By
From the * Immunological Diseases, Bristol-Myers Squibb Pharmaceutical Research Institute, Seattle,
Washington 98121; Department of Pathobiology and the § Division of Infectious Diseases,
Department of Medicine, University of Washington, Seattle, Washington 98195
Human monocytes undergo spontaneous apoptosis upon culture in vitro; removal of serum from the media dramatically increases the rate of this process. Monocyte apoptosis can be significantly abrogated by the addition of growth factors or proinflammatory mediators. We have evaluated the role of the endogenous Fas-Fas ligand (FasL) interaction in the induction of this spontaneous apoptosis and found that a Fas-immunoglobulin (Ig) fusion protein, an antagonistic anti-Fas monoclonal antibody and a rabbit anti-FasL antibody all greatly reduced the onset of apoptosis. The results indicate that spontaneous death of monocytes is mediated via an autocrine or paracrine pathway. Treatment of the cells with growth factors or cytokines that prevented spontaneous apoptosis had no major effects on the expression of Fas or FasL. Additionally, monocyte-derived macrophages were found to express both Fas and FasL but did not undergo spontaneous apoptosis and were not sensitive to stimulation by an agonistic anti-Fas IgM. These results indicate that protective mechanisms in these cells exist at a site downstream of the receptor-ligand interaction.
The Fas-Fas ligand (FasL) system is recognized as a major pathway for the induction of apoptosis (programmed
cell death) in cells and tissues (for reviews see references 1,
2). Fas (CD95), a type I membrane protein of ~45 kD, is a
member of the TNF-receptor (TNFR) family of proteins
(3). FasL is a type II membrane protein of ~37 kD, belonging to the TNF and CD40 ligand family of proteins (4,
5). Fas is widely expressed in many tissue types, either constitutively or following activation of the cells (6). In B
and T cells, Fas is expressed at low levels on the surface of
resting cells and expression is enhanced after lymphocyte activation (6, 11, 19). In contrast with Fas, the expression of
FasL is reported to be much more restricted and often requires cell activation (7, 12). Cell surface expression of
FasL is very low in resting lymphocytes but can be induced
on both T and B cells after activation of the cells (13, 14,
20). The interaction of FasL with Fas on a target cell stimulates an intracellular cascade of events that leads to the induction of apoptosis. Because the expression of FasL appears to be regulated more strictly, the cell surface
expression of FasL by the effector cells is thought to be the
triggering event in the induction of programmed cell
death. The Fas-FasL system has been shown to play a critical role in the development of the T and B cell repertoire
(15, 16). Additionally, it has been proposed that target cell
killing by CTLs is, in part, mediated through the interaction of FasL on the activated T cell with Fas on the target
cell (17).
Human monocytes cultured in vitro undergo spontaneous apoptosis without requiring additional external stimuli
(21). This process can be accelerated and enhanced by
the removal of serum. Even in the presence of 20% serum,
the majority of monocytes will undergo apoptosis over several days (23); surviving cells differentiate into macrophages. In
culture, it is possible to prevent the rapid onset of apoptosis
in monocytes by treatment with inflammatory mediators
such as TNF, LPS, the ligand to CD40 (CD154), and growth factors and cytokines including GM-CSF and IFN- In this report, we show that peripheral monocytes isolated by elutriation express both Fas and FasL and that the
onset of apoptosis of human peripheral monocytes in culture is prevented by the addition of a nonstimulatory antiFas mAb, an antagonistic rabbit anti-FasL Ab, or a soluble
Fas-Ig fusion protein, all of which block the interaction between Fas and FasL. Therefore, monocytes are able to undergo apoptosis via an autocrine or paracrine mechanism that is dependent on the expression of both Fas and FasL but
is independent of another source of FasL, such as activated
T cells. In contrast, monocyte-derived macrophages cultured
for 7 d in vitro developed resistance to Fas-induced apoptosis despite expressing significant levels of Fas and FasL on
the cell surface.
Cells.
