Antigen Presentation by Nonhemopoietic
Cells Amplifies Clonal Expansion of Effector
CD8 T Cells in a Pathogen-Specific Manner
This information is current as
of June 17, 2017.
Sunil Thomas, Ganesh A. Kolumam and Kaja
Murali-Krishna
J Immunol 2007; 178:5802-5811; ;
doi: 10.4049/jimmunol.178.9.5802
http://www.jimmunol.org/content/178/9/5802
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References
The Journal of Immunology
Antigen Presentation by Nonhemopoietic Cells Amplifies
Clonal Expansion of Effector CD8 T Cells in a
Pathogen-Specific Manner1
Sunil Thomas, Ganesh A. Kolumam, and Kaja Murali-Krishna2
T
he CD8 T cells play an important role in clearing intracellular viral and bacterial infections. Naive CD8 T
cells that are specific to the pathogen, once primed,
undergo clonal expansion, acquire effector functions, alter circulatory properties, and go on to recognize a wide variety of
infected targets in both lymphoid and nonlymphoid organs (1,
2). Clonal expansion is important not only for efficient clearance of the pathogen, but also for the generation of a higher
number of memory cells that are qualitatively superior compared with their naive counterparts (3, 4). An understanding of
the factors that contribute to clonal expansion in response to
live infection is critical for rational vaccination and therapeutic
strategies.
Intracellularly replicating pathogens can infect a wide variety
of cells. However, not every infected cell is capable of priming
CD8 T cell responses. Optimal priming of naive CD8 T cells
requires presentation of pathogen-derived peptides by specialized professional APCs. The well-characterized professional
Department of Immunology and Washington National Primate Center, University of
Washington, Seattle, WA 98195
Received for publication December 5, 2006. Accepted for publication February
9, 2007.
The costs of publication of this article were defrayed in part by the payment of page
charges. This article must therefore be hereby marked advertisement in accordance
with 18 U.S.C. Section 1734 solely to indicate this fact.
1
This work was supported in part by National Institutes of Health Grants
1R01AI053146 and R21AI051386 (to K.M.-K.) and by funds from the Washington
National Primate Center and the University of Washington Department of
Immunology.
2
Address correspondence and reprint requests to Dr. Kaja Murali-Krishna, Department of Immunology and Washington National Primate Center, Box 357650
HSB, 1959 Northeast Pacific Street, Seattle, WA 98195. E-mail address:
[email protected]
www.jimmunol.org
APCs, such as dendritic cells and macrophages, are of hemopoietic origin (1, 5–10). These cells have the ability to process
and present pathogen-derived peptides, to express costimulatory and inflammatory molecules, and to carry pathogen-derived peptides to the lymphoid tissues through which the naive
T cell precursors generally circulate, thereby acting as initiators
of adaptive immune responses during infection.
Infected cells of nonhemopoietic origin, despite displaying
pathogen-derived peptides, are thought to be inefficient in initiating T cell responses due to their inability to express costimulatory
molecules and traffic to lymphoid organs (11).
The primed effector T cells, in contrast to their naive counterparts, are generally less stringent in costimulatory requirements (11–14). This, combined with their ability to circulate
through both lymphoid and nonlymphoid organs (2, 15), raises
the question of whether effector CD8 T cell interaction with
infected targets of nonhemopoietic origin further influences
clonal expansion in vivo.
In this study, we addressed this question in vivo using four
different pathogens, all of which are known to infect cells of both
hemopoietic and nonhemopoietic origin. We found that when we
ablated one of the MHC restriction elements specifically in the
nonhemopoietic compartment, the expansion of virus-specific
CD8 T cells restricted to that particular MHC was diminished by
⬃90% during lymphocytic choriomeningitis virus (LCMV)3
infection.
Abbreviations used in this paper: LCMV, lymphocytic choriomeningitis virus; ␤2m,
␤2-microglobulin; Lm, Listeria monocytogenes; VSV, vesicular stomatitis virus; VV,
vaccinia virus.
3
Copyright © 2007 by The American Association of Immunologists, Inc. 0022-1767/07/$2.00
Downloaded from http://www.jimmunol.org/ by guest on June 17, 2017
Professional APCs of hemopoietic-origin prime pathogen-specific naive CD8 T cells. The primed CD8 T cells can encounter Ag on
infected nonhemopoietic cell types. Whether these nonhemopoietic interactions perpetuate effector T cell expansion remains
unknown. We addressed this question in vivo, using four viral and bacterial pathogens, by comparing expansion of effector CD8
T cells in bone marrow chimeric mice expressing restricting MHC on all cell types vs mice that specifically lack restricting MHC
on nonhemopoietic cell types or radiation-sensitive hemopoietic cell types. Absence of Ag presentation by nonhemopoietic cell
types allowed priming of naive CD8 T cells in all four infection models tested, but diminished their sustained expansion by
⬃10-fold during lymphocytic choriomeningitis virus and by <2-fold during vaccinia virus, vesicular stomatitis virus, or
Listeria monocytogenes infections. Absence of Ag presentation by a majority (>99%) of hemopoietic cells surprisingly also
allowed initial priming of naive CD8 T cells in all the four infection models, albeit with delayed kinetics, but the sustained
expansion of these primed CD8 T cells was markedly evident only during lymphocytic choriomeningitis virus, but not during
vaccinia virus, vesicular stomatitis virus, or L. monocytogenes. Thus, infected nonhemopoietic cells can amplify effector CD8
T cell expansion during infection, but the extent to which they can amplify is determined by the pathogen. Further understanding of mechanisms by which pathogens differentially affect the ability of nonhemopoietic cell types to contribute to T
cell expansion, how these processes alter during acute vs chronic phase of infections, and how these processes influence the
quality and quantity of memory cells will have implications for rational vaccine design. The Journal of Immunology, 2007,
178: 5802–5811.
The Journal of Immunology
Additional experiments confirmed that cognate interaction of
the effector CD8 T cells with nonhemopoietic targets greatly amplified clonal expansion, thereby contributing to the generation of
massive numbers of effector CD8 T cells following LCMV infection. By contrast, the ability to sustain the expansion of the primed
CD8 T cells was mostly limited to hemopoietic cells during vaccinia virus (VV), vesicular stomatitis virus (VSV), or Listeria
monocytogenes (Lm) infections.
