|
|
||||||||
B, IL-6, and IgE in Human B Lymphocytes1
Division of Basic Sciences, Department of Pediatrics, National Jewish Medical and Research Center, Denver, CO 80206
| Abstract |
|---|
|
|
|---|
B and
IL-6 have been postulated in the induction of IgE synthesis by
IL-4/CD40. We found that neither anti-CD40 Ab nor IL-4 alone was
able to induce significant proliferation of human B cells. However, the
combination of anti-CD40 and IL-4 was a potent inducer of B cell
proliferation in addition to IgE production from purified human B
cells. Furthermore, IL-4 and anti-CD40 synergized for the
production of IL-6. While neither IL-4 alone nor anti-CD40 alone
was able to induce significant NF-
B DNA binding activity, the
combination of IL-4 and anti-CD40 induced a strong activation of
NF-
B, a transcription factor that regulates IL-6 production. These
data indicate that both IL-4 and anti-CD40 are required to induce
NF-
B activation and IL-6 transcription and production, and implicate
these events in a signaling pathway augmenting IgE production in human
B lymphocytes. | Introduction |
|---|
|
|
|---|
mRNA expression, functional
gene
transcription, and IgE secretion (5, 6). The intracellular mechanisms
by which these surface-generated signals lead to enhanced IgE
production remain unclear.
Signaling through CD40 leads to the phosphorylation and/or
dephosphorylation of a number of proteins, including the Lyn, Fyn, and
Syk tyrosine kinases (7, 8). We have demonstrated that CD40 stimulation
of human B cells leads to selective activation of the c-Jun
kinase/stress-activated protein kinase pathway (9). Recent evidence has
implicated members of the TNF receptor-associated factor (TRAF)
family of signal transducers in mediating CD40-generated signals within
the cell (10, 11). Furthermore, protein tyrosine kinase inhibitors are
able to block the induction of IgE secretion by anti-CD40 and IL-4,
suggesting that such phosphorylation events may be critical in
mediating the differentiative effects of CD40/IL-4 stimulation of B
cells (12). It also has been reported that stimulation of B cells via
CD40 leads to activation of the NF-
B transcription factor (13, 14).
However, the relationship between these early signaling events and the
later differentiative events of the B cell response to IL-4 and CD40
stimulation has not been defined.
IL-4 induction of IgE secretion in PBMC or T and B cell mixtures appears to require IL-6, as depletion of monocytes from this population strongly diminishes the ability of IL-4 to induce IgE (15). Stimulation of highly purified B cells with IL-4, IL-5, and IL-6 nonetheless does not lead to IgE production, indicating that the second signal provided via CD40 is a requisite step. A neutralizing anti-IL-6 Ab strongly inhibits the ability of anti-CD40 Ab and IL-4 to induce IgE synthesis in highly purified human B cells, suggesting that the autocrine production of IL-6 is a necessary step in CD40-induced IgE production (16).
IL-6 is expressed by a number of cell types and induces a wide variety
of responses, including induction of hepatic acute phase responses,
differentiation of B cells, and augmentation of T cell responses (17).
The expression of IL-6 is regulated primarily through the binding of
the NF-
B transcription factor to IL-6 promoter sequences (18).
Stimuli that induce IL-6 gene expression, such as IL-1 and TNF-
,
also induce NF-
B DNA binding activity (19). Furthermore, the
deletion of the NF-
B sequences within the IL-6 promoter strongly
diminishes the induction of IL-6 gene expression (19, 20, 21).
NF-
B is a pleiotropic transcription factor that is involved in
regulating the expression of a number of genes, including Ig light
chain, IL-2, and c-myc, in addition to IL-6 (22, 23, 24).
NF-
B is a dimeric complex located in the cytosol in an inactive form
associated with an inhibitor, I
B (25). Cell stimulation by a number
of agents leads to the release of NF-
B from I
B and its subsequent
translocation into the nucleus (26, 27).
