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Binding by the Nonclassical Class I Molecule, Thymic Leukemia Antigen1
* Department of Pathology, School of Medicine and
Microchemical Facility, Emory University, Atlanta, GA 30322;
Division of Developmental Immunology, La Jolla Institute for Allergy and Immunology, San Diego, CA 92121; and
Laboratory of Immunobiology, Dana-Farber Cancer Institute, Boston, MA 02115
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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2-microglobulin in the presence or absence of a random
peptide library. Using a mAb, HD168, that recognizes a conformational
epitope on native TL molecules, we observed that protein folds
efficiently in the absence of peptide. Circular dichroism analysis
demonstrated that TL molecules have structural features similar to
classical class I molecules. Moreover, thermal denaturation experiments
indicated that the melting temperature for peptide-free TL is similar
to values reported previously for conventional class I-peptide
complexes. Our results also show that CD8
binding is not
dependent on either TL-associated peptide or TL
glycosylation. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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1
and 2 domains of these molecules (5). TL is expressed
at the cell surface in association with
2-microglobulin (2m)
and it is predicted to fold with a conformation similar to other MHC
class I proteins. The CD8 binding site is conserved and it has been
demonstrated that CD8 can serve as a coreceptor for CTL recognition of
a chimeric class I molecule containing the TL 3 domain
(6). In addition, there is evidence that TL may serve as a
restriction element for TCR and 
T cells
(7, 8, 9, 10, 11, 12, 13).
Recent work demonstrates that soluble TL produced in insect cells binds
to the homodimeric form of CD8, CD8, which is expressed on a
large subpopulation of intraepithelial lymphocytes (IEL) (13, 14). TL (T18d) tetramers selectively bind
CD8+ IEL and transfectants expressing
CD8. There is no evidence for a role for TCR in this interaction.
Binding experiments with rTL monomers generated using a baculovirus
expression system demonstrate that TL binds CD8 with an affinity
at least 10-fold higher than the affinity for CD8 heterodimers,
the usual form of CD8 on T cells (14). TL has a low
affinity for CD8, similar to that measured for
H-2Kb with either CD8 or CD8
(14, 15). Functional studies with primary T cells and T
cell hybridomas demonstrate that the interaction of CD8 on T
cells with TL on APC can strikingly promote TCR-mediated cytokine
production (14). By contrast, the CD8-TL interaction
does not enhance other functions of IEL, including proliferation or
cytotoxicity. Thus, TL appears to regulate TCR-mediated cytokine
production by CD8+ IEL through a mechanism
not requiring direct TCR recognition of TL.
The issue of whether TL can bind peptides remains an open question.
Conserved residues that form hydrogen bonds with the N and C termini of
bound peptides in class I molecules (16, 17) are retained
in TL. However, TL is efficiently expressed in TAP-deficient cell lines
(18, 19) and thymocytes (20). This
observation does not necessarily rule out a role for peptide ligands in
TL assembly and transport. For example, the class Ib molecule Qa-1 is
expressed efficiently on the surface of TAP-deficient cells (21, 22) despite its usual assembly with a TAP-dependent peptide
derived from the leader sequence of other class I molecules
(23) and its capacity to bind diverse peptide sequences
(24). Studies with transgenic mice expressing TL driven by
the H-2Kb promoter demonstrate that TL can act
as a transplantation Ag and that TL-specific CTL expressing TCR
can be induced (7, 8, 10, 11, 13). These CTL recognize TL
expressed in TAP-deficient RMAS and insect cell lines
(12), consistent with peptide-independent recognition or
presentation of unconventional Ags loaded on TL through a
TAP-independent pathway. The latter possibility has precedent because
Qa-1 can present insulin to TCR T cells through a TAP-independent
endosomal pathway (25). Peptide elution experiments with
TL isolated from a radiolabeled cell line demonstrated the apparent
presence of TL-associated peptides but no sequence information was
obtained by Edman degradation, possibly because of peptide N-terminal
modifications (8). No peptides were identified in elution
experiments with soluble TL expressed in insect cells
(18).
