MAL expression in lymphoid cells: further evidence for MAL as a distinct molecular marker of primary mediastinal large B-cell lymphomas.
ABSTRACT The MAL mRNA was initially identified during T-cell development and was later found in myelin-forming cells and certain polarized epithelial cell lines. It encodes a proteolipid believed to participate in membrane microdomains stabilization, transport machinery and signal transduction. Using a differential display reverse-transcription approach, we identified MAL as a distinct molecular marker of primary mediastinal large B-cell lymphoma compared with nonmediastinal diffuse large B-cell lymphomas. In the present study, we used immunohistochemistry to extend MAL expression analysis to normal lymphoid tissues; to 185 lymphomas representing most B, T, and Hodgkin lymphoma entities; and to the primary mediastinal large B-cell lymphoma derived B-cell line MedB-1. In addition, B and T cells from peripheral blood, tonsil, and spleen were analyzed by flow cytometry. Our results show that MAL is highly expressed in thymocytes, in a large percentage of peripheral CD4 T cells, and in a lower proportion of CD8 peripheral T cells. In the normal B-cell compartment, MAL expression appears to be restricted to a minor subpopulation of thymic medullary B cells and to occasional mature plasma cells located in the interfollicular areas of tonsil and lymph nodes. Among B-cell lymphomas (n = 110), MAL expression in tumor cells was observed in 21/33 primary mediastinal large B-cell lymphomas (70%) and in 3/5 plasmacytoma/myeloma, but not in all other B-cell lymphomas with the exception of 1/33 nonmediastinal diffuse large B-cell lymphomas. The MedB-1 B-cell line was also MAL positive. Among T-cell neoplasms, MAL was highly expressed in lymphoblastic tumors (5/6), whereas mature T-cell lymphomas were essentially MAL negative (27/28). Among 41 Hodgkin lymphomas, 3 nodular-sclerosing cases with mediastinal involvement showed MAL-positive Reed Sternberg cells. In conclusion, this study further supports thymic B cells as the putative normal counterpart of primary mediastinal large B-cell lymphomas and supports MAL as a distinct molecular marker of this lymphoma subtype among diffuse large B-cell lymphomas.
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ABSTRACT: Résumé: Les biopuces à ADN font partie des avancées technologiques importantes des toutes dernières années qui permettent d’ouvrir la voie à une compréhension plus globale et plus approfondie de la biologie tumorale. Par l’hybridation de l’ADN complémentaire synthétisé à partir d’un échantillon tumoral sur une surface contenant des séquences de gènes différents, cette technique va permettre en une seule étape d’évaluerde façon quantitative l’expression de plusieurs milliers de gènes au sein de cette tumeur. Les lymphomes malins, de par leur hétérogénéité tant biologique que clinique, constituent un modèle de choix pour l’utilisation de ce nouvel outil. Appuyée sur des analyses bioinformatiques complexes, l’analyse de plusieurs séries d’échantillons a récemment permis la description des voies de signalisation activées dans ces tumeurs lymphoïdes, aboutissant à la reconnaissance de la proximité ou au contraire à l’individualisation de certains sous-types histologiques, à l’identification de prédicteurs biologiques de diagnostic ou de pronostic, et enfin à la caractérisation de nouvelles cibles pour des agents pharmacologiques spécifiques. À travers les publications réalisées à ce jour, nous allons discuter dans cette revue l’impact de cette technique sur la compréhension de la biologie et la clinique des lymphomes malins, de type Hodgkinien et non Hodgkinien.Oncologie 05/2006; 8(4):314-321. · 0.08 Impact Factor
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ABSTRACT: Primary mediastinal B-cell lymphoma (PMBCL) is a relatively rare lymphoma subtype affecting mainly young adults. Its molecular signature and clinical features resemble classical Hodgkin lymphoma. The optimal chemotherapy for this lymphoma subtype has not been established. The addition of rituximab to anthracycline based chemotherapy improved response rates and survival. Many centers use R-CHOP as standard treatment, but the role of the intensified regimens and consolidation radiotherapy has to be clarified. Recent data coming from retrospective analyses and an ongoing prospective study addressing the problem of consolidation radiotherapy will help to better identify risk groups and apply risk-adapted and effective treatment strategies. The latest research has helped to understand molecular mechanisms of PMBCL pathogenesis and indicated targets of directed therapy for the future.Current Hematologic Malignancy Reports 06/2014;
