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T Cell Subset, Which Is Found in Large Numbers in the Spleen, Accumulates Inefficiently in an Artificial Site of Inflammation: Correlation with Lack of Expression of E-Selectin Ligands and L-Selectin1
Department of Veterinary Molecular Biology, Montana State University, Bozeman, MT 59717
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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T
cells has been widely reported; however, the mechanisms responsible for
this phenomenon are poorly understood. We describe a bovine T
cell TCR-associated subset that preferentially localizes in the spleen.
This subset was characterized by coexpression of CD8, and was found to
lack surface expression of E-selectin ligands, GR Ag ligands, as well
as low expression of L-selectin. The CD8-positive T cell subset
did not accumulate at sites of inflammation as efficiently as
CD8-negative T cells that, in contrast, express E-selectin and
GR ligands and high levels of L-selectin. This is the first
demonstration of a T cell subset, which exhibits a defined
tissue tropism, having a unique adhesion molecule expression profile.
These results demonstrate that in some cases tissue-specific
accumulation of T cell subsets can be predicted by expression,
or lack of expression, of defined homing
molecules. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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T cells,
there are many aspects of this population that are still poorly
understood. One intriguing attribute, which has come from studies in
mice and humans, is that discrete subsets of T cells, defined by
their TCR usage, specifically accumulate in certain tissues and organs
of the body. For example, mouse T cells associated with
epidermis (1, 2) and the mucosal epithelia of vagina, uterus, and
tongue (3) utilize a TCR repertoire consisting of distinct pairs of
and gene products. What accounts for this TCR-restricted,
tissue-specific T cell accumulation is not known. One study
suggests that some T cell subsets exhibit subtle differences in
the expression of homing and recruitment-associated molecules (4); yet,
the in vivo relevance of these observations has not been shown.
Ideally, to evaluate recruitment mechanisms, circulating cells should
be examined. This is technically difficult in mice, because of small
blood volume, and in adult humans, due to their minimal number of
T cells (5). In contrast to mice and humans, other animals, such
as young cattle, have very high numbers of T cells in
circulation that are easily isolated for study (6, 7, 8). Furthermore,
newborn calves can be used, thus minimizing complications that follow
antigenic stimulation of T cells, such as the generation of
activated/memory cells. The shortcomings in studying bovine T
cells are 1) reagents defining subsets based on TCR usage are only now
being developed, and 2) until recently, there has been no evidence that
bovine T cell subsets exhibit differential tissue tropism. These
shortcomings have recently been addressed. For example, it has been
shown that bovine T cells can be divided into subsets based on
TCR usage, as well as by the expression of other surface markers, and
that at least some of these subsets differentially accumulate in
certain tissues (9, 10, 11, 12). Specifically, a TCR-associated population,
which is also characterized by CD2 and CD8 coexpression, is a minor
subset of circulating cells, but is the predominant population in the
spleen (10, 12).
We have shown previously that most circulating bovine T cells
avidly bind selectins (13): molecules important in the initial step of
migration into a variety of tissues, such as skin, lymph nodes, and
Peyer’s patches (14, 15, 16). There have been no reports suggesting that
selectins are important in the accumulation of T cells in the spleen.
In this study, we show that the circulating T cell subset
defined by CD8 coexpression accumulates inefficiently in an
extralymphoid site of inflammation, whereas CD8-negative T cells
do. The lack of accumulation to inflammatory tissue correlates with the
inability of this subset to bind E-selectin and the recently described
bovine GR Ag. This subset is also deficient in L-selectin. This
constitutes the first demonstration of a T cell subset, which
exhibits a defined tissue tropism, having a unique adhesion molecule
expression profile.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Holstein calves were purchased from local producers and housed at the Montana State University Large Animal Facilities at the Veterinary Molecular Biology Laboratory (Bozeman, MT). Bovine tissue samples were collected from animals upon necropsy.
Reagents
IL-A29 (American Type Culture Collection, Manassas, VA) is a
mouse mAb that recognizes all molecularly characterized members of the
Workshop Cluster 1 (WC1) family (17). GD3.8, GD197, and GD3.1 are
anti-TCR mouse mAbs that define four bovine T cell subsets
(12). GD3.5 is a mouse mAb that recognizes a lineage-specific
molecule found on more than 90% of circulating bovine T cells
(18). GR284 is a mouse mAb that binds to the GR Ag, similar to the
previously described GR113 (19). DREG 56 is a mouse mAb against human
L-selectin that cross-reacts with bovine L-selectin (20). CC58
(anti-CD8) and CC42 (anti-CD2) (21) are mouse mAbs provided by
Chris Howard (Institute for Animal Health, Compton, U.K.).