Materials and Methods
Mice
C57BL/6 (B6) H-2Db⫺/⫺, H-2Kb⫺/⫺, Db⫺/⫺Kb⫺/⫺ ␤2-microglobulin
(␤2m)⫺/⫺ mice (16, 17), B6 Ly5.1 P14 TCR transgenic mice whose CD8
T cells recognize gp33– 41 epitope of LCMV in a Db-restricted fashion
(18), and B6 Thy1.1 OT-1 TCR transgenic mice whose CD8 T cells recognize OVA epitope in a Kb-restricted fashion (19) have been described.
Mice were maintained under specific pathogen-free conditions at the University of Washington under the guidelines of the Institutional Animal Care
and Use Committee.
B63 B6, B63 Db⫺/⫺, and B63 Kb⫺/⫺ chimeric mice were generated by
transferring i.v. 7 ⫻ 106 T and B cell-depleted bone marrow cells from B6
mice into lethally irradiated (950 rad) recipient B6, Db⫺/⫺, or Kb⫺/⫺ mice,
respectively. Db⫺/⫺3 B6, Kb⫺/⫺3 B6, or Db⫺/⫺Kb⫺/⫺␤2m⫺/⫺3 B6 chimeric mice were generated by transferring T and B cell-depleted bone
marrow cells from Db⫺/⫺, Kb⫺/⫺, or Db⫺/⫺Kb⫺/⫺␤2m⫺/⫺ mice, respectively, into lethally irradiated recipient B6 mice. Bone marrow chimeric
mice were used at 4 mo after bone marrow reconstitution.
T and B cell depletion
Bone marrow cells were isolated from tibia and femurs of adult mice by
flushing with RPMI 1640 medium with 1% FCS, subjected to RBC lysis,
followed by T and B cell depletion by incubating with a mixture of antiThy-1 and B220 Abs for 30 min, and followed by washing and incubating
with low toxicity guinea pig complement (Cedarlane Laboratories).
Abs, staining, and tetramers
All Abs were purchased from either BD Biosciences or eBioscience, except
the anti-human granzyme B Ab (clone GB12), which was purchased
from Caltag Laboratories. MHC tetramer Dbgp33– 41 was produced, as
described (20, 21). Intracellular staining was performed after stimulating 2 ⫻ 106 spleen cells with 0.1 ␮g/ml peptide in 96-well flat-bottom
plates for 5 h in the presence of brefeldin A, followed by surface and
intracellular staining. Intracellular staining was performed by using the
intracellular staining kit (BD Biosciences), as per the manufacturer’s
instructions (20). Intracellular staining for granzyme B was performed
exactly as described above, except that these cells were not in vitro
stimulated with peptide.
CFSE labeling and cell transfers
Cells were labeled with CFSE by incubating with 5 ␮M CFSE for 5 min,
followed by quenching with fetal calf serum and washing. Total splenocytes containing the appropriate numbers of transgenic CD8 T cells, as
indicated in the legends, were transferred i.v.
Lymphocyte preparation
Splenocyte preparation was done in RPMI 1640 medium containing 1%
FCS. RBC were lysed using 0.84% ammonium chloride, washed, and suspended in RPMI 1640 containing 10% FCS before in vitro stimulation.
Liver cell suspension was prepared in RPMI 1640 medium containing 1%
FCS and centrifuged in 35% Percoll gradient for 30 min at 4°C at 600 ⫻
g. The pellet was subjected to RBC lysis. The cells were washed twice
before FACS staining.
Virus, bacteria, and immunizations
LCMV (Armstrong) and VSV (Indiana) were plaque purified and grown in
baby hamster kidney cells, VV were plaque purified and grown in HeLa
cells. rVV expressing OVA or the LCMV glycoprotein (gp33– 41) (22),
and rVSV (23) and Lm (24) expressing OVA were previously described.
Unless otherwise stated, 2 ⫻ 105 PFU LCMV, 1 ⫻ 106 PFU VV, or 1 ⫻
106 PFU VSV were injected i.p., and 2 ⫻ 104 CFU Lm were injected i.v.
Soluble chicken OVA (0.5 mg/mouse) was administered i.p.
Results
Generation and characterization of bone marrow chimeras
Several studies have assessed the role of hemopoietic cells in initiating CD8 T cell responses, either by removing the restricting
MHC on radiation-sensitive bone marrow-derived cells or by targeted depletion of CD11c-positive cells (5–10, 25–27). These
studies unanimously show that hemopoietic cells, especially
CD11c-positive cells, are needed for optimal generation of detectable CD8 T cell responses both during immunization with model
Ags as well as during infection with various pathogens, including
VV, VSV, LCMV, Lm, and influenza A virus, although there was
some confusion with reference to LCMV (see discussion in later
sections). But none have addressed the consequence of primed
CD8 T cell interaction with infected nonhemopoietic targets. To
address this, we created radiation chimeras in which the restricting
MHC is expressed on all cell types or selectively removed on
nonhemopoietic cell types. This system allows us to deduce the
effect of Ag presentation by nonhemopoietic cells on the already
primed effector CD8 T cells. The following three types of bone
marrow chimeras were generated: 1) control B63 B6 chimeras
in which MHC class I molecules Db and Kb are expressed both
on hemopoietic and nonhemopoietic cells; 2) B63 Db⫺/⫺ chimeras in which MHC Kb is expressed on all cell types, but Db
expression is selectively absent in nonhemopoietic cell types;
and 3) B63 Kb⫺/⫺ chimeras in which MHC Db is expressed on
all cell types, but Kb expression is selectively absent in nonhemopoietic cell types. Chimerism was evaluated by staining
spleen cells for MHC expression 4 mo after reconstitution.
More than 98% of the CD11c⫹ spleen cells from the B63 B6,
B63 Db⫺/⫺, as well as B63 Kb⫺/⫺ mice were positive for expression of both Db and Kb, confirming that the chimeras were
properly reconstituted (Fig. 1A).
Lack of Ag presentation by nonhemopoietic cell types drastically
reduces LCMV-specific polyclonal CD8 T cell response in an
allele-specific manner
To assess Db- and Kb-restricted polyclonal CD8 T cell responses in
the chimeras, B63 B6, B63 Db⫺/⫺, and B63 Kb⫺/⫺ mice were
infected with LCMV, and the Db- or Kb-restricted CD8 T cell
responses were analyzed at day 8 postinfection. The unmanipulated B6, Db⫺/⫺, or Kb⫺/⫺ mice infected with LCMV were used as
controls.