In the current study, we demonstrate that TL, expressed as inclusion
bodies in Escherichia coli, can efficiently fold in vitro
with 2m in the absence of peptides or other
potential ligands. The empty TL molecules are shown to form a stable
conformation and to bind to rCD8 with high affinity. Tetramers
generated with this protein bind a large fraction of IEL and this
binding is blocked with mAb to CD8.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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A cDNA construct (18) was used as template to
amplify a truncated form of the T18d H chain. The
primers used were: sense,
5'-TACCATATGGGCTCACACTCGCTGAGGTACTTC-3', and antisense,
5'-GCGGGATCCACGAACAGTGGTCCTGTTGG-3', tagged with
NdeI and BamHI sites (in bold italics),
respectively. The PCR product was cloned inframe with a
biotin-binding cassette (BSP) at the 3' terminus into pET23a vector as
previously described (26). The protein-BSP was expressed
as inclusion bodies in E. coli BL21(DE3)pLys (Stratagene, La
Jolla, CA) after induction with 0.4 M
isopropyl--D-thiogalactopyranoside.
T18d and human 2m
(26) inclusion bodies were purified from bacterial lysates
and solubilized in 8 M urea. Solubilized inclusion bodies were filtered
through PD-10 columns (Amersham Pharmacia, Uppsala, Sweden) to remove
low m.w. materials. After further dilution with buffered 6 M guanidine
hydrochloride, 1 µM H chain, and 2 µM 2m
were injected into a 200-ml refolding mix in the presence or absence of
20 mg of randomized 9-mer peptide libraries as described
(26). The refolded T18d monomers
were concentrated in an Amicon chamber (Beverly, MA) with a
10K-exclusion membrane and separated from aggregated H chain and free
2m on a S300 gel filtration column (Pharmacia
Biotech, Peapack, NJ). Heterodimers were dialyzed against PBS at a
neutral pH. Similarly, a truncated H chain of HLA-A2 was generated and
refolded with or without peptide. HLA-A2-BSP and human
2m constructs have been described
(26). All refolded proteins were analyzed by SDS-PAGE
(12.5% gel) and visualized with Coomassie Blue.
Quantification of refolded T18d
Refolded heterodimers were quantified by a sandwich immunoassay.
Briefly, 96-well Immulon II plates were coated overnight at 4°C with
5 µg/ml mAb to human 2m (Immunotech,
Westbrook, ME) diluted in borate-buffered saline at pH 8.0. Plates were
blocked 30 min at room temperature with 50 mM Tris, pH 7.5, containing
5% nonfat dry milk, 0.1% BSA, and 0.1% Tween 20 (MTB) and thoroughly
washed in Tween 20 plus TBS (TTBS) (500 mM Tris-HCl, pH 7.5, and
0.1% Tween 20) before sample addition. Samples were diluted in MTB
containing 0.2% Nonidet P-40 (MTBN) and incubated in the wells for
1 h at 4°C. The plates were washed again as above. HD168 rat mAb
(27) diluted in MTBN to a final concentration of 20
µg/ml was added to the wells and incubated for 1 h at 4°C.
After washing, 5 µg/ml biotin-labeled goat anti-mouse Ab
(Southern Biotechnology Associates, Birmingham, AL) was added for
1 h at 4°C followed by a wash and the addition of 100 ng/ml
europium-labeled streptavidin (Wallac, Gaithersburg, MD) as previously
described (28). Detection occurred at 615 nm using a 1230
ARCUS time-resolved fluorometer (Wallac). Results are expressed as
fluorescence counts per second (cps x
10-3).
