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Thymic medullary epithelial cell differentiation, thymocyte emigration, and the control of autoimmunity require lympho-epithelial cross talk via LTbetaR.

Boehm T, Scheu S, Pfeffer K, Bleul CC - J. Exp. Med. (2003)

Bottom Line: The nature of these signals has been elusive so far.We show that thymocytes and medullary epithelial cells (MECs) communicate via the lymphotoxin beta receptor (LTbetaR) signaling axis.Impaired lympho-epithelial cross talk in the absence of the LTbetaR causes aberrant differentiation and reduced numbers of thymic MECs, leads to the retention of mature T lymphocytes, and is associated with autoimmune phenomena, suggesting an unexpected role for LTbetaR signaling in central tolerance induction.

View Article: PubMed Central - PubMed

Affiliation: Max Planck Institute for Immunobiology, Stuebeweg 51, 79108 Freiburg, Germany.

ABSTRACT
Thymocytes depend on the interaction with thymic epithelial cells for the generation of a diverse, nonautoreactive T cell repertoire. In turn, thymic epithelial cells acquire their three-dimensional cellular organization via instructive signals from developing thymocytes. The nature of these signals has been elusive so far. We show that thymocytes and medullary epithelial cells (MECs) communicate via the lymphotoxin beta receptor (LTbetaR) signaling axis. Normal differentiation of thymic MECs requires LTbetaR ligand on thymocytes and LTbetaR together with nuclear factor-kappaB-inducing kinase (Nik) in thymic epithelial cells. Impaired lympho-epithelial cross talk in the absence of the LTbetaR causes aberrant differentiation and reduced numbers of thymic MECs, leads to the retention of mature T lymphocytes, and is associated with autoimmune phenomena, suggesting an unexpected role for LTbetaR signaling in central tolerance induction.

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Normal development of thymic MECs requires LTβR signaling. (A) UEA-1 staining reveals the disturbed differentiation of MECs in LTβR−/− and aly/aly mice. Consecutive sections of thymic lobes stained with the lectin UEA-1 for MECs and a monoclonal antibody specific for cytokeratin 8 (K8) expressed by cortical epithelial cells are shown (top and bottom, respectively). The dark line marks the border between cortex and medulla. Panels in the middle represent higher magnification images of the top panels. (B) Stainings of medullary regions of thymi of the respective mice were performed with a polyclonal rabbit antiserum directed against the nonpolymorphic MHC class II antigen I-O and the monoclonal antibody MTS10. Hematoxylin and eosin stainings (H&E) show an increased density of lymphocytes in the medulla compared with wild-type mice. Cortical areas (C) and medullary areas (M) are indicated.
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fig1: Normal development of thymic MECs requires LTβR signaling. (A) UEA-1 staining reveals the disturbed differentiation of MECs in LTβR−/− and aly/aly mice. Consecutive sections of thymic lobes stained with the lectin UEA-1 for MECs and a monoclonal antibody specific for cytokeratin 8 (K8) expressed by cortical epithelial cells are shown (top and bottom, respectively). The dark line marks the border between cortex and medulla. Panels in the middle represent higher magnification images of the top panels. (B) Stainings of medullary regions of thymi of the respective mice were performed with a polyclonal rabbit antiserum directed against the nonpolymorphic MHC class II antigen I-O and the monoclonal antibody MTS10. Hematoxylin and eosin stainings (H&E) show an increased density of lymphocytes in the medulla compared with wild-type mice. Cortical areas (C) and medullary areas (M) are indicated.

