Q.99 A newborn was accidentally given a drug that destroyed the thymus. Which ONE of the following
would be the most likely outcome?
(A) Lack of class I MHC molecules
(B) Inability to rearrange antigen receptors
(C) Inability to differentiate to mature T cells
(D) Reduction in T-independent number of B cells
Thymus Destruction in Newborn: Impact on T Cell Development
A newborn given a drug destroying the thymus would face severe T cell deficiency. The correct answer is (C), as the thymus is essential for T cell maturation.
Correct Answer
(C) Inability to differentiate to mature T cells.
Thymus Role Explained
The thymus is the primary site for T cell maturation, where progenitors from bone marrow differentiate into mature CD4+ and CD8+ T cells through positive and negative selection.
Destruction halts this process, leading to profound T cell lymphopenia, as seen in DiGeorge syndrome or neonatal thymectomy models.
This outcome severely impairs adaptive immunity, especially cell-mediated responses, critical for molecular biology and immunology studies.
Option Breakdown
| Option | Explanation | Why Incorrect |
|---|---|---|
| (A) Lack of class I MHC molecules | Class I MHC is expressed ubiquitously on nucleated cells, produced independently of the thymus. | Thymus loss doesn’t affect MHC expression. |
| (B) Inability to rearrange antigen receptors | V(D)J recombination for TCR and BCR occurs in bone marrow progenitors, before thymic entry. | B cells and early T progenitors unaffected. |
| (C) Inability to differentiate to mature T cells | Thymus provides stromal support, selection signals for T cell maturation from double-negative to single-positive stages. | Correct: Direct consequence of thymic absence. |
| (D) Reduction in T-independent number of B cells | T-independent B cells respond to antigens without T help in spleen/mucosa; thymus irrelevant. | Primarily impacts T cells, not B cell subsets. |
Relevance to Biotech Studies
For bioinformatics and genetics students, this highlights thymic role in immune engineering, like HSCT or gene therapies targeting FOXN1 for thymus regeneration. Useful for exam revision on lymphoid organ functions.
