The Journal of Immunology, 1998, 161: 1231-1238.
Copyright © 1998 by The American Association of Immunologists
L-Selectin-Specific Autoantibodies in Murine Lupus: Possible Involvement in Abnormal Homing and Polarization of CD4+ T Cell Subsets1
Susumu Hattori*,
Hiroyuki Nishimura*,
,
Hiromichi Tsurui*,
Masayuki Kato
,
Naoki Endo
,
Masaaki Abe*,
Shin Akakura*,
Kenichi Mitsui*,
Sho Ishikawa*,
Sachiko Hirose* and
Toshikazu Shirai2,*
*
Department of Pathology, Juntendo University School of Medicine, Hongo Bunkyo-ku, Tokyo, Japan; and
Toin Human Science and Technology Center, Toin University of Yokohama, Kurogane-cho, Aoba-ku, Yokohama.
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Abstract
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One notable functional abnormality in murine and human systemic
lupus erythematosus (SLE) is the defect in the production of IL-2 in
association with the deficit in naive CD4+ T cells. The
mechanism is unknown, but one idea is that naturally occurring
autoantibodies with specificities to the naive CD4+ T cell
subpopulation are related to this event. We selected hybridoma
monoclonal autoantibodies from SLE-prone (New Zealand Black (NZB) x
New Zealand White (NZW))F1 mice that reacted with
restricted populations of CD4+ T cells. One of these, H32,
was specific for L-selectin, as determined by 1) distribution of Ag H32
on lymphoid cells similar to Mel-14, an epitope of L-selectin; 2)
shedding of 80-kDa molecules with epitope H32 from the surface of lymph
node cells coincidentally with Mel-14, when stimulated with phorbol
ester; 3) cross-inhibitory activities on Ag binding between H32 and
Mel-14; and 4) reactivity of H32 with recombinant mouse L-selectin.
Pretreatment of 51Cr-labeled lymphocytes from BALB/c mice
with H32 significantly inhibited their homing to lymph nodes in vivo.
The BALB/c splenic H32+ CD4+ T cell subset
produced few cytokines except IL-2, thus corresponding to naive
ThP-type cells. This subset was markedly selectively depleted in aged
(NZB x NZW)F1 mice. There was an age-associated
increase in frequencies and titers of anti-L-selectin
autoantibodies in sera from (NZB x NZW)F1 mice. Thus,
abnormalities of naive CD4+ T cell subset, including IL-2
production in subjects with SLE, are at least partly attributed to the
generation of autoantibodies to L-selectin.
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Introduction
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Varieties
of
anti-lymphocyte autoantibodies are present in sera from the great
majority of patients with systemic lupus erythematosus
(SLE)3 as well as in murine
lupus (1, 2). Although the significance of anti-lymphocyte
autoantibodies in SLE is still unclear, their association with clinical
indexes and immune dysregulation characteristic of this disease
suggests their relationship to immune system functional abnormalities
in patients with SLE (3, 4, 5). Potential mechanisms by which these
autoantibodies could alter immune system functions include immune
elimination of target lymphocytes either by killing or by altering
their pattern of migration and modulation of functioning molecules on
the lymphocyte surface by promoting shedding or capping (1).
One notable functional abnormality of peripheral CD4+ T
cells found in murine lupus is the defect in the production of IL-2
(6, 7, 8). In SLE-prone BXSB male mice, the age-associated decreases in
IL-2 production and in the message transcription by CD4+ T
cells are associated with the decrease in the number of
CD4+ T cells that phenotypically corresponds to naive
CD4+ T cells (9). Development of florid SLE in (NZB x
NZW)F1 female mice is associated with the deficit in the
production of and responsiveness to IL-2 by T cells (6, 7, 8) and with a
marked decrease in the number of CD4+ T cells positive for
CD45RC, an alternative exon 6-dependent epitope of CD45 (10). Upon in
vitro polyclonal stimulation in normal healthy mice, this
CD45RC+ CD4+ T cell subset produces few
cytokines except IL-2, hence corresponding to naive ThP-type cells.