Circular dichroism (CD) and thermal denaturation
CD spectra were measured on an AVIV 60DS spectropolarimeter
(Aviv Associates, Lakewood, NJ) equipped with a thermoelectric cell
holder. Refolded (T18d) samples were diluted in
0.15 M PBS, pH 7.0, to a final concentration of 250 µg/ml, determined
by absorbance at 280 nm, using an extinction coefficient of 2.0. Far-UV
spectra were recorded in a 0.1-cm path-length cuvette at 25°C using a
step size of 1 nm, a bandwidth of 1.5 nm, and a time constant of
2.0 s. The spectra shown in Fig. 3
represent the average of
three experiments, each representing the average of three repetitive
scans with a subtracted PBS background. Far-UV spectra are given as the
mean residue ellipticity [
]r. Standard
heating/cooling cycling of the samples was used to demonstrate the
reversibility of the thermal unfolding. The CD spectra of each sample
were first measured at 25°C, then the sample was heated to 79°C
(above the midpoint temperature of the thermal unfolding transition
(Tm) of T18d),
immediately cooled to 25°C, and spectra were recorded again after an
equilibration time of 1 h. The far-UV spectra recorded at high
temperatures were measured separately to avoid permanent denaturation
of the heterodimers due to long incubation times at high
temperatures.
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Averaged spectra and thermal denaturation curves were smoothed by a
least squares polynomial fit using the Aviv 60DS software, v4.1t
(polynomial order of 5, sliding window of 5). The
Tm was determined from the interpolated
maximum of a plot of d/dT vs T (
is ellipticity).
Peptide libraries
Random peptide libraries were assembled by Fmoc-based solid-phase synthesis at the 50 µmol per channel scale on a Wang resin using an Advanced ChemTech model 3480 multiple peptide synthesizer (Louisville, KY). Acylation of the resin was affected using a 6-fold molar excess of preformed hydroxybenzotriazole esters of all coded F-moc-protected amino acids (excluding cysteine) as described previously (29). A 50% molar excess of F-moc-Val, Fmoc-Arg(Mtr), and F-moc-Ile over other Fmoc-amino acids was used to compensate for their lower acylation rates (29, 30). After cleavage and deprotection (Reagent K, 2 h, 25°C), the peptides were precipitated with diethyl ether (-20°C, 4 h). The precipitate was collected by centrifugation and solubilized in neat trifluoroacetic acid (TFA), diluted with H2O, and lyophilized. These libraries were obtained in the form of their TFA salts. Quantitative amino acid analysis and N-terminal sequence analysis confirmed their expected composition and the randomness of their sequences.
Pool peptide sequencing
T18d and HLA-A2 were refolded together
with human 2m in the presence or absence of
9-mer peptide libraries as described above. PD-10 columns were used to
eliminate low m.w. contaminants of bacterial origin present in the
inclusion body preparations. Refolded complexes of
T18d and HLA-A2 (500 µg each) were concentrated
in Amicon chambers with a 10K exclusion membrane. Peptide was eluted by
diluting the samples in 2% TFA/10% acetonitrile and separated from H
chains and 2m using a Centricon 3 (Amicon)
concentrator pretreated with 2% TFA/10% acetonitrile. Eluted peptides
were dried by speed vacuum centrifugation. Edman degradation of
T18d and HLA-A2-bound peptides was performed in a
mode Procise cLC peptide sequencer (PE Biosystems, Wellesley, MA)
operated in the pulsed liquid mode as previously described (29, 31). Eluted peptides were analyzed by microbore reverse-phase
HPLC and separated using a Zorbax SB-C18 column (Frankfurt, Germany) as
previously described (24). Briefly, the column eluate was
monitored at 210 and 280 nm, the fractions absorbing at 210 nm were
manually collected, and matrix-assisted laser desorption ionization
time-of-flight (MALDI-TOF) mass spectrometry analysis was
performed as described (24).
