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Prepublished online as a Blood First Edition Paper on April 17, 2002; DOI 10.1182/blood-2002-01-0099.
REVIEW ARTICLE
From the Amgen Research Institute, Ontario Cancer
Institute, the Departments of Medical Biophysics and Immunology,
University of Toronto, Ontario, Canada.
The clinical and pathologic features of classical Hodgkin lymphoma
(cHL) reflect an abnormal immune response that is thought to be due to
the elaboration of a variety of cytokines by the malignant
Reed-Sternberg (RS) cells or surrounding tissues. The majority of cHL
cases are characterized by expression of tumor necrosis factor receptor
(TNFR) family members and their ligands, as well as an unbalanced
production of Th2 cytokines and chemokines. Activation of TNFR members
results in constitutive activation of nuclear factor- Classical Hodgkin lymphoma (cHL) is a lymphoid
malignancy with characteristic features that distinguish it from
nodular lymphocyte-predominant HL (NLPHL) and non-Hodgkin lymphomas
(NHLs).1,2 The malignant cells in cHL, termed the
Reed-Sternberg (RS) cells, constitute only a minor component of the
tumor, whereas the majority of the malignancy is composed of a mixed
inflammatory infiltrate variably composed of lymphocytes, eosinophils,
fibroblasts, macrophages, and plasma cells. Patients with cHL also
commonly present with constitutional symptoms such as fever, weight
loss, and night sweats, and an apparent systemic defect in
cell-mediated immune responses. Many of these distinctive clinical and
histopathologic features of cHL reflect an abnormal immune response
thought to be due largely to the effects of a wide variety of cytokines
and chemokines that are primarily produced by the RS cells, but also secondarily by the surrounding reactive infiltrate. This review summarizes the data on cytokine production in cHL, examines cytokine signaling, and discusses the role of cytokines in the clinical and
pathologic features of this disease.
Classical HL is now considered a distinct clinicopathologic entity from
NLPHL and can be divided into 4 morphologic subtypes: nodular sclerosis
cHL (NSHL), mixed cellularity cHL (MCHL), lymphocyte-rich cHL (LRCHL),
and lymphocyte-depleted cHL (LDHL).2 There are few data on
cytokine involvement in LRCHL and LDHL, because each disease comprises
less than 5% of all cHL cases. As a result, nearly all of the data on
the role of cytokines in cHL are derived from the study of NSHL and
MCHL cases.
Cytokines are low-molecular-weight proteins with a wide variety of
functions. They not only regulate immune and inflammatory responses but
also contribute to hematopoiesis, wound healing, and other biologic
processes. Cytokines are extremely potent molecules active in nanomolar
to picomolar concentrations. Typically, a cytokine either acts in a
paracrine manner to modulate the activity of surrounding cells, or in
an autocrine fashion to affect the cell that produced it. In the
context of cHL, cytokines produced by RS cells are thought to
contribute to the pathogenesis of this disease both by acting as
autocrine growth factors and by initiating and sustaining the reactive
infiltrate. Alternatively, cytokines produced by surrounding reactive
cells may be contributing to RS cell proliferation and survival.
The expression and activity of cytokines in cHL can be studied using
cell lines derived from RS cells and in primary cHL tissues. Each
approach has its limitations, so that a combination of both strategies
provides the most comprehensive information on the activity of a
specific cytokine. Cell lines derived from RS cells have been extremely
useful in the study of cHL.3,4 However, outgrowth of such
a cell line from cHL patient tissues is extremely rare, so that the few
cell lines available may not represent the full spectrum of clinical
and pathologic features of this disease. The RS cell lines that have
been established are overrepresentative of patients with advanced stage
disease, and those with disease involving pleural effusions, peripheral
blood, or bone marrow. Furthermore, only one cell line, L-1236, has
been definitively identified as being derived from RS
cells.5,6 Unequivocal proof that the other cell lines are
derived from RS cells is lacking, but extensive analysis of their
morphologic, phenotypic, and genetic features has led the research
community to generally regard most of them as being derived from RS
cells.3,4
Analysis of short-term cultures of primary cHL biopsy material is
hampered by the fragility of freshly isolated RS cells and contamination by the reactive infiltrate. Therefore, the activity of
cytokines on primary RS cells is difficult to demonstrate directly and
indirect evidence, such as the expression patterns of cytokines and
their receptors, activation of downstream signaling molecules, and
correlation of cytokine expression with expected pathologic features,
must be relied on. Because cytokines are active at very low
concentrations, methods for determining cytokine messenger RNA (mRNA)
and protein expression in primary tissues must be very sensitive.