Peripheral monocytes were prepared from healthy donors as described previously (23) in RPMI containing 2.5 mM
EDTA, 10 µg/ml polymyxin B, 100 U/ml penicillin, and 100 µg/ml streptomycin. In brief, the PBMC were separated on Ficoll and the T cells were depleted from the PBMC fraction by rosetting with SRBC. The monocytes were then separated from
the remaining PBMC by centrifugal elutriation. After elutriation,
the monocytes were collected from the appropriate fractions by
centrifugation and then resuspended in RPMI-1640 media with
additions as noted in the figure legends. The monocytes isolated
by this procedure were >90% pure as measured by staining the
cells to determine expression of CD14, CD16, CD19, and CD3. Staining of monocytes for FACS® analysis was performed immediately after isolation. Monocyte-derived macrophages were prepared from peripheral monocytes by culturing the cells in RPMI
containing 20% FBS, penicillin (100 U/ml) and streptomycin (100 µg/ml), in Teflon beakers at 37°C for 7 d; half the media was
changed after 4 d. Before analysis, dead cells were removed by
centrifugation over Histopaque (Sigma Chem. Co., St. Louis, MO).
Reagents and Antibodies.
The Fas-Ig and B7-Ig fusion proteins were constructed essentially as described previously (8, 23, 24),
based on published sequences of the extracellular domains (3, 25)
together with the constant region of human IgG1. Modified
pCDM8 vectors containing the fusion genes were transiently expressed in COS cells for 6 d. The cell supernatants were harvested, clarified by centrifugation, and the fusion proteins then
purified on protein A. Soluble recombinant FasL (CD8-FasL) was
expressed as a fusion protein consisting of the extracellular domain of murine CD8 fused to the entire extracellular domain of human FasL. CD8-FasL was produced by transient transfection of
COS cells and purified on immobilized anti-murine CD8 as described for sCD154 (23). Human GM-CSF, IFN- Analysis of Cell Surface Antigen Expression.
After the appropriate incubations, the cells were harvested, washed once in 2% FBS-
RPMI (staining media) at 4°C, resuspended in 200 µl 2% FBS-
RPMI containing 1 mg/ml BSA, and 250 µg/ml human IgG for
20 min. The cells were pelleted and resuspended in PBS containing 2% FBS, before the addition of the primary antibodies (at 10 µg/ml). The cells were incubated for 30 min at 4°C, washed once
with staining media, and then incubated with FITC-labeled antimurine IgG or anti-rabbit IgG (1:50 dilution) in staining media
for an additional 30 min at 4°C. For single color analysis, the samples were washed twice in PBS and fixed in 2% formaldehyde. In
most analyses, the cells were stained both for the uptake of propidium iodide and for specific antigen expression. For this two-color
staining, the cells were not fixed; instead, after staining cells with
Ab and washing them in PBS, propidium iodide (PI) (5 µg/ml)
was added immediately before analysis on a FACScan® analyzer
(Becton Dickinson and Co., Mountain View, CA). In the measurement of cell surface antigen expression, the gates of the analyzer
were set to exclude PI-positive cells. The FACS® data are reported as mean fluorescence ratios. This represents the mean fluorescence determined using the Fas or FasL Ab divided by the
mean fluorescence of the control Ab for each treatment of the
monocytes.
Assay of Apoptosis and DNA Fragmentation.
Monocytes were isolated
by elutriation and cultured at 1 × 106/ml in RPMI containing
500 ng/ml polymyxin B together with no further additions, or
with the agents as indicated in the text. After these incubations,
the cells were harvested by centrifugation and then either permeabilized with buffer containing sodium citrate (0.3%), Triton
X-100 (0.01%), and PI (50 µg/ml) for FACS® analysis or assayed
for cell viability by measuring the exclusion of Trypan blue. Alternatively, the binding of FITC-annexin V was used to follow
the expression of phosphatidylserine on early apoptotic cells (8, 26).
The staining was carried out essentially according to the manufacturer's instructions. After the appropriate incubations cells, 5 × 105/500 µl, were incubated with saturating concentrations of FITC- annexin V for 30 min at room temperature; the cells were then immediately analyzed by FACS®.
To evaluate the expression of Fas
and FasL on the cell surface, monocytes were isolated by
elutriation and analyzed immediately; human macrophages
were derived from peripheral monocytes by culturing the
cells for 7 d in Teflon culture dishes. The different cells were then analyzed, without fixation, by FACS®. The results showed that freshly isolated monocytes and cultured monocyte-derived macrophages expressed both Fas and FasL
on the cell surface (Fig. 1), although the levels of both Fas
and FasL were slightly lower in the macrophages (Fig. 1, C
and D). In the analysis of cells from seven different donors
the ratio of specific mean fluorescence of Ab to Fas relative
to the control Ab was 8.4 ± 0.7 and 5.5 ± 1.7 in monocytes and macrophages, respectively. For FasL, the ratio of
specific mean fluorescence to the control was 5.7 ± 0.5 and 4.7 ± 1.0 in monocytes and macrophages, respectively.
