The Role of Infectious Agents in B-cell Lymphomas
Moderators: Dr. Miguel A. Piris and Dr. Steven H. Swerdlow
Section 4 -
Hepatitis C Virus and Lymphoproliferative Disorders
The role of lymphoma microenvironment in Splenic Marginal Zone Lymphoma
B Herreros, A Sanchez-Aguilera, M Mollejo , MA Piris
Lymphoma group, Spanish Nacional Cancer Centre
elchor Fernandez Almagro
3. Madrid , Spain
The growth of lymphoma cells may depend not only on the accumulation of genetic alterations but also
on signals derived from the milieu that drives cell proliferation or inhibits apoptosis. The relevance
of the microenvironment to lymphoma pathogenesis has been highlighted by the observations linking
specific microbial and viral pathogens to specific types of lymphoproliferative syndromes. However, it
has also become apparent that lymphoma development requires a particular stromal microenvironment that
conditions the nature of the developed neoplasms. This evidence has come from a range of conditions such
as inflammation, bacterial and viral infection, endemic diseases and autoantigen stimulation of the
The Normal Marginal Zone
Presence of a discernible marginal zone was initially noticed in the spleen. It is usually a
well-developed functional and topographical area consisting of medium-sized lymphoid elements with
regular nuclei and a variable amount of clear cytoplasm  . Marginal zone cells in the spleen
are CD20+, CD79a+, IgM+, CD21+, alkaline phosphatase+, but CD23-, Bcl6-, and IgD-negative or weakly
IgD-positive. The size and immunophenotype of the splenic marginal zone may vary with age and specific
pathological conditions . Marginal zone B cells have also been described in normal lymph nodes, mainly in
those draining mucosae, and have a similar immunophenotype and topographical distribution to their
splenic counterparts. By analysis of the mutated IgVH genes, marginal zone cells have been demonstrated
to be mostly memory B cells, with a minor component of naive elements, the latter probably being
responsible for thymus-independent type 2 antigen responses, such as bacterial capsular polysaccharide.
Splenic marginal zone B cells play an important role in transporting circulating immune complexes into
the splenic follicles and depositing them on the surface of follicular dendritic cells .
This functional assignation seems to be consistent with the regular distribution of MZ B cells around
Splenic Marginal Zone Lymphoma
The term splenic marginal zone lymphoma (SMZL) was introduced by Schmid et al. in 1992, in relation
to a study performed on a series of 4 cases  . Subsequently, larger series have been
published, reediting some diagnostic criteria and increasing the knowledge of their molecular and
clinical characteristics  . Splenic marginal zone lymphoma is a relatively rare type of
lymphoma, which accounts for around 1-2% all non-Hodgkin's lymphomas.
The tumour in the spleen is characterized by a micronodular lymphoid infiltrate located in white
pulp, with variable red pulp infiltration, marginal zone differentiation and follicular replacement by
neoplastic cells. The white pulp tumoral nodules are composed of an inner central zone of small
lymphocytes, located in the mantle zone and replacing the germinal centre, and a peripheral zone of
medium-sized cells with clear cytoplasm and scattered blasts, the marginal zone component. Lymphoma
cells may have variable degree of plasmacytic differentiation, including as a characteristic feature the
presence of monoclonal plasma cells in the germinal centre. The tumour includes numerous admixed T
The bone marrow infiltration is characterised by intertrabecular polymorphic nodules and interstitial
and intrasinusoidal infiltration of small lymphocytes, with a pattern highly characteristic. The
morphology of the tumoral cells in the peripheral blood includes villous cells, small cells, plasmacytic
cells, centrocytoid cells and cells with monocytoid appearance.
Splenic hilar lymph node involvement shows a micronodular pattern, centred on pre-existing replaced
follicles. As in the bone marrow, marginal differentiation is generally absent. These morphological
variations suggest that SMZL cells, depending on their background, show morphological and
immunophenotypic changes that reflect the tumoral-growth dependence of the microenvironment. Thus, it
seems that marginal zone differentiation is mainly restricted to the spleen, while at other locations,
the lack of the appropriate architecture or signalling mechanisms does not induce marginal zone
differentiation. At the same time, the cell composition of the tumoral aggregates somehow reflects the
now-recognised capacity of marginal zone B cells to induce germinal centre development through the
transport of immune complexes to the follicular dendritic cells .
