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Once a thymocyte has productively rearranged a β-chain gene, all of the following events will occur subsequently except:

a. β binds to pTα and is expressed on the cell surface with the CD3 complex and ζ chain.
b. Rearrangement of β-, γ-, and δ-chain genes ceases as a result of the suppression of RAG-1 and RAG-2.
c. The pre-T cell proliferates and produces a clone of cells all expressing an identical β chain.
d. Expression of CD34 and CD44 gives rise to double-positive thymocytes.
e. α-, γ-, and δ-chain loci rearrange simultaneously

User Halflings
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1 Answer

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Final answer:

The event that does not occur after a thymocyte successfully rearranges a β-chain gene is that α-, γ-, and δ-chain loci rearrange simultaneously; this is incorrect as only the α-chain locus rearranges after successful β-chain rearrangement.

Step-by-step explanation:

Understanding Thymocyte Development

Once a thymocyte has productively rearranged a β-chain gene, several events ensue to ensure the maturation of the T cell. To clarify which events will occur and which will not, let's go through the given options:

  • β binds to pTα and is expressed on the cell surface with the CD3 complex and ζ chain. This is indeed a part of normal T cell receptor (TCR) development.
  • Rearrangement of β-, γ-, and δ-chain genes ceases as a result of the suppression of RAG-1 and RAG-2, halting further rearrangement after successful production of the TCR β-chain.
  • The pre-T cell proliferates and produces a clone of cells all expressing an identical β chain. This clonal expansion is essential for the development of a diverse T cell repertoire.
  • However, expression of CD34 and CD44 giving rise to double-positive thymocytes is not a subsequent event, as expression of these markers occurs at earlier developmental stages in thymocytes.
  • α-, γ-, and δ-chain loci do not rearrange simultaneously. After successful β-chain rearrangement, γ- and δ-chain rearrangement ceases, and only the α-chain locus goes through rearrangement.

Therefore, the correct answer is option (e): α-, γ-, and δ-chain loci rearrange simultaneously, which does not occur subsequent to the productive rearrangement of a β-chain gene in thymocytes. The arrangement of β-chain cessation leads to highly specialized TCR development, crucial for the adaptive immune response.

User Aman Aggarwal
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