Cytokine mRNA levels can be assessed in whole tissue extracts by
Northern analysis, but this method does not allow localization of
expression to specific cell populations, and may not be sufficiently
sensitive if the cytokine is expressed by a small population of cells.
In situ hybridization (ISH) techniques using radio-labeled RNA probes
have been very useful for detecting cytokine mRNA levels in
formalin-fixed, paraffin-embedded tissues. ISH is highly sensitive and
allows retention of the morphology of positively staining cells. mRNA
expression can also been studied on the single-cell level on RS cells
isolated from cell suspensions.7 However, the presence of
mRNA does not confirm the presence of the protein product, which
requires examination by immunohistochemistry (IHC). A combination of
ISH and IHC is therefore the most effective strategy for determining
cytokine expression in tissue sections.
The human adaptive immune response can be divided into 2 distinct
branches: the humoral immune response, which targets extracellular pathogens by stimulating B cells to produce antibodies, and the cell-mediated immune response, which targets intracellular pathogens by
activating CD8+ cytotoxic T cells and macrophages.
CD4+ helper T cells are crucial for regulating both types
of responses and can be classed into 2 mutually exclusive subsets: T
helper type 1 (Th1) and Th2 cells.8 Th1 cells, which
require interleukin 12 (IL-12) for their differentiation,
characteristically produce IL-2 and interferon- Th2 cytokines
IL-4 and IL-13.
Interleukin 4 and IL-13 are important cytokines that share many
biologic activities.9,10 Both IL-4 and IL-13 regulate the
humoral immune response by stimulating the proliferation and survival
of B cells and triggering Ig class switching. IL-4 (but not IL-13) is
required for the differentiation of Th2 cells.
 chain and an IL-13-specific receptor chain, IL-13R1. IL-4R expression has been demonstrated in 3 RS cell
lines21 but has not been investigated in primary cHL
samples. IL-13R1 is expressed by 6 RS cell lines
examined19,21 and by RS cells in 95% of cHL cases as
determined by ISH or IHC.19,20 The expression of both
IL-13 and its receptor by RS cells is consistent with a role for IL-13
as an autocrine growth factor for these cells. Indeed,
antibody-mediated neutralization of IL-13 in the IL-13+ RS
cell lines HDLM-2 and L-1236 led to a dose-dependent inhibition of
proliferation in both cell lines and the induction of apoptosis in
L-1236 cells (but not in HDLM-2 cells).14,18,21 However, treatment of the IL-13+ RS cell lines L-428 and KM-H2 with
the same anti-IL-13 antibody had no effect on cell proliferation.
IL-5. Interleukin 5 is a Th2 cytokine essential for the growth and differentiation of eosinophils. It is also a B-cell growth factor in mice (but not in humans).22 IL-5 is expressed by 2 of 6 RS cell lines11,18 and has been identified in primary RS cells from tumors with tissue eosinophilia.23 The proliferation of 2 IL-5+ RS cell lines (L-428, KM-H2) was not affected by antibody-mediated neutralization of IL-5, suggesting that IL-5 is not an autocrine growth factor for cHL.18 IL-6.
Interleukin 6 was first identified as a T cell-derived cytokine that
induces the maturation of B cells into antibody-producing plasma cells.
IL-6 also induces hematopoiesis from stem cells and acute phase
reactions by hepatocytes.24 IL-6 expression has been
widely studied in RS cell lines and in primary cHL cases by Northern
analysis, ISH, and IHC. IL-6 was expressed by 5 of 7 RS cell
lines,5,11,12,25 and in RS cells from 65% to 100% of cHL
cases.12,16,25-28 IL-6 was also occasionally expressed by
lymphocytes and macrophages within the reactive infiltrate. Interestingly, IL-6 expression was significantly higher in Epstein-Barr virus (EBV)+ cases of cHL versus EBV IL-9.
