In thymus maturation of T lymphocytes takes place which helps in cell mediated immunity.

The correct answer is option 'D': Loss of cell-mediated immunity.

The thymus is a small gland located in the chest, just behind the sternum. It is a crucial organ for the development and maturation of T cells, which are a type of white blood cell involved in cell-mediated immunity. Cell-mediated immunity refers to the immune response that involves the activation of T cells to directly attack and destroy infected or abnormal cells in the body.

The thymus plays a vital role in the development of T cells, particularly during childhood. It is responsible for the production and maturation of T cells, which are then released into the bloodstream to carry out their immune functions. Damage to the thymus in children can have significant implications for their immune system, particularly in relation to cell-mediated immunity.

Under normal circumstances, T cells are produced in the bone marrow and migrate to the thymus for maturation. Within the thymus, immature T cells undergo a process called positive and negative selection, where they are trained to recognize and respond to foreign antigens while avoiding self-reactivity. This process ensures that only functional and non-self-reactive T cells are released into circulation.

Damage to the thymus can disrupt the development and maturation of T cells, leading to a loss of cell-mediated immunity. This can have several consequences:

1. Reduced T cell production: Damage to the thymus can result in a decreased production of T cells. This can lead to a lower number of functional T cells available to mount an immune response against foreign pathogens or abnormal cells.

2. Impaired T cell maturation: The thymus is responsible for the maturation of T cells, which involves the acquisition of specific receptors that allow them to recognize and bind to specific antigens. Damage to the thymus can disrupt this maturation process, resulting in the release of immature or dysfunctional T cells into circulation.

3. Decreased immune response: Cell-mediated immunity is essential for the body's defense against viruses, certain bacteria, and tumor cells. Loss of cell-mediated immunity due to thymus damage can result in decreased immune responses against these pathogens, making individuals more susceptible to infections and malignancies.

It is important to note that damage to the thymus in children can have long-term consequences for their immune system. Since the thymus is most active during childhood and gradually undergoes involution with age, any damage to the thymus during this critical period can have significant and lasting effects on immune function. Therefore, preserving thymus health is crucial for maintaining a robust immune system in children.