The correct answer is option D) loss of cell-mediated immunity.

Explanation:
The thymus is a gland located in the upper chest region, just behind the sternum. It plays a crucial role in the development and maturation of T cells, which are a type of white blood cell involved in cell-mediated immunity.

1. Role of thymus:
The thymus gland is responsible for the production and maturation of T lymphocytes (T cells). These cells are crucial for the immune system's ability to recognize and destroy invading pathogens, cancer cells, and other abnormal cells. The thymus gland is most active during childhood and gradually decreases in size and function as a person reaches adulthood.

2. Cell-mediated immunity:
Cell-mediated immunity is an immune response that involves the activation of T cells. These T cells can directly destroy infected cells or cancer cells, or they can release chemicals called cytokines that stimulate other immune cells to carry out their functions. This type of immunity is especially important in fighting intracellular pathogens, such as viruses and some bacteria.

3. Effect of thymus damage:
If the thymus is damaged or dysfunctional in a child, it can lead to a loss of cell-mediated immunity. This means that the child's ability to mount an effective immune response against intracellular pathogens would be compromised. They may have difficulty in clearing viral infections and may be more susceptible to certain types of cancer.

4. Reduction in stem cell production:
While damage to the thymus may affect the production of stem cells, the reduction in stem cell production alone would not lead to a loss of cell-mediated immunity. Stem cells are precursors to various types of blood cells, including T cells, but the thymus is specifically responsible for their maturation and development into functional T cells.

5. Loss of antibody-mediated immunity:
Antibody-mediated immunity, also known as humoral immunity, is a different arm of the immune system that involves the production of antibodies by B cells. The thymus is not directly involved in antibody production, so damage to the thymus would not result in a loss of antibody-mediated immunity.

In conclusion, damage to the thymus in a child would primarily lead to a loss of cell-mediated immunity, compromising their ability to fight off intracellular pathogens and abnormal cells.

Thymus release thymosine which help in maturation of T-lymphocytes which is related to cell mediated immunity.
Thus, Damage to thymus lead to loss in cell mediated immunity.