Interleukin 9 is a T-cell and mast cell growth factor that can also
potentiate IL-4-induced IgG4 and IgE production.30
Although IL-9 mRNA was not detected in unstimulated L-428 cells, it was identified in 5 of 12 (42%) cases of cHL by Northern
analysis.31 In 5 of these cases, including 2 that were
IL-9 IL-10.
Interleukin 10 is a Th2 cytokine with strong anti-inflammatory
properties. IL-10 inhibits T-cell growth, blocks IL-2 and IFN- Th1 cytokines IL-12.
Interleukin 12 is required for Th1-cell differentiation.34
In the context of cHL, IL-12 has been detected by IHC in 28 of 33 (85%) cases, expressed by reactive cells but not by RS
cells.35 The level of IL-12 expression varied from tumor
to tumor, ranging from a few or absent IL-12+ cells in some
cases to clusters of positive cells around RS cells in others.
IL-12+ cells could be detected within the reactive
infiltrate in all 22 EBV+ cases, but in only 5 of 10 EBV IL-2. Interleukin 2 is a principal growth factor for T cells, and also augments the cytolytic activity of natural killer (NK) cells.36 IL-2 was not expressed by any of 7 RS cell lines examined,5,11,37,38 and expression of IL-2 in primary cHL cases has been extremely variable. Eight cHL cases were negative for IL-2 mRNA by Northern analysis.16 More recently, Dukers et al found that less than 5% of RS cells and reactive lymphocytes were IL-2+ in 27 cases of NSHL tested using IHC.17 However, Hsu et al could demonstrate IL-2+ RS cells in 10 cases of NSHL by IHC, with a range of 30% to 75% IL-2+ RS cells.37 Three IL-2 receptor chains have been identified: IL-2R (CD25, Tac),
IL2R , and the common  (c) chain. These chains combine to form
3 different IL-2 receptor complexes distinguished by their binding
affinity for IL-2: the low-affinity ( chain only),
intermediate-affinity ( and chains), and high-affinity (,
, and c chains) receptors. The cytoplasmic domain of the chain is essential for signal transduction in response to IL-2, such
that only the intermediate- and high-affinity receptors are able to
transduce IL-2 signals.39 IL-2R expression has been
demonstrated in 5 of 6 RS cell lines11,37,38,40,41 and in
primary RS cells by IHC in 75% of cHL cases.37,40-44
IL-2R chain expression, however, is less consistent in both cultured and primary RS cells. Using IHC, Hsu et al37 could not
detect IL-2R on 2 RS cell lines (HDLM-2 and KM-H2) or on primary RS cells from 10 cases of cHL. However, Tesch et al used the same antibody
to detect IL-2R protein by IHC on 5 RS cell lines (including HDLM-2
and KM-H2) and in primary RS cells from 7 of 13 cases of cHL.41 Similarly, Trumper et al detected transcripts for
IL-2R in 50% to 75% of RS cells from all 6 cHL cases in which mRNA
expression levels were determined on single RS cells isolated from cell
suspensions.7 Several investigators have shown that
recombinant IL-2 does not affect the proliferation of cultured RS
cells,37,45,46 even in a cell line shown to express
high-affinity IL-2R.41 In summary, the weight of evidence
indicates that RS cells do not express IL-2 and variably express
IL-2R, and that exogenous IL-2 has no effect on RS cell growth.
Therefore, IL-2 is unlikely to be an autocrine growth factor in cHL.
IFN-
Chemokines are chemoattractant cytokines that regulate the
selective migration of leukocytes through binding to specific chemokine receptors differentially expressed on various leukocyte populations. Approximately 50 chemokines and 20 chemokine receptors have been identified in humans50 but only a few have been studied in
cHL (Table 2).
