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*
Department of Microbiology-Immunology and Interdepartmental Immunobiology Center, Northwestern University Medical School, Chicago, IL 60611; and
The Ben May Institute for Cancer Research and the Committee for Immunology, The University of Chicago, Chicago, IL 60637
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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T cells require at least two signals for activation. One signal is Ag specific and is delivered by the MHC peptide complex on the APC via the TCR. The second "costimulatory" signal is delivered via the CD28 molecule on the T cell surface by its interaction with the ligands, B7-1 (CD80) or B7-2 (CD86). The importance of B7/CD28-mediated signaling, in preventing T cell inactivation and tolerance, has been shown in multiple systems in vitro and in vivo (3, 4, 5, 6, 7, 8). The presence of the two alternative costimulatory ligands, B7-1 and B7-2, both of which can bind CD28, led to studies addressing the individual functional role of these molecules. Some studies have suggested that B7-1 vs B7-2 costimulation leads to T cell differentiation along different pathways (9). It was proposed that B7-2-mediated costimulation induces IL-4 production in naive T cells pushing them toward Th2 development whereas B7-1 provides a more neutral signal resulting in high IL-2 production (10). However, other studies using B7-1 and B7-2 transfectants have not found any differences in the cytokine production following T cell costimulation (11, 12). Thus, the differences in B7-1 and B7-2 activity may reflect either intrinsic differences in the molecules or differential expression on individual cell types or at distinct times during an immune response (13).
In vivo studies, using reagents targeting B7-1 or B7-2, have led to similarly confusing results in different disease models. In nonobese diabetic (NOD) mice, treatment with anti-B7-2 prevented the development of diabetes, whereas anti-B7-1 mAb treatment resulted in exacerbated disease (14). In contrast to the NOD results, the same anti-B7-1 mAb administered to SJL mice during the induction phase of EAE blocked disease development, whereas anti-B7-2 treatment resulted in disease exacerbation (9). Recent studies in the murine model of Th2-dependent airway eosinophilia suggested that B7-1-mediated costimulation is not required for the induction of Th2 immune responses but rather for the amplification of lung inflammation (15). Though these results could be explained by the differences in the several models used, results from our lab using the same Abs in a similar model of R-EAE add to the intrigue. When these Abs were administered during the first remission after the acute phase of the disease, anti-B7-2 treatment had no effect, whereas blockade of B7-1/CD28 interactions using the F(ab) fragments of anti-B7-1 resulted in the blockade of disease relapses (16). This correlated with the blockade of the process of epitope spreading that mediates clinical relapses in diseased animals (17). Thus, B7-1 appeared to be the predominant costimulatory molecule in animals with established disease.
In the present study, we analyzed the dynamics of surface expression of the costimulatory ligands, B7-1 and B7-2, in the context of R-EAE. Active immunization of SJL mice with PLP139–151 in CFA resulted in a temporal up-regulation of surface B7-1 expression, relative to B7-2, on splenic B cells, T cells, and macrophages, similar to our previous report demonstrating B7-1 predominance on cells infiltrating the CNS of mice with active disease (16). Similar enhancement of B7-1 expression was induced on spleen cells by the adoptive transfer of EAE or by immunization with CFA alone. Surprisingly, B7-1 expression did not change significantly on the lymph node cells from any of these treated mice. The selective up-regulation of B7-1 on splenic and CNS APCs in animals with active disease was reflected in the functional predominance of B7-1 in these organs. In contrast, B7-2 remained functionally predominant in lymph nodes, correlating with its expression. These results demonstrate selective up-regulation of splenic B7-1 with a dichotomy in the costimulatory phenotype of the peripheral lymphoid organs during ongoing autoimmune disease and support the notion that this differential expression of B7-1 and B7-2 at different sites in the animal may lead to distinct functional consequences.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Female SJL/J mice, 6 to 7 wk old, were purchased from Harlan Laboratories (Indianapolis, IN) housed in the Northwestern University animal care facility and maintained on standard laboratory food and water ad libitum.
