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,
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Center for Pulmonary and Infectious Disease Control, and Departments of
Microbiology and Immunology and
Medicine, University of Texas Health Center, Tyler, TX 75708;
Department of Internal Medicine, University of North Texas Health Sciences Center, Fort Worth, TX 76107;
¶ Lautenberg Center for General and Tumor Immunology, Hebrew University-Hadassah Medical School, Jerusalem, Israel; and
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Department of Microbiology and Immunology, Faculty of Health Sciences, and Cancer Research Center, Ben Gurion University of the Negev, Beer Sheva, Israel
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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. NK
cell lytic activity against M. tuberculosis-infected
monocytes and NKp46 mRNA expression were reduced in tuberculosis
patients with ineffective immunity to M. tuberculosis
compared with findings in healthy donors. These observations suggest
that 1) the NKp46 receptor participates in NK cell-mediated lysis of
cells infected with an intracellular pathogen, and 2) the reduced
functional capacity of NK cells is associated with severe
manifestations of infectious disease. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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by NK
cells is critical for activation of macrophages and resistance to
intracellular bacterial infections (1, 5, 6). Human infection with Mycobacterium tuberculosis provides a model for study of the innate immune response to intracellular pathogens. Many persons who have worked with infectious tuberculosis patients for prolonged periods remain healthy and never develop a positive tuberculin skin test. This suggests that innate immunity controls the infection without the requirement for T cells to recognize M. tuberculosis Ags and mount a delayed hypersensitivity skin test response. To investigate the role of NK cytotoxic mechanisms in the human immune response to intracellular infection, we studied the capacity of freshly isolated NK cells from normal donors and tuberculosis patients to lyse monocytes infected with M. tuberculosis. We also evaluated cytokine production and expression of activating receptors by NK cells in response to M. tuberculosis-infected monocytes.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Blood was obtained from 15 healthy tuberculin reactors, four healthy tuberculin-negative subjects, and 15 HIV-seronegative patients with culture-proven pulmonary tuberculosis who had received <4 wk of anti-tuberculosis therapy. Informed consent was obtained from all patients. These studies were approved by the institutional review board of the University of Texas Health Center (Tyler, TX).
Cytofluorometric analysis
To measure the percentages of PBMC that expressed CD3 and CD56, we used FITC-conjugated anti-CD3 and PE-conjugated anti-CD56 (both from BD PharMingen, San Diego, CA), and immunostaining was performed by standard techniques (7). Based on forward and side scatter characteristics, we gated on lymphocytes, and the percentages of single- and double-stained cells were determined with an EPICS flow cytometer (Coulter, Hialeah, FL). For measurement of MHC class I expression, indirect immunostaining was performed, using a mouse anti-human MHC class I first Ab (W6/32; DAKO, Carpinteria, CA) and a FITC goat anti-mouse secondary Ab (Southern Biotechnology Associates, Birmingham, AL). After gating on monocytes, the mean fluorescence intensity of stained cells was measured.
To detect intracellular IFN- in cocultures of NK cells and M.
tuberculosis-infected monocytes, we used the Cytofix/Cytoperm Plus
kit (BD PharMingen). To induce intracellular accumulation of newly
synthesized proteins, Golgi Stop (0.7 µl/ml; BD PharMingen)
was added for 6 h to the cells in culture. Cells were then
harvested, and immunolabeling was performed. For double staining,
PE-conjugated anti-CD56 or anti-CD14 (BD Biosciences, San Jose,
CA) was first added. After washing with PBS and 5% FCS, cells were
fixed in Cytofix/Cytoperm and washed twice in 1x permeabilization/wash
solution. FITC anti-IFN- (BD PharMingen) was then added in
staining buffer and 1x permeabilization/wash solution. After
incubation at 4°C for 40 min, cells were washed in PBS and 5% FCS,
and analyzed by flow cytometry.