Most of the chemokines that have been studied in cHL are associated
with either a humoral or cell-mediated immune response, based on the
expression pattern of their receptors on Th1 and Th2
cells.51 Th1 cells express the chemokine receptors CXCR3 and CCR5 and therefore are attracted to sites of production of their
respective ligands. The ligands for CXCR3 include inducible protein 10 (IP-10) and monokine induced by IFN- Th2 chemokines Expression of TARC in cHL was first discovered using a serial gene expression analysis of RS cell lines.53 TARC was expressed by 4 RS cell lines examined, but absent in B-lymphoblastoid and NHL cell lines. TARC was also expressed by RS cells in 88% of cHL cases as determined by ISH or IHC.53,54 Cases of NSHL demonstrated stronger staining by IHC compared to MCHL cases. TARC was not expressed in NLPHL, and the majority of NHL cases were TARC , except
for a small number of ALCL and TCRBCL cases.53,54 Although
moderate to strong levels of CCR4 mRNA could be detected by reverse
transcription-polymerase chain reaction (RT-PCR) in 4 RS cell lines,
CCR4 expression could not be detected in primary RS cells by ISH.
However, a high proportion of the lymphocytes surrounding the RS cells
were CCR4+, consistent with an activated Th2-cell
phenotype.53
Although levels of MDC expression in cHL tissues as a group were not significantly different from those in normal lymphoid tissues, MDC expression among cHL subtypes was significantly higher in NSHL cases compared to MCHL cases.49 By IHC, 87% of cHL cases demonstrated MDC expression, primarily localized to RS cells.55 Eotaxin expression is higher in cHL tissues than in normal lymphoid
tissues, as demonstrated by RT-PCR.49 Within cHL subtypes, elevated eotaxin expression was preferentially associated with NSHL
cases. Eotaxin was detected by IHC in RS cells, fibroblasts, macrophages, and lymphocytes within cHL tissues, with more intense staining in NSHL than MCHL cases. Moreover, expression of eotaxin correlated with the number of eosinophils in the cHL tissue, suggesting that eotaxin contributes to eosinophil recruitment to cHL tissues. In
contrast to these findings, Jundt et al detected eotaxin mRNA in only 1 of 5 RS cell lines and could not detect eotaxin expression in primary
RS cells by IHC or ISH.56 They found that fibroblasts were
the major source of eotaxin with a minor contribution by macrophages.
Eotaxin expression could be induced in cultured fibroblasts separated
from cocultured RS cells by a micropore membrane, indicating that
soluble factors produced by the cultured RS cells stimulated the
up-regulation of eotaxin expression. The RS cell line L-1236 produces
high levels of TNF- Expression of CCR3 could not be demonstrated on RS cell lines by flow cytometry or on primary RS cells by IHC.57 However, strong expression of CCR3 could be detected by IHC on about half of the cells within the cHL reactive infiltrate, compared to very rare CCR3 expression in control lymph nodes. Flow cytometry indicated that CCR3 was expressed not only on T cells in cHL tissue but also on B cells, an unexpected finding because normal B cells do not express CCR3.57 Whether this observation represents a cHL-specific dysregulation of CCR3 expression or a more general phenomenon is unclear. Th1 chemokines The Th1-associated chemokines IP-10, Mig-1, MIP-1, MIP-1,
and RANTES are expressed at higher levels in cHL tissues compared to
benign lymphoid tissues.49,57 In contrast to eotaxin, TARC and MDC, which are associated with the nodular sclerosis (NS) subtype
of cHL, expression levels of IP-10, Mig-1, and MIP-1 were higher in
MCHL cases.49 Elevated expression of these chemokines was
also associated with EBV+ cHL cases. IP-10 and Mig-1
immunoreactivity was strongest in RS cells but also present in
endothelial cells, macrophages, lymphocytes, and fibroblasts. CCR5, the
receptor for MIP-1 and MIP-1, was not present on cultured or
primary RS cells but was expressed on approximately half of the cells
within the reactive infiltrate, including CD4+ T cells and
B cells.57 The expression of CXCR3, the receptor for IP-10
and Mig-1, was moderately up-regulated in the CD4+ T-cell
population.57
IL-8 Interleukin 8 is a potent neutrophil recruitment factor that binds to the chemokine receptors CXCR1 and CXCR2 on neutrophils. IL-8 mRNA was detected by ISH in 20 of 33 cases of cHL and its level correlated with the density of tissue neutrophilia.58 IL-8 was predominantly expressed by cells within the reactive infiltrate and could be detected in RS cells in only 3 cases.
