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,§,¶,
,¶
*
Howard Hughes Medical Institute,
Department of Immunology, National Jewish Medical and Research Center, and Departments of
Biochemistry and Molecular Genetics,
§
Pharmacology, and
¶
Medicine, University of Colorado Medical School, Denver, CO 80207
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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-chain that blocks signaling by
either IL-2 or IL-15. However, inhibition of IL-2 increases the numbers
of dividing clonal cells. Therefore, like normal memory
CD8+ T cells, expansion of the clones is driven by IL-15
and inhibited by IL-2 and is probably limited by the amounts of IL-15
and IL-2 present in the host. Control by these two cytokines may
account for the fact that, although the clones can be very large, they
do not overwhelm or kill their hosts. Nevertheless the clonal cells
compete successfully with normal memory CD8+ T cells for
growth. Perhaps the clonal cells use IL-15 more effectively or are more
resistant to the inhibitory effects of IL-2. Thus they might affect the
immune response of their hosts by competing for factors that stimulate
and inhibit normal CD8+ memory T
cells. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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TCR V repertoire of the
CD8+ T cells of their host (6, 11, 12).
The causes and consequences of these clones are not understood. In man
it has been suggested that clones bearing particular types of TCR
may be associated with certain autoimmune diseases
(13, 14, 15). Precursors of the clones may first have been
stimulated in either mice or man by infections. The fact that viral
infection induces very large expansions of polyclonal virus-specific T
cells, which normally rapidly disappear (16, 17, 18, 19, 20, 21, 22), has been
taken as suggestive evidence that the very large clones may be derived
from responses to persistent viral infections.
The large CD8+ clones are not apparently transformed. Aging human beings and mice rarely acquire CD8+ lymphomas and leukemias, and human beings and mice containing these clones live apparently normal life spans with only infrequent evidence of lymphoid malignancy (3). Nevertheless, the large CD8+ clones do outgrow their fellow CD8+ T cells, not only in their original host, but also after transfer into normal young recipients (3). These experiments indicate that although the clones are not overtly malignant, some event in the founder of these cells has converted them to a state that allows them to outgrow other cells.
Recently we and others have shown that nonclonal CD8+ T cells of memory phenotype divide slowly in normal animals (23, 24, 25). This division is driven by IL-15, made endogenously in normal animals, and is inhibited by IL-2 (25, 26). Such results suggest that the CD8+ T cell clones outgrow such memory cells either because they respond to the same factors differently or because their division is driven by a different mechanism.
The experiments described in this paper were designed to compare the properties of the large clones of CD8+ T cells with those of the nonclonal CD8+ memory phenotype cells in an attempt to find out what distinguishes the two types of cells. The results show that the two kinds of CD8+ T cells are very similar. Members of the large clones and nonclonal memory CD8+ T cells express similar molecules on their surfaces. Like memory phenotype CD8+ T cells, members of the large clones divide slowly in mice by a process that is probably Ag independent, driven by IL-15, and inhibited by IL-2. Division by the clonal cells differs only from that of the nonclonal CD8+ T cells by the fact that their proliferating progeny accumulate more rapidly. Thus the clonal cells may give rise to the large clones because they are more sensitive to the stimulatory effects of IL-15 or less sensitive to the inhibitory effects of IL-2 than their nonclonal counterparts. Because the clonal CD8+ T cells and nonclonal CD8+ memory T cells compete for the same survival and death factors, the clones may affect the immune function of their hosts by affecting the numbers of memory CD8+ T cells.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Six- to 8-wk-old C57BL/6J and B6D2F1 mice were purchased from The Jackson Laboratory (Bar Harbor, ME). Fifteen-month-old C57BL/6 and B6D2F1 mice were purchased from the National Institute on Aging colony maintained at Charles River Laboratories (Wilmington, MA). In previous experiments mice of various strains including C57BL/6J were obtained from The Jackson Laboratory and aged at National Jewish Medical and Research Center (Denver, CO) (1, 10, 11). We observed no difference in the properties of aged C57BL/6 mice obtained from The Jackson Laboratory or Charles River Laboratories.