Mentions: To investigate a possible role for LTβR signaling in thymic development, we stained sections from LTβR−/− and aly/aly mice with markers for medullary and cortical epithelial cells (Fig. 1 A). Cortical and medullary regions can be found in the thymi of these mutant mice with the same ratio observed in wild-type mice. However, although cortical epithelial cells marked by anticytokeratin 8 staining appeared unaffected, the normal configuration of MECs is lost in LTβR−/− and aly/aly mice. In wild-type mice, UEA-1–positive epithelial cells form a homogeneous, three-dimensional network of stellate cells that builds the thymic medulla (Fig. 1 A, middle). Although UEA-1–positive cells can still be detected in LTβR−/− and aly/aly mice, these cells form clumps rather than a network (Fig. 1 A). FACS® analyses confirmed the epithelial nature of UEA-1–positive cells from LTβR−/− thymi as they are large G8.8 positive cells that lack CD45 and CDR1 expression (unpublished data). MECs staining positive for UEA-1 have been shown previously to represent one of two subsets that make up the medullary epithelial stroma (27). The other subset is characterized by the expression of the nonpolymorphic MHC class II antigen I-O, and this subset is similarly affected in LTβR−/− and aly/aly mice when compared with wild-type mice (Fig. 1 B). Apart from epithelial cells, the stroma of the thymic medulla consists of dendritic cells, macrophages, and poorly defined cells of nonepithelial origin that are cytokeratin-negative but recognized by the monoclonal antibody MTS-10, which also stains epithelial cells (28). Dendritic cells and macrophages are readily detectable in LTβR−/− and aly/aly mice by MIDC-8 and F4/80 staining, respectively (Fig. S1, available at http://www.jem.org/cgi/content/full/jem.20030794/DC1). MTS-10 staining is strongly reduced in aly/aly mice but only mildly affected in LTβR−/− mice (Fig. 1 B). Although LTβR is expressed in stromal but not lymphoid cells (29–31), Nik has been shown to be ubiquitously expressed (32), and there is evidence that the aly/aly mutation affects cells which do not express LTβR (e.g., lymphocytes; reference 23). Thus, MTS10-positive cells of nonepithelial origin may be unaffected by the absence of LTβR but depend on the presence of undisturbed signaling through Nik. In hematoxylin and eosin stainings of thymus sections, the demarcation between cortex and medulla is blurred in LTβR−/− and aly/aly mice due to a significant increase in the density of strongly hematoxylin-positive nuclei (i.e., lymphocytes) in the medulla (Fig. 1 B). Collectively, the data reveal an aberrant development of thymic MECs in mice defective for LTβR signaling that affects UEA-1 as well as I-O–positive MECs.


Thymic medullary epithelial cell differentiation, thymocyte emigration, and the control of autoimmunity require lympho-epithelial cross talk via LTbetaR.

Boehm T, Scheu S, Pfeffer K, Bleul CC - J. Exp. Med. (2003)

Normal development of thymic MECs requires LTβR signaling. (A) UEA-1 staining reveals the disturbed differentiation of MECs in LTβR−/− and aly/aly mice. Consecutive sections of thymic lobes stained with the lectin UEA-1 for MECs and a monoclonal antibody specific for cytokeratin 8 (K8) expressed by cortical epithelial cells are shown (top and bottom, respectively). The dark line marks the border between cortex and medulla. Panels in the middle represent higher magnification images of the top panels. (B) Stainings of medullary regions of thymi of the respective mice were performed with a polyclonal rabbit antiserum directed against the nonpolymorphic MHC class II antigen I-O and the monoclonal antibody MTS10. Hematoxylin and eosin stainings (H&E) show an increased density of lymphocytes in the medulla compared with wild-type mice. Cortical areas (C) and medullary areas (M) are indicated.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2194183&req=5