Members of the tumor necrosis factor (TNF) family of receptors and
ligands play important roles in the pathogenesis of cHL. Approximately
25 TNF receptor (TNFR) members have been identified in normal tissues,
including TNFRI, TNFRII, CD40, CD30, CD27, OX40, receptor activator of
nuclear factor
TNF- was identified as a macrophage product
mediating cytotoxicity against certain cell types, especially
transformed cell lines. Subsequently, TNF- has been shown to play
important roles in inflammation, tissue remodeling, and wound
healing.60 TNF- enhances the phagocytic and
microbicidal activities of macrophages and stimulates the production of
other proinflammatory cytokines including IL-1 and IL-6. In the context
of cHL, TNF- expression at the mRNA and protein levels has been
demonstrated in 7 RS cell lines.5,11,26,61,62 TNF- was
detected by Northern analysis in all 19 cHL cases
examined,63 and by IHC or ISH in primary RS cells in 69%
of cHL cases examined in 6 studies.26,61,62,64-66 Cells
within the reactive infiltrate, including lymphocytes and macrophages,
were also TNF-+. TNF- can use 2 receptors called
TNFRI (p55) and TNFRII (p75).60 These receptors have been
studied in only a small number of primary tumors and not at all in RS
cell lines. Ryffel et al used IHC to examine malignant lymphomas
(including 4 cases of cHL) for the expression of TNFRI and TNFRII. Two
cHL cases contained TNFRII+ RS cells and one had
TNFRI+ RS cells.67 Treatment of the RS cell
lines HDLM-2 and KM-H2 with recombinant TNF- did not stimulate or
suppress cellular proliferation.46
Lymphotoxin CD40 CD40/CD40L-mediated contacts between B and T cells are required for the generation of T cell-dependent humoral immune responses. Activation of CD40 on B cells stimulates proliferation and mediates Ig class switching in conjunction with IL-4 and IL-13.68 Surface CD40 expression was detected in 4 RS cell lines examined by flow cytometry.32,69 O'Grady et al first studied CD40 expression in primary cHL by IHC and found strong membrane or cytoplasmic staining of RS cells in 26 of 37 (70%) cases.70 In contrast, CD40 expression was much weaker in normal lymphoid tissues and present in only 3 of 23 cases of B-cell NHL. Strong CD40 expression as determined by IHC was subsequently reported in primary RS cells in a total of 190 cHL cases.32,69,71,72 However, CD40 expression was not exclusive to cHL, because 105 of 127 B-cell NHLs stained weakly positive for CD40.32The activation of CD40 on a cell requires contact with CD40L expressed
on the surface of a neighboring cell. CD40L is absent on cultured and
primary RS cells, but is present on CD4+ T cells within cHL
tissues.69,71,72 Numbers of CD40L+ T cells
were increased in cHL tissues compared to normal lymphoid tissues. The
CD40L+ T cells were usually located in close proximity to
RS cells, with an average of 2.5 to 5 CD40L+ T cells
surrounding a single RS cell.71 In contrast, the malignant cell population and reactive component of cases of CD40+
B-cell NHL failed to express significant levels of CD40L. Treatment of
RS cell lines with soluble trimeric CD40L to activate CD40 stimulated
the release of IL-8, enhanced secretion of IL-6, TNF- CD40 signaling pathways can be activated by the latent membrane
protein-1 (LMP-1) of EBV. Approximately 40% of cHL cases from immunocompetent patients in Western countries are associated with EBV
infection and viral sequences can be detected within RS
cells.74-76 RS cells show a type II pattern of EBV latency
antigen expression, with expression of LMP-1, LMP-2, and Epstein-Barr
nuclear antigen-1 (EBNA-1). EBV LMP-1 can mimic CD40 signaling in a
ligand-independent and constitutive manner77 because the
cytoplasmic portions of CD40 and LMP-1 recruit many of the same
signal-transducing molecules, including members of the TNFR-associated