On day 8 postinfection, spleen cells were stimulated with either
Db-restricted LCMV peptide nucleoprotein 396 – 404, or Kb-restricted LCMV peptide nucleoprotein 205–212, and then stained
for intracellular IFN-␥ and TNF-␣. B63 Db⫺/⫺ mice, similar to
the Db⫺/⫺ mice, elicited a much more robust Kb-restricted CD8 T
cell response than the control B63 B6 mice (Fig. 1B, fourth panel
in bottom row), whereas the Db-restricted response was markedly
reduced (Fig. 1B, fourth panel in middle row). This pattern was
reversed in B63 Kb⫺/⫺ mice. In these mice, the Db-restricted CD8
T cell response was increased compared with the control B63 B6
mice (Fig. 1B, sixth panel in middle row), whereas Kb-restricted
CD8 T cell response was markedly reduced (Fig. 1B, sixth panel in
bottom row).
A compensatory increase in Db-restricted response in mice
lacking Kb, and vice versa, has been reported (16), and our
results are consistent with these studies. The diminished Dbrestricted CD8 T cell response in the B63 Db⫺/⫺ mice and
the diminished Kb-restricted CD8 T cell response in the
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Generation of bone marrow chimeras
5803
5804
NONHEMOPOIETIC CELL CONTRIBUTION TO CD8 T CELL EXPANSION
B63 Kb⫺/⫺ mice suggest a role for nonhemopoietic cell types
in determining the magnitude of CD8 T cell response to LCMV.
However, previous studies showed that virus-specific CD8 T
cells can be generated only against infected targets sharing the
same MHC determinant as the thymic stroma, implicating that
the presence of the MHC restriction element on thymic stroma
is required for efficient thymic positive selection (28). Because
the thymic stroma of the B63 Db⫺/⫺ mice in our experiments
do not express Db, the Db-restricted naive CD8 T cell repertoire
may not have developed efficiently in these mice. Similarly, the
Kb-restricted naive repertoire may not have developed in the
B63 Kb⫺/⫺ mice.
ocula tested (Fig. 2C). Thus, the vast majority of the robust
CD8 T cell expansion that occurs in response to LCMV infection is mediated by perpetuation of clonal expansion by infected
nonhemopoietic cells.
Lack of Ag presentation by nonhemopoietic cell types drastically
reduces clonal expansion of adoptively transferred naive TCR
transgenic T cells
To overcome the limitations posed by the impact of positive selection on repertoire development, and to stringently test the effect
of viral Ag presentation by nonhemopoietic cells, we adoptively
transferred congenically marked (Ly5.1⫹) Db-restricted LCMVspecific TCR transgenic naive CD8 T cells (P14 CD8 T cells) into
B63 B6 or B63 Db⫺/⫺ mice and compared their expansion following LCMV infection.
The Db-restricted donor P14 CD8 T cells, as expected, expanded massively in the spleens of the LCMV-infected B63 B6
chimeras (Fig. 2A, left panel). However, the expansion of the
P14 cells was drastically diminished (⬃10-fold) in LCMV-infected B63 Db⫺/⫺ mice compared with the B63 B6 mice,
either at day 5 (Fig. 2A, right panel) or at day 8 postinfection
(Fig. 2B). The diminished expansion of the Db-restricted donor
CD8 T cells in B63 Db⫺/⫺ chimeras is due to a specific absence of Db on nonhemopoietic cells because P14 cell expansion was not affected in LCMV-infected B63 Kb⫺/⫺ chimeras
(Fig. 2B, 〫). The expansion of the donor P14 CD8 T cells in
B63 Db⫺/⫺ chimeras was diminished at all doses of viral in-
FIGURE 2. Ag presentation by nonhemopoietic cells contributes to
clonal expansion of CD8 T cells in response to LCMV infection. Ten
thousand congenically marked (Ly5.1) CD8 T cells were transferred i.v.
into B63 B6 or B63 Db⫺/⫺ chimeric mice. Mice were infected with
2 ⫻ 105 PFU LCMV 24 h later. A, Donor P14 CD8 T cell frequency on
day 5 post-LCMV infection in spleen. Data are gated on CD8 T cells.
B, Expansion of the donor P14 CD8 T cells in the spleens of B63 B6,
B63 Kb⫺/⫺, and B63 Db⫺/⫺ chimeras at days 5 and 8 post-LCMV
infection (n ⫽ 3/group). Similar results were obtained in three other
experiments. Error bars indicate SD from the mean. C, Donor P14 CD8
T cell frequencies in peripheral blood of the B63 B6 or B63 Db⫺/⫺
chimeras infected with indicated doses of LCMV for 6 days.
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FIGURE 1. Bone marrow chimera
characterization. A, Splenocytes from
the indicated mice were stained with
anti-Db (left panels) and anti-Kb
(right panels) Abs. Data are gated on
CD11C⫹ cells. Similar results were
obtained when data were gated on total lymphocytes. B, Spleen cells isolated from the indicated groups of
mice day 8 post-LCMV infection
were left unstimulated or stimulated
in vitro for 5 h with the Db-restricted
or Kb-restricted LCMV peptides in
the presence of brefeldin A, and then
stained for surface CD8, followed by
intracellular staining for IFN-␥ and
TNF-␣. Data are gated on CD8 T
cells.
The Journal of Immunology
5805
LCMV-specific donor CD8 T cells receiving Ag presentation by
hemopoietic cell types only or by a mixture of hemopoietic and
nonhemopoietic cell types were similar in phenotype and
cytokine function
Because the Db-restricted donor CD8 T cells are likely to receive
qualitatively different signals in infected B63 B6 vs B63 Db⫺/⫺
chimeras, we asked whether these cells differ in phenotype or function. The P14 CD8 T cells responding to LCMV infection were
CD43high, CD44high, and CD62Llow in both groups (Fig. 3A). The
donor P14 effector CD8 T cells were capable of producing IFN-␥
(Fig. 3B) and TNF-␣ (data not shown) upon in vitro peptide stimulation, irrespective of whether they were primed in LCMV-infected B63 B6 or B63 Db⫺/⫺ mice. Donor P14 effector CD8 T
cells from both groups expressed the cytotoxic molecule granzyme
B (Fig. 3C).
Together, the above results allow us to deduce that nearly 90% of
the robust expansion of the effector CD8 T cells seen in response to
LCMV is mediated by Ag presentation by virally infected cell types
of the nonhemopoietic compartment. Limiting the Ag presentation to
only hemopoietic cell types decreased clonal expansion by ⬃10-fold,
but has little effect on the effector cytokine functions.
