By
From Experimental Immunology, Department of Research, University Hospital, 4031 Basel, Switzerland
Nonpeptidic compounds stimulate human T cells bearing the TCR- in the absence of major
histocompatibility complex restriction. We report that one of these ligands, 2,3-diphosphoglyceric acid (DPG), which induces expansion of V
9/V
T cells ex vivo, antagonizes the same
cell population after repetitive activation. Stimulation with DPG results in partial early protein
tyrosine phosphorylation and a prolonged, but reversible, state of unresponsiveness to agonist
ligands in V
9/V
2, but not in other T cells. These findings show that TCR antagonism is a
general phenomenon of T cells. However, in contrast to the clonal specificity of altered peptides antagonizing
T cells, all the tested V
9/V
2 polyclonal cell lines and clones become
unresponsive, a fact that may be relevant for the regulation of their response in vivo.
Human Cells and Cell Culture.
Cells were cultured in RPMI 1640 medium supplemented with 2 mM glutamax I, 100 µg/ml kanamycin, MEM nonessential amino acids, 1 mM Na pyruvate (all
from GIBCO BRL, Basel, Switzerland), human serum 5% (Blutspendezentrum, Bern, Switzerland), and 100 U of recombinant human IL-2 (IL-2), unless mentioned as IL-2-free medium. The
V Flow Cytometry.
V Proliferation Assay.
Proliferation assays were performed in IL-2-
free medium using 105 responder cells/well and 30 Gy-irradiated
PBMC (105/well) as APC. After 48 h, 1 µCi/well of [3H]thymidine (TRK120; Amersham Intl., Little Chalfont, England), was
added and the cultures were harvested after an additional 18 h.
Results are shown as mean cpm ± SD.
TNF Release Assay.
104 responder cells were incubated with
the indicated ligand, and culture supernatants were collected after
6 h. 15 × 103 WEHI 164.13 cells were incubated for 18 h with appropriately diluted supernatant in the presence of actinomycin D
(2.5 µg/ml). After a further 4 h incubation with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT; 500 µg/ml),
the cells were lysed and the reduced MTT dissolved by adding
an equal volume of HCl 0.04 N in isopropanol. OD560-OD650
was determined using a THERMOmax Microplate Reader with
SOFTmax (Molecular Devices Corp., Menlo Park, CA), and the released TNF calculated by comparison with the OD in the linear range of a standard curve simultaneously acquired with recombinant human TNF. Results are shown as mean pg/ml ± SD.
Cytotoxicity Assays.
In brief, PHA-stimulated T cell blasts
were labeled with 100 µCi51Cr (Amersham Intl.) and 5,000 cells/
well were incubated in round-bottom wells with V Analysis of Protein Tyrosine Phosphorylation.
Immunoblot analysis for protein tyrosine phosphorylation was performed with total cell lysates. Briefly, T cells (7.5 × 105 cell equivalents/lane)
were lysed with 100 µl/106 cells of lysis buffer containing 25 mM
Tris-HCl, pH 7.5, 150 mM NaCl, 1% NP40, inhibitors of proteases (1 mM PMSF, 4 µg/ml leupeptin, 4 µg/ml aprotinin), and
inhibitors of phosphates (10 mM EDTA, 1 mM sodium orthovanadate), for 20 min on ice. After removal of nuclear debris by
centrifugation, the supernatant was electrophoresed on 10% SDSPAGE and transferred to nitrocellulose membrane (Hybond-C;
Amersham Intl.). Protein tyrosine phosphorylation was detected
using the 4G10 mAb (Upstate Biotechnology Inc., Lake Placid,
NY). The same results were obtained using another phospho- tyrosine specific mAb (PTyr1; a gift from V. Horejsi). Blots were developed using horseradish peroxidase-conjugated second antibody (sheep anti-mouse Ig; Amersham Intl.) and enhanced chemiluminescence (ECL system; Amersham Intl.).