The pathogenesis of the selective depletion of ThP-type cells is
unknown. One idea is that naturally occurring autoantibodies with
specificities to the ThP-type naive CD4+ T cell subset may
be responsible, because a variety of anti-T cell autoantibodies,
some with distinct and restricted specificities, are produced in murine
lupus (11, 12, 13, 14, 15, 16, 17). In patients with SLE, naturally occurring
autoantibodies to isoforms of CD45 molecules (leukocyte common Ags)
were identified (18). Since the epitopes on alternative structures of
CD45 isoforms such as CD45RA, alternative exon 4-dependent epitope, in
humans and CD45RC in mice serve as markers for naive CD4+ T
cells (9, 19), we speculated that such autoantibodies may be
responsible for the ThP-type cell abnormality. Alternatively,
autoantibodies to other cell surface structures preferentially
expressed on ThP-type cells may be involved. Our studies indicate that
in (NZB x NZW)F1 mice, there exists a type of
autoantibody specific for L-selectin (CD62L), a homing receptor of
lymphocytes, which is preferentially expressed on ThP-type naive
CD4+ T cells. This has the potential to prevent the homing
of lymphocytes, a finding that implicates the role of this type of
autoantibodies for the age-associated selective decrease in ThP-type
naive CD4+ T cells in (NZB x NZW)F1 mice.
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Materials and Methods
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Mice
BALB/c and (NZB x NZW)F1 mice were originally
obtained from Shizuoka Laboratory Animal Center (Shizuoka, Japan) and
were maintained in the animal facilities at Juntendo University (Tokyo,
Japan).
Monoclonal Abs
The mAbs JH6.2 (anti-CD45RC) (10) and NTA260 (16) were
developed as previously described. Other mAbs used were anti-CD4
(GK1.5, Becton Dickinson, Mountain View, CA), Mel-14
(L-selectin-specific rat IgG mAb), anti-IFN
(PharMingen, San
Diego, CA), anti-B220 (6B2) (20), anti-CD3 (2C11) (21),
anti-CD25 (PC-61 and 3C7) (22, 23), anti-IL-4 (11B11) (24) and
anti-IL-10 (provided by Dr. H. Ishida, Kyoto University, Kyoto,
Japan). Two IgM mAbs originated from an 8-mo-old female (NZB x
NZW)F1 mouse (clones HOG.10 and ROB.8) with unknown
specificity were used for control studies. A mouse IgM mAb (clone
3H2.10) derived from a BALB/c mouse and a rat IgG mAb (clone 5.1.9)
from a Lewis rat were also used for control studies. These two mAbs
were of unknown specificity and did not react with lymphoid cells from
mice and rats, as determined by flow cytometric analyses. Hybridoma
mAbs against murine T cells were produced by fusing spleen cells from
an 8-mo-old female (NZB x NZW)F1 mouse that produces
a high serum level of naturally occurring autoantibodies against
thymocytes with P3X63-Ag8-653 myeloma cells, as described by Oi and
Herzenberg (25). Two weeks after the initiation of culture,
supernatants were screened by complement-dependent cytotoxicity test
and flow cytometric analysis for reactivity to thymocytes and spleen
cells from young BALB/c mice.
Flow cytometric analysis
Lymphocytes (1 x 106) were stained with an
appropriate amount of biotinylated mAb, followed by either
FITC-conjugated or phycoerythrin (PE)-conjugated streptavidin. For
two-color analysis, cells were incubated with biotinylated mAb 1 and
FITC-conjugated mAb 2, followed by PE-conjugated streptavidin. Flow
cytometric analysis and cell sorting were performed using FACStar
(Becton Dickinson) and LYSYS II software (Becton Dickinson).
Bioassay for cytokine
In vitro production of IL-2 and IL-4 by CD4+ T cells
upon stimulation with immobilized anti-CD3 mAb (2C11) was measured
by proliferative responses of the HT 2 cell line, as described by
Cherwinski et al. (26). A sandwich ELISA was performed to measure mouse
IL-10 and IFN-
levels in the culture supernatants of
CD4+ T cell subsets, as previously described (27).
