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Th0, Th1 and Th2 Cells – Cell-Mediated Immunity

by Peter Delves, PhD

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    00:01 We’ve looked at various types of T-helper cell, Th1, Th2, Th17 and so on.

    00:06 But these all arise from a precursor that is called a Th0 cell.

    00:14 The cytokines that are secreted by dendritic cells depend on which cell surface, cytoplasmic or endosomal Pattern Recognition Receptors are activated.

    00:25 And here we can see a Th0 cell interacting with a dendritic cell.

    00:32 So the optimal response is determined by the Pathogen Associated Molecular Patterns, which bind to the Pattern Recognition Receptors on the dendritic cell.

    00:43 So the Th0 cell could become a Th1, Th2 or Th17 cell.

    00:49 Which it becomes is determined by the pathogens that are present.

    00:53 And that is detected by the Pattern Recognition Receptors on the dendritic cell.

    00:57 So the dendritic cell instructs the Th0 cell, which type of cell to become to be specialized to deal with a particular type of infection that is present.

    01:09 It’s also influenced by the activation of other cell types.

    01:12 For example, natural killer cells secreting gamma interferon.

    01:16 So depending on which Pathogen Associated Molecular Patterns are present, particular Pattern Recognition Receptors on the dendritic cell will be stimulated.

    01:25 And then the dendritic cell will instruct the Th0 cell, either to become a Th1 if there is lots of interleukin-12 and gamma interferon present.

    01:36 In contrast, if the predominant cytokine is interleukin-4, then the Th0 cell will be instructed to become a Th2 cell.

    01:45 And if there’s lots of interleukin-6, interleukin-23 and transforming growth factor beta, then the instruction will be for the Th0 to differentiate into a Th17 cell.

    01:58 Looking now at the different populations of helper T-cells; once they become specialized into particular types, starting with the Th1 cell.

    02:08 So, Th1 cells typically secrete interleukin-2 that helps activate cytotoxic T-lymphocytes, gamma interferon that helps activate macrophages.

    02:23 Interleukin-2, also is able to activate B-cells.

    02:29 And gamma interferon down regulates the activity of Th2.

    02:36 So overall, Th1 cells activate cyctotoxic T-cells, activate macrophages, activate B-cells but inhibit Th2 cells.

    02:51 Let’s have a look at exactly how Th1 cells activate cytotoxic T-cells.

    02:57 So here we have a Th1 cell, it’s interacting with a dendritic cell.

    03:04 The Th1 cell is CD4+, so it will recognize peptides presented by MHC Class II.

    03:11 In contrast, the cytotoxic T-cell is CD8+, and therefore will recognize peptides presented by MHC Class I.

    03:18 And these two cell types can both be sitting on the surface of the dendritic cell, because remember dendritic cells express both MHC Class I and MHC Class II.

    03:30 Following activation, the Th1 cell will secrete the cytokine interleukin-2 amongst other cytokines.

    03:38 And this cytokine can be detected by interleukin-2 receptors present on the surface of the cytotoxic T-cell.

    03:47 This will lead to activation of the cyctotoxic T-cell.

    03:52 This cell can then leave the environment where it’s been activated, for example in a lymph node, and seek out where the infected cells are, and then subsequently kill them.

    04:04 Regarding the Th1 activation of macrophages, the macrophages are also MHC Class II positive as well as being Class I. And therefore they can also present peptides to the CD4+ Th1 cells. So here we have a macrophage containing phagocytosed bacteria, and a Th1 cell releasing the cytokine gamma interferon, which again will be detected by a specific receptor for that particular cytokine that is present on the macrophage; in other words, the gamma interferon receptor. And that will lead to activation of the macrophage. And the macrophage will then up-regulate its microbicidal mechanisms, resulting in the killing of engulfed microorganisms.

    04:57 Regarding Th2 cells, they typically secrete the cytokines interleukin-6, interleukin-5 and interleukin-4.

    05:04 And those cytokines are very helpful in activating B-lymphocytes.

    05:09 The cytokine interleukin-5 is also really good at activating eosinophils.

    05:17 Just like Th1 cells can down-regulate Th2 cells, so Th2 cells by virtue of the fact that they produce interleukin-4 can down-regulate the activity of Th1 cells.


    About the Lecture

    The lecture Th0, Th1 and Th2 Cells – Cell-Mediated Immunity by Peter Delves, PhD is from the course Humoral Immunity and Cell-Mediated Immunity. It contains the following chapters:

    • Th0 Cells
    • Th1 Cells
    • Th2 Cells

    Included Quiz Questions

    1. Interferon gamma (IFNγ)
    2. Inducible T-cell COStimulator (ICOS)
    3. Transforming growth factor beta (TGFβ)
    4. Interleukin 13 (IL-13)
    5. Interleukin 22 (IL-22)
    1. By influencing its maturation into the appropriate T cell lineage
    2. By influencing its maturation into a natural killer cell
    3. By influencing its maturation only into helper T cell 1
    4. By influencing its maturation only into helper T cell 2
    5. By influencing its maturation only into helper T cell 17
    1. Interferon gamma
    2. Interleukin 2
    3. Interleukin 13
    4. Interleukin 3
    5. Interferon alpha
    1. Interleukin 5 by T helper 1
    2. Interleukin 5 by T helper 2
    3. Interleukin 2 by T helper 1
    4. Interferon gamma by T helper 1
    5. Interleukin 13 by T helper 2

    Author of lecture Th0, Th1 and Th2 Cells – Cell-Mediated Immunity

     Peter Delves, PhD

    Peter Delves, PhD


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