Immunophenotype : The tumoral cells express surface IgM and IgD and are
CD20+, CD43-, IgD+, bcl2+, CD5-, CD23-, Cyclin D1-, bcl6-, CD10-, DBA44-/+. Immunostaining with bcl2
highlighted follicular replacement of bcl2- cells germinal centre by bcl2+ tumoral cells. The
proliferative index is low, and MIB1 staining shows a distinctive annular pattern, outlining the presence
of an increased growth fraction in the germinal centre and marginal zone.
Cytogenetic and molecular findings. Cytogenetic and molecular studies
have demonstrated that around 45% of SMZL cases have allelic loss in the
7q22-36 chromosomal region. This alteration is found more frequently in SMZL than in other small B-cell
lymphomas. Cases with 7q loss behave more aggressively and have more frequent tumoral progression.
Somatic mutations of IgVH genes have been observed in about half of the cases and, in those treated
with splenectomy, were associated with longer overall survival . This finding, similar to that observed
in CLL, reveals a striking parallel between these two conditions. Immunoglobulin gene studies have
additionally revealed that roughly half of the SMZL cases make selective use of the V(H)1-2 segment,
suggesting that this tumour derives from a highly selected B-cell population, which in turn implies that
either foreign or preserved autoantigens play a role in the genesis of the disease. In addition to IgVH,
a smaller proportion (13%) of SMZL cases display somatic mutations in the 5´ non-coding region of the
Gene profiling studies, in addition to confirming the relative homogeneity of this entity, indicate
potential diagnostic markers and pathogenic pathways involved in the survival of the tumoral cell. Thus,
the signature includes upregulated genes involved in apoptosis regulation, BCR and TNF signalling, and
NF-κB activation, such as SYK, BTK, BIRC3, TRAF3, TRAF5, CD40 and LTB  . Furthermore,
genes associated with the splenic microenvironment, like SELL and LPXN, were also overexpressed. Other
genes of particular interest are lymphoma oncogenes such as ARHH and TCL1 . The increased expression of
TCL1 is linked with the upregulation of genes associated with intracellular signalling via the AKT1
pathway found in SMZL, as described by Thieblemont et al  . Upregulation of the AP-1 and
Notch 2 transcription factors has also been described by Troen et al  . Consistently with
previous cytogenetic studies, genes located in the 7q31-7q32 region, such as CAV1, CAV2 and GNG11 are
The cellular origin of SMZL is still a controversial issue. Although the term seems to indicate a
close relationship with marginal zone B cells, the absence of IgVH somatic mutations in half of the
cases, the absence of marginal differentiation when the tumour is located outside the spleen and the
expression of IgD by the tumoral cells calls into question the marginal zone cell origin of this tumour,
and raises the possibility that SMZL tumoral cells could represent the tumoral expansion of hitherto
uncharacterised marginal zone precursor splenic B-cell subpopulation. This is supported also by the
findings of Troen et al., where Notch 2  , a transcription factor that induces marginal zone
B-cell differentiation is overexpressed in SMZL .
Splenic Marginal Zone Lymphoma, Viruses and Bacterias
The role of viral and bacterial antigens in the pathogenesis of splenic marginal zone lymphoma (SMZL)
is suggested from the findings of several studies:
- IgVH-biased selection. IgVH mutational studies have demonstrated that roughly half of the SMZL cases use
VH1.2, which contrasts with the use of this IgVH in normal B-cells, since only around 1% of normal
peripheral blood B-cells use this gene  .
- Association with malaria and idiopathic
. Two different lymphoproliferative
disorders, tropical splenic lymphoma, characterized by splenomegaly and circulating naive CD5-negative
villous B lymphocytes, and hyper-reactive malarial splenomegaly, have been described in malaria-endemic
areas. Although no relation has been found with other B-lymphotropic viruses, patients with tropical
splenic lymphoma have been found to exhibit raised EBV antibody levels.
- A relationship between HCV infection and SLVL has recently been established , which lends support to the
hypothesis that the stimulation of marginal zone B cells in the spleen by persistent HCV antigens,
particularly the E2 viral antigen, might be involved in the pathogenesis of SMZL. Thus, hepatitis C
infection was reported in 10-16% of SMZL patients . Significantly, a higher proportion of HCV positivity
(up to 50%) has been found in splenic DLBCL . Even regression of splenic lymphoma with villous
lymphocytes (SLVLs) has been described in patients with HCV after antiviral treatment, thereby
demonstrating a direct role of HCV in lymphomagenesis  . Interestingly, symptomatic mixed
cryoglobulinaemia was a common feature in these cases  .
- Nevertheless, the presence of HCV in lymphoid neoplasms seems to be a phenomenon characteristic of
precise geographic areas, such as Italy and Japan, and restricted to some tumor types, singularly SMZL
and other Marginal Zone Lymphomas
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