Isolation of mononuclear phagocytes and M. tuberculosis infection
PBMC were isolated from blood by differential centrifugation over Ficoll-Paque (Amersham Pharmacia Biotech, Piscataway, NJ). PBMC were centrifuged on a Percoll gradient (Pharmacia Biotech, Uppsala, Sweden). Monocyte fractions (1.2 x 106/well) were plated in 12-well plates (BD Labware, Franklin Lakes, NJ) in 1 ml RPMI 1640 (Life Technologies, Grand Island, NY) containing 10% heat-inactivated human serum. Some monocytes were uninfected, and others were infected with single-cell suspensions of 5 x 106 live M. tuberculosis (H37Ra or H37Rv), as previously described (8). Approximately 25–40% of the monocytes were infected. Cells were incubated for 4 h at 37°C in a humidified 5% CO2 atmosphere, washed to remove extracellular bacilli, and cultured in RPMI 1640 containing 10% heat-inactivated human serum. After 48 h cells were collected using a cell scraper and used as targets in cytotoxicity experiments. These cells were >90% monocytes, as assessed by staining with nonspecific esterase. Cell viability was >90%, as judged by trypan blue exclusion.
In some experiments live M. tuberculosis H37Ra was used to infect the monocytic THP-1 or MonoMac6 cell lines under the same conditions as those described above for monocytes.
Isolation of NK cells
CD3+ cells were depleted from PBMC with magnetic beads conjugated to anti-CD3 (Miltenyi Biotec, Auburn, CA), and from the negative cell fraction CD56+ cells were isolated by positive selection with magnetic beads conjugated to anti-CD56 (Miltenyi Biotec). The positive cells were 95–100% CD56+ and 95–97% CD3-, as measured by flow cytometry, and were used as effector cells.
Culture of monocytes and NK cells
Infected and uninfected monocytes were plated in round-bottom 96-well plates (BD Labware) at 5 x 103/well in 200 µl RPMI 1640 containing penicillin (Life Technologies) and 10% heat-inactivated human serum in the absence or the presence of NK cells (2 x 105/well; 40:1 E:T cell ratio). In some experiments culture supernatants were collected after 10 and 24 h to measure cytokine concentrations. In other experiments cells were used for RNA extraction, and real-time PCR was performed to quantify NK receptor molecules.
Cytotoxicity assay
NK cell cytotoxicity against infected and uninfected monocytes and K562 cells was assayed in a 10-h 51Cr release assay. Before the assay, target cells were labeled overnight with 100 µCi sodium chromate. Target cells were washed three times, and 5 x 103 cells/well were mixed with effector cells at E:T cell ratios ranging from 100:1 to 10:1 in 200 µl RPMI 1640 with 10% heat-inactivated human serum. All assays were performed in triplicate, and 10 h after incubation 100 µl supernatant was removed from each well, and radioactivity was measured in a gamma counter. The percentage of lysis was calculated as 100 x ((experimental release - spontaneous release)/(maximum release - spontaneous release)).
Generation of NK cell lines
PBMC were isolated from five healthy tuberculin reactors, as outlined above, and plated in a six-well plate (BD Labware) at 2 x 106 cells/well in 1 ml RPMI 1640 containing 10% heat-inactivated human serum. After incubation for 90 min, nonadherent cells were removed, and CD56+CD3- cells were isolated by immunomagnetic selection, as outlined above. These cells were plated in limiting numbers (ranging from 5 to 50 cells/well) in the presence of 104 irradiated mononuclear cells as feeders in RPMI 1640 supplemented with 10% FCS and 1% (µg/ml) PHA (Sigma-Aldrich, St. Louis, MO). After 2 days rIL-2 (10 ng/ml; BD PharMingen) rIL-12 (1 ng/ml; BD PharMingen), and rIL-15 (1 ng/ml; BD PharMingen) were added. Feeder cells, rIL-2, rIL-12, and rIL-15 were added weekly. NK cell lines were further expanded, phenotypically characterized, and used for functional assays.
Measurement of cytokine concentrations
For measurements of IL-18, IL-12, and IL-15, supernatants from
cultured cells were collected after 10 h; for measurement of
IFN-, supernatants were collected after 10 and 20 h and stored
at -70°C until cytokine concentrations were measured by ELISA.
Paired Abs were used to detect IFN- (BD PharMingen), IL-15, and
IL-12 p70 (both from R&D Systems, Minneapolis, MN). ELISA kits were
used to measure levels of IL-18 (MBL International, Nagoya, Japan). The
lower limits of detection were 5 pg/ml for IL-12 and IFN-, 8 pg/ml
for IL-15, and 13 pg/ml for IL-18. Cytokine concentrations were minimal
when cells were cultured in medium alone, and results are expressed as
the cytokine concentration in supernatants from NK cells and infected
monocytes minus that in supernatants from NK cells and uninfected
monocytes.