PE3-conjugated anti-human
IgG, PE- and FITC-conjugated anti-mouse IgG (Jackson
ImmunoResearch, West Grove, PA), and avidin-conjugated CyChrome
(PharMingen, San Diego, CA) were used. Porcine E-selectin chimera
(P11.4) was kindly provided by M. Robinson (Celltech Therapeutics,
Berkshire, U.K.) and used as previously described (22). EL86.10
is a mouse mAb that binds human E-selectin and was used as an
isotype-matched, negative control.
Lymphocyte preparation, E-selectin-binding assays, and flow-cytometric analysis
Peripheral blood was collected into sodium heparin anticoagulant
tubes by venipuncture, and PBMC were purified by Ficoll-Hypaque (Sigma,
St. Louis, MO) gradient centrifugation. In some assays, purified
mononuclear cells were incubated for 30 min at 37°C in T175 flasks
containing DMEM to remove monocytes. The nonadherent lymphocyte
population was washed in HBSS before use in the functional and
flow-cytometric assays. Two approaches were used to measure E-selectin
binding, as described in previous reports (13, 22). Briefly, in the
first method, the adhesion of bovine lymphocytes to E-selectin
cDNA-transfected mouse L cells was measured (13). This assay has been
well characterized, and lymphocyte binding has been shown to be
specifically mediated via the transfected E-selectin molecule, with
minimal lymphocyte binding to nontransfected control cells (13). In
this method, E-selectin-binding cells were purified from whole
lymphocyte preparations by incubation in T175 flasks coated with 7
x 106 adherent E-selectin cDNA L cell transfectants.
Unbound cells were discarded, and bound lymphocytes were released by
treatment with 2 mM EDTA/PBS (13). The procedure was then repeated a
second time, and samples of cells before the adhesion steps and after
each EDTA/PBS wash were analyzed by flow cytometry. In our second
approach, a E-selectin/Ig chimera was used in flow-cytometric assays to
study the phenotype of the selectin-binding population (22). In
previous studies, we showed that a porcine E-selectin/human IgG chimera
worked well in flow-cytometric assays of bovine T cells (22). In
this assay, PBL were incubated for 1 h on ice with supernatant
fluids from CHO transfectants producing the E-selectin chimera. Binding
of the chimera was revealed by a PE-labeled anti-human IgG
second-stage Ab. Specificity controls have included irrelevant chimeras
(human CD4/Ig), EDTA treatment, and function-blocking mAbs to reverse
or block chimera binding (22, 23). In this study, chimera binding was
combined with three-color flow-cytometric analysis, as described below.
GR Ag binding of T cells was determined by incubating PBMC in
platelet-derived, soluble GR Ag, as previously described (19). Briefly,
bovine platelets were collected and activated with thrombin for 4
h at 37°C, debris was removed by high speed centrifugation, and the
clarified supernatant fluid was used as a source of GR Ag. Bovine PBMC
were incubated in platelet supernatant fluid for 30 min at 37°C.
After the incubation period, the treated leukocytes were washed and
stained for flow-cytometric analysis to detect bound GR Ag and
determine the phenotype of the binding population.
Flow-cytometric analysis was performed as follows. Single-color
analyses were done with the mAb reagents and E-selectin chimera, as
previously described (22). The following procedure was followed for
three-color flow-cytometric analysis of cells. Bovine PBMC were
resuspended in HBSS containing Ca2+Mg2+
(HBSS-Ca2+Mg2+) at 1 x 107
cells/ml. Biotin-labeled GD3.8 (anti-pan T cell mAb) was
added along with the E-selectin chimera. The cells were incubated on
ice for 1 h, washed in PBS containing 5% horse serum (PBS-HS),
and resuspended in HBSS-Ca2+Mg2+. The cells
were then incubated with FITC-conjugated anti-CD8, avidin-CyChrome,
and PE-labeled anti-human IgG (preabsorbed and exhibiting minimal
reactivity with bovine and mouse Ig). After 30 min on ice, the cells
were washed in PBS-HS and then analyzed using a BD
FACSCalibur (Becton Dickinson Immunocytometry Systems,
Mountain View, CA). FL1 (FITC), FL2 (PE), and FL3 (CyChrome) detectors
were used, and the FACSCalibur was calibrated using Calibright beads
(Becton Dickinson). Compensation was set manually using single-color
stains of the various fluorochromes. In assays in which it was
necessary to analyze small subsets of cells, live gate acquisition was
utilized to acquire sufficient cell numbers for statistical analysis.