Cognate interactions with infected nonhemopoietic cells do not
efficiently perpetuate clonal expansion of effector CD8 T cells
during VV, VSV, or Lm infections
The level of CD8 T cell expansion is generally more robust in
response to LCMV than in response to many other pathogens,
including VV, VSV, and Lm in mice (29). To assess the ability of
nonhemopoietic cells to perpetuate the effector CD8 T cell expansion in the context of other infections, we performed experiments
using VV, VSV, or Lm. We transferred Kb-restricted OVA-specific OT-1 CD8 T cells into B63 B6 or B63 Kb⫺/⫺ chimeras. The
expansion of the donor OT-1 cells was analyzed after infecting the
mice either with rVV expressing OVA (rVV-OVA), with rVSV
expressing OVA (rVSV-OVA), or with rLm expressing OVA
(rLm-OVA). In the case of rVV-OVA, lack of the MHC restriction
FIGURE 4. Contribution of nonhemopoietic cells to the clonal expansion of CD8 T cells in mice infected with VV, VSV, or Lm. A–C, 25,000
congenically marked (Thy1.1) naive OT-1 CD8 T cells were transferred
into B63 B6 or B63 Kb⫺/⫺ chimeras. Mice were infected with rVV-OVA
(A), rVSV-OVA (B), or rLm-OVA (C). n ⫽ 3/group. Spleen cells were
analyzed on day 8 (rVV-OVA and rLm-OVA) or day 7 (rVSV-OVA)
postinfection. Similar results were obtained in two other experiments. Similar trends were seen when analysis was done at day 5 postinfection in a
separate experiment. D and E, 20,000 congenically marked (Ly5.1) naive P14
CD8 T cells were transferred into B63 B6 or B63 Db⫺/⫺ chimeras. Mice
were infected with either LCMV (D) or rVV-gp33 (E). Similar results were
obtained in a different experiment. Error bars indicate SD from the mean.
element on nonhemopoietic cells reduced donor CD8 T cell expansion only marginally (⬃2-fold) (Fig. 4A). Similar trends were
seen in the case of rVSV-OVA infection (Fig. 4B). In the case of
Lm, no reproducible effect was observed in several experiments
(Fig. 4C). Similar results as the one with rVV-OVA were obtained
when we repeated the experiment with a different VV expressing
the LCMV gp33 epitope (rVV-gp33). Whereas there was a substantial contribution of nonhemopoietic cells toward CD8 T cell
expansion in LCMV (Fig. 4D), their contribution was ⬍2-fold in
the case of rVV-gp33 (Fig. 4E). Together, the above results show
that nonhemopoietic cells greatly contribute to the sustained expansion of effector CD8 T cells in LCMV infection, but are less
efficient following VV, VSV, or Lm infections.
Ag presentation exclusively by radiation-resistant cells can
recruit naive CD8 T cells into proliferation early after infection
with LCMV, VV, VSV, or Lm, but the continued expansion of
these primed cells is sustained better during LCMV than during
VV, VSV, or Lm infections
The above experiments allow us to deduce that cognate interaction
of the primed effector CD8 T cells with infected nonhemopoietic
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FIGURE 3. The phenotype and functional characteristics of the Db-restricted P14 effector CD8 T cells were similar in LCMV-infected B63 B6
and B63 Db⫺/⫺ chimeras. A, Analysis of CD43, CD44, and CD62L expression on effector P14 CD8 T cells on day 8 post-LCMV infection (thick
lines). Thin lines indicate staining in naive CD8 T cells. B, IFN-␥ production upon in vitro peptide stimulation by effector P14 CD8 T cells. Data are
gated on donor CD8 T cells. Thin lines, no in vitro peptide stimulation.
Thick lines, in vitro peptide stimulation. C, Ex vivo granzyme B expression
by effector P14 CD8 T cells (thick lines). Thin lines, granzyme B expression in naive CD8 T cells.
5806
NONHEMOPOIETIC CELL CONTRIBUTION TO CD8 T CELL EXPANSION
FIGURE 5. Recruitment of CD8 T cells is similar during LCMV infection, regardless of whether only nonhemopoietic cells, only hemopoietic
cells, or a mixture of both cell populations participate in priming. A total
of 1 ⫻ 106 CFSE-labeled, congenically marked P14 CD8 T cells was
transferred into B63 B6 (thick black lines), B63 Db⫺/⫺ (thinner green
lines), or Db⫺/⫺3 B6 (thinnest red lines) chimeric mice. Mice were infected with LCMV 24 h later. Spleens were analyzed 35 h (middle panel)
or 60 h (bottom panel) postinfection. Top panel, Indicates staining on uninfected cells. Data are gated on donor P14 CD8 T cells. CFSE dilution,
CD25 up-regulation, and forward scatter are shown. Similar results were
obtained in a different experiment.
By 60 h post-LCMV, all the transferred cells had undergone at
least three rounds of cell division, up-regulated CD25, and increase in size in all the chimeras (Fig. 5, lower panel), and in vitro
stimulation with P14 peptide-pulsed Db⫹ feeder cells for 5 h
induced IFN-␥ production in P14 donor CD8 T cells, irrespective of whether they were primed in B63 B6, B63 Db⫺/⫺, or
Db⫺/⫺3 B6 chimeras (data not shown). These results make the
following three points: 1) absence of the restricting MHC on
nonhemopoietic cell types (as seen in B63 Db⫺/⫺ chimeras)
does not diminish initial recruitment of LCMV-specific naive
CD8 T cells (Fig. 5); 2) these recruited cells, however, expand
inefficiently at later stages (Fig. 2), because of the lack of nonhemopoietic cell-mediated perpetuation of clonal expansion in
B63 Db⫺/⫺ chimeras; 3) radiation-resistant cell types can also
cause initial activation and recruitment of LCMV-specific naive
CD8 T cells.
With reference to the initial activation or recruitment of naive
CD8 T cells into proliferation, our results with VV and VSV followed trends that were very similar to the ones seen in LCMV. For
these experiments, we transferred Db-restricted P14 CD8 T cells
into B63 B6, B63 Db⫺/⫺, or Db⫺/⫺3 B6 chimeras and infected
them with rVV-gp33. In a different set of experiments, we transferred Kb-restricted OT-1 CD8 T cells into B63 B6, B63 Kb⫺/⫺,
or Kb⫺/⫺3 B6 chimeras and infected them with rVV-OVA,
rVSV-OVA, or rLm-OVA. Data for rVV-gp33 is shown in Fig. 6.