All of the animals were kept in a specific pathogen-free animal
facility at the National Jewish Medical and Research Center. Mice over
the age of 15 mo were screened for CD8+ clones by
anti-V and anti-CD8 staining of their peripheral blood
(1, 11, 12). Mice of the same strain aged younger than 4
mo were used as the comparison group. Six- to 8-wk-old C57BL/6
2-microglobulin-deficient
(2MKO)4
mice were purchased from Taconic Farms (Germantown, NY).
T cell purification
Spleen cells were treated briefly with ammonium chloride solution to lyse RBC and then washed in balanced salt solution (BSS) once. T cells were purified from lymph node (LN) and spleen cells as previously described (27, 28). Briefly, the cells were resuspended in 1–1.5 ml of BSS plus 5% FCS and loaded onto sterile nylon wool columns, which had been washed and soaked in BSS plus 5% FCS for at least 30 min at 37°C before loading the cells. The cells were incubated on columns for 30–40 min at 37°C and eluted in an appropriate volume of BSS plus 5% FCS.
In experiments in which the total numbers of T cells in mice were counted, counts included cells in the spleen and the axillary, brachial, inguinal, mesenteric, periaortic, and superficial cervical LNs.
Abs and cell staining
Some anti-mouse Vs, anti-CD4 (GK1.5), anti-CD8
(53-6.7), and anti-C (H597) mAbs were prepared and conjugated
with fluorescein or biotin (bio) in our laboratory. All other PE-,
CyChrome-, and allophycocyanin-labeled mAbs were purchased from
PharMingen (San Diego, CA). These included a panel of PE-labeled
anti-mouse surface proteins, which were as follows: anti-CD28,
37.51; anti-CD44, IM7; anti-CD45RB, 16A; anti-CD62 ligand,
MEL-14; anti-CD69, H1.2F3; anti-IL-2R (anti-CD25), 3C7;
anti-IL-2R (anti-CD122), TM-1; anti-IL-2R
(anti-CD132), TUGm2; anti-Fas (anti-CD95), Jo2; and
biotinylated anti-IL-7R (anti-CD127), B12–1. Anti-mouse
Bcl-2 and streptavidin-CyChrome (SAv-CyC) were also obtained from
PharMingen. Cells were stained and analyzed as previously described
(27, 28, 29).
CFSE (Molecular Probes, Eugene, OR) was dissolved in DMSO and diluted in sterile BSS. Nylon wool-purified T cells from old mice were isolated and prepared as described above. The cells were labeled with 1 µM CFSE at 1 x 107 cell/ml for 15 min at 37°C and then washed twice in BSS (30). CFSE-labeled cells (0.5–1 x 107) were i.v. injected into nonirradiated, syngeneic young mice. The CFSE signal from these cells was detected on the FL-1 channel of FACScan flow cytometer (Becton Dickinson, San Jose, CA).
To analyze incorporation of 5-bromo-2'-deoxyuridine (BrdU) by
CD8+ T cells, cells were stained and sorted for
CD8+ expression. They were then stained with
bio-Ab to the V expressed on the clone and SAv-CyC, treated with
acid and stained with fluorescein anti-BrdU (Becton Dickinson) as
previously described (31).
Anti cytokine and anti-cytokine receptor Abs given to animals were
as follows: 3C7, anti-IL-2R (32); A7R34,
anti-IL-7R (33); TM-1, anti-IL-2R
(34); S4B6, anti-IL-2 (35); and M25,
anti-IL-7 (36). All the Abs used were rat in origin.
Abs were purified from culture supernatants by passage over protein G
columns. F(ab')2 preparations of the
anti-receptor Abs were prepared by pepsin digestion at pH 4.0 and
judged to be <1% contaminated with intact Ig by SDS PAGE. Mice were
given 1 mg of each Ab or F(ab')2 preparation
daily i.p.