Real-time PCR for quantification of NKp44 and NKp46 mRNA
Total RNA was extracted from 1 x 106 NK cells 10 h after culture with infected or uninfected monocytes, using TRIzol reagent (Life Technologies). RNA was treated with RQ RNase-free DNase (Promega, Madison, WI) and RNasin ribonuclease inhibitor (Promega), then extracted with phenol/chloroform using standard methods. Total RNA was reverse transcribed using the oligo(dT)15 primer (Promega) and Omniscript reverse transcriptase (Qiagen, Valencia, CA).
Primers and probes for the NKp44 and NKp46 cDNA were designed using
Primer Express software (PE Applied Biosystems, Foster City, CA) and
were synthesized by Operon Technologies (Alameda, CA). The forward and
reverse primers for NKp44 were 5'-TCCAAGGCTCAGGTACTTCAAAG-3' and
5'-GGGCGGGTACTGGCATCT-3', respectively. The probe was
5'-ACGGTTAGCGTCTGCCCTGCCC-3'. The forward and reverse primers for NKp46
were 5'-ACGGGACTCCAGAAAGACCAT-3' and 5'-CAGGCCCATCCGAAGGA-3',
respectively, and the probe was 5'-CCCTCTGGGATCACACTGCCCAGAA-3'. Both
probes were 5'-fluorescein phosphoramidite labeled and 3'-TAMRA
labeled. The TaqMan 
-actin control reagents (PE Applied Biosystems)
were used as internal standards. Both sets of primers and probes
spanned an intron, so that they detected NKp44 and NKp46 cDNA, but not
genomic DNA. Real-time PCR assays were performed in a sealed 96-well
microtiter plate (PE Applied Biosystems) on a spectrofluorometric
thermal cycler (7700 PRISM; PE Applied Biosystems). Each cDNA sample
was aliquoted into wells containing 1x TaqMan Universal PCR master mix
(PE Applied Biosystems), 5 pmol of either the NKp44 or NKp46 or
-actin primers, and 1 pmol of the corresponding probe in a total
volume of 25 µl. Standard curves for quantification of -actin,
NKp44, and NKp46 cDNA were generated using the corresponding primers
and probes to amplify serial 10-fold dilutions of cDNA in purified NK
cells stimulated with IL-12 and IL-2 for 48 h. PCR reactions were
performed in triplicate as follows: 50°C for 2 min, 95°C for 10
min, and 40 cycles of 95°C for 15 s and 60°C for 1 min. The
fluorescent signal was measured and plotted during each 60°C
annealing and extension step for all samples. Using the cycle threshold
(the number of PCR cycles required for the fluorescent dye to be
detectable) and the constructed standard curve for each cDNA, the
relative amounts of -actin, NKp44, and NKp46 cDNA in each sample
were determined.
Statistical analysis
Results are shown as the mean ± SE. For data that were normally distributed, comparisons between groups were performed using a paired or unpaired t test, as appropriate. For data that were not normally distributed, the Wilcoxon rank-sum test was used. Values of p < 0.05 were considered statistically significant.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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To determine whether NK cells contributed to lysis of M. tuberculosis-infected mononuclear phagocytes, we first identified the most appropriate target cells. We obtained freshly isolated NK cells from two healthy tuberculin reactors and cultured them with uninfected and H37Ra-infected autologous monocytes, THP-1, and MonoMac6 cells at different time points ranging from 4–10 h. Lysis of infected targets was greater than that of uninfected targets for autologous monocytes, but not for THP-1 or MonoMac6 cells, and maximum lytic activity was observed at 10 h, so this time point and autologous monocytes were used for subsequent experiments.
To determine whether the capacity of NK cells to lyse M.
tuberculosis-infected monocytes was affected by prior tuberculosis
infection, we obtained freshly isolated NK cells from four healthy
tuberculin-negative persons and 15 healthy tuberculin reactors. NK
cells from healthy tuberculin reactors lysed a higher percentage of
H37Ra-infected monocytes than uninfected monocytes (59 ± 7% vs
23 ± 5%, respectively; p < 0.001), similar to
findings in tuberculin-negative persons (77 ± 11% vs 41 ±
13%, respectively; p = 0.002; Fig. 1
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To confirm that the cytotoxicity observed above was due to NK
cells and not due to contaminating T cells, we tested the cytotoxic
potential of a homogeneous population of NK cells by generating NK cell
lines from PBMC of four tuberculin reactors. These cells were 99%
CD56+ and <1% CD3+, and
all showed more cytotoxicity against infected than uninfected monocytes
(67 ± 15% vs 34 ± 9%, respectively; p <
0.01; Fig. 3).