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ABSTRACT: Primary mediastinal B-cell lymphoma (PMBL) is a highly aggressive disease with a unique set of biological, clinical, morphological, immunological and in particular genetic features that in the molecular era of defining lymphomas clearly distinguishes it as a separate entity from other diffuse large B-cell lymphomas (DLBCL). A precise molecular diagnosis of PMBL can be achieved by gene expression profiling. The signature gene expression profile of PMBL is more closely related to classic Hodgkin lymphoma (cHL) than to other DLBCL subgroups. A number of common genetic aberrations in PMBL and cHL further underscore their close relationship. To investigate the pathobiology of lymphomas in depth, many groups have turned to cell lines that are suitable models facilitating molecular studies and providing unique insights. For the purposes of the current perspective, we focus on four bona fide PMBL-derived cell lines (FARAGE, KARPAS-1106, MEDB-1, U-2940) that we identified and validated as such through hierarchical cluster analysis among a large collection of leukemia-lymphoma cell lines. These gene expression profiles showed that the four PMBL cell lines represent a distinct entity and are most similar to cHL cell lines, confirming derivation from a related cell type. A validated cell line resource for PMBL should assist those seeking druggable targets in this entity. This review aims to provide a comprehensive overview of the currently available cellular models for the study of PMBL. Copyright © 2014 Elsevier Ltd. All rights reserved.Leukemia Research 11/2014; · 2.69 Impact Factor
MAL Expression in Lymphoid Cells: Further Evidence
for MAL as a Distinct Molecular Marker of Primary
Mediastinal Large B-Cell Lymphomas
Christiane Copie-Bergman, M.D., Anne Plonquet, M.D., Miguel A. Alonso, Ph.D.,
Marie-Laure Boulland, Ph.D., Jeanine Marquet, Ph.D, Marine Divine, M.D., Peter Möller, M.D.,
Karen Leroy, M.D., Ph.D., Philippe Gaulard, M.D.
Département de Pathologie, Service d’Immunologie Biologique, Service d’Hématologie Clinique, Hôpital
Henri Mondor, Créteil, France; Centro de Biología Molecular “Severo Ochoa,” Universidad Autónoma de
Madrid and Consejo Superior de Investigaciones Científicas, Madrid, Spain; and Institute of Pathology,
University of Ulm, Ulm, Germany
The MAL mRNA was initially identified during T-cell
development and was later found in myelin-
forming cells and certain polarized epithelial cell
lines. It encodes a proteolipid believed to partici-
pate in membrane microdomains stabilization,
transport machinery and signal transduction. Using
a differential display reverse-transcription ap-
proach, we identified MAL as a distinct molecular
marker of primary mediastinal large B-cell lym-
phoma compared with nonmediastinal diffuse large
B-cell lymphomas. In the present study, we used
immunohistochemistry to extend MAL expression
analysis to normal lymphoid tissues; to 185 lym-
phomas representing most B, T, and Hodgkin lym-
phoma entities; and to the primary mediastinal
large B-cell lymphoma derived B-cell line MedB-1.
In addition, B and T cells from peripheral blood,
tonsil, and spleen were analyzed by flow cytometry.
Our results show that MAL is highly expressed in
thymocytes, in a large percentage of peripheral CD4
T cells, and in a lower proportion of CD8 peripheral
T cells. In the normal B-cell compartment, MAL
expression appears to be restricted to a minor sub-
population of thymic medullary B cells and to oc-
casional mature plasma cells located in the interfol-
licular areas of tonsil and lymph nodes. Among
B-cell lymphomas (n ? 110), MAL expression in
tumor cells was observed in 21/33 primary medias-
tinal large B-cell lymphomas (70%) and in 3/5 plas-
phomas with the exception of 1/33 nonmediastinal
diffuse large B-cell lymphomas. The MedB-1 B-cell
line was also MAL positive. Among T-cell neo-
plasms, MAL was highly expressed in lymphoblastic
tumors (5/6), whereas mature T-cell lymphomas
were essentially MAL negative (27/28). Among 41
Hodgkin lymphomas, 3 nodular-sclerosing cases
with mediastinal involvement showed MAL-positive
Reed Sternberg cells. In conclusion, this study fur-
ther supports thymic B cells as the putative normal
counterpart of primary mediastinal large B-cell
lymphomas and supports MAL as a distinct molec-
ular marker of this lymphoma subtype among dif-
fuse large B-cell lymphomas.
KEY WORDS: B-cell lymphoma, Hodgkin lym-
phoma, Lymphoid cells, MAL.