In the absence of serum, freshly isolated human monocytes rapidly undergo programmed cell
death (21, 22); even in the presence of serum a significant
proportion of the cells die (23). Studies were undertaken to
determine the role of FasL in this spontaneous death of the
cells. Peripheral monocytes were isolated and then immediately placed into culture for 18 h in serum-free RPMI
alone, with the soluble fusion protein Fas-Ig, or with
blocking anti-Fas or anti-FasL antibodies. The spontaneous
apoptosis was markedly reduced by culturing the monocytes with Fas-Ig but not by the control fusion protein B7-
Ig (Fig. 2 A). An antagonistic mouse anti-Fas mAb (IgG1)
also protected the cells to a similar extent, whereas control
mouse IgG1 gave rise to only marginal protection. The polyclonal anti-FasL antibody (C20) was the most effective at inhibiting the spontaneous apoptosis of the peripheral monocytes; normal rabbit IgG yielded little protection (Fig. 2 A).
One of the early changes in cells undergoing apoptosis is
the exposure of phosphatidyl serine on the surface of the cells, which can be detected by the ability of the phospholipid to
bind annexin V (8, 26). FACS® analysis of changes in the
phospholipids in the plasma membrane of the monocytes
using FITC-annexin V confirmed the onset of apoptotic responses observed in Fig. 2 A. After 8 h in culture, 50-60%
of the peripheral monocytes bound annexin V, whereas
culture of the cells in Fas-Ig or anti-FasL reduced the number of positive staining cells to less than 20% (Fig. 2 B).
These results indicate that the autocrine or paracrine interaction of Fas and FasL is largely responsible for the spontaneous induction of programmed cell death that occurs
upon culture of peripheral monocytes in serum-free media.
It has previously been shown that different cytokines,
growth factors, and LPS can prevent the onset of apoptosis
in human monocytes (9, 21, 22). In agreement with these
earlier findings, we found that IFN-
Spontaneous apoptosis was evident in
peripheral monocytes, even when the cells were cultured
in the presence of 20% FBS (Fig. 4). As shown here (Fig. 4)
and reported previously (9), monocyte apoptosis in either
the absence or presence of serum significantly increased after the addition of a stimulatory anti-Fas mAb to the cells.
In contrast, human monocyte-derived macrophages were completely resistant to anti-Fas (Fig. 4) or sFasL-induced
(data not shown) apoptosis. Thus, despite expressing significant levels of Fas and FasL on the cell surface (see Fig. 1),
monocyte-derived macrophages were resistant to both spontaneous and anti-Fas-induced apoptosis.
While the function of the Fas-FasL system in the regulation of apoptosis in lymphocytes is well established (7, 11,
14), its role in other leukocytes is less well established, though recent reports suggest that here too it may play a crucial
function (8, 27, 28). Fas is constitutively expressed on other
phagocytes (8, 28) and stimulation of Fas with an agonistic mAb induces apoptosis in neutrophils and eosinophils
(8, 28). Additionally, it has been shown that the neutrophils, like activated T cells, can release biologically active
soluble FasL (7, 8). Furthermore, upon isolation and culture in vitro, neutrophils undergo programmed cell death
(8) mediated by interactions of Fas and FasL on the cells. It
has been proposed that this apoptotic response of leukocytes in vitro reflects one of the normal mechanisms for the
elimination of the cells in vivo. During an inflammatory response the eosinophils or neutrophils are recruited into the
tissue. Later, the subsequent resolution of the inflammation
requires that the leukocytes are removed from the site and
this may be mediated by apoptosis.
Monocytes undergo spontaneous apoptosis (9, 21).