Tetramer staining
Refolded T18d and HLA-A2 monomers were
biotinylated enzymatically by incubation with purified BirA for 12
h at 25°C as described (26). T18d
tetramers were prepared by mixing the biotinylated protein with
streptavidin-PE) at a molar ratio of 4:1. Tetramerization was confirmed
by gel electrophoresis. IELs, isolated as previously described
(32), and inguinal lymph node CD8 T cells were isolated
from C57BL/6 mice and incubated with FcR mAb 2.4G2 to prevent
nonspecific staining. Approximately 105 IELs or
lymph node cells were stained with 1 µg of PE-conjugated tetramer
protein and FITC-labeled anti-CD8 mAb, 53-6.7 (BD PharMingen, San
Diego, CA), and were analyzed on a FACScan (BD Biosciences, San Jose,
CA). For blocking of tetramer staining, Rat-anti-CD8 mAb RM2200
(Caltag Laboratories, San Francisco, CA) was used at 1 µg/50 µl of
resuspended cells. The cells were preincubated with the mAb for 10 min
before tetramer staining.
Surface plasmon resonance binding studies
Binding measurements were conducted on a Biacore X instrument
(Biacore International, Uppsala, Sweden) at 25°C at 5 µl/min.
Capture of soluble CD8 and CD8 molecules on the flow cell
has been described (14). The sensograms represent
subtracted data (experimental flow cell-control cell). Steady state
binding (Req) was determined by
averaging the plateau response phase of the binding curve. To determine
Kd,
Req data were plotted against
T18d concentration.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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2m in the
absence of peptide.
The question of whether TL can bind peptide Ags has not been
resolved (8, 18). We addressed this issue by generating
recombinant soluble T18d H chain molecules in
E. coli and refolding this protein with
2m in the presence or absence of a fully
random nonameric peptide library containing all natural amino acids
except Cys. This approach was successfully used to investigate the
peptide binding motif of another class Ib molecule, Qa-1
(24), in addition to class Ia molecules (33, 34). In Fig. 1, we show
chromatographs of the components present in the refolding reactions
resolved by S-300 gel filtration. Misfolded protein aggregates
remaining in the sample after concentration are eluted in the first
peak; the second peak, indicated by an arrow, represents the properly
folded class I molecules, eluting as a 40–45 kDa complex. Excess free
2m elutes in the third peak. Peptides are
eliminated from the samples during concentration of the folding mix
through a 10-kDa exclusion membrane. The data are representative of
several refolding experiments. Similar amounts of folded
T18d protein complexes were obtained, as measured
by UV absorbance at 280 nm, whether proteins were folded in the
presence or absence of the peptide library (Fig. 1A). By
contrast, peptide was required for in vitro folding of HLA-A2 (Fig. 1B). The yield of folded T18d
generated in the absence of peptide was similar to that obtained with
HLA-A2 folded in the presence of the peptide library. The yield was
8–10% of total protein added to the folding reaction. We routinely
obtained 5–7 mg of refolded protein per liter of solution.
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). The proteins were
resolved into two bands: one band migrating at 30 kDa represents the
truncated, unglycosylated form of H chain and a second band migrating
at 10 kDa corresponds to 2m. There was no
difference in the stoichiometry between these complexes. Samples were
analyzed in immunoassays using mAb to 2m to
capture refolded class I molecules and mAb HD168, which recognized
native T18d, for detection. Similar signals were
observed with T18d that had been folded in the
presence or absence of peptide, whereas only background was observed
with control HLA-A2 and unfolded T18d controls
(Fig. 2). These results demonstrated that the
T18d H chain assembles with
2m and that the refolded protein adopts a
native conformation as defined by reactivity with the HD168 mAb. We
concluded that T18d folds efficiently in vitro in
the absence of peptide or other potential ligands and that nonameric
peptides do not further promote the folding reaction.