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Monocytes are an important source of cytokines that activate NK
cells (9). To evaluate the involvement of these monokines
in NK cell-mediated cytotoxicity, we cocultured NK cells with either
infected or uninfected autologous monocyte from six healthy tuberculin
reactors. Higher levels of IL-18 were detected in supernatants of
infected monocyte and NK cells compared with those of control monocytes
and NK cells (107 ± 31 vs 26 ± 9 pg/ml, respectively;
p = 0.05; Fig. 4). IL-15
and IL-12 concentrations were slightly higher in cocultures containing
infected than uninfected monocytes, but the differences were not
statistically significant (Fig. 4). IFN- is produced by activated NK
cells and is essential for NK-mediated defenses against CMV infection
(10). Therefore, we measured IFN- concentrations, which
were increased 12-fold when NK cells were cocultured with infected vs
uninfected monocytes (p < 0.001; Fig. 4), and
these levels were further increased after 20 h to 5222 ±
1624 vs 145 ± 29 pg/ml (p < 0.001).
Because IFN- can be produced by macrophages, we combined surface
immunolabeling with CD14 or CD56 and intracellular staining to detect
IFN- in cocultures of NK cells and monocytes; 8.2% of the cells
were IFN-+CD56+, and
none was IFN-+CD14+,
indicating that NK cells were the source of IFN-.
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Because NK cells and infected monocytes produced high levels of
IL-18 and IFN-, we determined whether these cytokines contributed to
lysis of infected monocytes. In cells obtained from three healthy
tuberculin reactors, Abs to IL-18 and IFN-, alone or in combination,
did not reduce NK cell-mediated specific lysis against M.
tuberculosis-infected monocytes (Fig. 5).
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NK cells lyse autologous cells with reduced MHC class I expression because class I molecules engage inhibitory receptors on NK cells (11, 12). To determine whether MHC class I expression was reduced on M. tuberculosis-infected monocytes, we performed immunostaining with an anti-MHC class I Ab. In cells obtained from six healthy tuberculin reactors, the mean fluorescence intensities of infected and control monocytes were similar (44 ± 9 vs 45 ± 6).
NKp44 and NKp46 mRNA expression
Because lysis of monocytes by NK cells was not mediated by type 1
cytokines or by reduced MHC class I expression on monocytes, we next
evaluated the expression of NKp44 and NKp46, receptors, which are
present exclusively on NK cells and are associated with activation and
cytolysis (13, 14). We cocultured infected or uninfected
monocytes with NK cells from seven healthy tuberculin reactors and
quantified NKp44 and NKp46 mRNA expression using real-time PCR. To
normalize for the efficiency of RNA extraction and RT in different
samples, data were expressed as the ratio of NKp46 mRNA to -actin
mRNA, expressed in arbitrary units. NKp46 mRNA expression was
significantly up-regulated by coculturing NK cells with infected
monocytes compared with uninfected monocytes (14 ± 3 vs 2 ±
1 arbitrary units; p = 0.006; Fig. 6A). NKp44 mRNA expression was
not up-regulated in NK cells exposed to infected vs uninfected
monocytes (3 ± 1 vs 4 ± 2 arbitrary units, respectively;
Fig. 6B).
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To more definitively determine whether NK cell-mediated
cytotoxicity of infected monocytes was mediated by NKp46, we incubated
freshly isolated NK cells from five healthy tuberculin reactors with a
mouse antiserum raised against NKp46-Ig (15), before
coculture with M. tuberculosis-infected monocytes. The NKp46
antiserum reduced net percent specific lysis of infected monocytes from
33 ± 8% to 2 ± 1% (p = 0.01; Fig. 7). Treatment with the NKp46 antiserum
had no effect on the viability of the NK cells, as assessed by trypan
blue exclusion (data not shown).