Peptides
Peptides PLP139–151 (HSLGKWLGHPDKF) and VP2–70–86 (WTTSQEAFSHIRIPLPH) were synthesized as described previously (16, 18).
Immunization and induction of active and adoptive R-EAE
For active R-EAE, mice were immunized with 100 µl of a CFA emulsion containing 200 µg of Mycobacterium tuberculosis H37Ra (Difco, Detroit, MI) and 80 µg of PLP139–151 (2). Mice immunized with CFA alone received similar emulsion without the addition of peptide or an emulsion containing a nonencephalitogenic peptide (Theiler’s virus protein VP2–70–86) in CFA (18). Adoptively transferred EAE was induced by the transfer of in vitro activated PLP139–151-primed lymph node cells (19). Clinical severity was assessed on a 0 to 5 scale (16).
mAb staining
Mice were sacrificed on the indicated day following immunization
or transfer. Lymph node and spleen cells were pooled (two to three mice
per time point) and prepared as previously described (16).
FITC-conjugated mAbs to CD3 (T cells) and B220 (B cells) and
biotin-conjugated hamster Ig control were purchased from PharMingen (La
Jolla, CA). FITC-anti-F4/80 (macrophages) was purchased from Caltag
(South San Francisco, CA). Purified anti-B7-1 (clone 16–10A1),
anti-B7-2 (GL-1) mAbs, and rat Ig control were biotinylated using
NHS-LC-biotin (Pierce, Rockford, IL). Avidin-R-phycoerythrin (A-PE) was
purchased from Molecular Probes (Eugene, OR). Aliquots of
106 cells were incubated with a predetermined optimal
concentration of the appropriate FITC-conjugated mAb (anti-CD3,
anti-B220, or anti-F4/80) and the biotinylated anti-B7 mAbs
in 2.4G2 supernatant (anti-mouse FcR
II/III) in the dark for 30
min at 4°C. Cells were washed in isotonic buffered saline followed by
incubation with avidin-R-phycoerythrin for 30 min at 4°C. Cells were
washed and resuspended in 1 ml isotonic-buffered saline (Baxter;
containing 0.1% NaN3 and 1.0% normal goat serum)
containing 0.1 µg/ml propidium iodide (PI).
Flow cytometry
Data collection and analysis were performed on a FACScan flow
cytometer (Becton Dickinson, Mountain View, CA). Sufficient events were
collected to assure that at least 5 x 103 live
(propidium iodide-negative) events were analyzed per sample. Both B7-1
and B7-2 showed unimodal staining patterns, and expression was analyzed
by mean fluorescence intensity shift over nonspecific background
staining (
MFI). Nonspecific background staining was determined by
incubating samples with isotype control mAbs. The actual value of
MFI in a given experiment was dependent on several factors such as
Ab affinities, voltage settings, biotinylation efficiency, etc. Thus,
in any given set of experiments, all the settings and Ab stocks were
kept constant. Values for B7-1 and B7-2 MFI were used to calculate
the relative B7-1:B7-2 ratios over time, as reported previously (16),
and the patterns were consistent in multiple experiments. Percentage of
cells staining positive for B7-1 or B7-2 were determined based on the
histogram of cells obtained using relevant control Ig.
Isolation of CNS mononuclear cells
Mice in remission from the acute phase of adoptive R-EAE were
anesthetized with methoxyflurane (Pittman-Moore) and perfused through
the left ventricle with 
60 ml of PBS (20). Spinal cords were
extruded by flushing the vertebral canal with PBS, and rinsed in PBS.
Spinal cords were forced through 100-mesh stainless steel screens to
give a single cell suspension. CNS mononuclear cells were isolated by
centrifugation (500 x g) at 24°C over
30%/70% discontinuous Percoll (Pharmacia) gradients. Cells collected
from the 30%/70% interface were washed and resuspended in DMEM-7
(19). I-As-expressing F4/80+ macrophages and
microglia were enriched by a 2-h plastic adherence step at 37°C,
harvested by scraping at 4°C, washed two times in DMEM-7, and
assessed for their ability to endogenously activate a
PLP139–151-specific Th1 line.