T cell transfer from old mice to lethally irradiated young mice
Normal or 2MKO young mice were treated
with 0.04 ml rabbit anti-mouse thymocyte serum (The Jackson
Laboratory) to deplete them of mature T cells (37). Two
days later, bone marrow cells were harvested from these animals. Young
C57BL/6 or 2MKO mice were lethally irradiated
with 950 rad and immediately reconstituted with 1 x
107 syngeneic bone marrow cells. Four days later,
spleen and LN T cells were isolated from individual old mice with
CD8+ expansions bearing known Vs. Equal
numbers of these T cells from old mice were transferred i.v into the
lethally irradiated C57BL/6 and 2MKO
recipients such that each recipient was given 0.5–1 x
107 T cells. The animals were bled at intervals
thereafter to monitor survival or growth of the transferred cells.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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We and others have shown previously that healthy older mice or
humans contain very large clones of CD8+ T cells
(1, 2, 3, 4, 5, 6, 7, 11, 12). These clones have been identified in many
ways: by cDNA sequencing of the junctional regions of their TCR -
and -chains, by complimentarity-determining region-3 length analysis
and by the presence of an unexpectedly high percentage of
CD8+ T cells bearing a particular V and/or
V. For convenience, in this paper, clones of
CD8+ T cells will be defined by the presence in a
mouse of a percentage of CD8+ T cells bearing a
particular V that is more than two SDs above the percentage of
CD8+ T cells bearing that V in young animals.
Because the spectrum of percentages of CD8+ T
cells bearing particular Vs is very predictable in young animals
this identification of CD8+ clones by V
analysis has proven to be extremely reliable. In every case, TCR
sequencing or V analysis has shown that CD8+
expansions defined by V staining are indeed clones.
However, it must be borne in mind that some percentage of the
cells, defined as clones by V staining, will not be members of the
clones. For example, in one mouse we studied, about 25% of the
CD8+ T cells bore V9. In young mice of the
same strain, the percent of CD8+ T cells bearing
V9 was only about 5%. Therefore, we could estimate that about
5/25 x 100 (20%) of the CD8+
V9+ T cells in the old mouse were not members
of the clone, but rather the normal CD8+
V9+ T cells of the animal. Thus there will
always be a small contamination by normal cells of the cells identified
as part of the clone. This is unavoidable, because molecular methods of
identifying clonal cells destroy the cells and live cells were needed
for the experiments of this paper. However, in some cases we have
confirmed that the behavior observed was due to members of the clone,
because the TCR - and -chain junctional sequences of the
population studied were shown to be the same before and after the
experiment.
Members of the large CD8+ clones have the surface characteristics of memory T cells
T cells from nine old mice containing CD8+
clones and from young mice were stained with various Abs to surface
molecules. Results from a representative experiment are shown in Fig. 1
. The phenotypes of
CD8+ T cells from the old mice were similar,
whether or not they were members of a CD8+ clone.
Their surface markers were, on the whole, characteristic of memory or
activated cells because they were CD44high,
CD45RBmedium-low and they bore high levels of
IL-2R (but see below; Refs. 25, 38 , and
39). Unlike the large CD8+ clones
found in humans (40, 41) the mouse
CD8+ clones were, like the other
CD8+ cells in young and old mice,
CD28+. We previously reported that such cells
were CD28-. However, using an improved
anti-CD28 Ab, we found that all of the cells in the nine clones we
have recently analyzed were CD28+ (Fig. 1). The
staining with anti-CD28 was not nonspecific, because the Ab did not
stain T cells from CD28 KO mice (data not shown).
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Most CD8+ memory and memory phenotype cells
divide, albeit slowly, in mice (23, 24, 25). We used two
methods to find out whether this is also true for members of the
clones. First, several old mice that contained large
CD8+ clones were given BrdU continuously in their
drinking water. Twenty-one days later, the animals were sacrificed and
the percentage of clonal CD8+ T cells that had
incorporated BrdU was measured. As shown in Table I, both clonal and nonclonal cells
divided during this time. However, the percentage incorporating BrdU
was higher for the CD8+ clonal than for the
CD8+ nonclonal cells.