A ligand and intermediate potency, 2,3-diphosphoglyceric
acid (DPG), was compared with a ligand with high potency, IPP (4, 5). Fresh Throughout this study we have sued V
To investigate whether stimulation by DPG could result
in a state of altered responsiveness, V
Proliferation and lymphokine release both require nuclear gene activation. To study whether effects induced by
earlier signaling events are altered by DPG, we performed
cytotoxicity assays. IPP stimulates cytotoxic V
To determine which signal transduction pathways might
be affected, we applied various procedures described to
prevent anergy induction or restore responsiveness. While
cyclosporin A completely prevents anergy with
Alterations of the TCR proximal signals have been previously described for modified peptide ligands which induce unresponsiveness in TCR
The presented data show that TCR The hypophosphorylation observed after DPG stimulation indicates that the signal transduction cascade is affected, and this might be due to loss of molecules important
in the signaling pathway. Interestingly, the potency of DPG
as agonist is the same as its potency as antagonist (ED50 250 µM), thus implying that DPG interacts with its receptor
with the same affinity on both fresh and expanded A second important difference is that while most of the
TCR Table 1.
Unresponsiveness of V cells bearing the V
9 (TCRGV2S1)/
V
2(TCRDV102S1) TCR react to a variety of phosphorylated nonpeptidic ligands (1), some of which are
natural metabolites (5). The TCR participates in the stimulation of the cells by such ligands as evidenced by reconstitution of reactivity when V
9 and V
2, but not other V
or V
genes, are co-transfected into a nonresponder T cell
line (6).
T cell recognition of phosphorylated nonpeptidic ligands has two remarkable characteristics (5): (a) it is
highly specific, since minor modifications in the structure
of the ligand abolish recognition, and (b) all V
9/V
2 cells
ex vivo and clones show the same specificity since they are
broadly cross-reactive against different metabolites, and all
ligands display the same relative potency on all tested T cell
clones and polyclonal lines. Without exception, we observe
that in vitro cultivated
T cells progressively lose their
capacity to proliferate in response to the weaker ligands first, and to the stronger ones later on, while maintaining
their ability to react to mitogens and to express similar levels of TCR (monitored by flow cytometry analysis using
antibodies against CD3
, C
, V
9, and V
2, data not
shown). This consistent loss of proliferative capacity does
not necessarily imply a loss of reactivity, but might reflect a
change in biological responsiveness. We have investigated
the possibility that a ligand which functions as an agonist
during the beginning of the immune response, may act as
an antagonist on the same cells in later phases.
9/V
2 cell lines were raised by culturing 106 freshly isolated
human PBMC with a single dose of the indicated ligand (50 µg/
ml Mycobacterium tuberculosis [M. tub.]1 (Difco Laboratories, Detroit,
MI), 10 µl/ml protein-free extract from M. tub. (PFE), 1 mM
xylose-1-phosphate (X1P), 1 mM ribose-1-phosphate (R1P), or 100 µM isopentenylpyrophosphate (IPP; Sigma, Buchs, Switzerland).
After 72 h, 50 U of IL-2 was added to the cultures. T cell clones
were established as reported (7) by limiting dilution using PHA
(1 µg/ml; Wellcome, Dartford, UK), IL-2 (100 U/ml), and irradiated PBMC (5 × 105/ml). T cell clones were restimulated periodically following the same protocol (7).
9/V
2 cells were incubated in the presence of indicated stimuli for 3 h, and then maintained on ice during staining with mAbs against CD3
(TR66) or C
(
1), and analyzed using a FACScan® flow cytometer. Data analysis was
performed using CELLQuest (Becton Dickinson, San Jose, CA).
9/V
2 cells at
the indicated effector/target (E/T) ratios. After 6 h, the amount
of 51Cr released into the supernatant was measured as cpm and
expressed as percent of specific 51Cr release: (effector induced cpm
spontaneous cpm / maximum cpm
spontaneous cpm) × 100. Maximum cpm were obtained by target cell lysis with 1 M HCl.
T cells fully respond to both
compounds. However,
T cells in culture gradually lose
their proliferative response to DPG without a change in
their capacity to proliferate in response to IPP.
9/V
2 T cells
which proliferate to IPP, but no longer to DPG. Both
DPG and IPP induce downmodulation of the TCR
on
these cells (Fig. 1), confirming that activation by DPG and
IPP involves TCR stimulation (8). DPG induces TCR
downmodulation without cell proliferation, we investigated whether it might behave as a partial agonist or as an
antagonist (9, 10). DPG induces neither release of IFN
and TNF, nor transcription of IL-1, IL-2, IL-3, IL-4, IL-5,
GM-CSF, IFN-
, and TNF-
genes in V
9/V
2 cells (assessed by reverse transcriptase-PCR, data not shown), nor
killing of target cells by cytotoxic V
9/V
2 clones (data
not shown), which are all effects detected after stimulation
with IPP. Therefore, it is unlikely that DPG is a partial agonist. In another series of experiments,
T cells were cultured in the presence of both ligands simultaneously (Fig. 2). Although DPG no longer displays its agonistic properties on cultured
T cells, it nevertheless has a clear dosedependent effect whereby it inhibits IPP-induced activation in a noncompetitive manner. DPG lowers the efficacy
(maximal response) of IPP, but does not alter the potency
of IPP (dose for 50% of maximal effect). These results indicate that DPG does not displace IPP from its binding site,
but that it may act as a TCR antagonist.
