## **Core Concept**
The neonatal thymectomy is a procedure that involves the removal of the thymus gland in newborns. The thymus gland plays a crucial role in the development and maturation of T-lymphocytes (T cells), which are essential for cell-mediated immunity. The thymus is most active during early life, and its removal during the neonatal period can significantly impact the immune system.

## **Why the Correct Answer is Right**
The correct answer, , indicates that the change observed following neonatal thymectomy is a decrease in T cell-mediated immunity. The thymus is responsible for the maturation and selection of T cells. Removing the thymus in neonates severely impairs the development of T cells, leading to reduced T cell-mediated immune responses. This makes the individual more susceptible to infections, particularly those caused by viruses and fungi.

## **Why Each Wrong Option is Incorrect**
- **Option A:** - This option is incorrect because an increase in T cell-mediated immunity would not be a consequence of thymectomy, as the thymus is essential for T cell development.
- **Option B:** - This option is incorrect because an increase in B cell-mediated immunity is not directly related to the function of the thymus. B cells mature in the bone marrow, not the thymus.
- **Option C:** - This option might seem plausible but is incorrect in the context of the question, which focuses on the immediate and direct effects of neonatal thymectomy on T cell immunity.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the thymus is crucial for the development of T cells, and its removal, especially in early life, leads to severe immunodeficiency. This is evident in conditions like DiGeorge syndrome, where thymic hypoplasia or aplasia results in reduced T cell counts and function.

## **Correct Answer:** .