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This result was somewhat different from that observed when BrdU was
used to measure the division of the clones directly in their original
(old) hosts, which showed that only about 50% of the clonal cells
divided within 21 days (Table I
). This difference suggested that the
conditions in young mice may be more conducive to the division of
memory CD8+ cells. Such an interpretation was
supported by experiments in which CSFE labeled
CD8+ T cells from old mice were transferred to
either normal young and old mice. In this case, both the clonal and
nonclonal CD8+ T cells divided rather more
frequently in young than old mice (Table II). Perhaps this difference between old
and young recipients is due to the fact that older mice contain more
dividing CD8+ T cells than young animals do
(25) and these may compete for stimulatory factors with
the transferred cells.
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Clonal CD8+ cells divide more quickly and accumulate faster than nonclonal cells
The CFSE profiles and cell recoveries between days 6 and 36 after
transfer in the experiments illustrated in Fig. 2 allowed an estimate
of the rate of cell division and numbers of recovered
CD8+ clonal and nonclonal cells in the young
recipients. In an average of four experiments, the recovered clonal
CD8+ cells had divided approximately every 15
days, whereas the recovered nonclonal CD8+ T
cells had divided approximately every 22 days.
To find out whether the clonal or nonclonal cells had actually
increased in number over the course of these experiments, we counted
the total numbers of clonal or nonclonal CFSE labeled
CD8+ T cells recovered from mice 6 and 36 days
after transfer. The results of such experiments are shown in Fig. 3. For three of four
CD8+ clones, there was a dramatic increase in
cell number between days 6 and 36. This was not true for the nonclonal
cells, which were found in approximately equal numbers per mouse 6 and
36 days after transfer.
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Survival and division of clonal CD8+ T cells is not class I MHC dependent
The long-term maintenance of normal CD8+ memory T cells is well documented. In the normal immune response, following a sometimes extremely large Ag-driven expansion, most progeny CD8+ T cells disappear leading to a steady state in which a residual population of memory T cells is maintained, often for the life of the animal (16, 17, 18, 19, 20, 21, 22, 43, 44). Several experiments have shown that, unlike naive or actively responding CD8+ T cells, this persistent memory population is not dependent on Ag or even MHC class I for its survival (24, 45, 46, 47). However, as discussed above, these memory T cells do maintain their number by an equilibrium between slow cell division and cell death. Recently, we have shown that their division and survival is dependent on IL-15 and inhibited by IL-2 (25, 26).
Our experiments led us to hypothesize that the clonal CD8+ T cells were in fact derived from memory T cells through some alteration that allowed them to successfully compete with normal memory T cells during this maintenance phase. If this were the case, we predicted that the survival and expansion of the clonal cells should also be independent of MHC class I, dependent on IL-15, and inhibited by IL-2. Alternatively, were these cells to be maintained by some chronically presented Ag, they should be dependent on MHC class I and perhaps IL-2 as well.
We performed several experiments to test these ideas. First, we
transferred T cells from old mice into 2MKO
animals. APCs in these recipients express class I MHC very poorly and
hence are unlikely to present Ag to CD8+ T cells.
Unfortunately, CD8+ T cells from normal animals
were rejected very rapidly from normal 2MKO
mice (data not shown) because of recognition of class I MHC protein on
their surfaces by host T cells (48, 49). Hence, as an
alternate approach, the experiments were performed in
2MKO animals that had been T cell depleted,
lethally irradiated, and reconstituted with T cell-depleted
2MKO bone marrow 4 days before transfer of the
T cells to be tested. Control C57BL/6 recipients were treated
similarly. Because transfer into irradiated mice causes the immediate,
short term proliferation of donor T cells (50, 51), the
fate of the transferred cells was not evaluated until months later,
after the effects of irradiation had waned.