Fig. 1.
DPG induces downmodulation of the TCR . Overlaid
histograms of immunostaining of
1 mAB on V
9/V
2 clone Z1P 101 simulated with medium (
, median fluorescence intensity [MFI] 138, 100%), 1 mM DPG (
, MFI 99, 71%), IPP 100 µM (---, MFI 100, 72%), and PHA 1 µg/ml (\xc9 , MFI 55, 40%). Similar results were obtained with several different V
9/V
2 cell lines and clones, but not with
control clones bearing other types of TCR.
[View Larger Version of this Image (24K GIF file)]
Fig. 2.
DPG reduces the efficacy, but not the potency, of IPP. Proliferation (A) and TNF release (B) of the T cell line PG96 coincubated with different concentrations of IPP and DPG (1 mM,
; 500 µM,
;
250 µM,
; 125 µM,
), or medium (
). Comparable dose-response curves were obtained in four independent experiments.
[View Larger Version of this Image (25K GIF file)]
9/V
2 T cells were
preincubated with DPG, and then washed and challenged
with IPP. Preincubation with DPG blocks the subsequent
ability of IPP to stimulate TNF release and cell proliferation (Fig. 3) indicating that DPG induces a state of unresponsiveness which persists after removal of the ligand. This
prolonged unresponsiveness is not due to inadequate washout of the antagonist, since control cells are fully reactive in
the presence of equal numbers of DPG-preincubated cells
(data not shown). Incubation with DPG for only 5 min is
sufficient to block IPP-mediated TNF release (Fig. 3 A).
The rapidity with which DPG exerts its inhibitory effect
is consistent with observations that phosphorylated nonpeptidic ligands induce Ca2+ fluxes in V
9/V
2 T cells
within 2 min (11, 12). The IPP-unresponsiveness induced
by DPG is not a consequence of cell death since the number of viable cells recovered is the same (70-100%) as
controls, and the cells remain responsive to low doses (20 U/ml) of IL-2 (Fig. 3 B). Furthermore, once a state of unresponsiveness is induced, it lasts for 1-5 d (using different
cell lines and clones), after which the cells regain their
ability to respond to the agonist (Fig. 3 B). The induction
of unresponsiveness by DPG differs from the induction of
T cell refractoriness by repetitive stimulation with agonist
ligands. Indeed, (a)
cells stimulated by DPG become unresponsive without induction of effector functions, and
(b) the induction of unresponsiveness by DPG has a dominant effect even over simultaneous stimulation by IPP (Fig. 2).
Fig. 3.
DPG rapidly induces a prolonged, but reversible, state of unresponsiveness to IPP. (A) The V9/V
2 cell line BCI 31 was incubated with DPG for the time indicated on the x-axis. After extensive washing,
the TNF release stimulated by 50 µM IPP (
) or 1 µg/ml PHA (
) was
measured. (B) V
9/V
2 clone BCI 49 (2 × 106 cells/ml) was incubated
in IL-2-free medium with 1 mM DPG overnight and washed extensively. The cells were then rested in medium for the time indicated on the
x-axis. Proliferative responses to medium (
), 100 µM IPP (
), or 20 U/ml IL-2, (
) are shown.
indicates control proliferation to IPP (100 µM) of the same cells not preincubated with DPG. Results obtained in
four independent experiments using different V
9/V
2 clones showed
recovery of responsiveness after 1 to 5 d. Preincubation with DPG did
not affect the responsiveness of CD4+ TCR
cells to their specific peptide (data not shown).
[View Larger Version of this Image (25K GIF file)]
9/V
2 cells
to kill target cells at low E/T ratios; however, IPP does not
trigger killing by the same cells preincubated with DPG
(Fig. 4). These results suggest that in unresponsive cells, not
only late events, but also earlier signaling events leading to
cytotoxic activity are affected.
Fig. 4.