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The above experiments demonstrated that freshly isolated NK cells from healthy donors can kill M. tuberculosis-infected monocytes. To determine the relevance of these findings to the clinical manifestations of M. tuberculosis infection, we evaluated NK cell number and function in tuberculosis patients, who have an ineffective immune response to infection. By flow cytometry, the percentages of CD56+ cells in PBMC were similar in tuberculosis patients, healthy tuberculin reactors, and tuberculin-negative subjects (10.5 ± 2.8%, 8.2 ± 2.2%, and 13.0 ± 0.3%, respectively). The percentages of CD56+CD3- and CD56+CD3+ cells were also similar in all three groups (data not shown).
We next compared the functional activities of NK cells from 15 healthy
tuberculin reactors and 10 tuberculosis patients. Values were expressed
as net percent specific lysis, which was the percent lysis of M.
tuberculosis-infected monocytes, minus that of uninfected
monocytes. The net percent specific lysis of NK cells was significantly
reduced in tuberculosis patients compared with that in healthy
tuberculin reactors (16 ± 6% vs 39 ± 6%, respectively;
p = 0.01; Fig. 8). Lysis
of the classic NK targets, K562 cells, by NK cells was also reduced in
tuberculosis patients compared with that in healthy tuberculin reactors
(7 ± 1% and 50 ± 5%, respectively; p <
0.001; Fig. 8).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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. These findings
are relevant to the clinical manifestations of infection with M.
tuberculosis, because NK cell lytic activity against M.
tuberculosis-infected monocytes and NKp46 expression were reduced
in tuberculosis patients compared with findings in healthy donors. NK cells are believed to play a central role in the innate immune response to microbial pathogens, both through destruction of infected cells and by secretion of cytokines that shape the subsequent adaptive immune response. The lytic capacity of NK cells is controlled by a balance between inhibitory and activating receptors (11, 12). All normal nucleated cells express MHC class I molecules on their surface, which bind to inhibitory NK cell receptors and prevent triggering of the lytic machinery. NK cells also bear a variety of activating receptors, including some that are restricted to NK cells. These include the NKp30, NKp44, and NKp46 receptors, the enhanced expression of which is associated with lysis of tumor cells and virally infected cells (13, 14, 16).
Most studies of NK cells in infectious diseases have focused on the response to viruses. Viral infection of target cells inhibits MHC class I expression, leading to reduced ligation of the NK cell inhibitory receptors and lysis of infected cells. Limited studies have suggested that NK cells can destroy cells infected with intracellular bacteria, such as Listeria, Salmonella, and Legionella, but these studies used lymphokine-activated killer cells rather than highly purified NK cells (3, 17, 18). In mycobacterial infection, depletion of NK cells in C57BL/6 mice enhances the growth of Mycobacterium avium (19), and IL-12-stimulated human NK cells activate macrophages to inhibit the growth of M. avium in macrophages (20). Denis (21) first showed that freshly isolated NK cells from healthy donors can lyse M. tuberculosis-infected monocytes and reduce the rate of intracellular bacillary growth, but the mechanisms underlying these effects were not investigated. One study found that growth inhibition was mediated by soluble factors produced by NK cells, whereas another suggested that growth inhibition required contact between NK cells and monocytes and was associated with the induction of monocyte apoptosis (22, 23).
We found that freshly isolated NK cells from both tuberculin-positive and tuberculin-negative healthy subjects specifically lyse M. tuberculosis-infected monocytes, indicating that this activity was innate and independent of prior exposure to M. tuberculosis. Lysis of infected monocytes is associated with 7-fold enhanced expression of mRNA for NKp46, and antisera to NKp46 markedly inhibited lysis of infected cells. Compared with healthy tuberculin reactors, tuberculosis patients with ineffective immunity showed reduced lytic activity of infected monocytes, lower cytotoxic activity against K562 cells, and decreased NKp46 mRNA expression. These findings suggest that the NK cell response to M. tuberculosis infection correlates with the clinical manifestations of infection, and that NKp46 contributes to destruction of infected cells by freshly isolated NK cells. NKp44 expression was not enhanced in NK cells exposed to infected monocytes, perhaps reflecting the fact that freshly isolated NK cells bear NKp46, but not NKp44, receptors (13, 14). NK cells lysed monocytes infected with both virulent and avirulent strains of M. tuberculosis, suggesting that immunotherapeutic strategies that enhance NK cell function may be useful in selected patients with tuberculosis.