In vitro proliferation assays
Mice were primed with PLP139–151 in CFA. On the indicated days postimmunization, lymph node and spleen cells were harvested from groups of two to three immunized mice as well as age-matched naive controls. For use as APCs, cells were irradiated at 3000 rad and plated at 4 x 105 cells/well in 96-well plates. Column-purified responder T cells (>98% CD4+ by flow cytometry) were obtained from lymph nodes of mice primed with the unrelated, nonencephalitogenic Theiler’s virus peptide, VP2–70–86 (3 x 105 T cells/well) (18). Cells were cultured in the presence or absence (background) of Ag (VP2–70–86, 25 µM) in a total volume of 200 µl complete DMEM-7. Cells were allowed to incubate with the indicated Abs (10 µg/well) for 30 to 45 min at 37°C before the addition of the Ag. The following mAbs were employed (16, 21): hamster control Ig (Cappel Research Products, NC), rat control Ig (111/10), anti-CD80 (B7-1) mAb, 16–10A1 (Repligen Corp.); and anti-CD86 (B7-2) mAb GL-1. Cultures were pulsed with 1 µCi of [3H]TdR after 72 h and harvested at 96 h; [3H]TdR uptake was determined by scintillation counting. The actual counts of control cultures varied between groups, and, for comparison, results were expressed as mean percent proliferation (counts of test samples compared with relevant controls; hamster Ig for anti-B7-1; rat Ig for anti-B7-2, and a combination of hamster and rat Ig for both).
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Previous studies have shown that B7-2, but not B7-1, is primarily
expressed on naive spleen cells (22). However, we have observed
enhanced B7-1 expression during active EAE in SJL mice (16). Therefore,
a temporal analysis of B7-1 and B7-2 expression was performed in SJL
mice. As seen in Figure 1
, the basal
level of B7-2 expression was significantly greater than B7-1 on spleen
cells and lymph node cells from naive SJL mice. In multiple
experiments, naive animals at all ages showed similar findings and
served as age-matched controls for other experiments in these studies.
Figure 1A shows an example of a typical pattern of B7-1 and
B7-2 expression in the naive SJL spleen. The relative expression of
B7-1 to B7-2 was determined by the ratio of B7-1 fluorescence shift to
that of B7-2 (16) and ranged from 0.1 to 0.6 in different sets of
experiments (Fig. 1). Similarly, the percentage of total cells
expressing B7-1 (4.6%) was lower than those expressing B7-2 (23.3%).
Individual cell types, analyzed by gating for CD3+ T cells,
B220+ B cells, or F4/80+ macrophages, showed
similar patterns of B7 expression with B7-1:B7-2 ratios of less than
1.0 (Fig. 2). Naive lymph nodes also
exhibited low levels of B7-1 as compared with B7-2 (Fig. 1, C and D; B7-1:B7-2 ratio of 0.22), with a lower
percentage of cells expressing B7-1 (2.8%) as compared with B7-2
(9.9%). The same pattern of low or undetectable B7-1 expression was
seen on B cells and T cells. Significant numbers of F4/80+
cells were not detectable in lymph nodes to assess B7 expression on
macrophages in this tissue (data not shown).
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, A and B). Thus, the
B7-1:B7-2 ratio flipped to 3.38 (Fig. 2B) during
preclinical disease, as compared with 0.21 in age-matched naive
controls (Fig. 2A). These relative changes in
B7-1/B7-2 expression were seen as early as 5 to 7 days after
immunization of mice and were consistently found in the preclinical
phase, acute phase, remission, and first relapse phases of R-EAE (Fig. 2, and data not shown). These changes were reproduced over several
experiments and were similar to our previous observations in cells
isolated from the central nervous system of diseased mice
(16).