Early signaling events, necessary for cytolytic function, are altered in cells made unresponsive by DPG. The figure shows results of killing of PHA-blasts by V9/V
2 clone RNM.t.73 preincubated overnight
with medium (solid symbols) or DPG 1 mM (open symbols) in the presence
(squares) or absence (circles) of 100 µM IPP, at the indicated E/T ratios.
[View Larger Version of this Image (19K GIF file)]
T cells
(13, 14), it has only a partial effect on
T cells (data not
shown). This suggests that both the late signals blocked by
cyclosporin A, as well as other signals, participate in establishing unresponsiveness. IPP-unresponsive cells could be
stimulated by PHA or a combination of PMA and Ca2+
ionophore (Fig. 5). Importantly, reactivity to IPP could be
restored by PMA, which was not stimulatory by itself.
Thus, IPP can apparently still trigger unresponsive cells with
a signal that is mimicked by Ca2+ ionophore. In addition,
the ability of PMA to overcome unresponsiveness indicates
that the blockade of signaling in unresponsive cells most
likely occurs between the TCR and P21ras. Blockade of
proximal signaling has been recently shown in two
T cell anergy models (15, 16).
Fig. 5.
Unresponsiveness induced by DPG is the consequence of
the alteration of TCR proximal signals. V9/V
2 clone BCI 49 (106 cells/
ml) was incubated overnight in IL-2-free medium with 1 mM DPG
and washed extensively. Proliferative responses to medium, 100 µM IPP,
1 µg/ml PHA, 500 ng/ml Ca2+ Ionophore A23187 (Iono) 50 ng/ml PMA,
or the indicated combinations were measured.
[View Larger Version of this Image (14K GIF file)]
clones (17, 18). To investigate whether early signals are also altered in
T cells,
the IPP- and DPG-induced protein tyrosine phosphorylation patterns were compared. A similar spectrum of phosphorylated proteins was detected (Fig. 6). However, the overall level of phosphorylation induced by DPG was
quantitatively less than that induced by IPP.
Fig. 6.
Upon DPG treatment, tyrosine phosphorylation
of TCR-associated proteins is
reduced when compared to IPP
stimulation. V9/V
2 T cells
were incubated for 10 min with
either medium (C), 100 µM
IPP, 1 mM DPG, or 1 µg/ml
PHA. Protein tyrosine phosphorylation is visualized by immunoblotting of total cell lysates. Similar results were obtained in four
independent experiments using
V
9/V
2 cell lines and clones.
IPP and DPG did not induce any
protein tyrosine phosphorylation in TCR
cells (data not
shown).
[View Larger Version of this Image (70K GIF file)]
antagonism has
several characteristics in common with TCR
antagonism induced by altered peptide ligands (9, 19, 20). However, there are also important differences. In V
9/V
2 T
cells, the antagonistic effects of DPG occur only after cell
activation and extensive proliferation. Since the effects of
DPG are observed without changes in its structure, the
change in response must be due to a change occurring in
the T cells. Cultured
T cells, on which DPG has lost its
agonistic effects, express normal levels of TCR, which can
transduce a full signal after stimulation with IPP. Therefore, it is likely that molecules other than the TCR are involved in the altered responsiveness to DPG. In our case,
modified expression of costimulatory molecules seems unlikely, because cells which have lost the capacity to proliferate with DPG still proliferate with IPP, implying adequate costimulation. Yet, triggering the TCR with various
stimuli in the absence of costimulation always leads to
T cell anergy (21, 22). The finding that cytotoxicity, which
is not so dependent on costimulation (23), is lost in unresponsive cells also supports this conclusion.
cells
and that the nonproliferating
cells have not modified the receptor for DPG. We hypothesize that responsiveness
of V
9/V
2 cells is modulated by the expression levels of a
(unknown) molecule with a coreceptor-like function similar to that described for CD4 and CD8 coreceptors on
cells (24). Based on the presented data, our hypothesis
predicts that stimulation of
T cells with strong ligands
(e.g., IPP) is largely independent of coreceptor density,
while stimulation with weak ligands (e.g., DPG) would require a high density. If the coreceptor density is reduced, weak ligands switch their properties from being agonists to
antagonists. A progressive loss of the coreceptor might allow a given ligand to function as a full agonist in the early
phase of the immune response, and subsequently acquire antagonistic properties and regulatory functions.
antagonists are highly T cell clone specific, DPG
is broadly active on human V
9/V
2 T cells. When many
different
T cell lines and clones from various donors are
tested, all the V
9/V
2 cells become unresponsive, irrespective of the ligand used to expand the original cell lines
(Table 1). This is observed with assays detecting either proliferation or TNF release.