Because of the demonstrated synergistic effects of anti-CD40 mAbs
and IL-4 on IgE synthesis by purified normal human B cells, we examined
whether the signals generated by these two stimuli also synergize to
activate additional factors that may be involved in regulating IgE
production and secretion, namely NF-
B and IL-6. We found that IL-4
and anti-CD40 synergized to induce NF-
B activation and IL-6
production as well as IgE secretion, suggesting that these regulatory
events may be involved in the transmission of CD40/IL-4-activated
signals to enhance IgE production.
| Materials and Methods |
|---|
|
|
|---|
G285 anti-CD40 mAb was a gift from Dr. Edward Clark
(Seattle, WA). Recombinant IL-4 was provided by Paul Trotta (Schering
Plough, Kenilworth, NJ). Tritiated thymidine deoxyribonucleotide (6.7
Ci/mmol) and [
-32P]dCTP (25 Ci/mmol) were purchased
from ICN Pharmaceuticals (Irvine, CA). Oligonucleotides containing the
consensus NF-
B binding sequence (5'-GGGAGTTGAGGGGACTTTCCCAGGC) or
the consensus AP-13 binding
sequence (5'-CTTCGTGACTCAGCGGGATCCTTCGTGACTCAGCGG) were synthesized
by the Molecular Resource Center at the National Jewish Center (Denver,
CO). IL-6 cDNA (pBSF2.38.1) was provided by Dr. Toshio Hirano (Osaka,
Japan) (28). mAbs to p50 (SC-114) and p65 (SC-109) were purchased from
Santa Cruz Biotechnology (Santa Cruz, CA). Streptavidin-fluorescein
reagent and biotin-16-dUTP were purchased from Boehringer Mannheim
(Indianapolis, IN).
Blood sampling and cell preparations
PBMC were prepared from heparin-treated blood of healthy human volunteers by Ficoll-Hypaque (Pharmacia, Uppsala, Sweden) gradient centrifugation. B cells were purified by E rosette depletion and two-phase plastic adherence as previously described (29). B cells prepared in this manner typically were >95% positive for the B cell markers CD19 and CD20 as determined by flow cytometric analysis. For measurement of IL-6 production by ELISA, purified B cells were resuspended in serum-free medium and incubated for 24 h at 37°C to eliminate potential contamination by IL-6 from the serum. For all other experiments, cells were resuspended in RPMI 1640 tissue culture medium (Life Technologies, Grand Island, NY), supplemented with penicillin (100 U/ml), streptomycin (100 mg/ml), L-glutamine (2 mmol/L), and 10% heat-inactivated FCS.
ELISAs
B cells (1 x 106) were incubated in a total volume of 1 ml in 24-well plates. Cells were stimulated with anti-CD40 mAb (250 U/ml) or IL-4 (200 U/ml) as indicated. Supernatants were harvested after a 14-day culture. ELISA for the determination of total IgE was performed in flat-bottom 96-well plates (Dynatech, Alexandria, CA), coated with purified goat anti-human IgE (Tago, Burlingame, CA) as previously described (30). All cultures were performed in triplicate. The limit of detection in the ELISA was 100 pg/ml for IgE.
IL-6 accumulation measurements
IL-6 accumulation in supernatants was determined using an ELISA kit obtained from R&D Systems (Minneapolis, MN).
Nuclear extracts and electrophoretic mobility shift assay
After stimulation, B cells were lysed in hypotonic buffer, and
nuclear proteins were extracted as previously described (31). Nuclear
extracts were stored at -70°C until use. Binding reactions were
conducted with equal amounts of protein for each experiment (0.21.0
µg). A double-stranded oligonucleotide containing the NF-
B
sequence was end labeled with [
-32P]dCTP using Klenow
fragment of DNA polymerase I. Protein samples were incubated at room
temperature first with poly(dI-dC) (1 µg) for 10 min and then with
the radiolabeled probe for 15 min in a total volume of 15 µl. Samples
were analyzed using a 5% polyacrylamide gel under nondenaturing
conditions with 1x Tris borate electrophoresis buffer as the
running buffer. Following electrophoresis, the gels were dried and
analyzed by autoradiography. Films from four separate experiments were
scanned, and the densities of the bands were analyzed. Supershift
experiments were performed by preincubating nuclear extracts with
anti-p50 or anti-p65 Ab for 10 min before addition of
radiolabeled DNA probe.
| Results and Discussion |
|---|
|
|
|---|
|
|
|
B transcription factor has been implicated in the induction
of IL-6 gene expression (14). To assess whether the combination of
anti-CD40 and IL-4 could induce NF-
B activity, we prepared
nuclear extracts from stimulated human B cells and performed
electrophoretic mobility shift assays. As in the other assays, we found
that while neither IL-4 alone nor anti-CD40 alone induced NF-
B
DNA binding activity, the combination of IL-4 and anti-CD40 induced
a strong activation of NF-
B (Fig. 4
B activity were detected in unstimulated peripheral
blood B cells. These results differ from those of a previous report
that showed that anti-CD40 Ab alone was able to induce NF-
B DNA
binding activity in purified human B cells (14). However, tonsillar B
cells were used in this earlier study, while our experiments were
performed with resting, purified peripheral blood B cells. It is
possible that these differences in results reflect differences in the
activation status of tonsillar compared with peripheral blood B
cells (32).
|
|
B binding induced by
anti-CD40 and IL-4, mobility shift assays were performed using
unlabeled NF-
B or unlabeled AP-1 as competitor probes. As shown in
Figure 5
B effectively competed with the labeled NF-
B probe to
eliminate specific NF-
B binding activity, whereas unlabeled AP-1
probe had no competitive effect on the NF-
B band.
