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Cutting Edge |



*
Cancer Biology Program, Hematology/Oncology,
Infectious Diseases Division, and
Gastroenterology Division, Department of Medicine, Beth Israel-Deaconess Medical Center, Harvard Medical School, Boston, MA 02215
| Abstract |
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-chain expressing CD1d-reactive NKT cells, which
can cause model hepatitis. Invariant NKT
(CD56+/-CD161+) and recently identified
noninvariant CD1d-reactive T cells rapidly produce large amounts of
IL-4 and/or IFN-
and can regulate Th1/Th2 responses. Human liver
contains large numbers of CD56+ NKT cells but few invariant
NKT. Compared with matched peripheral blood T cell lines, primary IHL
lines from patients with chronic hepatitis C had high levels of CD161
and CD1d reactivity, but the invariant TCR was rare. CD1d-reactive IHL
were strikingly Th1 biased. IHL also demonstrated CD1d-specific
cytotoxic activity. Hepatocytes and other liver cells express CD1d.
These results identify a novel population of human T cells that could
contribute to destructive as well as protective immune responses in the
liver. CD1d-reactive T cells may have distinct roles in different
tissues. | Introduction |
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or 
TCR,
NK cell markers such as CD56, CD69, CD94, and CD161, and even killer
inhibitory receptor (1, 2). While a fraction of these
cells in the human react against the MHC-related nonpolymorphic
proteins CD1ac, molecules missing in the mouse (1, 2), a
subset of NKT recognize glycolipids associated with CD1d
(1, 2, 3, 4, 5). The classical CD1d-reactive T cell population
expresses a highly restricted TCR repertoire (invariant
-chain
rearrangement and limited V
chain usage: invariant NKT
(1, 2, 3); in the human these are V
24J
Q and
predominantly V
11 (4). Most CD1d-reactive invariant NKT
express CD161 and represent the majority of murine but not human NKT
(1, 2, 3, 4). Murine CD161+ and CD161- populations also include CD1d-reactive T cells using diverse TCR (6, 7, 8, 9, 10). In the mouse, invariant NKT preferentially accumulate in the liver and thymus, whereas noninvariant CD1d-reactive NKT are common in the spleen and bone marrow (9, 10). In contrast, a larger fraction of human peripheral blood T cells are NKT, but only a minor subset of these NKT are CD1d-reactive and express the invariant TCR and not killer inhibitory receptor (4). Although less is known of the diversity and functions of human NKT in general, noninvariant CD161+ CD1d-reactive T cells have recently been identified in the human bone marrow, where they are strongly Th2 biased (11).
Invariant NKT represent up to 50% of rodent intrahepatic lymphocytes
(IHL3; Refs. 8, 9 , and 12, 13, 14), consistent with expression of CD1d
within rodent and human liver (15, 16, 17). Invariant NKT
cause the liver damage in certain models of hepatitis
(18), both directly through perforin and/or Fas
ligand-mediated CD1d-specific cytotoxic activity (19, 20, 21)
and by activation of NK and other immune cells via Th1 cytokines such
as IFN-
as well as Th2-like IL-4, etc. (1, 4, 21). As a
consequence of their potential to kill infected cells and/or produce
cytokines, NKT may also play a protective role in clearance of
pathogens such as Salmonella and hepatitis B virus
(22, 23) and contribute to defense against tumors
(19, 24). CD1d-reactive T cells are essential for optimal
response to an acute viral infection (25).
NKT are substantially enriched in human liver relative to peripheral
blood (26, 27, 28, 29). There is also preferential expression of
V
24 used by invariant as well as other T cells (26, 28). However, invariant NKT are rare in human liver
(30), unlike the corresponding cells in murine liver
(8, 9, 12, 13, 14). Thus CD1d-reactive T cells in human
peripheral blood (4, 31, 32) and bone marrow
(11) and in rodents (8, 9, 12, 13, 14) display
diverse phenotypes. Using functional assays, we report high levels of
human hepatic Th1-biased CD1d reactivity in the absence of invariant
NKT enrichment. Human T cells from the liver of patients with chronic
hepatitis C virus (HCV) infection thus contained a large uniquely
Th1-like population of noninvariant CD1d-reactive T cells with
potentially protective and pathologic roles in hepatitis.
| Materials and Methods |
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Invariant NKT cells and transfectants were used as described
(4, 32). Released cytokines and chemokines from T cells
assayed with transfectants and PMA were determined by ELISA. SDs are
shown in
Figs. 25![]()
![]()
![]()
. Anti-CD3 12F6 and bifunctional CD3/8 were kindly
provided by Dr. J. Wong (Massachusetts General Hospital, Boston, MA).