An example of such an experiment is shown in Fig. 4. T cells were purified from an old
C57BL/6 mouse that contained a CD8+ clone bearing
V6. These cells were transferred into the reconstituted normal and
2MKO C57BL/6 mice and growth of the clone was
evaluated by sampling peripheral blood at intervals thereafter. After a
short recovery period in the uninjected reconstituted C57BL/6 mice,
normal host CD8+V6+ T
cells rose to a steady level of about 4% of PBL (Fig. 4A,
). In the uninjected reconstituted 2MKO
mice, of course, there were virtually no
CD8+V6+ T cells (Fig. 4B, ).
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6+ clonal cells
grew in both of these types of recipients. Because in both types of
recipients, the clone took a long time to reach a percentage that was
detectable by anti-V staining, there was no evidence that its
proliferation was unduly affected by the irradiation. In the C57BL/6
recipients, the clonal cells reached a level in PBL up to 3-fold higher
than that of the host V6+
CD8+ cells in the uninjected host (Fig. 4A, compare • and ). The clonal cells increased in
percentage in the PBL of the 2MKO recipients
as well (Fig. 4B, •). After subtraction of the 4%
background due to host V6+
CD8+ T cells in the wild-type recipients,
comparison of the rates of appearance of the
V6+ CD8+ clonal cells
revealed that they accumulated a little more slowly in
2MKO hosts than they did in normal mice.
Perhaps this reflects some survival advantage conferred on the T cells
by expression of class I in the wild-type recipients.
To measure the actual number of the clonal cells rather than just their
percentages in PBL, recipient mice were sacrificed about 200 days after
transfer and their LN and spleen cells were pooled. Three types of
cells were analyzed. From the 2MKO mice both
CD8+V6+ and
CD8+V6- donor T cells
were analyzed, because the presence of class I on the donor cells
allowed us to distinguish them accurately from the host cells. In the
case of the C57BL/6 recipients, only the greatly expanded
CD8+V6+ cells were
analyzed, because we could not accurately distinguish the donor
CD8+V6- cells from the
cells already present in the host. The results of transfer of four
different clones in four independent experiments (I-IV) are given in
Fig. 5.
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A) with sometimes greater than 10-fold
more cells recovered than injected. Given that only 5–10% of the
cells survive the initial injection, this is a very dramatic expansion.
Three of the four CD8+ clones also expanded
similarly in the 2MKO recipients (Fig. 5B). In the case of the other clone (III), although fewer
cells were recovered than injected, again this probably represents a
net expansion, given the low initial survival of the injected cells.
The nonclonal CD8+ T cell also survived in the
2MKO recipients (Fig. 5C), but
their expansion was on average less dramatic than seen with the clonal
cells. Overall these results indicate that the clones, like nonclonal
memory CD8+ T cells, do not need host-presented
class I MHC (or, by inference, Ag) to survive and divide. Division of clonal CD8+ T cells is IL-15 dependent and inhibited by IL-2
In mice, the continuous division of CD8+ T
cells of memory phenotype is driven by IL-15 and inhibited by IL-2
(25, 26). To find out whether this is also true for the
members of the CD8+ clones, T cells were isolated
from three old mice, each with an identifiable
CD8+ clone. The cells were labeled with CFSE and
cells from each donor were transferred into four unmanipulated young
syngeneic recipients. Two days later, the four recipients of each clone
were divided into four different groups. One group received daily
injections of anti-IL-2 plus F(ab)'2
anti-IL-2R Abs. The second group received
F(ab)'2 anti-IL-2R Ab. The third group
received anti-IL-7 plus F(ab)'2
anti-IL-7R Abs. The fourth, control, group received equivalent
amounts of normal rat IgG. The anti-receptor Abs were converted to
F(ab)'2 to avoid artifacts due to binding of
intact Ab to the T cells and subsequent death by complement activation
or ADCC. The object of this experiment was to block transmission of
signals delivered by IL-2 in group-1 mice, by IL-2 and IL-15 in group-2
mice (anti-IL-R blocks the action of IL-2 and IL-15 equally
well; data not shown, and Ref. 52) and by IL-7 in group-3
mice. Unfortunately a good anti-IL-15R Ab was not available.