To confirm that the DNA binding activity induced by anti-CD40 and
IL-4 was due to authentic NF-
B, we performed experiments using Abs
to the p65 component of NF-
B. As shown in Figure 5
, anti-p65 Ab,
but not control Abs, reduced NF-
B binding. These results confirmed
that the DNA binding activity induced by anti-CD40 and IL-4 in
purified human B cells was indeed NF-
B. The combination of
anti-p50 and anti-p65 Abs also caused a marked reduction in the
NF-
B band (data not shown).
Stimulation of human B lymphocytes via the CD40 receptor in the
presence of IL-4 leads to a marked up-regulation in IgE production and
secretion (6). While anti-CD40 Ab is not able to induce germline
gene transcription, it does lead to a significant enhancement of
germline
mRNA production in the presence of IL-4 (5). IL-4 alone is
not able to induce switch recombination to the C
gene and requires
the CD40 signal provided by CD4+ T cells for class
switching and functional IgE secretion (33). Furthermore, the
observation that the defective expression of gp39 underlies the
hyper-IgM syndrome in humans confirms that CD40 signaling plays an
integral role in all Ig gene switching (34, 35, 36, 37, 38, 39).
Stimulation of B lymphocytes by cross-linking the B cell Ag receptor
complex with anti-IgM leads to programmed cell death. Activation of
the CD40 receptor rescues such anti-IgM-stimulated cells from
undergoing apoptosis (3). It has been suggested that the activation of
the zinc finger protein, A20, by CD40 leads to the prevention of
programmed cell death (40). Others have suggested that the
bcl-x gene product plays an important role in CD40
modulation of the apoptotic response of B lymphocytes (41, 42).
Recently, CD40 ligation has been shown to prevent the
anti-IgM-induced activation of CPP32, one of the caspases known to
deliver a death signal (43). Our observation that anti-CD40
stimulation of resting peripheral blood B cells in the absence of IL-4
fails to induce any significant NF-
B activation implies that NF-
B
itself is not involved in the CD40-mediated rescue of B cells from
anti-IgM-induced apoptosis. Berberich et al. (14) demonstrated that
anti-CD40 Ab alone was able to induce NF-
B DNA binding activity
in purified tonsillar human B cells. More recently, Hess et al. (44)
found that anti-CD40 Ab induced NF-
B mobilization in
nonhemopoietic cells. One possible explanation for the differences
between these results and those we describe here is that while our
studies were performed with resting peripheral blood human B cells, the
other groups used other sources of cells, activated or cycling to
various degrees.
Our results suggest that NF-
B and IL-6 are intermediaries in
sequential signaling pathways activated through both CD40 and IL-4
receptors in human B cells, leading to IgE production and secretion.
Warren and Berton found that stimulation of murine B cells using a
membrane-bound version of the CD40 ligand leads to detectable germline
transcription (45). This induction appeared to be independent of
the effects of other cytokines, most notably IL-4. Furthermore,
stimulation with CD40 ligand and IL-4 together had a significant
synergistic effect on germline
transcription. The observed
synergism between CD40 and IL-4 receptor signaling is not surprising
given the demonstrated triggering of independent pathways by these
receptors. IL-4R stimulation has been shown to lead to the induction of
specific transcription factors, particularly STAT6 (46, 47). In
contrast, CD40 has been shown to activate the c-Jun kinase pathway (9).
The convergence point appears to lie upstream of NF-
B activation and
may occur at the step of inactivation of I
B, the natural inhibitor
of NF-
B. Recently, Iciek and co-workers found that nuclear complexes
composed of both STAT6 and NF-
B proteins were induced
synergistically by CD40 and IL-4 receptor stimulation (48).