It was apparent from the flow cytometric profiles that B7-1 was
significantly up-regulated on a subpopulation of splenic cells (4.6%
B7-1+ cells in naive spleen vs 14.2% in the preclinical
phase). Therefore, individual subsets were examined, as shown in Figure 2C. The changes in both the levels of B7-1 expression and
the percentage of B7-1+ cells, observed in the overall
splenic population (Fig. 2A), were also reflected in
the individual cell types, including T cells, B cells, and macrophages
(Fig. 2C), reaching highest levels on the surface of
F4/80+ macrophages.
Interestingly, these changes in surface expression patterns of B7-1 and
B7-2 did not occur in the draining lymph node cell population (Fig. 3). Lymph node cells taken at various
time points following immunization (as early as day 2 and as late as
day 40; data not shown) continued to express relatively constant levels
of surface B7-2 during the immune response on both T cells and B cells,
and at no time point was a detectable increase in B7-1 expression
observed. This lack of change was evident in both the draining lymph
nodes (Fig. 3) as well as cells isolated from remote (periaortic) lymph
nodes (data not shown). Thus, there appears to be a selective
enhancement of B7-1 in the central nervous system (16) and the spleen
(Fig. 2), but not in the lymph nodes (Fig. 3), during this chronic
autoimmune disease.
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The basis of the selective up-regulation of B7-1 in the CNS
and the spleen might be the active CNS inflammation induced subsequent
to the peptide injection or the inflammatory response mediated by the
CFA immunization. Therefore, we examined the expression of B7-1 and
B7-2 following the induction of disease by the adoptive transfer of in
vitro-activated PLP139–151-specific cells. This protocol establishes
demyelinating inflammation in the CNS without peripheral CFA-induced
inflammation. Mice were analyzed for B7-1 and B7-2 expression at
varying time points following adoptive transfer. As seen in Figure 4, there was consistent temporal
up-regulation of B7-1 expression in the spleen, with a B7-1:B7-2 ratio
of greater than 1.0 during the acute phase of disease (day 10–14).
Thus, the pattern of B7-1/B7-2 expression was similar to that seen in
active disease (Fig. 2A), although the kinetics were
slightly delayed. Analysis of individual cell subsets, including T
cells, B cells, and macrophages, showed similar up-regulation of B7-1
expression as seen in the whole population (data not shown). In
contrast, lymph node cells from these animals showed no enhancement in
B7-1 expression (data not shown), similar to our observations in active
disease (Fig. 3). Thus, Th1-mediated CNS inflammation was sufficient to
induce changes in B7-1 expression in the spleen.
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). Spleen cells from these mice
showed an enhanced B7-1:B7-2 ratio (Fig. 5A), which
was evident within 5 to 7 days following immunization (data not shown),
but to a lesser degree than mice with ongoing EAE. In this system, B7-2
expression on splenic cells remained relatively constant, as opposed to
the decreased B7-2 expression in the disease models. Consistent with
other experiments, lymph node cells from these mice showed low or
undetectable B7-1 expression and a consistently low B7-1:B7-2 ratio
(Fig. 5B).
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Functional relevance of B7-1 and B7-2 expression patterns
We next analyzed the functional consequences of changes in the
relative expression of B7-1 and B7-2 in the lymph nodes, spleens, and
of mice immunized with PLP139–151/CFA. Draining lymph node cells and
spleen cells from immunized mice and age-matched naive controls were
harvested at varying time points and used as APCs in proliferation
assays. Ag-specific responder T cells were isolated from the lymph
nodes of mice immunized with a non-cross-reactive,
I-As-binding peptide from the Theiler’s virus
protein, VP2–70–86 (18). Proliferation assays were conducted in the
presence of CTLA4-Ig, anti-B7-1 mAb, anti-B7-2 mAb, or a
combination of these mAbs (or their relevant controls). Figure 6 shows the results of a representative
assay using APCs from mice 10 days postimmunization. Correlating with
the relative expression of B7-1 and B7-2 in the different cell
populations, anti-B7-2 mAb preferentially inhibited proliferation
when naive splenocytes (Fig. 6C) or primed lymph node
cells (Fig. 6A) were used as APCs. In contrast, when
splenocytes from immunized animals were used, the proliferation was
preferentially inhibited by anti-B7-1 mAb (Fig. 6B). In all cases, the addition of a combination of
both Abs had the most inhibitory effect, similar to CTLA-4Ig, a
molecule that binds both B7-1 and B7-2. Similar results were obtained
during the preclinical and acute phases of disease (data not shown).