This cell death can be inhibited by treatment of the monocytes with LPS, TNF- In the work reported here, we show that resting monocytes constitutively express FasL on the cell surface. This expression was not readily detected in an earlier study using
the fusion protein Fas-Ig to detect FasL (9) due to the
lower affinity of the reagent and due to high background
binding of the Ig protein to the Fc receptors. In addition,
our results indicate that spontaneous apoptosis of monocytes in vitro is mediated by the interaction of Fas and FasL
on the cell surface, because apoptosis could be suppressed
by reagents that block the interaction of Fas and FasL. These
agents included a Fas-Ig soluble fusion protein and antagonistic antibodies to Fas or FasL. Because of the inability of
any of these agents to provide complete protection from
death, we cannot rule out that other mechanisms may also
contribute to the induction of spontaneous apoptosis.
However, it is clear that other factors beyond the expression of Fas and FasL on the cell surface also ultimately
contribute to the sensitivity of monocytes to the apoptotic
pathway (27). We found that treatment of peripheral
monocytes with TNF- The presence of FasL on the cell surface of both monocytes and macrophages suggests that the ligand may play a
role, other than regulating self-apoptosis, in the effector
functions of the cell. This has also recently been proposed
for neutrophils that were found to both express FasL on the
cell surface and also release biologically active sFasL in the
cell supernatants (8). In preliminary experiments, we have
found that it is possible to stimulate monocytic cells to release biologically active sFasL (data not shown). Together,
these results indicate that it is very likely that FasL plays a
very important role in mediating some of the physiological
functions of monocytes and macrophages.
(21).
Monocytes and macrophages express low but detectable
levels of Fas but the role of the endogenous Fas and FasL in
the spontaneous apoptosis has not been established. Recent
reports have shown that monocytes in medium containing
serum can rapidly undergo apoptosis following the ligation
of the Fas on the surface of the cells with an agonistic mAb
to Fas (mAb CH-11) (9). However, no studies have been
presented on the direct role of endogenous FasL in the
spontaneous apoptosis of purified monocytes. Furthermore,
the regulation of expression of FasL and its role in monocyte
and macrophage function has not been explored.
, IL-4, TNF-
,
and FITC-labeled annexin V were obtained from R & D Systems
(Minneapolis, MN). LPS (Escherichia coli 055:B5) was from Whittaker Bioproducts (Walkersville, MD). The mouse monoclonal
anti-Fas IgM and anti-Fas IgG1 were obtained from Immunotech
(Westbrook, ME); rabbit anti-FasL polyclonal antibodies (C20 and
N20) were obtained from Santa Cruz Labs (Santa Cruz, CA);
anti-FasL mAb was from Transduction Laboratories (Lexington, KY); FITC-labeled anti-rabbit and anti-mouse antibodies were
from Jackson ImmunoResearch Labs., Inc. (West Grove, PA) or
Tago (Burlingame, CA). Human IgG and all other reagents were
from Sigma.
Expression of Cell Surface Fas and FasL on Human Monocytes and Macrophages.
Fig. 1.
Cell surface staining of Fas and FasL on monocytes and
monocyte-derived macrophages. Dotted line, control antibodies; solid line,
Fas or FasL Abs as indicated. Peripheral monocytes were isolated by elutriation and then stained immediately (A and B), or cultured for 7 d in Teflon dishes (C and D) and then stained for cell surface expression of FasL
(A and C, using anti-FasL polyclonal Ab, C20) and Fas (B and D, using
anti-Fas, murine IgG1) as described in Material and Methods. Staining with
control antibodies was carried out using mouse IgG1 or rabbit IgG as appropriate. The histograms are from a single experiment representative of seven experiments with cells from different donors.
[View Larger Version of this Image (0K GIF file)]
Fig. 2.
Effect of fusion proteins and antibodies on spontaneous apoptosis of peripheral monocytes. (A) Staining of nuclei with PI. (B) Staining
of the cell surface with annexin V. Elutriated peripheral monocytes were
cultured at 1 × 106/ml in polypropylene tubes in RPMI media containing 1 µg/ml polymyxin B together with no additions, 50 µg/ml Fas-Ig,
50 µg/ml B7.1-Ig, 10 µg/ml anti-Fas IgG, 10 µg/ml muIgG1, 10 µg/ml
rabbit anti-FasL (C20) or 10 µg/ml rabbit IgG. For PI staining, the cells
were harvested by centrifugation after 18 h at 37°C ; they were then analyzed for apoptotic nuclei with PI as described in Materials and Methods.
n, the number of different donors in each treatment set. For staining with
annexin V the cells were harvested after 8 h in culture, washed, and then
stained for 30 min with FITC-annexin V. The bars represent the mean ± SEM of the number (n) of different donors.