Data from up to 20,000 cells were acquired and reported in
two-dimensional dot plots or histograms. Negative controls included 1)
single-color stains, 2) irrelevant isotype-matched Ab stains, and 3)
second-stage reagent controls. Experiments were done to ensure that the
anti-human Ig second-stage reagents did not cross-react with the
mouse mAbs and that the CyChrome second-stage reagent was specific for
the biotin-labeled GD3.8 mAb. Marker placement, for statistical
analysis, was determined by placing the marker outside the upper limit
of background staining of control Abs. We found no evidence that the
CyChrome reagent bound nonspecifically, as previously described for
some reagents conjugated to this fluorochrome (24, 25).
Generation of inflammatory populations of bovine lymphocytes
Experiments were conducted to determine the phenotype of
T cells that entered an extralymphoid site of inflammation. The
following method was used to generate a fluid-phase inflammatory
population of leukocytes, which could be easily sampled and analyzed by
flow cytometry. Briefly, plastic balls (4 cm diameter) with multiple
holes (wiffle balls) were sterilized by autoclaving and surgically
inserted under the dermis of 1-mo-old calves. The balls rapidly became
encapsulated within 1 wk, and for the next 3 wk the center of the balls
remained as a fluid that could be sampled by a hypodermic needle and
syringe. To induce an overt leukocyte response in the wiffle balls, PHA
alone (250 µg/ml), a PHA-stimulated lymphocyte supernatant fluid, or
LPS (10 µg/ml) was injected into the fluid-filled balls 10 days
postsurgery. Fluid was withdrawn from the site 24 h following
injection of the inflammatory agents. Previous studies have shown that
this method leads to the accumulation of all leukocyte types, including
T cells, into the inflammatory site (E. Wilson, unpublished
results). PBMC in the fluid were separated by centrifugation through
Ficoll-Hypaque and analyzed by flow cytometry.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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T cell subset
Previous studies, including our own, have shown that the major
population of T cells in the bovine spleen express CD8 and CD2
(10, 12), whereas these markers are found on only a minor subset of
T cells in the blood (ranging from 2–31%, mean 
5%). We have also characterized mAbs against TCRs that help
further define this population of cells (12). As shown in Fig. 1
, the majority of GD3.1 and GD197 (TCR
subset-specific anti- T cell mAbs) staining cells did not
coexpress CD8. However, 
50% of the GD197- and GD3.1-negative
T cells expressed CD8. Thus, most of these cells have a unique TCR
profile. The CD8+ T cells also expressed CD2, but
lacked expression of the putative homing molecules WC1 and GD3.5 (Fig. 2). For simplicity, this unique subset of
T cells will be referred to as CD8+ T cells
throughout the rest of this work.
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T cells do not accumulate in appreciable
numbers at sites of inflammation
To determine whether CD8+ T cells accumulate in
inflammatory tissues, plastic wiffle balls were inserted under the skin
of a calf and allowed to become encapsulated, and then inflammatory
reactions were induced with PHA, a PHA/lymphocyte supernatant fluid, or
LPS, as described in Materials and Methods. The advantage of
this method is that the center of the ball remains fluid, and can be
sampled with a hypodermic needle and syringe and the cells stained for
multicolor flow-cytometric analyses, which is required to identify
CD8+ T cells in a mixed population. Phenotypic
analyses of the T cells in inflammatory lesions showed that the
frequency of CD8+ T cells was far more in the
peripheral blood (Fig. 3A)
than in the inflammatory fluid (Fig. 3B). These results show
that CD8+ T cells have a greatly reduced capacity to
enter into these artificial sites of inflammation. Perhaps just as
dramatic, T cells that lacked CD8 were preferentially found in
the inflammatory site. Thus, the accumulation patterns of two different
T cell subsets correlate with either expression of or lack
of CD8.