These results suggest that B7-2 is the functionally dominant
costimulatory molecule in the naive splenic environment and the
draining lymph node environment, whereas B7-1 functionally dominates in
the spleen of immunized mice.
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, splenic APCs from naive SJL/J mice
failed to induce proliferation of the PLP139–151-specific T cell line
in the absence of added peptide. In contrast, direct culture of CNS
APCs with the peptide-specific T cell line in the presence of control
hamster Ig induced a vigorous proliferative response indicating that
the immunodominant PLP139–151 epitope was endogenously associated with
surface I-As on these F4/80+ cells in the
inflammatory demyelinating environment within the CNS of mice with
ongoing R-EAE. As with splenic APCs from mice with ongoing EAE, this
response was preferentially inhibited by anti-B7-1 mAb.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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One likely explanation for these conflicting results is that costimulatory ligands may be differentially expressed at different sites in the body, on different cell types, and/or at different times during the autoimmune response. In vitro data suggests that B7-1 and B7-2 are differentially regulated on APCs as well as T cells (13, 22, 26, 27, 28). However, little information is available on the in vivo expression patterns of these costimulatory molecules on different cell types during an immune response.
The present study was conducted to examine the surface expression of
B7-1 and B7-2 in different organs during the course of a Th1-mediated
demyelinating disease, R-EAE. As described previously in various
systems, naive SJL mice preferentially expressed surface B7-2 in both
the lymph nodes and the spleen (Fig. 1) (13, 22). We have shown
previously that during the course of R-EAE there was heightened B7-1
expression, relative to B7-2, on CNS-infiltrating T cells, B cells, and
macrophages (16). In this study, similar up-regulation of B7-1
expression with concomitant B7-2 down-regulation was observed on spleen
cells following active disease induction. These changes in B7-1/B7-2
expression were very consistent over multiple experiments. Moreover,
the changes in the expression patterns in both the spleen and on
CNS-infiltrating F4/80+ cells had important functional
consequences as B7-1 became the predominant costimulatory ligand in
proliferation assays (Figs. 6 and 7). Interestingly, our results
indicate that, in the inflammatory demyelinating milieu of the CNS of
mice with active disease, resident F4/80+
macrophages/microglia endogenously display a significant amount of
surface I-As-associated myelin epitopes, including the
immunodominant PLP139–151 determinant (Fig. 7) and other less dominant
epitopes such as PLP178–191 and MBP84–104 (data not shown),
associated with epitope spreading and disease relapses (17). Thus,
following induction of EAE in SJL mice, B7-1 becomes the dominant
costimulatory molecule in the spleen and in the CNS. This could explain
our findings that anti-B7-2 treatment of mice during disease
remission had no detectable effect on R-EAE progression, whereas
blockade of B7-1-mediated interactions inhibited disease relapses (16).
Up-regulation of B7-1 may be a normal consequence of chronic
inflammation as treatment with anti-B7-2 mAb also failed to affect
the progression of diabetes when administered to NOD mice at 10 wk of
age or later (14).
Interestingly, while relative B7-1 up-regulation was seen in the CNS
(16) and in the spleen (Fig. 2), B7-1 expression was low or
undetectable in the lymph nodes throughout the disease course (Fig. 3).