Seven days after transfer, the recipients were sacrificed. Saturation
of the cytokine receptors by the F(ab')2
preparations given to the animals was confirmed by the fact that the
cells isolated from the animals stained poorly or not at all with Abs
against the appropriate receptors (data not shown). Division of the
transferred cells in the animals was assessed from their CFSE profiles
after harvesting. The results for cells transferred from one of the old
donors are shown in Fig. 6.
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and stimulated by anti-IL-2 plus
anti-IL-2R (25). Similar results were observed for
the members of the CD8+ clone. During this
relatively short experiment, about one third of the surviving
transferred clonal cells had divided in the recipient given normal rat
Ig. This result was unaffected by anti-IL-7 plus anti-IL-7R
F(ab)'2. The presence of anti-IL-2R
(Fab')2 inhibited division of the clone. This was
due to blockage of signals delivered by IL-15 rather than IL-2, because
specific inhibition of IL-2 with anti-IL-2 plus anti-IL-2R
(Fab')2 actually stimulated division by the
clone. As summarized in Table III,
similar results were obtained with cells from two other old mice. In
all cases, blockage of IL-2 increased the rate of appearance of
dividing clonal cells and anti-IL-2R
(Fab')2 inhibited division of the clones.
Inhibition was not complete. This may either have been due to
incomplete blockage of the IL-15R by the anti-IL-2R or to
stimulation of growth of the clones by factors in addition to IL-15.
However, overall, these results showed that division of the clonal
cells, like that of the nonclonal memory CD8+ T
cells, is stimulated, at least in part, by IL-15 and inhibited by
IL-2.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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and CD28,
which are increased by comparison with naive cells. Previous
experiments and the data reported here indicate that
CD8+ memory T cells divide in the absence of Ag.
It appears that the clonal CD8+ T cells can do
this too, because they expand in 2MKO mice,
animals that should not be able to present Ag to these cells. As for
their nonclonal counterparts, division of the clonal cells is inhibited
by anti-IL-2R and stimulated by anti-IL-2 plus
anti-IL-2R. Anti-IL-2R inhibits the action of IL-2 and IL-15
equally well (data not shown). However, the inhibitory effects of anti
IL-2R must be due to inhibition of IL-15 action, because inhibition
of IL-2 action increased the appearance of dividing clonal cells. Thus,
like their nonclonal counterparts, division of the
CD8+ clones is stimulated by IL-15. This
conclusion is supported by the fact that both types of cells contain
high levels of Bcl-2, a protein that is induced in T cells by IL-2
family members (53, 54, 55). For both the clonal and nonclonal
CD8+ cells, IL-2 inhibits the appearance of the
dividing cells. Experiments in vitro suggest that the IL-2 is not
directly inhibitory for either type of cell (data not shown).
Preliminary results suggest that IL-2 may operate in vivo via the IL-2
dependent CD25+ regulatory cells that have been
described by others(data not shown, and Refs. 56, 57, 58, 59). The Ab inhibition experiments described here indicate the presence of both IL-15 and IL-2 in our old and young pathogen-free mice. IL-15 is made constitutively in animals (60), but IL-2 is thought to be produced only by activated T cells, so its source in these animals is not clear. Because the clonal cells are thought to be relatively nonproductive, the clonal cells probably do not make the IL-2 themselves. A recent paper showed that IL-2 is bound to extracellular matrix, even in animals that are not overtly confronted with Ag (61), so that IL-2 made at earlier times may be stored and active at this site.