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Far-UV CD spectroscopy has been used to analyze the
structure and thermal stability of a variety of classical and
nonclassical MHC molecules (17, 35, 36, 37, 38, 39, 40). The far-UV
spectra of T18d are shown in Fig. 3
. The spectra are nearly identical for
T18d folded in the presence or absence of peptide
and they are very similar to spectra previously reported for other MHC
class I molecules. These results confirm that
T18d folded in the absence of peptide assumes a
class I-like conformation with similar secondary structure. Thermal
denaturation experiments were performed to analyze the stability of
empty T18d and determine whether protein folded
in the presence of peptide acquires increased stability. When spectra
were measured at 79°C, there was a loss of CD signal corresponding to
a change of conformation due to heat denaturation (Fig. 3). After
heating to 79°C, the samples were cooled rapidly and allowed to
renature slowly over a 1-h incubation at room temperature. The
subsequent spectra taken at 25°C are similar to those obtained with
unheated samples, demonstrating that thermal denaturation is largely
reversible under the conditions used. Thermal denaturation profiles
demonstrated a Tm of 54°C, reflecting
dissociation and unfolding of the H chain (35). The
Tm is identical for
T18d folded in the presence or absence of the
nonameric peptide library. A second transition with
Tm >60°C characterized by a sign
reversal of the CD signal probably represents unfolding of free
2m (35, 40). The 54°C
Tm of empty T18d
is similar to that reported for H-2Kd peptide
complexes (54–57°C) (35, 38) and greater than that
reported for the class Ib protein T10 (49°C) (40), which
does not bind peptides. Thus empty T18d molecules
are relatively stable and folding the protein in the presence of
peptide does not increase its stability.
Analysis of peptides eluted from HLA-A2 and T18d
Although T18d folded in the presence or
absence of peptide exhibit identical thermal stability, we further
analyzed the protein to confirm the absence of bound peptides. Low m.w.
material acid eluted from HLA-A2 and T18d, folded
in the presence of peptide library, was analyzed by MALDI-TOF mass
spectrometry. A m/z profile consistent with a highly complex mixture of
nonameric peptides was obtained with acid-eluted material from HLA-A2
(Fig. 4). This material was subjected to
several cycles of Edman degradation, revealing a significant enrichment
in Met and Leu at position 2, consistent with the HLA-A2
peptide-binding motif. By contrast, very few species were identified in
the acid eluate of T18d that could be derived
from the input peptide library (Fig. 4). This material was fractionated
by capillary reverse-phase HPLC and one peak was successfully sequenced
(GSLHHILD). However, this peptide does not appear to bind
T18d (data not shown). These results support the
conclusion that peptides from the nonamer library do not bind to
T18d during folding in vitro.
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Recent experiments demonstrate that tetramers generated from
soluble T18d molecules expressed in insect cells
bind a large fraction of IEL through a TCR-independent interaction with
CD8 homodimers expressed on IEL (14). Although it
seems likely that the insect cell-derived protein does not contain
bound peptides (18), the presence in this material of
peptides loaded through a TAP-independent mechanism or other Ags such
as glycolipids cannot be excluded. To definitively address this issue,
we generated tetramers with T18d molecules from
bacterial inclusion bodies refolded in the absence of peptides or other
potential ligands. The bacteria-derived tetramers were observed to
stain a large fraction of both TCR+ and
TCR+ IEL isolated from B6 mice (Fig. 5, A and B), but
not lymph node T cells (Fig. 5E), which express exclusively
CD8 rather than CD8. Indeed, almost all IEL that express
CD8 bind the tetramer. T18d tetramer staining
of IEL was completely inhibited with an appropriate blocking
CD8-specific mAb (Fig. 5, C and D). The mAb
used for costaining CD8 (53-6.7) does not block tetramer
staining.
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, direct binding
studies were performed by surface plasmon resonance. Bacteria-derived
T18d monomer binding to CD8 immobilized on
a biosensor chip showed fast association and dissociation rates, with
an equilibrium Kd of 11 µM (Fig. 6). This value is very similar to the
value (Kd = 12 µM) previously
obtained with insect cell-derived TL monomers (14). Thus,
we conclude that neither peptides nor other ligands associated with the
peptide-binding groove of T18d are required for
binding to CD8 molecules.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Thermal melting experiments demonstrate a Tm of 54°C for TL generated in folding reactions in the absence of peptides, identical to the value obtained with TL generated in the presence of a peptide library. Analysis of low m.w. material acid-eluted from TL demonstrated only a few candidate peptides. One of these was sequenced and we could not confirm that a synthetic version of this peptide binds TL. By contrast, a diverse mixture of peptides was present in acid eluates of control HLA-A2 molecules generated with the same random nonamer peptide library. Thus, we conclude that empty TL molecules are generated even in folding reactions that contain a source of peptides. We cannot rule out the possibility that TL can bind shorter or longer peptides, or peptides with specific modifications not represented in the synthetic peptide library. The latter is true for the class Ib molecule, H-2 M3, which selectively binds N-formylated peptides (41, 42). Despite this formal possibility, it is clear that empty TL molecules are quite stable.