The costimulatory phenotype of the lymph node environment also remained
B7-2 predominant (Fig. 6). Several previous reports have shown that
B7-2 is the predominant costimulatory molecule in the induction of
immune responses (14, 29). Interestingly, these studies employed
immunization protocols that induced the initial immune response in the
draining lymph nodes or used naive spleen cells as MLR stimulators,
sites where B7-2 provides the predominant costimulatory signal based on
both expression (Fig. 1) and function (Fig. 6C).
However, responses that arise in an inflammatory environment, such as
in a relapsing autoimmune disease, may well be B7-1 dependent.
B7-1-mediated costimulation was recently shown to be important in the
induction of local lung eosinophilia, but not in the generation of
systemic eosinophilia or IgE responses in a Th2-dependent model of
airway eosinophilia (15). In a relapsing Th1-mediated autoimmune
disease like R-EAE, ongoing tissue destruction is dependent on the
continued recruitment of new T cell responses to endogenously presented
tissue epitopes, a phenomenon termed epitope spreading (17, 30). In
PLP139–151-induced disease, the first clinical relapse is
predominantly mediated by T cells specific for a secondary PLP epitope,
PLP178–191 (17). The two most likely sites in the animal where the
priming and spreading of such immune responses may occur are the CNS,
the site of destruction, and the spleen, where tissue breakdown
products may be concentrated and presented. Both these environments are
high in B7-1 expression and function. This explains why blockade of
B7-1-mediated interactions, using F(ab) fragments of anti-B7-1 mAb
(16), results in the blockade of epitope spreading and an inhibition of
ongoing disease. Similar enhancement of B7-1 expression has been shown
in multiple sclerosis (31); thus, B7-1 could serve as an important
target for therapeutic intervention in established disease.
One of the interesting issues that remains to be resolved is the
molecular basis of selective up-regulation of B7-1 in these tissues. To
date, in vitro studies of cellular expression of B7-1 and B7-2,
employing mitogens, Abs, or cytokines to activate the cells, have not
found selective B7-1 up-regulation (13, 22). However, our in vivo
studies suggest that relative B7-1 up-regulation is a generalized
response to a Th1-type inflammation, whether initiated in the periphery
or the CNS. Destructive inflammatory stimuli, such as immunization of
mice with CFA alone (Fig. 5) or induction of R-EAE by adoptive transfer
of encephalitogenic T cells (Fig. 4), are sufficient to induce these
changes in the splenic cell populations. The kinetics of B7-1
up-regulation is slightly delayed in the case of adoptive disease, as
compared with CFA-immunization, probably due to the time required to
induce peripheral effects following initiation of inflammation within
the CNS following adoptive transfer of encephalitogenic cells. Also,
the patterns of changes in B7-2 expression are different in
CFA-immunized mice (constant expression) vs the disease-inducing models
(decreased expression). The changes in B7-1/B7-2 expression patterns
are most striking in active disease (Fig. 2) and are probably an effect
of both the CFA-induced inflammation (early) as well as the CNS
inflammation (late). The mechanism of this up-regulation of B7-1,
relative to B7-2, still remains to be understood. It is likely that
local cellular interactions or cytokines and chemokines secreted in the
inflammatory milieu may be responsible for the selective up-regulation
of B7-1. Cytokines, such as IFN-, TNF-
, IL-4, IL-5, and IL-10,
which are present in the CNS of diseased animals (Ref. 32, and our
unpublished observations), have been shown to regulate the surface
expression of costimulatory molecules on several cell types (22, 33, 34). These factors, alone or in combination, could result in the
selective up-regulation of B7-1 in vivo. However, the interplay of
these factors and the exact molecular events involved in these
processes need to be elucidated.