Mod Pathol 2002;15(11):1172–1180
MAL mRNA was initially identified by a differential
screening approach during the search for T-cell
maturation-associated cDNAs and was shown to be
associated with the intermediate and later stages of
intrathymic T-cell differentiation (1). Subsequently,
MAL expression was observed in rat myelin-
forming cells (2) and in polarized epithelial cell
lines derived from dog kidney and rat thyroid (3, 4).
MAL is an integral membrane protein located in
called lipid rafts, and is believed to participate in
membrane microdomains’ stabilization, transport
machinery, and signal transduction (5–10).
Using a differential-display reverse transcription
approach, we identified MAL as a distinct molecu-
lar marker of primary mediastinal large B-cell lym-
Copyright © 2002 by The United States and Canadian Academy of
VOL. 15, NO. 11, P. 1172, 2002 Printed in the U.S.A.
Date of acceptance: July 20, 2002.
M.A.A. is supported by grants from the Dirección General de Enseñanza
Superior (PM99–0092), and Fondo de Investigación Sanitaria (01/0085–
01). An institutional grant from the Fundación Ramón Areces to the
Centro de Biología Molecular “Severo Ochoa” is also acknowledged.
Address reprint requests to: Christiane Copie-Bergman, M.D., Départe-
ment de Pathologie, Hôpital Henri Mondor, 51 avenue du Maréchal de
Lattre de Tassigny, 94010 Créteil, France; e-mail: christiane.copie@ hm-
n.ap-hop-paris.fr; fax: 33-1-4981-2733.
phomas compared with nonmediastinal diffuse
large B-cell lymphomas (11). MAL recurrent expres-
sion in primary mediastinal large B-cell lymphomas
transcription-polymerase chain reaction (RT-PCR),
and immunohistochemical studies in a limited se-
ries of primary mediastinal large B-cell lymphomas,
nonmediastinal diffuse large B-cell lymphomas,
and neoplastic B-cell lines. These results were in
line with the hypothesis that primary mediastinal
large B-cell lymphoma represents a distinct lym-
phoma subtype among diffuse large B-cell lympho-
According to the literature, MAL protein is ex-
pressed in lymphoid cells derived from the T-cell
CD4?CD8?helper, and CD4?CD8?cytotoxic ma-
ture T-cell clones and leukemic T-cell lines) but is
not expressed in the B-cell lineage (1, 10, 13, 14).
However, extensive studies of MAL protein expres-
sion in normal lymphoid tissues and lymphoid ma-
lignancies have not been performed yet. The aims
of our study were first to analyze the pattern of MAL
expression in peripheral blood lymphocytes and
normal lymphoid tissues, including the thymus,
tonsil, reactive lymph node, and spleen and sec-
ondarily, to further extend the immunohistochem-
ical analysis of MAL protein expression to a large
series of B- and T-cell lymphoid malignancies and
to the primary mediastinal large B-cell lymphoma–
derived B-cell line MedB-1 (15).
MATERIALS AND METHODS
Peripheral blood was obtained from blood do-
nors and handled according to established clinical
guidelines. Tonsils were obtained from children op-
erated on for benign reactive hyperplastic tonsils.
Spleen samples were obtained from patients under-
going splenectomy as treatment against immune
thrombocytopenic purpura. Peripheral mononu-
clear cells and mononuclear cells obtained after
dilaceration of tonsil or spleen were isolated on
Ficoll preparations and frozen in dimethylsulfoxide
The following monoclonal antibodies (mAb) were
used: CD3(HIT3?) and CD19(HD 237), both directly
conjugated to phycoerythrin-Texas Red (ECD) from
Beckman-Coulter (Hialey, FL), CD4(53–5; Tricolor)
from Caltag (Burlingame, CA). Anti-MAL 6D9 mAb
directed against amino acids 114–123 of the human
MAL protein (4; gift from Miguel Alonso, Madrid,
Spain) was used in an indirect staining in combi-
nation with GAM-F(ab')2FITC (fluorescein isothio-
cyanate) anti IgG (H?L; Tebu, Le-Perray-en-
Yvelines, France) as secondary antibody. Briefly,
cells were thawed in RPMI plus fetal calf serum
(FCS), washed once, and incubated 15 minutes at 4°
C with the directly conjugated surface monoclonal
antibodies for lymphocyte subset determination.