Recombinant mouse L-selectin/human Fc (
) chimeric protein
Poly(A)+ mRNA was isolated from spleen cells from a
2-mo-old NZB mouse and was reverse transcribed with Moloney murine
leukemia virus reverse transcriptase (Life Technologies, Gaithersburg,
MD) using a random hexamer primer, as previously described (28). A
murine cDNA encoding the lectin-, epidermal growth factor-like-, and a
part of CR domains of mouse L-selectin (29) was amplified by PCR using
a pair of oligonucleotide primers with sequences
CGGTCGACGAGGCTGAGGCTGCAGAGAGACT and GAGGATCCGATGCTCCACACTGTGTTTCTG,
in which sequences for the recognition by restriction endonucleases
SalI and BamHI, respectively, were added at the
5' termini. The amplified cDNA cleaved by these restriction enzymes was
inserted at the BamHI-SalI site of the plasmid
pSKM13+ (Stratagene, La Jolla, CA). The mouse L-selectin cDNA fragment
was isolated and subsequently ligated to a pCDrLEC-IgG vector digested
with restriction endonucleases XhoI and BamHI
(30), an expression vector for the recombinant fusion protein of the
rat L-selectin and human Ig (IgG1) constant region (provided by Dr.
Masayuki Miyasaka, Osaka University, Osaka, Japan). The resultant
vector pCDmLEC-IgG was propagated in Escherichia coli, then
transfected into COS-7 cells (31). Recombinant mouse L-selectin/human
Fc(
) chimeric protein secreted in the culture medium was purified
using a protein G-Sepharose column (Pharmacia Biotech, Uppsala,
Sweden).
Stimulation of lymph node cells with phorbol ester
Mesenteric lymph node cells from 2-mo-old BALB/c mice were
cultured in RPMI 1640 medium containing 10% FCS, 50 µM 2-ME, and
varying concentrations (0.1100 ng/ml) of PMA (Sigma, St. Louis, MO)
for 1 h at 37°C. After washing once with ice-cold PBS, cells
were subjected to flow cytometric analysis to determine the cell
surface expression of H32 and Mel-14, as described above.
Immunoblotting of soluble L-selectin
Lymph node cells (4 x 108) were cultured in 1
ml of the serum-free RPMI 1640 medium containing PMA (100 ng/ml) for 20
min at 37°C. Culture supernatant (50 µl) was subjected to
SDS-acrylamide gel electrophoresis with 2-ME, as described by Laemmli
(32). The gel was transferred electrophoretically to a Clear Blot
Membrane-P (Atto Co., Tokyo, Japan). The blotted membrane was first
incubated with biotinylated H32 (5 µg/ml), followed by alkaline
phosphatase-conjugated avidin (Vector Laboratories, Burlingame, CA).
Bands were visualized using nitro blue tetrazolium and
5-bromo-4-chloro-3-indoryl phosphate substrate solutions (Promega
Biotec, Madison, WI).
Cross-inhibition studies
Lymph node cells from 2-mo-old BALB/c mice at 1 x
106 cells/20 µl of PBS containing 0.2% BSA were
incubated first with varying concentrations of H32 (110,000 µg/ml)
or Mel-14 mAbs (151,500 µg/ml) for 30 min on ice. As
isotype-matched control mAbs for H32 and Mel-14, a mouse IgM mAb (clone
HOG.10) and rat IgG mAb (clone 5.1.9) were used, respectively.
Following incubation, 20 µl of either biotin-conjugated Mel-14 or H32
at suboptimum concentrations for staining (1 µg/ml for Mel-14 and 10
µg/ml for H32) was added, and the plates were incubated for an
additional 30 min on ice. Cells were then washed three times with PBS
containing 0.2% BSA and incubated with FITC-conjugated streptavidin
for 30 min on ice. After washing with PBS, the intensity of
immunofluorescence was measured using FACStar (Becton Dickinson).
Test for lymphocyte homing
BALB/c mouse lymph node cells were labeled with
[51Cr]sodium chromate in sterile isotonic solution
(Amersham/Searle Corp., Arlington Heights, IL), according to the method
of Bainbridge and Gowland (33). Cells in RPMI 1640 with 15% FCS were
incubated with [51Cr]sodium chromate for 30 min at 37°C
at a concentration of 0.93 MBq/108 cells. After washing
twice in medium RPMI 1640 with 15% FCS, aliquots of 5 x
106 radiolabeled cells were incubated with 0.25 ml of
pooled sera from 2-mo-old BALB/c mice, either alone (Control-1) or
together with mAb H32 or a control (NZB x NZW)F1 IgM
mAb HOG.10 that is nonreactive to murine lymphocytes (Control-2) at a
concentration of 100 µg mAb/ml for 60 min at 4°C, and the mixture
was then given i.v. to five 2-mo-old BALB/c mice. Twenty-four hours
later, the radioactivities in the blood (0.25 ml), lymph nodes
(bronchial, axillary, inguinal, and mesenteric), spleen, liver, and
thymus were measured using a Microbeta Plus scintillation counter
(Wallac, Purku, Finland). Results are expressed as a percentage of
localized labeled cells in recipient tissues relative to the injected
dose.