Cell division, CD25 up-regulation, and increase in cell size at 35 h
postinfection were similar in B63 B6 and B63 Db⫺/⫺ chimeras,
and less efficient, but clearly evident in Db⫺/⫺3 B6 chimeras. By
60 h post-rVV-gp33, all the transferred cells had undergone at least
three rounds of cell division, up-regulated CD25, and increased in
size in all the chimeras (Fig. 6, lower panels). Similar results were
seen with rVSV-OVA (Fig. 7) and rVV-OVA (data not shown).
These results make the following three points: 1) Absence of the
restricting MHC on nonhemopoietic (radiation-resistant) cell types
as seen in B63 Db⫺/⫺ or B63 Kb⫺/⫺ chimeras does not diminish
initial recruitment of VV or VSV-specific naive CD8 T cells (Figs.
6 and 7). 2) The continued expansion of the primed cells in these
chimeras was similar to that seen in B63 B6 chimeras at later
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targets greatly perpetuates clonal expansion during LCMV, but
such interactions do not perpetuate clonal expansion during VV,
VSV, or Lm infections. Two previous studies, by using
parent3 F1 bone marrow chimeras, found that although expression
of restricting MHC only on radiation-resistant cell types does not
lead to induction of detectable CD8 T cell responses during three
infections (VV, influenza A, and Lm), it does lead to induction of
detectable CD8 T cell responses by day 8 LCMV infection (5, 7).
These observations lead to the interpretation that Ag presentation
by radiation-resistant cells does not prime naive CD8 T cells during VV, influenza, or Lm, but can somehow prime naive CD8 T
cells during LCMV infection. But a more recent study, using the
approach of targeted depletion specifically of Db⫹ CD11c-positive
cells in B6 ⫹ Db⫺/⫺3 Db⫺/⫺ chimeras showed that hemopoietic
cell types indeed are required for priming CD8 T cell response
even during LCMV (25). The discrepancy between this and the
earlier studies was explained by speculating that a small number of
radiation-resistant host hemopoietic cells that persist in the
parent3 F1 chimeras would have contributed to efficient recruitment of naive CD8 T cells during LCMV, but not during infection
with VV, Lm, or influenza viruses, although experimental evidence in support of this was lacking. It was postulated that the
intense innate activation associated with high antigenic load provided by LCMV might have conditioned these residual host-derived hemopoietic cells to optimally recruit naive CD8 T cells far
more effectively than during infections with the other pathogens.
If this were indeed the case, the residual radiation-resistant host
hemopoietic cells should recruit naive CD8 T cells into proliferation early after LCMV, but not after VV, VSV, or Lm infections.
Alternatively, if this discrepancy was due to the differences in the
ability of nonhemopoietic cells in perpetuating clonal expansion of
the primed CD8 T cells in LCMV vs the other three pathogens (as
suggested by our results above), the residual numbers of radiationresistant hemopoietic cells should recruit naive CD8 T cells into
proliferation early after infection with either LCMV, VV, VSV, or
Lm, but the continued expansion of these recruited cells should be
sustained during LCMV, but not during VV, VSV, or Lm infections. We directly tested this by generating B63 B6, B63 Db⫺/⫺,
B63 Kb⫺/⫺, and the reverse of the latter two, i.e., Db⫺/⫺3 B6 or
Kb⫺/⫺3 B6 chimeras, and assessing the pattern of naive CD8 T
cell activation and recruitment into proliferation soon after infection with various pathogens.
TCR transgenic naive CD8 T cells were transferred into bone
marrow chimeric mice expressing restricting MHC on all cell
types (B63 B6), on radiation-sensitive hemopoietic cell types
(B63 Db⫺/⫺ or B63 Kb⫺/⫺), or on radiation-resistant nonhemopoietic cell types plus a minor fraction of hemopoietic cells
(Db⫺/⫺3 B6 or Kb⫺/⫺3 B6). In these reverse (Db⫺/⫺3 B6 or
Kb⫺/⫺3 B6) chimeras, ⬍1% of the CD11c or CD11b-positive
spleen cells stained positive for Db or Kb expression, respectively, at
4 mo postreconstitution (data not shown), and this is consistent with
the residual numbers of radiation-resistant host hemopoietic cells seen
in radiation chimeras in other studies (5, 6, 7, 9).
Congenically marked CFSE-labeled Db-restricted P14 cells
were transferred into B63 B6, B63 Db⫺/⫺, or Db⫺/⫺3 B6 chimeras at 4 mo postbone marrow reconstitution. These chimeras
were then infected with LCMV. Mice were sacrificed either at 35
or 60 h postinfection. The transferred donor CD8 T cells were
assessed for cell size (based on forward scatter), IL-2R ␣-chain
(CD25) expression, and cell division. By 35 h postinfection, there
was minimal cell division, but marked CD25 up-regulation and
increase in cell size. These activation events were seen in all chimeras, albeit with less efficiency in the Db⫺/⫺3 B6 chimeras (Fig.
5, middle panel).
The Journal of Immunology
stages (Fig. 4, A and B), because during VV or VSV infections, the
nonhemopoietic cells were anyway inefficient in perpetuating the
clonal expansion of the primed CD8 T cells. 3) Surprisingly, the ability of radiation-resistant cell types to cause initial activation and recruitment of naive CD8 T cells is seen not only during LCMV, but
also during VV or VSV infections.
In the case of Lm, the initial recruitment events followed the
same trends that were seen with VV and VSV; however, we found
a much more severe defect in all three parameters tested, i.e.,
CFSE dilution, CD25 up-regulation, and increase in cell size (Fig.
8), in a scenario when the only cells that were capable of presenting the Ag were radiation-resistant cell types.
These results together show that in all the four pathogens we
studied, early recruitment events were largely unaffected, regard-
FIGURE 7. Recruitment of CD8 T cells is similar during rVSV-OVA
infection, regardless of whether only nonhemopoietic cells, only hemopoietic cells, or a mixture of both cell populations participate in priming. A
total of 1 ⫻ 106 CFSE-labeled, congenically marked naive OT1 CD8 T
cells was transferred into B63 B6 (thick black lines), B63 Kb⫺/⫺ (thinner
green lines), or Kb⫺/⫺3 B6 (thinnest red lines) chimeric mice. Mice were
infected with VSV OVA 24 h later. Spleens were analyzed 35 h (middle
panel) or 60 h (bottom panel) postinfection. Top panel, Indicates staining
on uninfected cells. Data are gated on donor OT1 CD8 T cells. CFSE
dilution, CD25 up-regulation, and forward scatter are shown. Similar results were obtained in a different experiment.
