immunologists
References
In this issue