After washing once, cells were permeabilized in
phosphate-buffered saline (PBS) containing 0.1%
saponin and FCS at 5%. MAL antibody or control-
irrelevant primary antibody was added, and cells
were incubated for 30 minutes at 4° C. After two
washes, secondary antibody was added for another
incubation of 15 minutes at 4° C.
Irrelevant murine monoclonal antibodies were
used to definebackground
phycoerythrin, IgG2b-ECD, from Beckman-Coulter,
IgG2a-Tricolor from Caltag, and total mouse Ig
(Tebu) with GAM-FITC as a negative control for
MAL staining. MAL/CD19 and MAL/CD3/CD4 mul-
tiple labeling were performed to assess expression
of MAL in B- and T-cell subsets of peripheral blood,
tonsils, and spleens. Lymphocytes were identified
by forward- and side-scatter analysis. CD4 T cells
were defined as CD4?CD3?cells, CD8 T cells as
CD4?CD3?cells, and B cells as CD19?cells. Light
compensation for each combination of antibodies
had been established in our laboratory before this
study. Flow cytometry was performed with a
Coulter EPICS® XL within 24 hours from the stain-
ing. Listmode parameters were analyzed and stored
on System II software (Beckman-Coulter).
Histology and Immunohistochemistry
Eight samples of reactive lymphoid tissues were
studied: two tonsils, two spleens, two reactive
lymph nodes, and two thymuses (one neonatal and
one from a 19-year-old man). All were fixed in
Bouin’s fixative, paraffin embedded, and routinely
processed. An additional portion of one of the two
thymuses was also snap-frozen in liquid nitrogen
and stored at ?80° C for phenotypic studies.
One hundred eighty-five cases of lymphoid ma-
lignancies were retrieved from the files of the De-
partment of Pathology, Henri Mondor hospital,
Créteil, France. Material consisted of Bouin’s-,
formalin-, or AFA (alcohol, formalin, and acetic
hematoxylin-eosin for histological studies. Lym-
phomas were classified according to the World
Health Organization classification (16) using both
morphological and immunophenotypic criteria.
This series included 33 cases of primary mediastinal
large B-cell lymphomas, 33 cases of nonmediastinal
large B-cell lymphomas, and most B- and T/NK-cell
neoplasms and comprised the 12 cases of primary
mediastinal large B-cell lymphomas and the 8 cases
of nonmediastinal diffuse large B-cell lymphomas
analyzed for MAL expression in our initial study
MAL Expression in Lymphoid Cells (C. Copie-Bergman et al.)1173
(11). Pathological specimens of primary mediasti-
nal large B-cell lymphoma consisted of 27 medias-
tinal biopsies and 6 peripheral lymph node biop-
sies. Specimens of nonmediastinal diffuse large
B-cell lymphomas included 28 peripheral lymph
node biopsies, 2 extranodal diffuse large B-cell lym-
phomas (spleen and small bowel), and 3 cases of
pyothorax-associated B-cell lymphomas.
This series also included 31 cases of classical
Hodgkin lymphoma and 10 cases of nodular
Among classical Hodgkin lymphomas, 25 patients
presented with mediastinal disease and 2 patients
without; this information was not available for 4
Hodgkin lymphomas consisted of mediastinal bi-
opsies for 6 cases and of peripheral lymph nodes for
Immunohistochemistry was performed on paraffin-
embedded tissue sections using the Ventana auto-
mated immunostainer (Ventana Medical Systems,
Tucson, AZ) and their diaminobenzidine detection
kit, according to the manufacturer’s recommenda-
tions. All cases were evaluated for B- and T-cell
differentiation antigens. When appropriate, antigen
retrieval was performed by microwave heating in
citrate or EDTA buffer.
MAL protein expression was evaluated using
anti-MAL 6D9 mAb. Variable intensity of the MAL
immunostaining was observed depending on the
fixative used: Bouin’s fixative appeared to be the
best fixative to preserve MAL immunoreactivity. In
contrast, EDTA or citrate pretreatment were neces-
sary for formalin or AFA-fixed specimens to high-
light MAL immunoreactivity. Therefore, most cases
were evaluated in triplicate in various conditions:
without pretreatment, microwave heating in citrate
buffer (12 min at 750W, 2 times for 10 min at 350W
in citrate buffer, pH 6.7), and microwave heating in
EDTA buffer (12 min at 750W, 3 times for 10 min at
350W in EDTA buffer, pH 8.0). The pattern of MAL
immunoreactivity consisted of membrane with or
without paranuclear dotlike staining of the tumor
cell. Intratumoral positive small lymphoid cells
consistent with reactive T cells were present in all
cases. Samples without internal positive control
were considered noninterpretable and were ex-
cluded from the study.