factor (TRAF) family78,79 (discussed below in NF- CD30 CD30 is expressed on RS cells from virtually all cases of cHL.80 Several cells within cHL tumors express CD30L, allowing potential activation of CD30 on neighboring RS cells. CD30L expression could not be detected in cultured RS cells by Northern analysis,81 flow cytometry,82 or RT-PCR.83 By IHC, however, weak expression of CD30L could be detected in primary RS cells in all cHL cases examined.82,83 However, RS cells demonstrated cytoplasmic staining without membrane reactivity; therefore, it remains unclear whether primary RS cells express CD30L on their surfaces. However, several other cell populations within the reactive infiltrate express CD30L, including eosinophils84 and mast cells.85 Circulating eosinophils from cHL patients expressed higher CD30L levels than cells from healthy donors.84Activation of CD30 induces significantly different responses in
different CD30+ lymphoma cell lines. This was first
demonstrated by Smith et al who showed that CD30L activation stimulated
proliferation of the CD30+ RS cell line HDLM-2 but had no
effect on the proliferation of the CD30+ RS cell lines
KM-H2 and L-428.86 In contrast, CD30L stimulation of the
CD30+ ALCL cell line KARPAS-299 induced cytotoxic cell
death. These investigations were extended by Gruss et al who found that
CD30 could also stimulate the proliferation of the RS cell line L-540, but had cytotoxic effects on 6 of an additional 7 CD30+
ALCL cell lines,87 results subsequently confirmed by other groups.84,85 Hsu and Hsu also found that activation of
CD30 induced increased proliferation of L-428 and KM-H2 cells and of enriched RS cells from primary patient material.83 Like
CD40 activation, CD30 activation increased the secretion of IL-6,
TNF- RANK RANKL is a member of the TNF ligand family that plays a role in osteoclast differentiation, activation of mature osteoclasts, and interactions between T cells and dendritic cells. RANKL binds to 2 receptors, RANK and osteoprotegerin (OPG). RANK, RANKL, and OPG are all expressed by L-428, KM-H2, and HDLM-2 cells.89 RANK can be also detected by IHC in primary RS cells from both NSHL and MCHL cases. Activation of RANK in RS cell lines by soluble RANKL up-regulates the expression of several cytokines, including IFN-, IL-9, IL-13, and
IL-15. However, treatment of these RS cell lines with soluble RANKL, or
inhibition of RANK-RANKL interactions between cultured RS cells, has no
effect on the proliferation or survival of these
cells.89
Several cytokines that do not belong to the previously discussed
groups, including IL-1, TGF-
IL-1 Interleukin 1 is a potent proinflammatory cytokine.90 IL-1 has 2 distinct forms (IL-1 and IL-1) that bind to the same receptor and have identical biologic activities. With respect to cHL, 3 of 6 RS cell lines were positive for IL-1,11,91 and IL-1
has been detected in cHL tissues in 58% of cases examined by IHC or
ISH.64-66,92,93 In most instances, IL-1 was expressed predominantly by RS cells, but was also seen in lymphocytes,
granulocytes, and macrophages. Recombinant IL-1 had no effect on the
proliferation of HDLM-2 or KM-H2 cells.46
TGF- has potent anti-inflammatory
effects. It suppresses B- and T-cell proliferation and the cytolytic activity of NK cells, and stimulates fibroblast proliferation and
collagen synthesis.94 The RS cell line L-428 produces
TGF- mRNA and secretes a high-molecular-weight form of TGF-
protein that is active at physiologic pH.95 Using IHC,
Kadin et al first identified TGF- in primary RS cells from 6 of 8 cases of NSHL but not in 4 cases of MCHL or 1 case of
LDHL.96 TGF-+ RS cells were typically
located near zones of necrosis and at the margins of collagen bands.
Subsequently, ISH was used to show that TGF- transcripts were
present in eosinophils from cases of NSHL but absent in RS cells,
suggesting that eosinophils are the major source of TGF- in cHL and
that the RS cell immunoreactivity in the previous study represented
secondary binding and uptake by RS cells.97 Interestingly,
Newcom and Gu were able to detect TGF- in RS cells of predominantly
NSHL cases by both IHC and ISH.98 In short, although the
cellular source of TGF- is unclear, this cytokine is
characteristically expressed in the NS subtype of cHL.