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T cell subset does not bind E-selectin
or GR Ag and has low expression of L-selectin
E- and L-selectin are adhesion molecules important in directing
lymphocytes to lymph nodes and sites of inflammation. L-selectin is
expressed by the lymphocyte, whereas E-selectin is expressed by
endothelial cells. In previous studies, we found that up to 90% of the
circulating T cells in most calves avidly bind E-selectin and
are L-selectin positive (13, 26). The GR Ag is expressed on chronically
inflamed endothelium and bovine platelets, and is believed to function
as a homing molecule for bovine T cells, the majority of which
express ligands for GR Ag (19). Experiments were performed to determine
whether the inability of CD8+ T cells to accumulate
in inflammatory lesions correlated with a lack of expression of
L-selectin or interactions with E-selectin and the GR Ag.
We used two approaches to examine the binding interaction of T
cells with E-selectin. In the first assay, mixed populations of bovine
lymphocytes were sequentially passed over monolayers of
E-selectin-transfected L cells. After each adhesion step, the
monolayers were washed to remove nonadherent cells, and the adherent
cells were released for flow-cytometric analysis by incubation in
EDTA/PBS to reverse the selectin-mediated binding event. The frequency
of CD8+ T cells was reduced dramatically after only
one adhesive interaction with monolayers of E-selectin-expressing L
cells, and then remained constant during successive adhesion steps
(Fig. 4). Reciprocal experiments were
also done to determine whether nonadherent cells were enriched for
CD8+ T cells. Mixed populations of bovine lymphocytes
were sequentially passed over monolayers of E-selectin-transfected L
cells, and the nonadherent cells were collected after each round of
binding. As expected, these experiments produced a cell population
enriched for CD8+ T cells (data not shown). This
suggested that the majority of CD8+ T cells did not
bind E-selectin, whereas CD8- T cells did bind.
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T cell-specific mAbs, and anti-CD8 was then done to directly
examine the phenotype of the E-selectin-binding population.
CD8+ T cells represented a minor population in the
peripheral blood (5% of the total T cell pool).
Interestingly, few of these cells were stained by the E-selecting/Ig
chimera, whereas most of the CD8- T cells were
stained (Fig. 5A). Pooled data
from multiple experiments show a significant difference in the capacity
of CD8+ versus CD8- T cells to bind
E-selectin (Fig. 5B).
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T cells to sites of inflammation. Three-color
analysis was done to determine the expression of L-selectin on
CD8+ and CD8- T cells, as well as the
ability of these cells to bind the GR Ag. Heterogeneous expression of
L-selectin was observed on CD8+ T cells; the majority
of these cells expressed no or minimal amounts of L-selectin.
Conversely, L-selectin expression was uniformly high on
CD8- T cells (Fig. 6A). Analysis of GR Ag
ligands, via an assay in which lymphocytes bind soluble GR Ag, showed
that the GR Ag binding follows the same general pattern as L-selectin
expression. These results indicate that very few CD8+
T cells expressed GR Ag ligands, whereas CD8- T
cells showed high expression of the ligands (Fig. 6B).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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T cells is their unique
tissue tropism. Like human and murine T cells, bovine T
cells can be separated into TCR-defined subsets that selectively
accumulate in certain tissues (9, 10, 11, 12). In this study, we show that
CD8+ bovine T cells, which are found in large
numbers in the spleen, do not accumulate in appreciable numbers in
sites of inflammation. In contrast, bovine T cells that lack CD8
selectively accumulate at these sites.
Two molecular mechanisms could account for this selective tissue
accumulation: selective retention and proliferation or selective
recruitment. To date, there have been few examples supporting either
possibility in the context of tissue-specific T cell
accumulation. To enter a tissue, a leukocyte follows a multistep
process that involves initial recognition of the vascular endothelium,
followed by rolling along the vessel wall, tight adhesion and stopping,
and eventually transendothelial migration (27). Adhesion molecules
expressed by the T cell and endothelium regulate each of these steps.
Members of the selectin family of adhesion molecules, which includes
L-selectin on leukocytes, E-selectin on endothelium, and P-selectin on
endothelium and platelets, are important in regulating rolling
interactions. Recently, we defined another molecule, GR Ag, that is
expressed by chronically activated endothelial cells and supports
rolling of different leukocyte subsets (19). We have not yet confirmed
whether the GR Ag is a new molecule or a different form of a previously
characterized molecule.
Bovine T cells avidly bind E-selectin, P-selectin, and
the GR Ag, and these interactions are thought to be important in
regulating the entry of these cells into different inflammatory lesions
(13, 19, 23). T cells also express L-selectin. Leukocyte
L-selectin is important in the homing of lymphocytes to lymph nodes
(20, 28), and in the trafficking of neutrophils and other leukocytes to
sites of inflammation (29, 30, 31). Interestingly, L-selectin is expressed
at 3–5 times the level on the majority of T cells as compared
with other lymphocytes (26), where it is localized at the tips of
microvilli and mediates both binding to endothelium in lymph nodes and
other immobilized T cells (32, 33).