FIGURE 8. Recruitment of CD8 T cells is similar during rLm-OVA
infection, regardless of whether only nonhemopoietic cells, only hemopoietic cells, or a mixture of both cell populations participate in priming. A
total of 1 ⫻ 106 CFSE-labeled, congenically marked OT1 CD8 T cells was
transferred into B63 B6 (thick black lines), B63 Kb⫺/⫺ (thinner green
lines), or Kb⫺/⫺3 B6 (thinnest red lines) chimeric mice. Mice were infected with rLm-OVA 24 h later. Spleens were analyzed 35 h (middle
panel) or 60 h (bottom panel) postinfection. Top panel, Indicates staining
on uninfected cells. Data are gated on donor OT1 CD8 T cells. CFSE
dilution, CD25 up-regulation, and forward scatter are shown. Similar results were obtained in a different experiment.
less of whether the initiation events were mediated by radiationsensitive cell types, radiation-resistant cell types, or a combination
of both.
We next compared sustained expansion of the donor CD8 T
cells in mice that express restricting MHC on all cell types
(B63 B6) vs mice expressing restricting MHC only on radiationresistant cell types (Db⫺/⫺3 B6 or Kb⫺/⫺3 B6). We transferred
Db-restricted P14 CD8 T cells into Db⫺/⫺3 B6 or B63 B6 chimeric mice, and compared their expansion following LCMV infection. Despite the delayed kinetics of early recruitment of donor
P14 CD8 T cells seen in Db⫺/⫺3 B6 chimeras (Fig. 5, middle
panel), the sustained expansion of these recruited cells was largely
unaffected (Fig. 9A). This result makes the following two points: 1)
Radiation-resistant cell types in Db⫺/⫺3 B6 chimeras recruit
LCMV-specific naive CD8 T cells with somewhat delayed kinetics. 2) These recruited cells expand nearly as much in Db⫺/⫺3 B6
chimeras compared with B63 B6 chimeras at later stages because
of the perpetuation of their expansion by nonhemopoietic cell
types.
By contrast, Kb-restricted OVA-specific OT-1 donor CD8 T
cells transferred into Kb⫺/⫺3 B6 chimeras did not expand well
(compared with B63 B6 chimeras) after infection with either
rVV-OVA (Fig. 9B), rLm-OVA (Fig. 9C), or rVSV-OVA (data
not shown). Similarly, Db-restricted LCMV gp33– 41 epitopespecific P14 donor CD8 T cells transferred into Db⫺/⫺3 B6
chimeras did not expand well (compared with B63 B6 chimeras) after infection with rVV-gp33– 41 or rLm-gp33 (data not
shown). Together, these experiments demonstrate that radiation-resistant cell types can recruit naive CD8 T cells into response in all the four infection models tested, although with
delayed kinetics, but their ability to perpetuate the expansion of
the recruited cells was more efficient during LCMV, but less
efficient during VV, VSV, or Lm infections. This may perhaps
be a contributing factor for the most robust expansion of the
effector CD8 T cells typically seen during LCMV, but not during infection with the other three pathogens (29).
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FIGURE 6. Recruitment of CD8 T cells is similar during rVV-gp33
infection, regardless of whether only nonhemopoietic cells, only hemopoietic cells, or a mixture of both cell populations participate in priming. A
total of 1 ⫻ 106 CFSE-labeled, congenically marked P14 CD8 T cells was
transferred into B63 B6 (thick black lines), B63 Db⫺/⫺ (thinner green
lines), or Db⫺/⫺3 B6 (thinnest red lines) chimeric mice. Mice were infected with rVV-gp33 24 h later. Spleens were analyzed 35 h (middle
panel) or 60 h (bottom panel) postinfection. Top panel, Indicates staining
on uninfected cells. Data are gated on donor P14 CD8 T cells. CFSE
dilution, CD25 up-regulation, and forward scatter are shown. Similar results were obtained in a different experiment.
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NONHEMOPOIETIC CELL CONTRIBUTION TO CD8 T CELL EXPANSION
FIGURE 9. Nonhemopoietic cells perpetuate clonal expansion of CD8
T cells more in LCMV than during VV or Lm. A–C, 25,000 congenically
marked naive P14 (A) or OT-1 CD8 T cells (B and C) were transferred into
B63 B6, Db⫺/⫺3 B6 (A), or Kb⫺/⫺3 B6 chimeric mice (B and C). Mice
were infected with LCMV (A), rVV-OVA (B), or rLm-OVA (C). n ⫽
3/group. Spleen cells were analyzed on day 7 postinfection. Dot plots are
gated on CD8 T cells. Numbers within plots indicate the fraction of CD8
T cells that are Db gp33 tetramer⫹ in LCMV infection (A) or Kb SIINFEKL
tetramer⫹ cells among CD8 T cells in rVV-OVA (B) or rLm-OVA infection (C). Similar results were obtained in two other experiments.
to process and present exogenously administered OVA to OVAspecific naive CD8 T cells and cause their initial activation and
proliferation.
