Question

1. Explain why T cells are more likely to develop into alpha beta T cells than gamma delta T cells? T cells are three times more likely to become TCR-αβ cells versus TCR-γδ cells. Why is this the case considering T-cell development mechanisms within the thymus? 2. In what way do the four double-negative stages of T-cell development demonstrate the organization of T-cell development according to spatial parameters? 3. Compare and contrast the affinity hypothesis and altered peptide hypothesis to explain the thymic selection paradox (why we don't negatively select all cells that we positively select). 4. At first glance, the logic of positive selection appears to be lacking. Predict what might happen in the absence of positive thymic selection.

          1. Explain why T cells are more likely to develop into alpha beta T cells than gamma delta T cells? T cells are three times more likely to become TCR-αβ cells versus TCR-γδ cells. Why is this the case considering T-cell development mechanisms within the thymus?
2. In what way do the four double-negative stages of T-cell development demonstrate the organization of T-cell development according to spatial parameters?
3. Compare and contrast the affinity hypothesis and altered peptide hypothesis to explain the thymic selection paradox (why we don't negatively select all cells that we positively select).
4. At first glance, the logic of positive selection appears to be lacking. Predict what might happen in the absence of positive thymic selection.

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Added by Latasha B.

Biology for AP Courses

Julianne Zedalis, John Eggebrecht

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Solved by Expert Lochan U

03/22/2022

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During T cell development in the thymus, the rearrangement of the T cell receptor beta chain occurs first. Only T cells that undergo proper rearrangement of the beta chain with the alpha chain will proceed to further development. This results in a higher Show more…

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1. Explain why T cells are more likely to develop into alpha beta T cells than gamma delta T cells? T cells are three times more likely to become TCR-αβ cells versus TCR-γδ cells. Why is this the case considering T-cell development mechanisms within the thymus? 2. In what way do the four double-negative stages of T-cell development demonstrate the organization of T-cell development according to spatial parameters? 3. Compare and contrast the affinity hypothesis and altered peptide hypothesis to explain the thymic selection paradox (why we don't negatively select all cells that we positively select). 4. At first glance, the logic of positive selection appears to be lacking. Predict what might happen in the absence of positive thymic selection.

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Transcript

00:01 Today we are going to discuss about the t cells.

00:04 The t cells are part of the immune system and t cells are specific to the type of immune response.

00:26 The t cells develop in the stem cells of the bone marrow and then migrates to the thymus for development.

00:46 The rearrangement t -cell receptor occurs in two stages.

00:57 At the dn3 stage, the t -cell receptor beta is rearranged.

01:10 The t -cell receptor beta is paired up with t -alpha to produce pre -t cell receptor.

01:20 This results into the t -cell receptors, many of them, which are non -functional.

01:31 This is because only the t -cell receptor which has undergone proper binding of t -cell receptor beta with the t -alpha to form functional free t -cell receptor will undergo development.

01:58 These t -cell receptor font can react with the t -cell receptor protein and thus they are considered to be rightly functional and will pass the tn3 stage of development.

02:24 In the thymus, when the cell begins to express the cd2 but not yet arranged the t -cel receptor gene, they are considered to be double negative for cd4 and cd8, which are the markers for p helper cells and the cytotoxic cells.

02:58 Of the double negative found in the thymus, 20 % have rearranged their gamma delta t cell receptor.

03:09 20 % will have homogeneous alpha beta t cell receptor and 60 % becomes mature alpha beta b cells...

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