In this study, we show that CD8+ T cells in
bovine blood have a greatly diminished capacity to bind to E-selectin
and soluble GR Ag. In our first analysis, CD8+ T cell
binding to cell surface-expressed E-selectin was measured. In our
second approach, we measured the binding of soluble E-selectin chimera
to the T cell by flow cytometry. The first approach is more
physiologically relevant, since E-selectin mediates cell-cell binding.
However, this assay cannot distinguish between a lack of ligand or
simply reduced expression of ligand below the threshold needed to
support cell-cell binding. The flow-cytometric assay measured
quantitative differences in ligand expression, and from these studies
we found that the majority of the CD8+ T cells
totally lack the capacity to bind E-selectin, suggesting that they
simply do not express E-selectin ligands. Flow cytometry also confirmed
that these cells lack ligands for soluble GR Ag.
E-selectin is a lectin that binds carbohydrate ligands on
target cells (34). It is likely that the GR Ag is a lectin as well
(19). Selectin-binding carbohydrates are modified to their functional
form by fucosyltransferases, enzymes that catalyze the final step in
ligand synthesis (35, 36). Therefore, lack of selectin binding could be
due to lack of the appropriate carbohydrates or the protein backbone
they are found on. Analysis of selectin-binding carbohydrates on bovine
cells is not straightforward, since reagents that recognize human
ligands (HECA 452, for example) do not cross-react with bovine
counterparts. However, we are in the process of sorting enough
CD8+ and CD8- T cells to analyze mRNA
for specific fucosyltransferases that are required to construct
selectin carbohydrates, an approach that is beyond the scope of this
initial study.
We have partially characterized a glycoprotein on T cells, which
is decorated by appropriate carbohydrates and binds E-selectin, using
the E-selectin chimera described in this work (22). The
E-selectin-binding glycoprotein is 250 kDa, but we have not yet
generated specific mAbs against the protein portion, thus we cannot
address whether it is lacking on the CD8+ T cells.
However, our data strongly support the possibility that the protein
backbone of the ligand could be missing. Strikingly,
CD8+ T cells are not stained by mAbs directed against
a number of different large molecular mass surface glycoproteins. For
example, these cells lack WC1 (Mr 180–210 kDa),
GD3.5 Ag (Mr 230 kDa), and L-selectin
(Mr 90 kDa). Although we have no evidence that
any of these molecules bind E-selectin or GR Ag (22), it may be that
the expression of the protein component of the selectin ligand is
regulated in a similar fashion.
Although bovine CD8+ T cells lack certain Ags, it is
important to point out that it is a very selective deficiency. For
example, these cells express the functionally important CD18
(Mr 90 kDa), CD5 (Mr 67
kDa), CD44 (Mr 90 kDa) (E. Wilson, unpublished
results), and CD2 (Mr 45–58 kDa) (10) Ags, in
addition to CD8. Thus, CD8+ T cells exhibit a unique
pattern of gene expression, differing from other T cells in the
expression of several proteins, including molecules important in
leukocyte recruitment.
It is not known whether this unique adhesion molecule phenotype of
CD8+ T cells is developmentally or environmentally
regulated. Work in mice has shown two different lineages of T
cells, one passing through the thymus and the other originating in the
gut and comprising the majority of intraepithelial lymphocytes (37, 38). In the mouse, gut-derived T cells express CD8; however,
unlike the CD8
ß heterodimer expressed on thymically derived T
cells, the gut-derived CD8 cells express the CD8 homodimer (39).
These cells have been shown to play an important role in protection
against gut pathogens (40). In contrast, bovine CD8+
T cells express the CD8ß heterodimer (41). These CD8ß
T cells may represent yet another lineage of T cells, or could
possibly represent the bovine lineage equivalent to the mouse CD8
T cell. If CD8+ T cells do represent a
separate lineage of cells, they may never express high levels of
L-selectin or GR Ag and E-selectin ligands, as seen on
CD8- T cells. Conversely, some T cells may
respond to environmental stimuli that induce changes in gene regulation
of some surface proteins. It may be that the expression of CD2 or CD8
genes in T cells correlates with the suppression of E-selectin
ligand and L-selectin, as well as WC1 gene transcription.
