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T-Cell Development in Thymus and Genetic Recombination of TCR – Lymphocyte Development

by Peter Delves, PhD
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    Let’s now look in a little bit more detail about the actual development process in the thymus. We’ve heard that the T-cells migrate through the cortex and into the medulla. So exactly what’s going on during those migration processes? Well when the T-cells first enter the thymus, having come from the bone marrow, they lack expression of two molecules - CD4 and CD8. We therefore refer to them as being CD8 negative (CD8-), CD4 negative (CD4-). And immunologists use a bit of jargon that’s called ‘double negative T-cell’. So if you hear an immunologist talk about double negative T-cells, you wouldn’t know what on earth they were talking about. But what they’re actually referring to is cells that are CD4-, CD8-, lacking both of those molecules. Shortly after arrival in the thymus, the genes for both of those molecules are switched on and these T-cells become CD4 positive (CD4+), CD8 positive (CD8+); in other words in the jargon, ‘double positive T-cells’. These are now ready to undergo thymic education. And the first step in thymic education which takes place in the cortex is interactions of the T-cells with thymic epithelial cells. And the purpose of this interaction is to ensure that the T-cell receptor that has been generated by random recombination is able to recognize our own MHC variants. It’s no good if the T-cell receptor can’t recognize MHC because we’re talking about alpha beta (αβ) T-cells here. They need to recognize peptide presented by MHC. They need to recognize peptide presented by our own variants of the MHC, not somebody else’s variant. So the first stage in thymic education is called positive selection. And T-cells are selected positively if they are able to recognize peptides presented by our own MHC molecules. If they fail to do so, they die...

    About the Lecture

    The lecture T-Cell Development in Thymus and Genetic Recombination of TCR – Lymphocyte Development by Peter Delves, PhD is from the course Adaptive Immune System. It contains the following chapters:

    • T-Cell Development in the Thymus
    • Genetic Recombination of TCR Genes

    Included Quiz Questions

    1. CD4 and CD8
    2. An αβ and a γδ T-cell receptor
    3. A TCR and a BCR
    4. MHC class I and MHC class II
    5. CD3 and CD4
    1. ...positive selection: T cells that can recognize self MHC are saved from apoptosis.
    2. ...positive selection: T cells that recognize self MHC undergo apoptosis.
    3. ...positive selection: assigning CD4 and CD8 molecules to T cells- making them double positive.
    4. ...negative selection: selecting out any T cells that are CD4 or CD8 negative.
    5. ...negative selection: T cells that recognize self MHC undergo apoptosis.
    1. ...mature T cells do not recognize autoantigen.
    2. ...mature T cells contain either CD4 or CD8.
    3. ...mature T cells recognize self MHC.
    4. ...mature T cells are double negative.
    5. ...mature T cells do not exhibit central tolerance.

    Author of lecture T-Cell Development in Thymus and Genetic Recombination of TCR – Lymphocyte Development

     Peter Delves, PhD

    Peter Delves, PhD


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