Another consistent finding in these studies was that lymph node cells from these animals did not significantly up-regulate surface B7-1 expression, despite the fact that under some conditions these nodes were draining the sites of CFA-induced inflammation. Despite the failure to up-regulate B7-1 in vivo, we (data not shown) and others (26) have shown that lymph node T cells from PLP139–151-primed mice up-regulate B7-1 expression in vitro following peptide-specific activation. There are several possible explanations for these findings. Some cell type or soluble factor in the lymph node environment in vivo may actively suppress B7-1 up-regulation. Alternatively, activated T cells may traffic out of the lymph node before they up-regulate significant levels of B7-1. This latter hypothesis is supported by the finding that T cells expressing high levels of B7-1 are found in the CNS-infiltrating population from diseased mice (16). However, trafficking of activated cells may be only part of the explanation for differential B7-1 expression in peripheral lymphoid compartments, considering that all the cell types tested (T cells, B cells, and macrophages) showed similar lack of B7-1 up-regulation. Finally, the spleen may contain certain cell types, such as granulocytes, that may produce factors that up-regulate B7-1 expression during the inflammatory response. Thus, our future studies will focus on the poorly understood factors intrinsic to the spleen and lymph nodes that are likely to affect the microenvironments and influence B7 expression.
The implications of the dichotomy in B7-1 and B7-2 expression in the
two lymphoid compartments are multifold. B7-1 interacts with the CD28
homologue, CTLA-4, with higher avidity and differential kinetics as
compared with B7-2 (35, 36). CTLA-4 has been shown to function as a
negative regulator of T cell activation (37, 38) and is an important
down-regulator of R-EAE (19). Based on the higher avidity of
CTLA-4/B7-1 interactions and their similar delayed kinetics of
expression, B7-1 may be the preferred ligand for CTLA-4 during an
immune response (23). In fact, following in vitro activation of
PLP139–151-specific T cells, CTLA-4 and B7-1 show very similar delayed
expression kinetics (Ref. 19, and data not shown). It is tempting to
speculate that the enhancement of B7-1 could be involved in the
down-regulation of an ongoing immune response. Thus, the absence of
B7-1 up-regulation in lymph nodes may preserve these sites for
promoting immune responses to incoming Ags, whereas local sites of
inflammation and the spleen may be involved, not only in the initial
promotion of inflammation, but also the active modulation of an ongoing
response. The exacerbating effect of anti-B7-1 mAb treatment on NOD
mice and on ongoing EAE (23, 25) could be partially due to inhibition
of B7-1-mediated down-regulation. However, it is clear that B7-1 can
also serve as a positive costimulator of CD28-mediated signals. For
example, intact anti-B7-1 inhibited EAE induction (9), while
anti-B7-1 F(ab) treatment was shown to prevent disease relapses
(16). In addition, B7-1 is the dominant costimulatory ligand for in
vitro activation of primed PLP139–151-specific T cells, which express
low levels of CTLA-4 (Figs. 6 and 7). Thus, B7-1/CTLA-4-mediated
down-regulation probably depends on the site and timing of expression
of these molecules. Additional studies in other disease models where
B7-1 up-regulation is not sustained throughout the disease course may
be helpful in resolving the mechanisms behind these opposing functions.
It is also possible that B7-1-expressing T cells may be responsible for
regulatory T cell-T cell interactions as there is evidence that
engagement of this costimulatory molecule may lead to direct signaling
of these cells (25, 39).
In summary, during the course of R-EAE, an inflammatory Th1-mediated autoimmune disease, there is an enhancement of B7-1 expression (and function), relative to B7-2, at the site of inflammation and in the splenic environment. In contrast, the lymph node environment maintains a B7-2-predominant phenotype. This dichotomy in the B7-1/B7-2 costimulatory phenotype of different lymphoid microenvironments may reflect their diverging roles during the course of an immune response. Further insight into the functional role of differential regulation of costimulatory ligands in the modulation of immune responses would be a very important step toward the development of rational therapeutic strategies for autoimmune diseases.
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Footnotes |
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3 Address correspondence and reprint requests to Dr. Stephen D. Miller, Department of Microbiology-Immunology, Northwestern University Medical School, 303 East Chicago Avenue, Chicago, IL 60611. E-mail address:
4 Abbreviations used in this paper: R-EAE, relapsing-remitting experimental autoimmune encephalomyelitis; PLP, proteolipid protein; CNS, central nervous system; NOD, nonobese diabetic; MFI, mean fluorescence intensity shift.