Reactivity of mAbs to recombinant L-selectin
To examine the binding ability of mAbs to immobilized
recombinant mouse L-selectin molecules, a sandwich ELISA was performed.
Microtiter plates (Dynatech Laboratories, Chantilly, VA) were coated
with purified rabbit anti-human IgG Abs (Jackson Laboratories, West
Grove, PA), washed with PBS, blocked with 3% BSA in PBS, and reacted
with the supernatant of COS-7 cell culture containing recombinant mouse
L-selectin/human Fc (
) chimeric protein. Binding of biotinylated
H32, Mel-14, and MRL-2 (rat L-selectin-specific) mAbs toward
recombinant L-selectin was detected using alkaline
phosphatase-conjugated avidin and p-nitrophenyl phosphate.
ELISA to detect L-selectin-specific autoantibodies
In the ELISA to detect L-selectin-specific autoantibodies in
sera from mice, precoating of the microtiter plates with rabbit
anti-human IgG Abs to capture mouse L-selectin/human Fc (
)
chimeric protein resulted in nonspecific binding of mouse natural
heteroantibodies to rabbit Igs. To exclude these, microtiter plates
were directly coated with purified recombinant mouse L-selectin/human
Fc(
) overnight at 4°C, blocked with 3% BSA in PBS, and reacted
with mouse sera serially diluted in PBS containing 40 µg/ml of human
IgG and 0.05% Tween-20 for 2 h at 4°C. After extensive washings
in PBS containing 0.1% BSA and 0.05% Tween-20, binding of Abs was
examined using alkaline phosphatase-conjugated anti-mouse Igs and
p-nitrophenyl phosphate. Data were expressed as
OD, by
subtracting OD405 with medium alone from that with test
serum samples.
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Results
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Generation of L-selectin-specific hybridoma mAb from untreated
(NZB x NZW)F1 mouse
An IgM hybridoma mAb H32, selected from 8-mo-old (NZB x
NZW)F1 mouse spleen cell hybridomas for the reaction to a
limited population of 2-mo-old syngeneic mouse lymphocytes from various
sources, was cytotoxic in nature in the presence of rabbit complement.
Flow cytometric analyses showed that Ag H32 was positive for
approximately 30% thymocytes, 37% spleen cells, 60% mesenteric lymph
node cells, 53% peritoneal lymphocytes, 20% PBL, and 10% bone marrow
cells from 2-mo-old BALB/c mice. Because such distribution of H-32 Ag
was similar to that of Mel-14, expressions of H32 and Mel-14 on
CD3+ T and B220 (6B2)+ B cells were compared,
using two-color flow cytometric analyses of spleen cells from 2-mo-old
BALB/c mice. As shown in Figure 1
, H32
and Mel-14 Ags showed much the same distribution. A control IgM mAb
from a (NZB x NZW)F1 mouse with unknown specificity
was negative for the staining in the same experiments (data not shown).

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FIGURE 1. Two-color flow cytometric profiles of spleen cells from 2-mo-old BALB/c
mice for B220 (6B2) vs H32 (a), for 6B2 vs Mel-14
(b), for CD3 vs H32 (c), and for CD3 vs
Mel-14 expression (d). Spleen cells were incubated with
the following combinations of mAbs: PE-conjugated 6B2 and
FITC-conjugated H32 (a), PE-conjugated 6B2 and
FITC-conjugated Mel-14 (b), PE-conjugated anti-CD3
and FITC-conjugated H32 (c), and PE-conjugated
anti-CD3 and FITC-conjugated Mel-14 (d).