Hematopoietic growth factors Hematopoietic growth factors include IL-3, IL-7, granulocyte-macrophage colony stimulating factor (GM-CSF), and macrophage-CSF (M-CSF).99 IL-3 stimulates colony formation of erythroid, megakaryocyte, eosinophil, basophil, and monocyte lineages, whereas IL-7 is a growth factor for progenitor B and T cells and mature T cells. GM-CSF is a differentiation factor for granulocytic and monocytic cells, whereas M-CSF is a growth and differentiation factor for macrophages and their progenitors.Expression of IL-3 protein was not detected in 6 RS cell lines examined,11 and IL-3 mRNA was detected in only 2 of 8 cases of cHL by Northern analysis.16 Exogenous IL-3 had no effect on the proliferation of HDLM-2 or KM-H2 cells.46 IL-7 mRNA was detected in RS cells from 24 of 31 cases of cHL, but identified in only 1 of 10 cases of lymphoblastoid lymphoma and in no cases of chronic B-lymphocytic leukemia.100 GM-CSF expression was detected in 2 of 6 RS cell lines11,18 but not in 8 cHL cases examined by Northern analysis.16 Exogenous GM-CSF had no effect on the proliferation of HDLM-2 or KM-H2 cells.46 L428 and 2 sublines expressed M-CSF and its receptor, the product of the proto-oncogene c-fms. However, only one of the sublines showed any evidence that M-CSF could act as an autocrine growth factor.101 Although M-CSF was detected by IHC in primary RS cells from 100% of cHL cases in one study,102 and 75% of cHL cases in another,103 c-fms mRNA expression could not be detected in primary RS cells.7,104
STAT signaling The interaction of cytokines with their specific cell surface receptors triggers the activation of intracellular signaling cascades that ultimately have effects on multiple cellular functions. The earliest event is the activation of Janus kinase (Jak) family members, which then phosphorylate substrates crucial for the transduction of cytokine signals. One of the most important substrates is the family of signal transducer and activator of transcription (STAT) proteins.105 STATs are latent transcription factors residing in the cytoplasm that become activated by phosphorylation on a single tyrosine residue. This phosphorylation is carried out by Jak family members activated in response to cytokine receptor stimulation. Tyrosine phosphorylation leads to STAT dimerization and translocation of the activated transcription factor to the nucleus, where it stimulates transcription resulting in changes to gene expression. Seven members of the STAT family have been identified, STAT1, STAT2, STAT3, STAT4, STAT5a, STAT5b, and STAT6, and each is activated by a distinct set of cytokines (reviewed by Leonard and O'Shea105).STAT6. Interleukin 4 and IL-13 are the primary activators of STAT6,106 and its pivotal role in signaling of these cytokines has been demonstrated in mice deficient for STAT6, which show impaired proliferation of B and T cells in response to IL-4, and abrogation of Ig class switching and Th2 cytokine production.107-109 Additionally, STAT6 is involved in the expression of Th2 chemokines, including eotaxin, TARC, and MDC.110,111 All 5 RS cell lines examined demonstrated constitutive STAT6 phosphorylation, which was shown to be due to autocrine secretion of IL-13 in HDLM-2 and L-1236 cells.14 Nuclear staining of phospho(P)-STAT6 was present in primary RS cells from 78% of cHL cases, whereas it was rarely detected in the reactive infiltrate.14 In cHL subtypes, STAT6 activation was present in 95% of NSHL cases, but in only 50% of MCHL cases. P-STAT6 expression was rare in normal lymphoid tissue, and among NHLs it was present only in a minority of ALCL and TCRBCL cases. P-STAT6 expression was associated with IL-13 expression in cHL cases, consistent with the active signaling of IL-13 in primary RS cells that would be expected for an autocrine growth factor. STAT3.
STAT3 plays a role in oncogenesis, being involved in both
hematolymphoid and solid tumors (reviewed by Bowman et
al112). A wide range of cytokines activates STAT3,
including the IL-6 family of cytokines, IL-10, and cytokines whose
receptors use the | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Top
Abstract
Introduction
B (NF-
25 pg/mL) by enzyme-linked immunosorbent assay (ELISA) in L-428
and HDLM-2 cells