Cytospin preparations of MedB-1 mediastinal
B-cell line (15) were also evaluated for MAL protein
expression by immunocytochemistry using the
Ventana automated immunostainer.
Expression of MAL together with B-cell marker
CD79a were evaluated in thymus, tonsil, and reac-
tive lymph node paraffin-embedded tissue sections
using double immunofluorescence labeling. Frozen
sections of one of the thymuses were also evalu-
ated. Briefly, paraffin-embedded tissue sections
were dewaxed and microwave pretreated in citrate
buffer, as described previously. Frozen tissue sec-
tions were fixed in acetone for 10 minutes. Slides
were first incubated with 10% goat serum (Santa
Cruz, Tebu, Le-Perray-en-Yvelines, France) for 20
minutes, followed by primary anti-MAL 6D9 mAb
(IgG2a) at 1:50 dilution for 1 hour. After PBS
washes, slides were incubated in the dark with goat
anti-mouse IgG-Cy3 antibody (Caltag, Tebu, Le-
Perray-en-Yvelines, France) at 1:50 dilution for 30
minutes. After PBS washes, slides were incubated
with secondary anti-CD79a antibody (IgG1; Dako,
SA, Glostrup, Denmark) at 1:50 dilution for 1 hour.
Slides were washed in PBS and then incubated with
goat anti-mouse IgG1-FITC antibody (Santa Cruz,
Tebu, Le-Perray-en-Yvelines, France) at 1:200 dilu-
tion for 30 minutes. After PBS washes, slides were
mounted in Vectashield (Vector, Burlingame, CA)
medium and kept in the dark at 4° C until analyzed.
Sections were viewed on a Leica microscope
equipped for fluorescence.
MAL Protein Expression in Peripheral Blood
Lymphocytes, Lymphoid Suspensions of Tonsil,
and Spleen by Flow Cytometry
Expression of MAL protein in mature B lympho-
cytes and in CD4 and CD8 T lymphocyte subsets
was assessed by flow cytometry in four peripheral
blood lymphocyte samples and in cell suspensions
of two tonsils and of two spleens. The results are
shown in Table 1 and illustrated in Figure 1. MAL
was consistently expressed in a large proportion of
CD4 T cells (range: 65–90%; Fig. 1A), except in one
tonsil sample, where MAL expression was lower
(31%). MAL antigen was less frequently expressed
in CD8 T cells (range: 22–50%) and was very scarce
in one spleen sample (5%). MAL was not signifi-
cantly expressed in peripheral blood B cells (Fig.
1B) or in B-cell subsets of tonsil and spleen.
MAL Protein Expression in Thymus, Tonsil,
Reactive Lymph Node, and Spleen
In the thymus, two distinct zones were observed.
Lymphoid cells from the thymic cortex were
strongly positive for MAL (Fig. 2A). In contrast, the
medulla, where most B cells are located (Fig. 2B),
displayed occasional MAL-positive lymphoid cells.
Squamous epithelial cells from Hassall’s corpuscles
were also found positive.
The pattern of MAL immunoreactivity was simi-
lar in the tonsils and in the reactive lymph nodes.
MAL protein expression was restricted to small lym-
phoid cells that were scattered in the interfollicular
1174 Modern Pathology
zone and occasionally located in the germinal cen-
ter of lymphoid follicles (Fig. 2C). These cells were
distinct from centrocytes or centroblasts and pre-
sented a pattern consistent with small T lympho-
cytes. The number of MAL-positive lymphoid cells
was variable from case to case, accounting for
about 5 to 30% of interfollicular small lymphoid
cells. In addition, MAL protein expression was also
observed in occasional mature plasma cells located
in the interfollicular areas, in superficial squamous
epithelial cells, and in nerve sections (Fig. 2D). In
the spleen, rare positive small lymphoid cells were
observed in the red pulp and within the periarterial
lymphatic sheath of the white pulp.
Double Immunofluorescence Labeling of
Thymus, Tonsil, and Reactive Lymph Nodes
Tissue Sections with Anti-MAL and
Double immunofluorescence labeling of two thy-
muses revealed that a minor fraction of thymic
medullary B cells displayed MAL immunoreactivity.
These MAL-positive B cells were either small and
round or asteroid shaped (Fig. 3). In tonsil and
reactive lymph node tissue sections, occasional
plasma cells of the interfollicular areas displayed
both CD79a and MAL immunoreactivity.
MAL Protein Expression in
The results are shown in Table 2 and illustrated in
Figure 4. Among 33 cases of primary mediastinal
large B-cell lymphomas, 21 cases (70%) demon-
strated MAL protein immunoreactivity. The per-
centage of positive tumor cells ranged from 10% to
virtually all tumor cells (Fig. 4A). Interestingly, the
MedB-1 B-cell line was found to be positive for MAL
(Fig. 4B). About a third of the cells displayed cyto-
plasmic and paranuclear dot-like immunoreactiv-
ity, with a variable intensity from cell to cell. We did
not observe any differences between the MAL-
FIGURE 1. Flow cytometry analysis of MAL expression in peripheral blood lymphocyte subsets. After permeabilization with 0.1% saponin PBS,
peripheral blood lymphocytes were double-stained with MAL antibody after permeabilization with 0.1% saponin PBS and CD4 or CD19 antibody.
Analysis was restricted to elements in the lymphocyte gate. A, MAL is expressed in 77% of CD4? lymphocytes. B, MAL is not expressed in normal
peripheral B lymphocytes.
TABLE 1. MAL Protein Expression in Lymphocyte Subsets in Normal Peripheral Blood, Tonsil, and Spleen Samples
T Cells (%)
T Cells (%)
Peripheral blood lymphocytes1
The percentages represent the proportion of positive elements in the lymphocyte gate. Results were obtained by two multiple-labelings, MAL/CD19,
and MAL/CD3/CD4 combinations under permeabilization conditions (0.1% saponin).
aB cells were defined as CD19?cells, CD4 T cells as CD4?CD3?cells, and CD8 T cells as CD4?CD3?cells.
MAL Expression in Lymphoid Cells (C. Copie-Bergman et al.) 1175
positive and MAL-negative primary mediastinal
large B-cell lymphoma cases in terms of histology
or immunophenotype. Among 33 cases of nonme-
diastinal diffuse large B-cell lymphomas, only one
case (3%) demonstrated MAL-positive tumor cells.
This case was a large B-cell lymphoma of polymor-
phic centroblastic subtype located in a lymph node,
without documented mediastinal location. All other
diffuse large B-cell lymphoma cases, as well as Bur-
kitt’s lymphomas, remained negative (Fig. 4C).
Tumor cells of all low grade B-cell malignancies,
including B-cell chronic lymphocytic leukemia,
mantle cell lymphoma, follicular lymphoma (Fig.
4D), and marginal zone lymphoma, were negative
for MAL immunostaining. Three of five plasmacy-
toma/myeloma showed numerous positive tumor
In the T-cell lineage, five of six T-lymphoblastic
lymphomas were strongly positive (Fig. 4E). Among
peripheral T-cell lymphomas (PTCLs), all cases of
PTCLs unspecified, angioimmunoblastic, nasal-
type NK/T-, hepatosplenic, and adult T-cell lym-
phomas HTLV1? remained negative, except for ap-
parently reactive small lymphocytes. One case of
ALK-negative anaplastic large cell lymphoma lo-
cated in a lymph node demonstrated MAL positivity
in the Golgi area of many neoplastic cells.
Most cases (28/31) of classical Hodgkin lympho-
mas were negative for MAL (Fig. 4F). Three cases
FIGURE 2. Immunohistochemical analysis of thymus, reactive lymph node and nerve tissue sections. A, thymic tissue section showing strong MAL
expression in the cortex whereas the medulla displays few positive lymphocytes (arrows) and positive Hassal’s corpuscles. B, thymic tissue section
stained with anti-CD20 for comparison, showing that thymic B-cells (arrow) are conversely distributed in the medulla. C, reactive lymph node
stained with anti-MAL antibody showing scattered positive small lymphocytes in the interfollicular areas (arrow) and occasionally in the germinal
center. D, nerve section positive for MAL (arrow).
FIGURE 3. Double immunofluorescence labeling of paraffin-
embedded thymic tissue sections with anti-MAL and anti-CD79a
antibodies. Staining for MAL (red) picks out the cortex on the right,
which is highly positive, and occasional MAL-positive cells in the
medulla (left and below). Staining for CD79a (green) picks out thymic
B cells which are located in the medulla. One asteroid-shaped B cell
displays MAL immunoreactivity (arrowhead) giving a yellow signal.