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Figure 2
shows that pretreatment of cells
with nonbiotinylated mAb Mel-14 completely inhibited the subsequent
staining with biotinylated H32 (Fig. 2
, ae). A control rat
IgG mAb (clone 5.1.9) failed to compete with H32 (Control 1, Fig. 2
, fj). Pretreatment of cells with nonbiotinylated mAb H32
also inhibited the staining with biotinylated Mel-14 almost completely
(Fig. 2
, ko), suggesting that mAbs H32 and Mel-14 probably
recognize the same epitope. Again, a control (NZB x
NZW)F1 IgM mAb HOG.10 did not inhibit the binding of Mel-14
(Control 2, Fig. 2
, pt).

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FIGURE 2. Competitive binding of mAbs H32 and Mel-14 to lymph node cells from
2-mo-old BALB/c mice. Lymph node cells (1 x 106) were
first incubated with varying concentrations (0, 1.5, 15, 150, and 1500
µg/ml) of unconjugated Mel-14 (ae) or a control rat
IgG mAb (Control-1; fj), followed by a suboptimum
concentration of biotinylated H32 (10 µg/ml). Alternatively, cells
were first incubated with varying concentrations (0, 10, 100, 1,000,
and 10,000 µg/ml) of unconjugated H32 (ko) or a
control mouse IgM mAb (Control-2; pt), followed by a
suboptimum concentration of biotinylated Mel-14 (1 µg/ml). The cells
were then stained with FITC-conjugated avidin and were subjected to
flow cytometry analysis.
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L-selectin expressed on peripheral lymphocytes is shed from the
cell surface when cells are stimulated by phorbol ester (34). As shown
in Figure 3
, both Mel-14 and H32 epitopes
disappeared when the cells were exposed to 1 ng/ml or more of PMA.

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FIGURE 3. Disappearance of Mel-14 and H32 expressions on lymph node cells upon
treatment with varying concentrations of PMA in vitro. Mesenteric lymph
node cells from 2-mo-old BALB/c mice were incubated in serum-free RPMI
1640 medium containing varying concentrations of PMA at 37°C for 20
min. The cells were subsequently stained with biotinylated mAb (Mel-14,
H32, or CD4) followed by FITC-avidin.
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Figure 4
shows data on the immunoblotting
analysis, using culture supernatants of mesenteric lymph node cells
prestimulated with PMA. The molecular mass of the shed H32 Ag was
estimated to be 80 kDa, in keeping with the reported molecular size of
L-selectin molecule (35).

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FIGURE 4. Immunoblotting analysis with H32 mAb of the culture supernatant of
lymph node cells treated with PMA. Mesenteric lymph node cells from
2-mo-old BALB/c mice were incubated in serum-free RPMI 1640 medium
containing PMA (100 ng/ml) at 37°C for 20 min. Proteins in the
culture supernatants were concentrated by precipitation with saturated
ammonium sulfate, then subjected to SDS-PAGE with 2-ME. The gel was
transferred electrophoretically to a Clear Blot Membrane-P (Atto Co.,
Tokyo, Japan). Bands were visualized using nitro blue tetrazolium (NBT)
and 5-bromo-4-chloro-3-indoryl phosphate (BCIP) substrate solutions
(Promega Biotec), as described in Materials and Methods.
Lane 1, The blot was incubated with biotinylated H32 (5
µg/ml) followed by alkaline phosphatase-conjugated avidin;
lane 2 (control), The blot was incubated with PBS
followed by alkaline phosphatase-conjugated avidin.
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To examine the reactivity of H32 to L-selectin, recombinant chimeric
proteins, rat L-selectin/human Fc(
) and mouse L-selectin/human
Fc(
), were immobilized on plates coated with rabbit anti-human
IgG Abs, and binding of biotinylated Mel-14 and H32 mAbs was examined.
As shown in Table I
, both Abs reacted to
mouse, but not to rat, L-selectin chimeric protein.
Inhibitory effect of H32 on homing of L-selectin-positive
lymphocytes
We then asked whether mAb H32 would affect the homing of
lymphocytes into lymphoid tissues. BALB/c mice at 2 mo of age were
given i.v. a mixture of 51Cr-labeled lymph node cells
(5 x 106 cells) and mAb H32 that had been incubated
for 60 min at 4°C. As controls, mice were given
51Cr-labeled lymph node cells either alone (Control-1) or
mixed with the control (NZB x NZW)F1 IgM mAb HOG.10
(Control-2). Twenty-four hours later, tissue and blood samples from the
recipients were examined for radioactive content. As shown in Table II
, compared with average proportions of
radioactivities recovered from the control groups, the experimental
group showed a marked decrease in the recovery in lymph nodes and, in
turn, an increase in the spleen, indicating the inhibitory effect of
mAb H32 on homing of recirculating lymph node cells into lymph nodes.