[View Larger Version of this Image (0K GIF file)]
, TNF-
, GM-CSF,
and LPS all effectively reduced the degree of apoptosis of
monocytes when added at the initiation of the cell culture
(Fig. 3 A). In addition, IL-4 alone appeared to provide
slight protection from apoptosis (Fig. 3 A), but, as reported
previously (21, 22), it was able to abrogate most of the rescue of the cells mediated by TNF (data not shown). Over
the time course of these incubations (18 h), no major
changes in the level of cell surface expression of Fas or FasL
(Fig. 3, B and C) were observed. However, TNF and LPS
did appear to induce a small decrease in the level of expression of FasL, and IL-4 induced a small increase in the expression of FasL. These results suggest that while the Fas-
FasL interaction is essential for the spontaneous induction
of programmed cell death in monocytes, the effect of cytokines, growth factors, and LPS on the apoptotic process is
at a site downstream of the cell surface receptors.
Fig. 3.
Effect of IFN-, IL-4, GM-CSF, TNF-
, and LPS on the Fas apoptotic pathway in peripheral monocytes. (A) Apoptosis. Elutriated peripheral monocytes were cultured at 1 × 106/ml in polypropylene tubes in RPMI media containing 1 µg/ml polymyxin B together with no additions, 10 ng/
ml TNF-
, 500 U/ml IL-4, 500 U/ml IFN-
, 5 µg/ml LPS or 10 ng/ml GM-CSF. After 18 h at 37°C, the cells were harvested by centrifugation and
analyzed for apoptotic nuclei as described in Materials and Methods. (B and C) Cell surface expression of Fas (B) and FasL (C). Elutriated peripheral monocytes were cultured at 1 × 106/ml in polypropylene tubes in RPMI media containing 1 µg/ml polymyxin B together with no additions, 500 U/ml IFN-
,
10 ng/ml GM-CSF, 500 U/ml IL-4, 5 µg/ml LPS or 10 ng/ml TNF-
. After 18 h, the cells were harvested and stained for cell surface expression of Fas
(anti-Fas, murine IgG1) and FasL (anti-FasL, polyclonal Ab, C20) as described in Materials and Methods. Staining with control antibodies was carried out
using mouse IgG1 or rabbit IgG as appropriate. The data are expressed as ratio of the mean fluorescence intensity (mfi) of Ab against the specific antigen,
relative to the mfi of control Abs for each treatment. The data represent mean ± SEM of four independent experiments.
[View Larger Versions of these Images (0 + 0K GIF file)]
Fig. 4.
Induction of apoptosis in peripheral monocytes and monocyte-derived macrophages. Elutriated peripheral monocytes were cultured for 18 h alone or with 20% FBS, in the absence or presence of 200 ng/ml
anti-Fas mAb (CH-11). Monocyte-derived macrophages were cultured
for 7 d in RPMI containing 20% FBS and then harvested, washed once, and
then resuspended in RPMI containing 20% FBS. The cells were then cultured for an additional 18 h in the presence of 200 ng/ml anti-Fas mAb.
No spontaneous apoptosis of these cells was observed over the final 18 h.
Cells were harvested by centrifugation and analyzed for apoptotic nuclei
with PI. The bars represent the mean ± SEM of eight (monocytes) or six
(macrophages) experiments with different donors.
[View Larger Version of this Image (0K GIF file)]
, GM-CSF, IFN-
, and sCD154
(21). Monocytes express Fas, but the reports vary considerably on the extent to which the cells are sensitive to
apoptosis induced by the anti-Fas mAb (9, 10, 29). In addition, treatment of monocytes with inflammatory mediators
such as TNF-
and IL-1
partially protects the cells from
anti-Fas-induced apoptosis whereas LPS pretreatment fully protects the cells (9, 21, 22). These treatments are reported not to alter the level of Fas (9). Thus, both growth and
proinflammatory factors enhance the survival of monocytes.
The role of FasL in the spontaneous apoptosis of monocytes has not been explored. Furthermore, the effect of inflammatory mediators and growth factors on FasL expression is not known.