Received for publication January 9, 1998. Accepted for publication March 3, 1998.
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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 D. Odobasic, A. R. Kitching, T. J. Semple, J. R. Timoshanko, P. G. Tipping, and S. R. Holdsworth Glomerular Expression of CD80 and CD86 Is Required for Leukocyte Accumulation and Injury in Crescentic Glomerulonephritis J. Am. Soc. Nephrol., July 1, 2005; 16(7): 2012 - 2022. [Abstract] [Full Text] [PDF]
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 A Davidson, B Diamond, D Wofsy, and D Daikh Block and tackle: CTLA4Ig takes on lupus Lupus, March 1, 2005; 14(3): 197 - 203. [Abstract] [PDF]
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S. Hussain and T. L. Delovitch Dysregulated B7-1 and B7-2 Expression on Nonobese Diabetic Mouse B Cells Is Associated with Increased T Cell Costimulation and the Development of Insulitis J. Immunol., January 15, 2005; 174(2): 680 - 687. [Abstract] [Full Text] [PDF]
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D. Yadav, V. Judkowski, M. Flodstrom-Tullberg, L. Sterling, W. L. Redmond, L. Sherman, and N. Sarvetnick B7-2 (CD86) Controls the Priming of Autoreactive CD4 T Cell Response against Pancreatic Islets J. Immunol., September 15, 2004; 173(6): 3631 - 3639. [Abstract] [Full Text] [PDF]
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A. Monsonego, J. Imitola, V. Zota, T. Oida, and H. L. Weiner Microglia-Mediated Nitric Oxide Cytotoxicity of T Cells Following Amyloid {beta}-Peptide Presentation to Th1 Cells J. Immunol., September 1, 2003; 171(5): 2216 - 2224. [Abstract] [Full Text] [PDF]
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M. Srinivasan, I. E. Gienapp, S. S. Stuckman, C. J. Rogers, S. D. Jewell, P. T. P. Kaumaya, and C. C. Whitacre Suppression of Experimental Autoimmune Encephalomyelitis Using Peptide Mimics of CD28 J. Immunol., August 15, 2002; 169(4): 2180 - 2188. [Abstract] [Full Text] [PDF]
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 B. Salomon, L. Rhee, H. Bour-Jordan, H. Hsin, A. Montag, B. Soliven, J. Arcella, A. M. Girvin, S. D. Miller, and J. A. Bluestone Development of Spontaneous Autoimmune Peripheral Polyneuropathy in B7-2-deficient NOD Mice J. Exp. Med., September 4, 2001; 194(5): 677 - 684. [Abstract] [Full Text] [PDF]
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C. Tanchot, D. L. Barber, L. Chiodetti, and R. H. Schwartz Adaptive Tolerance of CD4+ T Cells In Vivo: Multiple Thresholds in Response to a Constant Level of Antigen Presentation J. Immunol., August 15, 2001; 167(4): 2030 - 2039. [Abstract] [Full Text] [PDF]
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L. D. Hazlett, S. McClellan, R. Barrett, and X. Rudner B7/CD28 Costimulation Is Critical in Susceptibility to Pseudomonas aeruginosa Corneal Infection: A Comparative Study Using Monoclonal Antibody Blockade and CD28-Deficient Mice J. Immunol., January 15, 2001; 166(2): 1292 - 1299. [Abstract] [Full Text] [PDF]
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Y. Katz-Levy, K. L. Neville, J. Padilla, S. Rahbe, W. S. Begolka, A. M. Girvin, J. K. Olson, C. L. Vanderlugt, and S. D. Miller Temporal Development of Autoreactive Th1 Responses and Endogenous Presentation of Self Myelin Epitopes by Central Nervous System-Resident APCs in Theiler's Virus-Infected Mice J. Immunol., November 1, 2000; 165(9): 5304 - 5314. [Abstract] [Full Text] [PDF]
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