9/V
2 Polyclonal Lines and Clones After Overnight Incubation with DPG
Response to:
Medium
IPP
IL-2
PHA
Preincubation with DPG:
No
Yes
No
Yes
No
Yes
No
Yes
Donor
Raised against
Proliferation
cpm
OP
M. tub.
2,039
1,280
15,175
1,160
11,785
10,584
13,961
15,927
VJ
M. tub.
6,353
3,366
12,061
3,087
12,827
13,003
10,488
14,474
GDL
M. tub.
1,320
5,075
27,385
6,899
31,537
36,617
16,890
23,029
GDL
R1P
628
1,360
19,198
1,870
12,086
16,345
15,123
17,415
GDL
X1P
7,324
5,757
12,104
6,171
17,094
16,486
23,042
22,941
GDL
PFE
10,607
8,178
70,393
7,326
ND
ND
ND
ND
BCI 49*
IPP
381
706
37,324
1,767
44,938
50,429
19,102
19,514
BCI 5*
IPP
411
323
24,857
1,080
ND
ND
6,350
8,388
TNF release
pg/ml
GDL
M. tub.
ND
744
14,746
2,295
ND
ND
ND
ND
GDL
IPP
ND
101
5,147
956
ND
ND
4,658
3,102
BCI 13*
IPP
ND
475
7,585
1,736
ND
ND
ND
ND
G2C25*
PHA
<15
<15
2,369
155
ND
ND
ND
1,649
*
V 9/V
2 T cell clone. PFE, protein-free extract from M. tub.; R1P, ribose-1-phosphate; X1P, xylose-1-phosphate. Each line or clone was tested
two to four times.
The induction of a state of unresponsiveness in a whole
lymphocyte subpopulation may have important consequences
for the immune response of T cells. It has been proposed
that
T cells provide an efficient first line of defense against
infectious agents (30, 31). This property may derive from
their ability to broadly cross-react with many ligands (5)
and with diverse microorganisms (7, 32). However, this
promiscuous ligand recognition might lead to an uncontrolled expansion of V
9/V
2 T cells with harmful effects
for the organism. The presently described regulatory mechanism could control the whole V
9/V
2 T cell population
in a late phase of the immune response. A paradigmatic example might be malaria infection where either plasmodium
ligands or DPG, which is present inside red blood cells at a
physiological concentration of ~5 mM, are released after
massive erythrocyte rupture. In patients with acute malaria,
a synchronized erythrocyte rupture is followed by hyperactivation of the V
9/V
2 population (37, 38) and by a massive release of TNF resulting in a severe clinical picture (39). The recurrent release of nonpeptidic ligands from
ruptured red blood cells and the successive activation and
expansion of
T cells could change
T cell reactivity,
and thereby result in a beneficial unresponsiveness. Indeed,
patients with the chronic form of malaria experience neither V
9/V
2 cell expansion nor raised TNF serum levels
and have an asymptomatic clinical course (38).
In summary, the presented data provide a rationale for
manipulating the reactivity of the whole V9/V
2 T cell
population and offer a new model with which to assess
whether TCR antagonism is an important principle of T cell
regulation.
Address correspondence to Gennaro De Libero, Experimental Immunology, Department of Research, University Hospital, Hebelstrasse 20, CH-4031 Basel, Switzerland.
Received for publication 9 July 1996
This work was supported by the Swiss National Fund grants No. 31-36450-92 and No. 31-045518.95 to G. De Libero and the Marie-Heim Vögtlin grant No. 32-38848-93 to L. Mori.We thank A. Lanzavecchia, R. Nisini, and T. J. Resink for reading the manuscript.
1. |
Pfeffer, K.,
B. Schoel,
H. Gulle,
S.H. Kaufmann, and
H. Wagner.
1990.
Primary responses of human T cells to mycobacteria: a frequent set of ![]() ![]() |
2. |
Constant, P.,
F. Davodeau,
M.A. Peyrat,
Y. Poquet,
G. Puzo,
M. Bonneville, and
J.J. Fournie.
1994.
Stimulation of
human ![]() ![]() |
3. |
Tanaka, Y.,
S. Sano,
E. Nieves,
G. De Libero,
D. Rosa,
R.L. Modlin,
M.B. Brenner,
B.R. Bloom, and
C. Morita.
1994.