, IFN-
, GM-CSF, or LPS, agents
that protect the cells from spontaneous apoptosis, did not
markedly alter the expression of either Fas or FasL. In addition, despite the expression of both Fas and FasL on the
surface, monocyte-derived macrophages were able to survive 7 d in culture and were also resistant to direct stimulation of Fas with the agonistic anti-Fas mAb. This is in contrast with a report where differentiation of monocytes by
adherence to plastic enhanced their sensitivity to the mAb
(29). The pathways that give rise to protection of these cells
are currently being explored.
Address correspondence to Peter A. Kiener, Bristol-Myers Squibb Pharmaceutical Research Institute, 3005 First Avenue, Seattle, Washington 98121.
Received for publication 9 January 1997 and in revised form 24 February 1997.
W.C. Liles is a Pfizer Postdoctoral fellow.1. | Nagata, S.. 1996. Fas and Fas ligand: a death factor and its receptor. Adv. Immunol. 57: 129-144 . |
2. | Nagata, S., and P. Golstein. 1995. The Fas death factor. Science (Wash. DC). 267: 1449-1456 [Medline]. |
3. | Itoh, N., S. Yonehara, A. Ishii, M. Yonehara, S.I. Mizushima, M. Sameshima, A. Hase, Y. Seto, and S. Nagata. 1991. The polypeptide encoded by the cDNA for human cell surface antigen Fas can mediate apoptosis. Cell. 66: 233-243 [Medline]. |
4. | Takahashi, T., M. Tanaka, J. Inazawa, T. Abe, T. Suda, and S. Nagata. 1994. Human Fas ligand: gene structure, chromosomal location and species specificity. Int. Immunol. 6: 1567-1574 [Abstract]. |
5. | Suda, T., and S. Nagata. 1994. Purification and characterization of the Fas-ligand that induces apoptosis. J. Exp. Med. 179: 873-879 [Abstract]. |
6. |
Miyawaki, T.,
T. Uehara,
R. Nibu,
T. Tsuji,
A. Yachie,
S. Yonehara, and
N. Taniguchi.
1992.
Differential expression of
apoptosis-related Fas antigen on lymphocyte subpopulations
in human peripheral blood.
J. Immunol.
149:
3753-3758
|
7. | Tanaka, M., T. Suda, T. Takahashi, and S. Nagata. 1995. Expression of the functional soluble form of human Fas ligand in activated lymphocytes. EMBO (Eur. Mol. Biol. Organ.) J. 14: 1129-1135 [Abstract]. |
8. | Liles, W.C., P.A. Kiener, J.A. Ledbetter, A. Aruffo, and S.J. Klebanoff. 1996. Differential expression of Fas (CD95) and Fas ligand on normal human phagocytes: implications for the regulation of apoptosis in neutrophils. J. Exp. Med. 184: 429-440 [Abstract]. |
9. | Um, H.-D., J.M. Orenstein, and S.M. Wahl. 1996. Fas mediates apoptosis in human monocytes by a reactive oxygen intermediate dependent pathway. J. Immunol. 156: 3469-3477 [Abstract]. |
10. |
Iwai, K.,
T. Miyawaki,
T. Takizawa,
A. Konno,
K. Ohta,
A. Yachie,
H. Seki, and
N. Taniguchi.
1994.
Differential expression of bcl-2 and susceptibility to anti-Fas-mediated cell
death in peripheral blood lymphocytes, monocytes, and neutrophils.
Blood.
84:
1201-1208
|
11. | Schattner, E., and S.M. Friedman. 1996. Fas expression and apoptosis in human B cells. Immunol. Res. 15: 246-257 [Medline]. |
12. | Suda, T., T. Takahashi, P. Golstein, and S. Nagata. 1993. Molecular cloning and expression of the Fas ligand, a novel member of the tumor necrosis factor family. Cell. 75: 1169-1178 [Medline]. |
13. | Hahne, M., T. Renno, M. Schroeter, M. Irmler, L. French, T. Bornand, H.R. MacDonald, and J. Tschopp. 1996. Activated B cells express functional Fas ligand. Eur. J. Immunol. 26: 721-724 [Medline]. |
14. |
Suda, T.,
T. Okazaki,
Y. Naito,
T. Yokota,
N. Arai,
S. Ozaki,
K. Nakao, and
S. Nagata.
1995.
