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. IFNγ
    2. ICOS
    3. TGFβ
    4. IL-13
    5. IL-22
    1. Dendritic cells release cytokines in response to PAMPs- these cytokines influence the maturation of the Th0 cell into the appropriate T cell lineage.
    2. Dendritic cells activate NK cells which release cytokines that determine the maturation of the Th0 cell.
    3. Dendritic cells reverts Th1 and Th2 cells back to Th0 cells so that they can be reused in an appropriate response.
    4. Dendritic cells release INFγ in response to PAMPs- which influences Th0 cells.
    5. Dendritic cells only present antigen to Th0 cells and have no other influence on their differentiation.
    1. IL2- Th2
    2. IL2- cytotoxic T cells
    3. IFNγ- macrophages
    4. IL2- B cells
    5. IFNγ- Th2
    1. IL5- Th1
    2. IL5- Th2
    3. IL2- Th1
    4. IFN-gamma- Th1
    5. IL6- Th2

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

     Peter Delves, PhD

    Peter Delves, PhD

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