Similar findings were obtained in experiments using mAb Mel-14 (data
not shown). The increase in the proportion of radioactivity in the
spleen, but not other tissues, suggests that the spleen is the major
site of terminal accumulation of sensitized cells.
Selective age-associated decrease of H32+
CD4+ T cell subsets with ThP-type functions in (NZB x
NZW)F1 mice
Figure 5
shows the two-color flow
cytometric profile of spleen cells and peripheral lymph node cells from
2-mo-old BALB/c mice for the expression of CD4 vs H32. The
CD4+ T cells were clearly separated into two subsets, one
positive and one negative for H32. Such distribution of H32 on
CD4+ T cells was similar to that of CD45RC Ag, which is
mainly distributed on naive CD4+ T cells (10). We then
determined functional properties of FACS-sorted H32+
CD4+ and H32- CD4+ splenic T cells
in terms of the potential to produce IL-2 and IL-4 upon stimulation
with immobilized anti-CD3 mAb in vitro in either the presence or
the absence of accessory cells. In accordance with the previous report
by Croft et al. (36) demonstrating the functional difference between L-
selectin+ naive and L-selectin-
memory CD4+ T cells, we found that
H32+CD4+ T cells responded to immobilized
anti-CD3 Abs to produce IL-2 only in the presence of accessory
cells, while H32- CD4+ T cells produced both
IL-2 and IL-4 in either the presence or the absence of accessory cells
(data not shown).

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FIGURE 5. Two-color flow cytometric analysis of spleen cells and peripheral lymph
node cells from 2-mo-old BALB/c mice for CD4 vs H32. The cells were
stained and analyzed described as in Figure 1 . The values in the
figures represent the population (percentage) in total CD4+
T cells.
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As shown in Figure 6
, splenic
CD4+ T cells from 2-mo-old (NZB x NZW)F1
mice contained both H32+ CD4+ and
H32- CD4+ T cells (Fig. 6
a), while
splenic CD4+ T cells from 8-mo-old mice were mostly
composed of H32- cells (Fig. 6
b). In keeping
with our earlier findings of CD4+ T cells stained with mAbs
CD45RC and NTA260 (8), double staining of cells with mAbs H32 and
NTA260 clearly separated CD4+ T cells from 2-mo-old
(NZB x NZW)F1 mice into four phenotypically distinct
subsets (Fig. 6
c). Notably, there was a marked
age-associated decrease in CD4+ T cell subsets with each
H32+ NTA260-, H32+
NTA260+, and H32- NTA260+
phenotype, and the remainder was virtually composed of
H32- NTA260- CD4+ T cells
(Fig. 6
d).

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FIGURE 6. Age-associated changes in H32 expression on splenic CD4+ T
cells from (NZB x NZW)F1 mice. Spleen cells from 2-mo-old
(a and c) and 8-mo-old (b and
d) (NZB x NZW)F1 mice were stained with a
mixture of FITC-conjugated anti-CD4 (GK1.5) and biotinylated H32,
followed by PE-conjugated avidin. The stained cells were subjected to
two-color flow cytometric analysis for CD4 vs H32 (a and
b). Alternatively, cells were stained with FITC-conjugated
NTA260, biotin-conjugated H32, and PE-conjugated CD4, and finally with
allophycocyanine-conjugated avidin. The stained cells were subjected to
three-color analysis, and profiles for NTA260 vs H32 expression of
CD4+ T cells are shown (c and
d).
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Age-associated increase in serum levels of L-selectin-specific
autoantibodies in (NZB x NZW)F1 mice
Figure 7
shows data of binding
activities of sera from young and old BALB/c and (NZB x
NZW)F1 mice to the recombinant mouse L-selectin/human Fc
(
) chimeric protein. To exclude the possible involvement of
anti-human Fc (
) reactivities in mouse sera, all sera were
serially diluted in PBS containing human IgG. While sera from young and
old BALB/c and young (NZB x NZW)F1 mice showed only
low levels of reactivity, sera from aged (NZB x
NZW)F1 mice exhibited increased binding activities in a
high frequency. Such reactivities of sera from the aged (NZB x
NZW)F1 mice were blocked by preincubation of the sera with
soluble mouse L-selectin chimeric protein, but not with human IgG, in a
dose-dependent manner (data not shown).