The Tm value of 54°C is similar to
the values (54 and 57°C) reported for H-2Kd
bound to specific peptide ligands (35, 38). Most class Ia
molecules, like HLA-A2 in the present study, fail to assemble in the
absence of appropriate peptides, indicating that peptide is an integral
component of the properly folded molecules. H-2Kd
is unusual in that it can be generated as an empty molecule. However,
the Tm of empty
H-2Kd (45°C) (35) is considerably
lower than the value for peptide-free TL. Thermal denaturation studies
have been performed with one additional nonclassical class I molecule,
T10 (40). T10 and the closely related T22 (94% identity)
are recognized by a subpopulation of T cells in mice without a
requirement for bound peptide or other components (40, 43). The crystal structure of T22 demonstrates a severely
modified MHC-like fold, lacking a classical peptide-binding groove
(44). The thermal stability of T10
(Tm = 49°C) is significantly lower
than that of TL. These comparisons support the hypothesis that TL
functions not as an Ag-presenting molecule, but rather as an invariant
ligand that regulates lymphocyte function.
Recent work has demonstrated that TL binds selectively to CD8
homodimers expressed on IEL, promoting cytokine production induced by
TCR signaling (14). This function is independent of direct
TCR recognition of TL. Given its selective localization on intestinal
epithelial cells, one can conclude that TL acts in a site-specific
manner to regulate mucosal immune responses. Data presented in this
study formally demonstrate that TL molecules, lacking bound peptide,
glycosylation, other posttranslational modifications specific to
eukaryotic cells, or other associated proteins, bind CD8 with the
same affinity as TL molecules generated in insect cells. Previous
studies with transgenic mice expressing TL (T3b)
driven by an H-2Kb promoter demonstrated that TL
can act as a transplantation Ag and that both and CTL can
recognize TL (7, 8, 9, 10, 11, 12, 13). It is unlikely that these previous
results can be explained by expansion of a population of
CD8+ T cells that are stimulated by TL
through a TCR-independent mechanism. It was reported that Abs to either
TCR or TL block the killing of TL-expressing target cells by
CD8+ CTL (10). In addition,
TL-specific CD4-CD8-
CTL can be generated in CD8 T cell-depleted mice transplanted with skin
from TL transgenic donors (10). Thus, it appears that
under certain experimental conditions, T cells with true specificity
for TL can be generated and that TL recognition does not require
expression of CD8.
The potential requirement for TL-bound peptides, lipids, or other
antigenic moieties in TCR-mediated recognition of TL remains to be
established. It has been demonstrated that TL-specific CTL clones kill
TAP-deficient RMAS and insect cells (12). In
addition, TL tetramers generated using a baculovirus expression system
were used to enrich TL-specific CTL from polyclonal populations
generated in mixed leukocyte cultures (13). These findings
are most consistent with the idea that T cells recognize empty TL
molecules. Alternatively, some ubiquitous unconventional ligand could
be involved. It is possible that there is a population of "natural"
T cells with specificity for TL, in analogy to NK-T cells selected by
interaction with CD1d expressed on thymocytes. Joyce et al.
(20) reported a numerical increase in
TCR+NK1.1+ in thymi
of mice expressing TL in the thymus. However, specificity for TL was
not demonstrated. It is clear that the vast majority of NK T cells
recognize CD1d (45, 46). Nevertheless, the possibility
that a dedicated population of T cells exists with specificity for TL
needs further investigation.