Hemagglutinin of the influenza virus and hemagglutinin-neuraminidase of the Sendai virus have recently been identified as the first microbial ligands for NKp46 (15). A basic local alignment search tool search did not reveal any M. tuberculosis proteins that are likely to be expressed on the cell surface and that share significant homology with these viral proteins. However, it is possible that glycosylated mycobacterial proteins may interact with sialic acid residues on NKp46, which were found to be required for binding to viral hemagglutinin (15). It is intriguing to speculate that one of the mechanisms by which NK cells contribute to innate immunity is through recognition by NKp46 of conserved conformational molecular structures of intracellular pathogens that are expressed on the surface of infected cells, in a manner analogous to that of Toll-like receptors on macrophages.
The dominant mechanisms that mediate NK cell cytotoxicity against cells infected with different organisms are likely to vary. Viruses and several intracellular bacteria, such as Salmonella, Yersinia, and Chlamydia pneumoniae, may induce NK cell lytic activity by lowering MHC class I expression on mononuclear phagocytes (24, 25, 26). In contrast, we found that M. tuberculosis did not reduce MHC class I expression, confirming prior reports (27, 28). These findings are also consistent with studies showing that NK cells expressing NKp46 can lyse target cells, independent of the presence of MHC class I molecules (11).
NK cells produce cytokines that are likely to shape the subsequent
adaptive immune response by T cells in response to intracellular
pathogens. We found that NK cells produced larger amounts of IFN- in
response to M. tuberculosis-infected monocytes than in
response to uninfected monocytes. However, IFN- was not required for
cytotoxicity, which was unaffected by addition of anti-IFN- Abs.
Similarly, IFN- does not mediate the capacity of NK cells to kill
intracellular M. tuberculosis (23). Although
IFN- produced by NK cells in response to M.
tuberculosis-infected macrophages does not directly mediate
cytotoxicity, it may contribute to immune defenses by favoring the
development of a protective type 1 response, as IFN- can enhance the
production of both IL-12 and IL-18 in response to M.
tuberculosis (29, 30). We and others have previously
shown that M. tuberculosis-induced IFN- production is
reduced in PBMC of tuberculosis patients, compared with healthy
tuberculin reactors (31, 32), and depletion of NK cells
from PBMC markedly reduces Ag-induced IFN- production (K.
Vankayalapati, unpublished observations), suggesting that NK cells
affect subsequent cytokine production by T cells stimulated with
mycobacterial Ags. Further studies are needed to understand the
mechanisms by which the innate immune response modulates adaptive T
cell immunity to M. tuberculosis and other intracellular
pathogens.
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Peter F. Barnes, Center for Pulmonary and Infectious Disease Control, University of Texas Health Center, 11937 U.S. Highway 271, Tyler, TX 75708-3154. E-mail address: peter.barnes{at}uthct.edu
Received for publication October 1, 2001. Accepted for publication January 22, 2002.
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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production in murine splenocytes: role of NK cells and macrophages. J. Immunol. 150:3973.[Abstract]
are costimulators of interferon production by natural killer cells in severe combined immunodeficiency mice with listeriosis, and interleukin 10 is a physiologic antagonist. Proc. Natl. Acad. Sci. USA 90:3725. in defense against murine cytomegalovirus infection and enhancement of this defense pathway by interleukin 12 administration. J. Exp. Med. 182:1045.. J. Infect. Dis. 174:1073.[Medline]
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 C. E. Foster, M. Colonna, and P. D. Sun Crystal Structure of the Human Natural Killer (NK) Cell Activating Receptor NKp46 Reveals Structural Relationship to Other Leukocyte Receptor Complex Immunoreceptors J. Biol. Chem., November 14, 2003; 278(46): 46081 - 46086. [Abstract] [Full Text] [PDF]
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M. R. Daws, P. M. Sullam, E. C. Niemi, T. T. Chen, N. K. Tchao, and W. E. Seaman Pattern Recognition by TREM-2: Binding of Anionic Ligands J. Immunol., July 15, 2003; 171(2): 594 - 599. [Abstract] [Full Text] [PDF]
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), or with K562
cells, and the percentage of cytotoxicity was determined. The mean
values and SEs are shown for net percentage of specific lysis in the
case of infected monocytes and for percentage of lysis in the case of
K562 cells.