Nonpeptide ligands for human ![]() ![]() |
4. |
Tanaka, Y.,
C.T. Morita,
Y. Tanaka,
E. Nieves,
M.B. Brenner, and
B.R. Bloom.
1995.
Natural and synthetic non-peptide antigens recognized by human ![]() ![]() |
5. |
Bürk, M.R.,
L. Mori, and
G. De Libero.
1995.
Human V![]() ![]() |
6. |
Bukowski, J.F.,
C.T. Morita,
Y. Tanaka,
B.R. Bloom,
M.B. Brenner, and
H. Band.
1995.
V![]() ![]() |
7. |
De Libero, G.,
G. Casorati,
C. Giachino,
C. Carbonara,
N. Migone,
P. Matzinger, and
A. Lanzavecchia.
1991.
Selection
by two powerful antigens may account for the presence of
the major population of human peripheral ![]() ![]() |
8. |
Padvoan, E.,
G. Casorati,
P. Dellabona,
S. Meyer,
M. Brockhaus, and
A. Lanzavecchia.
1993.
Expression of two T cell
receptor ![]() |
9. | Jameson, S.C., and M.J. Bevan. 1995. T cell receptor antagonists and partial agonists. Immunity. 2: 1-11 [Medline] . |
10. | Kersch, G.J., and P.M. Allen. 1996. Essential flexibility in the T-cell recognition of antigen. Nature (Lond.). 380: 495-498 [Medline] . |
11. |
Lang, F.,
M.A. Peyrat,
P. Constant,
F. Davodeau,
A.J. David,
Y. Poquet,
H. Vie,
J.J. Fournie, and
M. Bonneville.
1995.
Early activation of human V![]() ![]() |
12. |
Morita, C.T.,
E.M. Beckman,
J.F. Bukowski,
Y. Tanaka,
H. Band,
B.R. Bloom,
D.E. Golan, and
M.B. Brenner.
1995.
Direct presentation of nonpeptide prenyl pyrophosphate antigens to human ![]() ![]() |
13. |
Jenkins, M.K.,
J.D. Ashwell, and
R.H. Schwartz.
1988.
Allogenic non-T spleen cells restore the responsiveness of normal
T cell clones stimulated with antigen and chemically modified antigen-presenting cells.
J. Immunol.
140:
3324-3330
|
14. | Sloan-Lancaster, J., B.D. Evavold, and P.M. Allen. 1993. Induction of T-cell anergy by altered T-cell-receptor ligand on live antigen-presenting cells. Nature (Lond.). 363: 156-159 [Medline] . |
15. | Li, W., C.D. Whaly, A. Mondino, and D.L. Mueller. 1996. Blocked signal transduction to the ERK and JNK protein kinases in anergic CD4+ T cells. Science (Wash. DC). 271: 1272-1276 [Abstract] . |
16. | Fields, P.E., T.F. Gajewski, and F.W. Fitch. 1996. Blocked ras activation in anergic CD4+ T cells. Science (Wash. DC). 271: 1276-1278 [Abstract] . |
17. | Sloan-Lancaster, J., A.S. Shaw, J.B. Rothbard, and P.M. Allen. 1994. Partial T cell signaling: altered phospho-zeta and lack of zap70 recruitment in APL-induced T cell anergy. Cell. 79: 913-922 [Medline] . |
18. | Madrenas, J., R.L. Wange, J.L. Wang, N. Isakov, L.E. Samelson, and R.N. Germain. 1995. Zeta phosphorylation without ZAP-70 activation induced by TCR antagonists or partial agonists. Science (Wash. DC). 267: 515-518 [Medline] . |
19. | Germain, R.N., E.H. Levine, and J. Madrenas. 1995. The T-cell receptor as a diverse signal transduction machine. The Immunologist. 3/4:113-121. |
20. | Sloan-Lancaster, J., and P.M. Allen. 1996. Altered peptide ligand-induced partial T cell activation: molecular mechanisms and a role in T cell biology. Annu. Rev. Immunol. 14: 1-27 [Medline] . |
21. | Jenkins, M.J., and R.H. Schwartz. 1987. Antigen presentation by chemically modified splenocytes induces antigen-specific T cell unresponsiveness in vitro and in vivo. J. Exp. Med. 165: 302-309 [Abstract] . |
22. | Schwartz, R.H.. 1990. A cell culture model for T lymphocyte clonal anergy. Science (Wash. DC). 248: 1349-1356 [Medline] . |
23. | Otten, G.R., and R.N. Germain. 1991. Split anergy in a CD8+ T cell: receptor-dependent cytolysis in the absence of interleukin-2 production. Science (Wash. DC). 251: 1228-1231 [Medline] . |
24. |
Alexander, J.,
K. Snoke,
J. Ruppert,
J. Sidney,
M. Wall,
S. Southwood,
C. Oseroff,
T. Arrhenius,
F.C.A. Gaeta,
S.M. Colon, et al
.