We next compared sustained expansion of OVA-specific OT-1
CD8 T cells and LCMV-specific P14 CD8 T cells side by side in
Radiation-resistant cell types are also capable of presenting
exogenously administered OVA to naive CD8 T cells and
causing their initial recruitment into response, but are incapable
of sustaining their proliferation
The above experiments suggested that Ags presented by radiationresistant cell types can cause early recruitment of naive CD8 T
cells into proliferation. Whether these radiation-resistant cell types
arise from hemopoietic or nonhemopoietic compartments was unclear. Only ⬍1% of the hemopoietic APCs in these mice was
comprised of radiation-resistant host cells expressing the relevant
restricting MHC. It was not clear whether such residual numbers
were sufficient to cause efficient naive CD8 T cell recruitment. To
address this, we transferred Kb-restricted OT-1 cells into Kb⫺/⫺
3 B6 chimeras and then immunized them with both LCMV and
soluble OVA protein at the same time. Because cross-priming
function is generally known to be restricted to bone marrow-derived cells (19, 30), we reasoned that the exogenously administered OVA protein can be presented to OT-1 cells and cause their
proliferation under the conditions of the adjuvant effect mediated
by LCMV only if the host-derived bone marrow cells that resisted
radiation (Kb⫹ in this case) were sufficiently high in these chimeras. The OT-1 donor CD8 T cells were recruited into proliferation,
up-regulated CD25, and increase in size in B63 B6, B63 Kb⫺/⫺,
as well as the Kb⫺/⫺3 B6 chimeras (Fig. 10). This result suggested that the host bone marrow-derived Kb⫹ APCs that were
radiation resistant, although few in number, were sufficient enough
FIGURE 11. Sustained expansion of cross-primed OVA-specific CD8
T cells is deficient in the absence of Ag presentation by a majority of
hemopoietic cells, whereas expansion of LCMV-specific cells does not
require hemopoietic cells. A total of 100,000 OT1 and 25,000 P14 CD8 T
cells was transferred into B63 B6 or Db⫺/⫺Kb⫺/⫺␤2m⫺/⫺3 B6 chimeric
mice. Mice were immunized with LCMV along with soluble OVA 24 h
later. Analysis was done on day 7 postimmunization. Dot plots are gated on
CD8 T cells. Numbers within plots indicate fraction of CD8 T cells that are
positive for the Db gp33 tetramer and CD44 (top panels) and Kb SIINFEKL
tetramer and CD44 (bottom panels). A, Top panels, Expansion of P14 CD8
T cells in the spleen. Left panel, Db⫺/⫺Kb⫺/⫺␤2m⫺/⫺3 B6 chimera. Right
panel, B6 mice. Bottom panels, Expansion of OT1 CD8 T cells in the
spleen. Left panel, Db⫺/⫺Kb⫺/⫺␤2m⫺/⫺3 B6 chimera. Right panel, B6
mice. B, Fold expansion of P14 CD8 T cells (top) and OT1 CD8 T cells
(bottom) in the above experiment.
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FIGURE 10. Recruitment of CD8 T cells is similar during immunization with LCMV plus soluble OVA, regardless of whether only nonhemopoietic cells, only hemopoietic cells, or a mixture of both cell populations
participate in priming. A total of 1 ⫻ 106 CFSE-labeled, congenically marked
OT1 CD8 T cells was transferred into B63 B6, B63 Kb⫺/⫺, or Kb⫺/⫺3 B6
chimeric mice. Mice were immunized with LCMV along with soluble OVA
24 h later. CFSE dilution, CD25 up-regulation, and forward scatter on donor
OT1 CD8 T cells at 35 h or 60 h post-LCMV plus OVA immunization in
spleen. Similar results were obtained in a different experiment.
The Journal of Immunology
Discussion
Our study makes the following contributions toward understanding
the role of nonhemopoietic cells in CD8 T cell expansion in infections: First, our experiments show that Ag presentation by cells
of nonhemopoietic origin can contribute markedly to the clonal
expansion of effector CD8 T cells. Second, the ability of nonhemopoietic cells to perpetuate clonal expansion was drastically different depending upon the infectious agent. Nonhemopoietic cells
were strikingly efficient in perpetuating effector CD8 T cell expansion during LCMV infection, but are highly inefficient during
VV, VSV, or Lm infections. Third, our study shows that the
effector CD8 T cells that receive TCR signals exclusively from
hemopoietic cells were similar in their phenotypic and cytokine
functional aspects to the effector CD8 T cells receiving a mixture
of TCR signals from both hemopoietic and nonhemopoietic cells.
It was originally thought that under the conditions of LCMV
infection, nonhemopoietic cells are capable of priming naive CD8
T cells. Sigal et al. (6) compared VV-specific polyclonal responses
in B63 B6 vs TAP⫺/⫺3 B6 radiation chimeras, and showed that
the TAP⫺/⫺3 B6 mice failed to generate vaccinia-specific responses. Lenz et al. (5) compared VV, Lm, and LCMV-specific
responses in parent3 F1 bone marrow chimeric mice, and showed
that when the restricting MHC was lacking on radiation-sensitive
cells, VV- or Lm-specific polyclonal CD8 T cells were undetectable, whereas LCMV-specific polyclonal CD8 T cells were readily
detectable. Three possible, mutually nonexclusive interpretations
were offered to explain the difference between VV or Lm vs
LCMV infections in these findings, as follows: One was that the
LCMV-specific naive CD8 T cell repertoire is somewhat at a
higher frequency in these mice. The second was that hemopoietic
cells are the only ones that initiate naive CD8 T cells into response
during VV or Lm, but nonhemopoietic cells can also initiate naive
CD8 T cell response during LCMV. The third explanation was that
features of LCMV (e.g., its noncytopathic nature) enable it to selectively use the residual radiation-resistant (but hemopoietic) professional APCs of the host that persist in low numbers following
irradiation and reconstitution. Sigal and Rock (7) subjected
parent3 F1 bone marrow chimeric mice to a second round of ra-
diation and reconstitution (parent3(parent3 F1)) and showed that
these mice still have ⬍1% residual host bone marrow-derived professional APCs (although this is much lower than the ⬃5% residual bone marrow-derived APCs seen in single radiation chimeras)
and that these (parent3(parent 3 F1)) chimeras still elicit detectable, but much less of polyclonal CD8 T cell response against
LCMV compared with the parent3 F1 chimeras, although there
were differences in this pattern dependent upon which LCMV
epitope-specific responses they were looking at.
One limitation of assessing endogenous polyclonal responses in
the above mentioned studies is the possibility of differences in
repertoire selection in different chimeras. Another limitation is the
lack of knowledge, whether the difference in LCMV vs other infections was due to differences in early naive CD8 T cell recruitment. More recently, Probst and van den Broek (25) used transgenic
CD11c/DTR mice that allow targeted depletion of CD11c-positive
cells. These authors generated (CD11cDTR⫹ plus H-2Db⫺3 H2Db⫺) chimeras, into which they later transferred H-2Db-restricted
P14 cells, followed by specific depletion of H-2Db-bearing CD11cpositive cells and LCMV infection. This study showed that the depletion of Db⫹ CD11c⫹ cells specifically diminishes the expansion of
the Db-restricted donor P14 CD8 T cells, but does not diminish expansion of endogenous Kb⫹-restricted CD8 T cells, at least in the
peripheral blood compartment that was analyzed. However, the
early recruitment of naive CD8 T cells was not analyzed in this
study either. All these studies, together, demonstrate the following: 1) bone marrow chimeras do have some residual numbers of radiation-resistant host-derived hemopoietic cells; 2)
these residual numbers of radiation-resistant host-derived hemopoietic cells were unable to elicit detectable response either
in VV or Lm, or influenza virus infections, but are able to elicit
detectable responses during LCMV for reasons that were unclear. Our study, in addition to showing for the first time that
nonhemopoietic cells perpetuate primed CD8 T cell expansion
during LCMV, also clarifies the possible reasons for the discrepant observations between earlier studies with reference
to LCMV.