What is it that allows some CD8+ T cells to grow into the very large clones at the expense of the other CD8+ T cells in older animals? The data presented in this paper show that after transfer into normal recipients, the clones increase in numbers whereas the nonclonal cells do not, even though some of these latter cells are in fact dividing. Thus either the clonal T cells divide more rapidly or are less likely to die than the normal memory phenotype T cells. Our data do not allow us to distinguish these two possibilities. In our CFSE-labeling experiments, the clonal cells do appear on average to have been through more rounds of division at any time point than the nonclonal T cells. However, we cannot tell whether this is due to an intrinsically faster division rate or to the higher probability of survival of proliferating clonal vs nonclonal T cells.
What molecular changes might account for these differences between
clonal and nonclonal CD8+ T cells? One
possibility is that the clonal T cells are more sensitive to IL-15. In
preliminary experiments in vitro, where we do not see the inhibitory
effects of IL-2, the clonal cells outgrew their nonclonal counterparts
in cultures containing IL-15 (data not shown). It seems unlikely that
this is due to differences in surface expression of IL-2R because
the clonal cells have only slightly more of this protein (186 ±
16 in arbitrary fluorescence units) than the nonclonal cells (179
± 9). However, perhaps this small difference or differences in other
components of the receptor or its downstream signaling molecules
account for the behavior of the two types of cells.
The successful competition of the clonal CD8+ T cells for apparently the same niche as that occupied by normal memory CD8+ T cells raises the possibility that they may inhibit the normal maintenance of memory T cells. We have no direct evidence for this possibility at the moment, although the observation that the clonal and nonclonal cells grow more slowly in old than in young recipients suggests, very indirectly, that some sort of competition for growth factors may occur in vivo. Alternatively, the susceptibility of the clonal cells to the inhibitory effects of IL-2 raises another intriguing possibility. These cells may act as a decoy for this inhibitory mechanism and in fact protect normal memory CD8+ T cells.
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Acknowledgments |
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Footnotes |
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2 Current address: Stanford University School of Medicine, Department of Pediatrics, Division of Infectious Diseases, 300 Pasteur Drive, Grant Building S366, Stanford, CA 94305-5208.
3 Address correspondence and reprint requests to Dr. Philippa Marrack, Department of Immunology, National Jewish Medical and Research Center, 1400 Jackson Street, Denver, CO 80207.
4 Abbreviations used in this paper: 2MKO, 2-microglobulin-deficient; BSS, balanced salt solution; LN, lymph node; bio, biotin; SAv-CyC, streptavidin-CyChrome; BrdU, 5-bromo-2'-deoxyuridine.
Received for publication August 21, 2000. Accepted for publication November 15, 2000.
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  A. Lang, J. D. Brien, I. Messaoudi, and J. Nikolich-Zugich Age-Related Dysregulation of CD8+ T Cell Memory Specific for a Persistent Virus Is Independent of Viral Replication J. Immunol., April 1, 2008; 180(7): 4848 - 4857. [Abstract] [Full Text] [PDF]
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S. Mostbock, M. E. C. Lutsiak, D. E. Milenic, K. Baidoo, J. Schlom, and H. Sabzevari IL-2/Anti-IL-2 Antibody Complex Enhances Vaccine-Mediated Antigen-Specific CD8+ T Cell Responses and Increases the Ratio of Effector/Memory CD8+ T Cells to Regulatory T Cells J. Immunol., April 1, 2008; 180(7): 5118 - 5129. [Abstract] [Full Text] [PDF]
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I. Messaoudi, J. Warner, and J. Nikolich-Zugich Age-Related CD8+ T Cell Clonal Expansions Express Elevated Levels of CD122 and CD127 and Display Defects in Perceiving Homeostatic Signals. J. Immunol., September 1, 2006; 177(5): 2784 - 2792. [Abstract] [Full Text] [PDF]
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200 days after transfer of cells
from old mice. Cells were harvested from the spleens and LNs of each
animal, counted, and stained as described in Fig. 4
) and present in each animal 
). Numbers above the bars indicate the percent of
transferred cells recovered on the day of sacrifice, that is the
numerical difference represented by comparison of the open and filled
bars. For 