1993.
Functional consequences of engagement
of the T cell receptor by low affinity ligands.
J. Immunol.
150:
1-7
|
25. | Jameson, S.C., K.A. Hogquist, and M.J. Bevan. 1994. Specificity and flexibility in thymic selection. Nature (Lond.). 369: 750-752 [Medline] . |
26. | Vignali, D.A.A., and J.L. Stromiger. 1994. Amino acid residues that flank core peptide epitopes and the extracellular domains of CD4 modulate differential signaling through the T cell receptor. J. Exp. Med. 179: 1945-1956 [Abstract] . |
27. | Luescher, I.F., E. Vivier, A. Layer, J. Mahiou, F. Godeau, B. Malissen, and P. Romero. 1995. CD8 modulation of T-cell antigen receptor-ligand interactions on living cytotoxic T lymphocytes. Nature (Lond.). 373: 353-356 [Medline] . |
28. |
Mannie, M.D.,
J.M. Rosser, and
G.A. White.
1995.
Autologous rat myelin basic protein is a partial agonist that is converted into a full antagonist upon blockade of CD4.
J. Immunol.
154:
2642-2654
|
29. | Vidal, K., B.L. Hsu, C.B. Williams, and P.M. Allen. 1996. Endogenous altered peptide ligands can affect peripheral T cell responses. J. Exp. Med. 183: 1311-1321 [Abstract] . |
30. | Janeway, C.R. Jr.. 1988. Frontiers in the immune system. Nature (Lond.). 333: 804-806 [Medline] . |
31. |
Asarnow, D.M.,
W.A. Kuziel,
M. Bonyhadi,
R.E. Tigelaar,
P.W. Tucker, and
J.P. Allison.
1988.
Limited diversity of ![]() ![]() |
32. |
Holoshitz, J.,
F. Koning,
J.E. Coligan,
J. De Bruyn, and
S. Strober.
1989.
Isolation of CD4![]() ![]() |
33. |
Fisch, P.,
M. Malkovsky,
S. Kovats,
E. Sturm,
E. Braakman,
B.S. Klein,
S.D. Voss,
L.W. Morrissey,
R. DeMars,
W.J. Welch, et al
.
1990.
Recognition by human V![]() ![]() |
34. |
Munk, M.E.,
A.J. Gatrill, and
S.H. Kaufmann.
1990.
Target
cell lysis and IL-2 secretion by ![]() ![]() |
35. |
Roussilhon, C.,
M. Agrapart,
J.J. Ballet, and
A. Bensussan.
1990.
T lymphocytes bearing the ![]() ![]() |
36. |
Hara, T.,
Y. Mizuno,
K. Takaki,
H. Takada,
H. Akeda,
T. Aoki,
M. Nagata,
K. Ueda,
G. Matsuzaki,
Y. Yoshikai, and
K. Nomoto.
1992.
Predominant activation and expansion of
V![]() ![]() ![]() |
37. |
Ho, M.,
P. Tongtawe,
J. Kriangkum,
T. Wimonwattrawatee,
K. Pattanapanyasat,
L. Bryant,
J. Shafiq,
P. Suntharsamai,
S. Looareesuwan,
H.K. Webster, and
J.F. Elliott.
1994.
Polyclonal expansion of peripheral ![]() ![]() |
38. |
Perera, M.K.,
R. Carter,
R. Goonewardene, and
K.N. Mendis.
1994.
Transient increase in circulating ![]() ![]() |
39. | Karunaweera, N.D., G.E. Grau, P.E. Gamage, R. Carter, and K.N. Mendis. 1992. Dynamics of fever and serum levels of tumor necrosis factor are closely associated during clinical paroxysms in Plasmodium vivax malaria. Proc. Natl. Acad. Sci. USA. 89: 3200-3203 [Abstract] . |