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Acknowledgments |
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Peter E. Jensen, Department of Pathology and Laboratory Medicine, School of Medicine, Emory University, Woodruff Memorial Building, Room 7-309, 1639 Pierce Drive, Atlanta, GA 30322. E-mail address: pjensen{at}emory.edu
3 Abbreviations used in this paper: TL, thymic leukemia; 2m, 2-microglobulin; IEL, intestinal epithelial lymphocyte; CD, circular dichroism; MALDI-TOF, matrix-assisted laser desorption ionization time-of-flight.
Received for publication August 1, 2002. Accepted for publication September 11, 2002.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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CTL by TL antigen expressed in the thymus. J. Exp. Med. 184:2175. and the nonclassical MHC class I molecule, TL. Science 294:1936. interact differently with 2-microglobulin of the class I molecules H-2Kb and thymic leukemia antigen, while similarly with their 3 domains. J. Immunol. 168:3881.2-microglobulin-associated thymus-leukemia antigen is independent of TAP2. Eur. J. Immunol. 25:1001.[Medline]
T cell receptors in transporters associated with antigen presentation-1 null and thymus leukemia antigen positive mice. J. Exp. Med. 184:1579.2-microglobulin but is TAP independent. J. Immunol. 160:3217./ T cells by the class Ib gene product, Qa-1b. J. Exp. Med. 188:961.+ T cells are positively selected in the thymus by agonist self-peptides. Immunity 16:355.[Medline]
T cell, G8. J. Exp. Med. 185:1223. T cells that recognize an inducible MHC class Ib molecule. Science 287:314. T cell receptor ligand T22: a truncated MHC-like fold. Science 287:310.This article has been cited by other articles:
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  X. Tang, I. Maricic, N. Purohit, B. Bakamjian, L. M. Reed-Loisel, T. Beeston, P. Jensen, and V. Kumar Regulation of Immunity by a Novel Population of Qa-1-Restricted CD8{alpha}{alpha}+TCR{alpha}beta+ T Cells J. Immunol., December 1, 2006; 177(11): 7645 - 7655. [Abstract] [Full Text] [PDF]
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N. Pardigon, K. Takeda, B. Saunier, F. Hornung, J. Gibbs, A. Weisberg, N. Contractor, B. Kelsall, J. R. Bennink, and J. W. Yewdell CD8{alpha}{alpha}-Mediated Intraepithelial Lymphocyte Snatching of Thymic Leukemia MHC Class Ib Molecules In Vitro and In Vivo J. Immunol., August 1, 2006; 177(3): 1590 - 1598. [Abstract] [Full Text] [PDF]
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M. A. Williams and M. J. Bevan Cutting Edge: A Single MHC Class Ia Is Sufficient for CD8 Memory T Cell Differentiation J. Immunol., August 15, 2005; 175(4): 2066 - 2069. [Abstract] [Full Text] [PDF]
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A. Attinger, L. Devine, Y. Wang-Zhu, D. Martin, J.-h. Wang, E. L. Reinherz, M. Kronenberg, H. Cheroutre, and P. Kavathas Molecular Basis for the High Affinity Interaction between the Thymic Leukemia Antigen and the CD8{alpha}{alpha} Molecule J. Immunol., March 15, 2005; 174(6): 3501 - 3507. [Abstract] [Full Text] [PDF]
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 N. Pardigon, S. Darche, B. Kelsall, J. R. Bennink, and J. W. Yewdell The TL MHC class Ib molecule has only marginal effects on the activation, survival and trafficking of mouse small intestinal intraepithelial lymphocytes Int. Immunol., September 1, 2004; 16(9): 1305 - 1313. [Abstract] [Full Text] [PDF]
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K. Tsujimura, Y. Obata, E. Kondo, K. Nishida, Y. Matsudaira, Y. Akatsuka, K. Kuzushima, and T. Takahashi Thymus leukemia antigen (TL)-specific cytotoxic T lymphocytes recognize the {alpha}1/{alpha}2 domain of TL free from antigenic peptides Int. Immunol., November 1, 2003; 15(11): 1319 - 1326. [Abstract] [Full Text] [PDF]
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