Our study is not designed to address whether nonhemopoietic
cells prime naive CD8 T cells or not. But some of our experiments
presented in this study suggest that radiation-resistant cell types
can prime initial naive CD8 T cell activation and early proliferation not only during LCMV, but also during VV, VSV, and Lm
infections (Figs. 5–11). Moreover, our results show that these radiation-resistant cell types can also cross-prime. However, we do
not know whether these so-called radiation-resistant cells that are
capable of priming naive CD8 T cells under these different conditions represent truly nonhemopoietic cell types, or represent the
small numbers of the host-derived hemopoietic cell types that resist radiation, or a combination of both. It is also possible that
entirely different, hitherto less appreciated radiation-resistant
APCs that can prime naive CD8 T cells may exist, but these cells
may not be able to sustain the clonal expansion of such primed
cells. Because bone marrow chimeras contain a small number of
host-derived APCs that resist radiation, and because the APCs are
highly efficient in priming naive CD8 T cells even in small numbers, we favor the idea that these radiation-resistant cell types capable of priming naive CD8 T cells under the conditions tested in
this study are most likely of hemopoietic origin, but additional
experiments are needed to test this stringently.
Why are nonhemopoietic cells more efficient in causing the expansion of effector cells in LCMV compared with the other three
infections? All four pathogens used in this study infect cells of
nonhemopoietic origin (31–34). Hence, the diminished contribution by nonhemopoietic cell types in VV, VSV, and Lm cannot
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the same host, under conditions in which both the cell populations
are initially primed to proliferate by radiation-resistant APCs. For
this, we generated Db⫺/⫺Kb⫺/⫺␤2m⫺/⫺3 B6 chimeras and transferred a mixture of Db-restricted P14 cells and Kb-restricted OT1
cells into these or B6 mice as controls and immunized them with
LCMV plus soluble OVA.
Mice were analyzed on day 7 postimmunization. We found that
the OT-1 donor CD8 T cells expanded only in B6 mice, but failed
to expand in Db⫺/⫺Kb⫺/⫺␤2m⫺/⫺3 B6 chimeras. By contrast, the
cotransferred LCMV-specific P14 donor CD8 T cells expanded
well in both B6 mice as well as in the Db⫺/⫺Kb⫺/⫺␤2m⫺/⫺3 B6
chimeras (Fig. 11). The presence of P14 response, but the lack of
OT-1 response in Db⫺/⫺Kb⫺/⫺␤2m⫺/⫺3 B6 chimeras makes the
following two points: 1) The residual numbers of bone marrowderived, but radiation-resistant APCs expressing the restricting
MHC in the Db⫺/⫺Kb⫺/⫺␤2m⫺/⫺3 B6 chimeras were sufficient to
recruit naive CD8 T cells into response, but insufficient to mediate
the sustained expansion of the recruited cells. Thus, despite efficient initial recruitment, no visible level of OVA-specific CD8 T
cell response was observed in Db⫺/⫺Kb⫺/⫺␤2m⫺/⫺3 B6 chimeras
at day 7 postimmunization. 2) The LCMV-specific P14 CD8 T
cells in the same Db⫺/⫺Kb⫺/⫺␤2m⫺/⫺3 B6 chimeras, however,
continued to expand, resulting in a robust response by day 7, due
to the ability of LCMV-infected nonhemopoietic cell types in perpetuating the expansion of the primed effector CD8 T cells.
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Acknowledgments
We thank C. B. Wilson and M. J. Bevan for helpful discussions and for
critical reading of the manuscript; P. J. Fink for OT-I mice; and members
of the Kaja laboratory for helpful discussions, as well as K. Madhavi for
technical assistance.
Disclosures
The authors have no financial conflict of interest.
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simply be attributed to lack of infection. For T cells, the requirement for costimulation, the capacity to respond to various types of
APCs, the propensity to live or die, and the decision to proliferate
or to undergo tolerization are largely determined by a combination
of two major factors, as follows: 1) the differentiation state of the
T cell, and 2) the type and status of the cell that presents Ag to the
T cell. There are significant differences in the type of cells each
pathogen infects, the inflammatory cytokines they induce, and the
level of cytopathicity. LCMV, VV, and VSV infect a wide variety
of hemopoietic and nonhemopoietic cell types. Lm, in contrast,
predominantly infects macrophages, dendritic cells, and a limited
repertoire of nonhemopoietic cells, especially hepatocytes, which
are generally known to provide a strong tolerization signal to activated T cells (35), although under some conditions the liver may
be an excellent priming site for naive CD8 T cells (36).
Recent studies from our laboratory showed that the effector CD8
T cells require direct IFN-I signals for proper survival and expansion (20, 37), and that the level of IFN-I dependence is highest in
the case of LCMV and lower in the case of VV, VSV, and Lm
(29). IFN-I is made not only by professional APCs, but also by
virtually all infected cells (38 – 40). LCMV is not known to produce any molecules that interfere with the action of IFN-I, whereas
VV induces soluble IFN-I receptor-like molecules that neutralize
IFN-I (41). LCMV is noncytopathic to most cells that it infects,
and hence, LCMV Ags are most likely to be presented by infected
cells for a longer time. In contrast, VV and VSV are highly cytopathic to the cells they infect. We think some or all of these factors
would determine the inflammation milieu and the Ag loads in the
four pathogens that we have tested. We expect these to be different
not only across different pathogens, but also in chimeras responding to the same pathogen, but different in the kind of cell population involved in the priming/perpetuation of CD8 T cells. Indeed,
the early kinetic differences we see in cell size, CD25 up-regulation, and division we believe are wholly or in part a consequence
of differences in the kinetics/magnitude of such parameters as Ag
load/inflammation.
In summary, our studies demonstrate that expansion and effector
programs initiated by hemopoietic APCs can be perpetuated by
nonhemopoietic cells during some, but not all infections. This has
implications for designing immune therapies for chronic diseases
that often involve reservoirs of infections maintained in nonhemopoietic tissues. Understanding how the quality and quantity of
memory cells vary depending upon whether memory cells originated from effector T cells that received cognate signals exclusively through hemopoietic cell types, or a mixture of both hemopoietic and nonhemopoietic cells types, is currently underway in
our laboratory. Such knowledge will have important implications
for rational vaccine design.
The Journal of Immunology
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