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Clonal deletion of thymocytes can occur in the cortex with no involvement of the medulla.

McCaughtry TM, Baldwin TA, Wilken MS, Hogquist KA - J. Exp. Med. (2008)

Bottom Line: However, the kinetics in vivo indicated that apoptosis was activated asynchronously relative to TCR activation.We found that radioresistant antigen-presenting cells and, specifically, cortical epithelial cells do not efficiently induce apoptosis, although they do cause TCR activation.Rather, thymocytes undergoing clonal deletion were preferentially associated with rare CD11c(+) cortical dendritic cells, and elimination of such cells impaired deletion.

View Article: PubMed Central - PubMed

Affiliation: Center for Immunology, Laboratory Medicine, and Pathology, University of Minnesota, Minneapolis, MN 55454, USA.

ABSTRACT
The thymic medulla is generally held to be a specialized environment for negative selection. However, many self-reactive thymocytes first encounter ubiquitous self-antigens in the cortex. Cortical epithelial cells are vital for positive selection, but whether such cells can also promote negative selection is controversial. We used the HY(cd4) model, where T cell receptor for antigen (TCR) expression is appropriately timed and a ubiquitous self-antigen drives clonal deletion in male mice. We demonstrated unambiguously that this deletion event occurs in the thymic cortex. However, the kinetics in vivo indicated that apoptosis was activated asynchronously relative to TCR activation. We found that radioresistant antigen-presenting cells and, specifically, cortical epithelial cells do not efficiently induce apoptosis, although they do cause TCR activation. Rather, thymocytes undergoing clonal deletion were preferentially associated with rare CD11c(+) cortical dendritic cells, and elimination of such cells impaired deletion.

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Colocalization of active Caspase 3 and Thy1.2 identifies male-reactive thymocytes undergoing clonal deletion throughout the cortex. Thymus tissue sections from mice in Fig. 3 were analyzed by immunofluorescence for Thy1.2, active Caspase 3, and G8.8. (A) Images were overlayed and examined for colocalization between Thy1.2 and active Caspase 3. White lines are drawn around G8.8+ cells to identify the medulla and boxes identify colocalized cells. C, cortex; M, medulla. Bar, 250 μm. (B) Colocalization was confirmed at high magnification. Bar, 5 μm. (C) The frequency of colocalization is expressed as the number of colocalized cells per total Thy1.2+ cells in ten different images per thymus. Data represent the mean from four different males ± SD. (D) The relative distance of colocalized cells from the medulla was digitally calculated using Photoshop. The drawn line indicates the median of the dataset. The entire figure is representative of two individual groups of chimeras and three replicates of immunofluorescence staining.
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fig5: Colocalization of active Caspase 3 and Thy1.2 identifies male-reactive thymocytes undergoing clonal deletion throughout the cortex. Thymus tissue sections from mice in Fig. 3 were analyzed by immunofluorescence for Thy1.2, active Caspase 3, and G8.8. (A) Images were overlayed and examined for colocalization between Thy1.2 and active Caspase 3. White lines are drawn around G8.8+ cells to identify the medulla and boxes identify colocalized cells. C, cortex; M, medulla. Bar, 250 μm. (B) Colocalization was confirmed at high magnification. Bar, 5 μm. (C) The frequency of colocalization is expressed as the number of colocalized cells per total Thy1.2+ cells in ten different images per thymus. Data represent the mean from four different males ± SD. (D) The relative distance of colocalized cells from the medulla was digitally calculated using Photoshop. The drawn line indicates the median of the dataset. The entire figure is representative of two individual groups of chimeras and three replicates of immunofluorescence staining.

Mentions: A summary of mixed BM chimeras generated for these studies


Clonal deletion of thymocytes can occur in the cortex with no involvement of the medulla.

McCaughtry TM, Baldwin TA, Wilken MS, Hogquist KA - J. Exp. Med. (2008)

Colocalization of active Caspase 3 and Thy1.2 identifies male-reactive thymocytes undergoing clonal deletion throughout the cortex. Thymus tissue sections from mice in Fig. 3 were analyzed by immunofluorescence for Thy1.2, active Caspase 3, and G8.8. (A) Images were overlayed and examined for colocalization between Thy1.2 and active Caspase 3. White lines are drawn around G8.8+ cells to identify the medulla and boxes identify colocalized cells. C, cortex; M, medulla. Bar, 250 μm. (B) Colocalization was confirmed at high magnification. Bar, 5 μm. (C) The frequency of colocalization is expressed as the number of colocalized cells per total Thy1.2+ cells in ten different images per thymus. Data represent the mean from four different males ± SD. (D) The relative distance of colocalized cells from the medulla was digitally calculated using Photoshop. The drawn line indicates the median of the dataset. The entire figure is representative of two individual groups of chimeras and three replicates of immunofluorescence staining.
© Copyright Policy
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2571932&req=5

fig5: Colocalization of active Caspase 3 and Thy1.2 identifies male-reactive thymocytes undergoing clonal deletion throughout the cortex. Thymus tissue sections from mice in Fig. 3 were analyzed by immunofluorescence for Thy1.2, active Caspase 3, and G8.8. (A) Images were overlayed and examined for colocalization between Thy1.2 and active Caspase 3. White lines are drawn around G8.8+ cells to identify the medulla and boxes identify colocalized cells. C, cortex; M, medulla. Bar, 250 μm. (B) Colocalization was confirmed at high magnification. Bar, 5 μm. (C) The frequency of colocalization is expressed as the number of colocalized cells per total Thy1.2+ cells in ten different images per thymus. Data represent the mean from four different males ± SD. (D) The relative distance of colocalized cells from the medulla was digitally calculated using Photoshop. The drawn line indicates the median of the dataset. The entire figure is representative of two individual groups of chimeras and three replicates of immunofluorescence staining.
Mentions: A summary of mixed BM chimeras generated for these studies

Bottom Line: However, the kinetics in vivo indicated that apoptosis was activated asynchronously relative to TCR activation.We found that radioresistant antigen-presenting cells and, specifically, cortical epithelial cells do not efficiently induce apoptosis, although they do cause TCR activation.Rather, thymocytes undergoing clonal deletion were preferentially associated with rare CD11c(+) cortical dendritic cells, and elimination of such cells impaired deletion.

View Article: PubMed Central - PubMed

Affiliation: Center for Immunology, Laboratory Medicine, and Pathology, University of Minnesota, Minneapolis, MN 55454, USA.

ABSTRACT
The thymic medulla is generally held to be a specialized environment for negative selection. However, many self-reactive thymocytes first encounter ubiquitous self-antigens in the cortex. Cortical epithelial cells are vital for positive selection, but whether such cells can also promote negative selection is controversial. We used the HY(cd4) model, where T cell receptor for antigen (TCR) expression is appropriately timed and a ubiquitous self-antigen drives clonal deletion in male mice. We demonstrated unambiguously that this deletion event occurs in the thymic cortex. However, the kinetics in vivo indicated that apoptosis was activated asynchronously relative to TCR activation. We found that radioresistant antigen-presenting cells and, specifically, cortical epithelial cells do not efficiently induce apoptosis, although they do cause TCR activation. Rather, thymocytes undergoing clonal deletion were preferentially associated with rare CD11c(+) cortical dendritic cells, and elimination of such cells impaired deletion.

Show MeSH
Related in: MedlinePlus