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HCV seropositive donors with detectable HCV RNA but moderate
elevations in liver enzymes and inflammation provided noncirrhotic
liver biopsies under written informed consent during routine clinical
evaluation. None were HIV seropositive or had been treated with IFN or
ribavirin. IHL T cell lines were obtained by a single expansion as
described (33). Five-millimeter sections were cultured
with 100 U/ml IL-2 (Hoffman-LaRoche, Nutley, NJ), followed by
CD3 or CD3/8 Abs and irradiated (30 Gy) allogeneic feeders at
2
days. Matched PBL lines were obtained at time of biopsy by identical
stimulation. Studies were approved by the institutional committee on
clinical investigations.
| Results |
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Murine liver lymphoid cells contain high levels of CD1d-reactive
invariant NKT (8, 9, 12). Fig. 1
shows representative results of
phenotypic analysis of human IHL T cell samples expanded from
HCV-infected donors in comparison to matched PBL T cell lines derived
at the same time. Whereas short-term PBL T cell lines contained
5%
NKT (CD3+CD161+), matched
IHL lines contained 18 to >30% NKT (Fig. 1
). Elevated numbers of NKT
IHL did not correlate with expression of V
24 TCR used by invariant
NKT (4). A small V
24+ population
was routinely detectable from PBL (12%), but IHL were not
significantly enriched for invariant NKT-like cells (
1%; Fig. 1
).
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CD1d is the natural ligand of human invariant NKT
(4), CD161 is costimulatory for these NKT
(20), and NKT also include CD1ac-reactive T cells
(2). Therefore, it was determined whether high levels of
NKT in IHL translated into elevated functional responses to CD1
molecules. Fig. 2
, A and
B, shows that whole IHL preparations, but not PBL from the
same donor collected on the same day, responded with readily measurable
CD1d-specific proliferation. CD1d-specific proliferative responses of
both IHL (Fig. 2
A) and control invariant NKT cells
(4) were specifically blocked by anti-CD1d mAb,
whereas other CD1 molecules failed to elicit more than minimal
proliferative responses (data not shown).
Similar to the results with proliferation, these same IHL also
responded specifically to human CD1d transfectants with substantial
IFN-
secretion (Fig. 2
C). Cytokine responses of IHL to
CD1d were blocked by anti-CD1d mAb (Fig. 2
C). Notably,
the CD1d-specific IFN-
responses of whole IHL preparations (Fig. 3
, B and C) were
also comparable to those of invariant NKT clones (Fig. 3
A).
All 12 independent IHL preparations raised with 12F6 or CD3/8 mAb from
nine donors responded specifically to CD1d transfectants at levels
>10% above their response to mitogen and frequently comparably
to mitogen and invariant NKT clones (Fig. 3
, AC). In contrast, there were only minimal IHL
responses to CD1a, -b, or -c, as with control invariant NKT (Fig. 3
, AC). Unlike in the bone marrow
(11), CD1d-reactive IHL and invariant NKT responded to
both B cell-derived and epithelial CD1d transfectants (Figs. 2
, A and C, and 3, B and
C).
In contrast to the results with IFN-
, little IL-4 was produced by
IHL in response to CD1d (Fig. 3
D). However, these same IHL
did produce significant levels of IL-4 in response to mitogen,
indicating the presence of Th2-like conventional T cells. Somewhat
higher levels of IL-4 were readily detectable in control supernatants
from matched PBL treated with mitogen, indicating that they contained
generally more conventional Th2 activity. Finally, as previously
described (4), invariant NKT analyzed alongside made
comparably high levels of IL-4 and IFN-
in response to CD1d and
mitogen (Fig. 3
D).
Invariant NKT produce large amounts of other cytokines and chemokines
as well as IL-4 and IFN-
(4). These can include GM-CSF,
RANTES, IL-8, Th1-like IL-2, macrophage-inflammatory
protein-1
, TNF-
, Th2-like IL-5, IL-13, and regulatory
(Th3) TGF-
and IL-10. In addition to the prototypical cytokines
shown above (high IFN-
, no detectable IL-4), CD1d-reactive IHL
produced a markedly, though not pure, Th1-like spectrum (Fig. 4
). In particular, CD1d-reactive IHL
could secrete substantial amounts of macrophage-inflammatory
protein-1
(one of four lines tested) and detectable TNF-
(two of
four lines tested), as well as IL-13 (one of four lines tested), but
only trace RANTES (one of four lines tested; 52 pg/ml) and no
detectable IL-8, TGF-
, or IL-10 (< 10 pg/ml; Fig. 4
).