What accounts for the preferential accumulation of
CD8+ T cells in the spleen is still not understood.
Immunohistologic studies show that the CD8+ T cells
are selectively localized to the splenic red pulp (10). To date, there
is no evidence for a role of selectins in the homing of T cells to the
spleen. In fact, studies in L-selectin-deficient mice have shown that
the spleen of these mice contain more lymphocytes than their wild-type
littermates (42). E- and P-selectin-deficient mouse studies have
reported similar results, showing no decrease in the number of splenic
lymphocytes (43, 44). Human studies have also shown a population of
splenic lymphocytes that do not express L-selectin (45). Thus, a lack
of expression of L-selectin and selectin ligands does not inhibit
migration to the spleen.
T cells can enter the spleen via two routes: migration across vessels
in the marginal zone or accumulation via blood in the red pulp of the
spleen (46). Potentially, all T cells enter the spleen by one or
both of these routes; however, the CD8+ T cells
remain in the spleen, whereas the CD8- T cells may
rapidly reenter the circulation. Support for this possibility has come
from experiments in which we have examined the homing of bovine
T cells in mice. When bovine T cells are injected into the
circulatory system of mice, they exhibit the same pattern of tissue
distribution as they do in cattle, i.e., few cells in lymph nodes
versus many in the spleen (26). This xenogeneic system, although
clearly artificial, allows one to test whether selective recruitment of
CD8+ T cells occurs in the spleen. In short-term
homing assays, we have been unable to detect any preferential homing of
bovine CD8+ T cells to the mouse spleen (data not
shown). It may very well be that homing to bovine spleen is regulated
differently, or that there is not sufficient homology between mouse and
bovine to support the splenic homing of CD8+ T cells.
If selective localization of CD8+ T cells to the
spleen does occur, it may be mediated through integrin-associated
adhesion, or by yet uncharacterized adhesion molecules.
Work by Haru-Hisa et al. (47) has recently proposed a functional role
for the WC1 molecule demonstrating that cross-linking WC1 induces a
reversible G0/G1 growth arrest. This cell cycle
arrest is mediated via reduced expression of the transcription factor
E2F1 (48), apparently resulting in cell cycle arrest through the
interruption of the IL-2 signaling pathway (49). IL-2 mediates cell
proliferation via the high affinity IL-2R found on activated, but not
resting T cells (50). Considering these results, it is possible that
an, as of yet, unidentified WC1 ligand binds splenic
WC1+ T cells, resulting in
G0/G1 growth arrest of IL-2-responsive
CD8- T cells. Conversely, IL-2-responsive
CD8+ T cells, which do not express WC1, would not
undergo cell cycle arrest, and proliferate in response to IL-2
signaling. This scenario would explain the large numbers of
CD8+ T cells compared with CD8- T
cells found in the spleen, through the selective expansion of
WC1- T cells. Work is currently underway to analyze the cell
cycle phase of blood and spleen WC1+ and WC1- T cells
to better determine whether the splenic microenvironment results in a
G1/G0 growth arrest of WC+.
In summary, we provide a clear example of tissue-specific T cell
subset accumulation correlating with a functional adhesive phenotype.
T cell, TCR subset-defined localization has been well documented
and intensively studied. However, previous reports have not
demonstrated a defined adhesive phenotype correlating to the
localization of these cells in vivo. Our data demonstrate that T
cells expressing GR Ag ligands, E-selectin ligands, and L-selectin, but
lacking CD8 specifically accumulate at sites of inflammation.
Conversely, the homing and/or retention mechanisms responsible for the
accumulation of CD8+ T cells in the spleen are still
unclear. The lack of or low expression of defined homing molecules on
these cells, including E-selectin ligands, GR Ag ligands, and
L-selectin, suggests that these molecules are not involved in the
selective accumulation of CD8+ T cells to the spleen.
This combined with studies showing the WC1 molecule to be involved in
mediating cell cycle arrest suggests that CD8+ T cell
localization may be due at least in part to selective expansion of this
subset in the spleen. This potential selective expansion may also be
combined with selective retention and/or selective homing via as of yet
unidentified homing molecules.
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Acknowledgments |
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Mark A. Jutila, Department of Veterinary Molecular Biology, Montana State University, Bozeman, MT 59717. E-mail address:
3 Abbreviation used in this paper: PE, phycoerythrin.
Received for publication October 13, 1998. Accepted for publication January 28, 1999.
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