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FIGURE 7. Age-associated increase in serum levels of L-selectin-specific
autoantibodies in (NZB x NZW)F1 mice. Sera from
2-mo-old (a) and 8-mo-old BALB/c (b) and
from 2-mo-old (c) and 8-mo-old (NZB x
NZW)F1 (d) mice were serially diluted in PBS
containing human IgG (40 µg/ml) and reacted with plate-coated
recombinant mouse L-selectin/human Fc ( ) chimeric protein for 2
h at 4°C. Bindings of autoantibodies to plate-coated recombinant
L-selectin were detected as described in Materials and
Methods.
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 |
Discussion
|
|---|
The present studies provide evidence that in SLE-prone (NZB
x NZW)F1 mice, there exists a type of autoantibody
specific for L-selectin that has the potential to eliminate
L-selectin-positive CD4+ T cells either by killing or by
preventing their homing to lymph nodes. Thus, the abnormal deficit of a
ThP-type naive CD4+ T cell subset bearing L-selectin
molecules as well as the well documented defect in IL-2 production by T
cells in aged (NZB x NZW)F1 mice can be at least
partly attributed to the effect of this type of autoantibodies.
The L-selectin molecule, characterized as a homing receptor of
lymphocytes, is an integral membrane glycoprotein (95 kDa) with a short
intracytoplasmic domain. The outer membrane region of the molecule is
composed of three known types of modules, i.e.,
Ca2+-dependent lectin domain at the N-terminus, a domain
with sequence homology with epidermal growth factor, and two copies of
units characteristic of complement binding proteins (29, 37). As mAb
Mel-14 recognizes the lectin domain of the molecule (38), and as mAbs
H32 and Mel-14 showed cross-inhibitory effects on binding to L-selectin
molecules, the H32 epitope probably also resides on the lectin domain
of the molecule. L-selectin is differentially expressed on peripheral
CD4+ T cells and has served as a marker for naive
CD4+ T cells (39, 40). Indeed, the mAb H32 separated
peripheral CD4+ T cells from young BALB/c mice into two
functionally distinct subpopulations: 1) H32+
CD4+ T cells producing IL-2, but not other cytokines, when
stimulated with immobilized anti-CD3 mAb, thus representing the
property of naive cells analogous to ThP-type clones (36, 41); and 2)
H32- CD4+ T cells producing IL-2, IL-4, IL-10,
and IFN-
upon stimulation, hence presumably including Th1-, Th2-,
and Th0-type CD4+ T cells (41, 42, 43). Thus, it is reasonable
to speculate that autoantibodies with specificities to L-selectin are
at least in part involved in the age-associated selective depletion of
ThP-type naive CD4+ T cells in (NZB x
NZW)F1 mice.
The significance of the observed deficit in L-selectin-positive, naive
CD4+ T cells in autoimmune disease of (NZB x
NZW)F1 mice is unclear. In this context, there was a marked
difference in the accessory cell dependency in cytokine production
between H32+CD4+ and H32-
CD4+ T cells, in which the former, but not the latter, was
dependent. As accessory cell-dependent naive CD4+ T cells
are susceptible to anergy, when stimulated in the absence of accessory
signals (44), the age-associated decrease in H32+
CD4+ T cells in (NZB x NZW)F1 mice may
promote the loss of peripheral tolerance of CD4+ T cells to
self peptides. If so, then, why is the Ag expressed on naive T cells
preferentially targeted? As large numbers of naive lymphocytes undergo
apoptosis in lymphoid organs, they may provide nuclear and cellular
autoantigens, including L-selectin, that are recognized to be
immunogenic in individuals with genetic susceptibility to systemic
autoimmune diseases.