CD1d-specific cytotoxic activity of CD161+ IHL T cells
Activated human invariant NKT have potent perforin-mediated
CD1d-specific cytotoxic activity (20). Fig. 5
shows that after subtraction of
reactivity against mock transfectants, whole IHL retained significant
CD1d-specific cytotoxic activity. Higher backgrounds of IHL presumably
reflect activated alloreactive CTL and/or lymphokine-activated
killer-like cells in these preparations. Therefore, as for
proliferative and Th1-like cytokine responses, IHL contained measurable
CD1d-reactive cytotoxic activity. Combined with high levels of NKT and
trace amounts of invariant-like T cells, these results indicate that
human liver lymphocyte lines contained high levels of noninvariant
Th1-like CD1d-reactive T cells.
| Discussion |
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24+ cells are reported to make up to
1%
of IHL, irrespective of HCV infection (26, 28). Recent
reports using staining with
-galactosylceramide-loaded soluble CD1d
show that most NKT are invariant in rodent liver (13, 14),
but very few within human liver are invariant NKT (0.030.34%),
comparable to the low numbers in human blood (30),
therefore providing a lowest possible estimate for the number of
CD1d-reactive NKT. Approximately 50% of human bone marrow CD161+ T cells are noninvariant CD1d-reactive NKT (11). This report demonstrates a comparably high level of CD1d-reactive T cells in IHL lines from HCV+ donors. Levels of functionally CD1d-reactive T cells in healthy human liver and in other diseases remain to be determined. Although most human blood NKT are not CD1d reactive, high levels of CD1d-reactive IHL suggest that, as in bone marrow, these were NKT. A substantial fraction of human IHL (26) and murine hepatic NKT are apoptotic, although the latter have high regenerative potential (14, 34). This study used single round expansion after brief incubation to rest active cells. Cell lines analyzed could not be apoptotic. However, this would indicate that we underestimated CD1d reactivity by use of cell lines. CD1d-reactive T cells have potentially distinct immunoregulatory functions in different anatomical locations.
The major CD1d-reactive population within IHL had a pronounced Th1 bias, whereas conventional T cells in the same IHL made IL-4, albeit less than matched blood T cells, consistent with previous phenotypic reports of IHL NKT and conventional T cells (28, 33, 34, 35, 36). This contrasts with healthy human bone marrow, where noninvariant CD161+ CD1d-reactive T cells are Th2 biased (11). Phenotypic and functional compartmentalization of conventional T cells also occurs in chronic HCV infection, where intrahepatic HCV-specific T cells are more numerous, recognize distinct epitopes, produce different cytokines, and use distinct TCR (33, 34, 35, 36, 37). Irrespective of whether our findings result from normal physiology or are a result of pathology, we demonstrate both phenotypic and functional compartmentalization of human CD1d-reactive T cells.
IFN-
from CD1d-reactive IHL and CD8+
HCV-specific CTL fails to prevent HCV replication
(33, 34, 35, 36, 37). Instead, these cells may cause tissue damage.
Invariant NKT mediate Con A- and Salmonella-induced
hepatitis (18, 22). Activation of invariant NKT results in
their apoptosis and concomitant liver damage (34).
In addition to potential cytotoxicity against hepatic cell surface CD1d
induced by infection or inflammation, up-regulation of Fas ligand on
activated CD1d-reactive NKT may induce apoptosis of
Fas-expressing hepatocytes (18). NKT also could directly
and perhaps indirectly increase TNF-
levels.
In summary, we have found that human liver, like bone marrow, but unlike blood, contains large numbers of CD1d-reactive noninvariant NKT. However, IHL CD1d-reactive T cells were Th1 polarized, representing a novel lineage from the previously defined invariant and bone marrow NKT. Such cells have the potential for distinct functions uniquely expressed within the liver microenvironment.
| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. Mark A. Exley, Cancer Biology Program, Hematology/Oncology, Beth Israel-Deaconess Medical Center, Harvard Medical School, HIM 1047, 330 Brookline Avenue, Boston, MA 02215. E-mail address: mexley{at}bidmc.harvard.edu ![]()
3 Abbreviations used in this paper: IHL, intrahepatic lymphocyte; HCV, hepatitis C virus. ![]()
Received for publication November 12, 2001. Accepted for publication December 14, 2001.
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14 NKT in IL-12-mediated rejection of tumors. Science 278:1623.
24J
Q T cell receptor. J. Exp. Med. 188:867.
14+NK1+ T cells for liver injury induced by Salmonella infection in mice. Hepatology 29:1799.[Medline]
-glycosylceramides enhance the antitumor cytotoxicity of hepatic lymphocytes obtained from cancer patients by activating CD3-CD56+ NK cells in vitro. J. Immunol. 165:1659.
24+ T cells and rapid elimination of effector cells by apoptosis. Eur. J. Immunol. 28:3448.[Medline]
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