fig1: Normal development of thymic MECs requires LTβR signaling. (A) UEA-1 staining reveals the disturbed differentiation of MECs in LTβR−/− and aly/aly mice. Consecutive sections of thymic lobes stained with the lectin UEA-1 for MECs and a monoclonal antibody specific for cytokeratin 8 (K8) expressed by cortical epithelial cells are shown (top and bottom, respectively). The dark line marks the border between cortex and medulla. Panels in the middle represent higher magnification images of the top panels. (B) Stainings of medullary regions of thymi of the respective mice were performed with a polyclonal rabbit antiserum directed against the nonpolymorphic MHC class II antigen I-O and the monoclonal antibody MTS10. Hematoxylin and eosin stainings (H&E) show an increased density of lymphocytes in the medulla compared with wild-type mice. Cortical areas (C) and medullary areas (M) are indicated.
Mentions: To investigate a possible role for LTβR signaling in thymic development, we stained sections from LTβR−/− and aly/aly mice with markers for medullary and cortical epithelial cells (Fig. 1 A). Cortical and medullary regions can be found in the thymi of these mutant mice with the same ratio observed in wild-type mice. However, although cortical epithelial cells marked by anticytokeratin 8 staining appeared unaffected, the normal configuration of MECs is lost in LTβR−/− and aly/aly mice. In wild-type mice, UEA-1–positive epithelial cells form a homogeneous, three-dimensional network of stellate cells that builds the thymic medulla (Fig. 1 A, middle). Although UEA-1–positive cells can still be detected in LTβR−/− and aly/aly mice, these cells form clumps rather than a network (Fig. 1 A). FACS® analyses confirmed the epithelial nature of UEA-1–positive cells from LTβR−/− thymi as they are large G8.8 positive cells that lack CD45 and CDR1 expression (unpublished data). MECs staining positive for UEA-1 have been shown previously to represent one of two subsets that make up the medullary epithelial stroma (27). The other subset is characterized by the expression of the nonpolymorphic MHC class II antigen I-O, and this subset is similarly affected in LTβR−/− and aly/aly mice when compared with wild-type mice (Fig. 1 B). Apart from epithelial cells, the stroma of the thymic medulla consists of dendritic cells, macrophages, and poorly defined cells of nonepithelial origin that are cytokeratin-negative but recognized by the monoclonal antibody MTS-10, which also stains epithelial cells (28). Dendritic cells and macrophages are readily detectable in LTβR−/− and aly/aly mice by MIDC-8 and F4/80 staining, respectively (Fig. S1, available at http://www.jem.org/cgi/content/full/jem.20030794/DC1). MTS-10 staining is strongly reduced in aly/aly mice but only mildly affected in LTβR−/− mice (Fig. 1 B). Although LTβR is expressed in stromal but not lymphoid cells (29–31), Nik has been shown to be ubiquitously expressed (32), and there is evidence that the aly/aly mutation affects cells which do not express LTβR (e.g., lymphocytes; reference 23). Thus, MTS10-positive cells of nonepithelial origin may be unaffected by the absence of LTβR but depend on the presence of undisturbed signaling through Nik. In hematoxylin and eosin stainings of thymus sections, the demarcation between cortex and medulla is blurred in LTβR−/− and aly/aly mice due to a significant increase in the density of strongly hematoxylin-positive nuclei (i.e., lymphocytes) in the medulla (Fig. 1 B). Collectively, the data reveal an aberrant development of thymic MECs in mice defective for LTβR signaling that affects UEA-1 as well as I-O–positive MECs.

Bottom Line: The nature of these signals has been elusive so far.We show that thymocytes and medullary epithelial cells (MECs) communicate via the lymphotoxin beta receptor (LTbetaR) signaling axis.Impaired lympho-epithelial cross talk in the absence of the LTbetaR causes aberrant differentiation and reduced numbers of thymic MECs, leads to the retention of mature T lymphocytes, and is associated with autoimmune phenomena, suggesting an unexpected role for LTbetaR signaling in central tolerance induction.

View Article: PubMed Central - PubMed

Affiliation: Max Planck Institute for Immunobiology, Stuebeweg 51, 79108 Freiburg, Germany.

ABSTRACT
Thymocytes depend on the interaction with thymic epithelial cells for the generation of a diverse, nonautoreactive T cell repertoire. In turn, thymic epithelial cells acquire their three-dimensional cellular organization via instructive signals from developing thymocytes. The nature of these signals has been elusive so far. We show that thymocytes and medullary epithelial cells (MECs) communicate via the lymphotoxin beta receptor (LTbetaR) signaling axis. Normal differentiation of thymic MECs requires LTbetaR ligand on thymocytes and LTbetaR together with nuclear factor-kappaB-inducing kinase (Nik) in thymic epithelial cells. Impaired lympho-epithelial cross talk in the absence of the LTbetaR causes aberrant differentiation and reduced numbers of thymic MECs, leads to the retention of mature T lymphocytes, and is associated with autoimmune phenomena, suggesting an unexpected role for LTbetaR signaling in central tolerance induction.

Show MeSH
Related in: MedlinePlus