Our studies implicate two mutually unexclusive roles of
L-selectin-specific autoantibodies for immunologic abnormalities in
these mice: 1) a selective depletion of L-selectin-positive
CD4+ T cells, due to immune clearance of sensitized cells
in the spleen; and 2) inhibition of lymphocyte homing into lymphoid
tissues. L-selectin on lymphocytes recognizes a sialylated
glycoprotein, GlyCAM-1, on high endothelial venules (45, 46)
and mediates rolling of lymphocytes on the endothelial cell surface, an
initial event in the process of lymphocyte homing (30). Thus, it is
conceivable that L-selectin-specific autoantibodies can interfere with
this process, resulting in abnormal polarization of CD4+ T
cells to L-selectin-negative population in lymphoid tissues of aged
(NZB x NZW)F1 mice.
Although autoantibodies specific for isoforms of CD45 were reported to
be present in patients with SLE (18), we could not obtain hybridoma
clones of this type of specificity from (NZB x NZW)F1
mice. In earlier studies, we obtained evidence that each naive
CD4+ T cell, as defined by expression of the
CD45RBhigh CD45RC+ phenotype, and memory
CD4+ T cell, as defined by CD45RBlow
CD45RC- phenotype, can be separated into two
phenotypically distinct subsets, either positive or negative for
expression of the Ag recognized by a monoclonal natural thymocytotoxic
autoantibody, NTA260 (8), a mAb generated from an autoimmune NZB mouse
(16). The biochemical nature of this antigenic structure remains to be
characterized. However, the striking finding was that the four subsets
of CD4+ T cells, CD45RC+ NTA260-,
CD45RC+ NTA260+, CD45RC-
NTA260+, and CD45RC- NTA260- were
functionally distinct in terms of their pattern of cytokine production,
and that with advancing age of (NZB x NZW)F1 mice,
there was an age-associated polarization of CD4+ T cells to
a subset that is negative for both CD45RC and NTA260 expressions in
association with a marked decline in the cytokine production of Th1 and
Th2 types (8). The present studies revealed that the
CD45RC- NTA260- subset was similar to the
subset with the H32- NTA260- phenotype,
indicating that L-selectin is preferentially expressed on the
CD45RC+ CD4+ T cell subset. Because NTA260-type
autoantibodies are produced in high titers in NZB and (NZB x
NZW)F1 mice (11, 12), in parallel with an age-associated
decrease in the NTA-sensitive population of T cells (47), and because
these autoantibodies also have potential to prevent the homing of
lymphocytes (48), the age-associated polarization of CD4+ T
cells to the CD45RC- NTA260- subset can be
attributed to the concurrence of both H32-type and NTA260-type
autoantibodies. Further characterization of the CD45RC-
NTA260- CD4+ T cell subset is important,
because this contains a functional subset responsible for the
generation of high affinity, pathogenic IgG anti-DNA Abs in
(NZB x NZW)F1 mice (49).
The pathologic role ascribed to lymphocyte autoantibodies in autoimmune
diseases is controversial (50, 51). In genetic studies using (NZB
x NZW)F1 x NZW backcross progeny, however, Yoshida et al.
(52) showed that an accelerated onset and the highest incidence of
lupus nephritis occurred in the progeny with coincidence of
anti-dsDNA Abs and lymphocyte autoantibodies. In light of the
present findings, the effects of lymphocyte autoantibodies,
particularly those that react with specific functional molecules,
should be given attention as a possible cause of immunologic
abnormalities. While lymphocyte autoantibodies per se may be the effect
rather than the primary cause of autoimmune disease, selection,
expansion, and maturation of autoreactive B cell clones, which occur
under genetic controls (53, 54), would in consequence facilitate,
modify, and/or characterize autoimmune disease
manifestations.
 |
Acknowledgments
|
|---|
We thank M. Ohara for critical comments and M. Morita for
secretarial services.
 |
Footnotes
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|---|
1 This work was supported by a grant from a Special Coordination Fund for Senescence Research, Japan; a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports, and Culture, Japan; and CREST (Core Research for Evolutional Science and Technology) of Japan Science and Technology Corporation. 
2 Address correspondence and reprint requests to Dr. Toshikazu Shirai, Department of Pathology, Juntendo University School of Medicine, 21-1, Hongo Bunkyo-ku, Tokyo 113-8421, Japan. E-mail address: 
3 Abbreviations used in this paper: SLE, systemic lupus erythematosus; NZB, New Zealand Black; NZW, New Zealand White; NTA, natural thymocytotoxic autoantibodies; PE, phycoerythrin. 
Received for publication July 22, 1997.
Accepted for publication April 3, 1998.
 |
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