Expression of the Fas
ligand in cells of T cell lineage.
J. Immunol.
154:
3806-3813
|
15. | Ramsdell, F., M.S. Seaman, R.E. Miller, T.W. Tough, M.R. Alderson, and D.H. Lynch. 1994. gld/gld mice are unable to express a functional ligand for Fas. Eur. J. Immunol. 24: 928-933 [Medline]. |
16. | Takahashi, T., M. Tanaka, C.I. Brannan, N.A. Jenkins, N.G. Copeland, T. Suda, and S. Nagata. 1994. Generalized lymphoproliferative disease in mice, caused by a point mutation in the Fas ligand. Cell. 76: 969-976 [Medline]. |
17. | Kagi, D., F. Vignaux, B. Ledermann, K. Burki, V. Depraetere, S. Nagata, H. Hengartner, and P. Golstein. 1994. Fas and perforin pathways as major mechanisms of T-cell mediated cytotoxicity. Science (Wash. DC). 265: 528-530 [Medline]. |
18. | Lowin, B., M. Hahne, C. Mattmann, and J. Tschopp. 1994. Cytolytic T-cell cytotoxicity is mediated through perforin and Fas lytic pathways. Nature (Lond.). 370: 650-652 [Medline]. |
19. | Anel, A., A.K. Simon, N. Auphan, M. Buferne, C. Boyer, P. Golstein, and A.M. Schmitt-Verhulst. 1995. Two signaling pathways can lead to Fas ligand expression in CD8+ cytotoxic T lymphocyte clones. Eur. J. Immunol. 25: 3381-3387 [Medline]. |
20. |
Nishimura, Y.,
A. Ishii,
Y. Kobayashi,
Y. Yamasaki, and
S. Yonehara.
1995.
Expression and function of mouse Fas antigen on immature and mature T cells.
J. Immunol.
154:
4395-4403
|
21. |
Managan, D.F.,
G.R. Welch, and
S.M. Wahl.
1991.
Lipopolysaccharide, tumor necrosis factor-![]() ![]() |
22. |
Managan, D.F., and
S.M. Wahl.
1991.
Differential regulation
of human monocyte programmed cell death (apoptosis) by
chemotactic factors and pro-inflammatory cytokines.
J. Immunol.
147:
3408-3412
|
23. | Kiener, P.A., P. Moran-Davis, B.M. Rankin, A.F. Wahl, A. Aruffo, and D. Hollenbaugh. 1995. Stimulation of CD40 with purified soluble gp39 induces proinflammatory responses in human monocytes. J. Immunol. 155: 4917-4925 [Abstract]. |
24. | Hollenbaugh, D., and A. Aruffo. 1994. Construction of immunoglobulin fusion proteins. Curr. Prot. Immunol. 2: 10-19 . |
25. |
Freeman, G.J.,
A.S. Freedman,
J.M. Segil,
G. Lee,
J.F. Whitman, and
L.M. Nadler.
1989.
B7, a new member of the Ig
superfamily with unique expression on activated and neoplastic B cells.
J. Immunol.
143:
2714-2722
|
26. | Martin, S.J., C.P.M. Reutelingsperger, A.J. McGahon, J.A. Rader, R.C.A.A. van Schie, D.M. LaFace, and D.R. Green. 1995. Early redistribution of plasma membrane phosphatidylserine is a general feature of apoptosis regardless of the initiating stimulus: inhibition by overexpression of Bcl-2 and Abl. J. Exp. Med. 182: 1545-1556 [Abstract]. |
27. | Squier, M.K.T., A.J. Sehnert, and J.J. Cohen. 1995. Apoptosis in leukocytes. J. Leukoc. Biol. 57: 2-10 [Abstract]. |
28. |
Matsumoto, K.,
R.P. Schleimer,
H. Saito,
Y. Likura, and
B.S. Bochner.
1995.
Induction of apoptosis in human eosinophils by anti-Fas antibody treatment in vitro.
Blood.
86:
1437-1443
|
29. | Richardson, B.C., N.D. Lalwani, K.J. Johnson, and R.M. Marks. 1994. Fas ligation triggers apoptosis in macrophages but not endothelial cells. Eur. J. Immunol. 24: 2640-2645 [Medline]. |