Furthermore, these complexes bound to a region of the germline
promoter required for mediation of the synergistic effects of CD40 and
IL-4 receptor stimulation on germline
transcription. Cumulatively,
these observations support the idea that CD40 and the IL-4 receptor
activate pathways with distinct yet synergistic effects on IgE
production.
| Acknowledgments |
|---|
| Footnotes |
|---|
2 Address correspondence and reprint requests to Dr. Erwin W. Gelfand, National Jewish Medical and Research Center, Denver, CO 80206. ![]()
3 Abbreviation used in this paper: AP-1, activating protein-1. ![]()
Received for publication August 5, 1996. Accepted for publication April 15, 1998.
| References |
|---|
|
|
|---|
2. J. Exp. Med. 179:673.
B by TNF receptor 2 and CD40. Science 269:1424.
B, AP-1, and NF-AT during B cell stimulation through the CD40 receptor. Int. Immunol. 7:151.
B. J. Immunol. 153:4357.[Abstract]
B synergistically activate transcription of the inflammatory cytokines, interleukin 6 and interleukin 8. Proc. Natl. Acad. Sci. USA 90:10193.
B-like sequence. Mol. Cell. Biol. 10:3818.
B. Proc. Natl. Acad. Sci. USA 91:2225.
B transcription factor. Mol. Cell. Biol. 10:2327.
B. J. Immunol. 147:416.[Abstract]
B-like factors mediate interleukin 1 induction of c-myc gene transcription in fibroblasts. J. Exp. Med. 176:787.
B: structure-function relationship of its protein subunits. Biochem. J. 290:297.
B in vivo is regulated by multiple phosphorylations. EMBO J. 13:4597.[Medline]
B
which can be prevented by the immunosuppressant rapamycin. J. Biol. Chem. 269:30077.
B
in mediation of immunosuppression by glucocorticoids. Science 270:283.
B in B cells. J. Exp. Med. 177:1215.
promoter: regulation by NF-IL-4, a C/EBP family member and NF-
B/p50. J. Exp. Med. 181:181.
Ig gene expression in murine B cells. J. Immunol. 155:5637.[Abstract]
activation site-like sequence upstream of the Ie exon in a human B cell line. J. Clin. Invest. 96:907.
B. J. Immunol. 158:4769.[Abstract]
This article has been cited by other articles:
![]() |
D. Frasca, A. M. Landin, R. L. Riley, and B. B. Blomberg Mechanisms for Decreased Function of B Cells in Aged Mice and Humans J. Immunol., March 1, 2008; 180(5): 2741 - 2746. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. Merlo, C. Tenca, F. Fais, L. Battini, E. Ciccone, C. E. Grossi, and D. Saverino Inhibitory Receptors CD85j, LAIR-1, and CD152 Down-Regulate Immunoglobulin and Cytokine Production by Human B Lymphocytes Clin. Vaccine Immunol., June 1, 2005; 12(6): 705 - 712. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. E. Duddy, A. Alter, and A. Bar-Or Distinct Profiles of Human B Cell Effector Cytokines: A Role in Immune Regulation? J. Immunol., March 15, 2004; 172(6): 3422 - 3427. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. Zamorano, A. L. Mora, M. Boothby, and A. D. Keegan NF-{kappa}B activation plays an important role in the IL-4-induced protection from apoptosis Int. Immunol., December 1, 2001; 13(12): 1479 - 1487. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. Pioli, L. Gatta, V. Ubaldi, and G. Doria Inhibition of IgG1 and IgE Production by Stimulation of the B Cell CTLA-4 Receptor J. Immunol., November 15, 2000; 165(10): 5530 - 5536. [Abstract] [Full Text] [PDF] |
||||
![]() |
P. Zelazowski, Y. Shen, and C. M. Snapper NF-{kappa}B/p50 and NF-{kappa}B/c-Rel differentially regulate the activity of the 3'{alpha}E-hsl,2 enhancer in normal murine B cells in an activation-dependent manner Int. Immunol., August 1, 2000; 12(8): 1167 - 1172. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. Cerutti, A. Schaffer, R. G. Goodwin, S. Shah, H. Zan, S. Ely, and P. Casali Engagement of CD153 (CD30 Ligand) by CD30+ T Cells Inhibits Class Switch DNA Recombination and Antibody Production in Human IgD+ IgM+ B Cells J. Immunol., July 15, 2000; 165(2): 786 - 794. [Abstract] [Full Text] [PDF] |
||||
![]() |
P. Revy, C. Hivroz, G. Andreu, P. Graber, C. Martinache, A. Fischer, and A. Durandy Activation of the Janus Kinase 3-STAT5a Pathway After CD40 Triggering of Human Monocytes But Not of Resting B Cells J. Immunol., July 15, 1999; 163(2): 787 - 793. [Abstract] [Full Text] [PDF] |
||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |