Early Steps of a Thymic Tumor in SV40 Transgenic Mice: Hyperplasia of Medullary Epithelial Cells and Increased Mature Thymocyte Numbers Disturb Thymic Export
Developmental Immunology, December
1044-6672
Early Steps of a Thymic Tumor in SV40 Transgenic Mice: Hyperplasia of Medullary Epithelial Cells and Increased Mature Thymocyte Numbers Disturb Thymic Export*
BERNADETTE NABARRA 0 4
CATHERINE MARTINON 1 4
CE? CILE GODARD 0 4
FLORENCE VASSEUR 0 4
GEOFFROY DE RIBAINS 3 4
LUCILE MIQUEROL 3 4
AXEL KAHN 3 4
SOPHIE EZINE 0 4
0 INSERM U.345, Institut Necker , 75730, Paris Cedex 15 , France
1 INSERM U.238, CEA , 38054, Grenoble Cedex 9 , France
2 ; DP , double positive CD4
3 INSERM U. 129, CHU Cochin-Port-Royal, 75014, Paris , France
4 Abbreviations: DN , double negative CD4
Bone marrow progenitors migrate to the thymus, where they proliferate and differentiate into immunologically competent T cells. In this report we show that mice transgenic for SV40 T and t antigens under the control of the L-pyruvate kinase promoter develop, in a first step, thymic hyperplasia of both thymocytes and epithelial cells. Morphological studies (histology, immunohistolabeling and electron microscopy) revealed modifications of the thymic microenvironment and gradual expansion of medullary epithelial cells in 1 month-old mice, taking over the cortical region. Then, a thymic carcinoma develops. Two-color labeling of frozen sections identified the transgene in medullary epithelial cells. Flow cytometry analysis demonstrated a marked increase in mature CD4? and CD8? thymocytes in adult mice (39 ^ 10 ? 106 in transgenic mice and 12 ^ 5 ? 106 in age-matched controls). Furthermore, thymocyte export was disturbed.
Immunohistolabeling; Ultrastructure; Thymic medullary tumor; L-pyruvate kinase promoter
INTRODUCTION
In the thymic microenvironment, the epithelial
compartment is organized into cortical and medullary zones that
mediate different aspects of thymocyte differentiation.
The different processes controlling the growth and
organization of the epithelial compartment depend largely
on cell interactions involving thymocytes and stromal
cells for selection, differentiation and maturation of
T cells
(Duijvestin et al., 1981; Weissman et al., 1982;
Kendall, 1986; Nabarra, 1987; 1991a; Marrack, 1988;
von Bohmer, 1988; Sprent et al., 1988; Brekelmans and
van Ewijk, 1990; van Ewijk, 1991; Boyd et al., 1993)
.
Furthermore, thymic stroma cells included also
nonepithelial cells (bone marrow-derived cells) as
macrophages and interdigitated cells (IDC) which are also
involved in these process.
In this milieu, thymocytes are in symbiotic
developmental relationship involving the different stromal cells
and various signaling molecules, cytokines, cytokine
receptors and chemokines
(Zlotnik and Moore, 1995;
Norment and Bevan, 2000)
. T cell precursors migrating
from the bone-marrow to the thymus undergo an ordered
differentiation process. After different migrations steps
across the organ, mature T cells are generated and exit the
thymus for the periphery
(Scollay et al., 1980; Pe?nit,
1986)
. Migration and homing are partly dependent on
adhesion molecules
(Imhof et al., 1991; Aurrand-Lions
et al., 1996)
. Virtually nothing is known about the precise
thymic location from which mature thymocytes emigrate
from the thymus to peripheral lymphoid organs. However,
the cortico-medullary junction has been suggested
important in this process in association with maintenance
of a normal architecture.
The studies of all these parameters, particularly
elucidation of the cross-talk between thymocytes and
epithelial cells
(van Ewijk et al., 1994; Pe?nit et al., 1996)
,
is difficult to appreciate in steady state conditions.
Nevertheless, the studies of modification and disruption of
the thymic microenvironment organization in different
pathologic mice, and recently of genetically engineered
mice, appeared to be a good approach in relation with
observations of cellular modifications, alterations in the
developmental program and phenotype of thymocytes
(Rouse and Weissman, 1981; Kendall, 1986; Nabarra and
Dardenne, 1991b; Naquet et al., 1999)
.
In this way, both naturally occurring and
experimentally-induced tumors were used as models for dissecting in
vivo these different sequences of T cell education, and
disruption of thymic stroma.
Transgenic model of pure thymic tumor is rarely
described. Today only one team has described a thymic
carcinoma issued of an extanded thymic hyperplasia in Tg
mice made with SV40 Simian Virus T antigen 40 (SV40)
associated with it own promoter
(Park et al., 1996; Lee
et al., 1998)
.
We have generated a second mouse model with SV40 T
and t Ag with a different promoter (L-pyruvate kinase).
SV12 transgenic mice develop early in life a massive
thymic hyperplasia concerning both thymocytes and
epithelial cells. Immuno-histological studies, confirmed
by electron microscopy studies, demonstrate a large
hyperplasia of expanded medullary epithelial cells,
carrying the transgene. With time, large angiogenesis,
numerous cellular atypies concerning the cytoplasm and
the nucleus and a larg (...truncated)